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Construction and Performance Monitoring of Innovative Ultra-High-Performance Concrete Bridge

Construction and Performance Monitoring of Innovative Ultra-High-Performance Concrete Bridge infrastructures Article Construction and Performance Monitoring of Innovative Ultra-High-Performance Concrete Bridge 1 1 1 1 , 2 2 Haena Kim , Byungkyu Moon , Xinyu Hu , Hosin (David) Lee *, Gum-Sung Ryu , Kyung-Taek Koh , 2 2 3 Changbin Joh , Byung-Suk Kim and Brian Keierleber Iowa Technology Institute, University of Iowa, Iowa City, IA 52242, USA; haena612@gmail.com (H.K.); byungkyu-moon@uiowa.edu (B.M.); xinyu-hu@uiowa.edu (X.H.) Department of Infrastructure Safety Research, Korea Institute of Civil Engineering and Building Technology, Goyang, Gyeonggi 10223, Korea; ryu0505@kict.re.kr (G.-S.R.); ktgo@kict.re.kr (K.-T.K.); cjoh@kict.re.kr (C.J.); bskim@kict.re.kr (B.-S.K.) Buchanan County, 1511 First Street Independence, Iowa City, IA 50644, USA; bkeierleber@co.buchanan.ia.us * Correspondence: hosin-lee@uiowa.edu; Tel.: +1-801-512-4202 Abstract: The application of Ultra-High-Performance Concrete (UHPC) materials in rehabilitating bridges and constructing primary bridge components is increasing rapidly across the world because of their superior strength and durability characteristics when compared to regular concretes. However, there have been few new bridges constructed using UHPC materials with regular formworks, ready- mix trucks, and construction equipment. This paper presents a comprehensive report encompassing the design, construction, and performance monitoring of a new bridge constructed in Iowa using a unique UHPC technology that includes steel fibers of two different lengths embedded in the concrete. By using optimized lengths of steel fibers, both the tensile strength and the toughness were increased. The UHPC material was produced with local cement and aggregates in the US Citation: Kim, H.; Moon, B.; Hu, X.; using typical ready-mix concrete equipment. This paper discusses the experience gained from Lee, H.; Ryu, G.-S.; Koh, K.-T.; Joh, C.; the design and construction process including mix design, batching, delivery of steel fibers to the Kim, B.-S.; Keierleber, B. Construction ready-mix concrete batch unit, and post-tensioning of precast slabs at the jobsite. For four years and Performance Monitoring of after construction, the joints of the bridge decks were monitored using strain sensors mounted on Innovative Ultra-High-Performance both sides of the deck joints. The strain values were quite similar between the two sides of each Concrete Bridge. Infrastructures 2021, 6, 121. https://doi.org/10.3390/ joint, indicating a good load transfer between precast bridge girders. A bridge was successfully infrastructures6090121 constructed using a unique UHPC technology incorporating two different lengths of steel fibers and utilizing local cement and aggregates and a ready-mix truck, and has been performing satisfactorily Academic Editor: Moncef L. Nehdi with a good load transfer across post-tensioned precast girder joints. Received: 23 July 2021 Keywords: UHPC; strain gauge; field construction; post-tensioning; monitoring; bridge; joint; Accepted: 24 August 2021 steel fibers Published: 30 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional affil- Concrete is the most commonly used building material in the world. A total of iations. 4.1 billion tons of cement were used in 2019, contributing approximately 7% of global CO emissions, assuming 0.9 pounds of CO generated for the manufacturing of 1 pound of cement [1]. The proposed Ultra-High-Performance Concrete (UHPC)’s significantly higher strength allows for the use of a slender member with smaller cross-sections and with a Copyright: © 2021 by the authors. longer service life, which will reduce the amount of CO emissions associated with building Licensee MDPI, Basel, Switzerland. concrete bridges [2]. This article is an open access article Concrete technology has evolved through the optimization of mix ingredients to distributed under the terms and improve strength, workability, and durability. In the 1980s, High-Performance Concretes conditions of the Creative Commons (HPCs) were developed, with significantly improved durability and compressive strengths Attribution (CC BY) license (https:// ranging from 48 to 117 MPa [3]. In the 1990s, UHPC was introduced in France and the first creativecommons.org/licenses/by/ UHPC pedestrian bridge, with a span of 60 m, was built in Quebec, Canada [4]. The first 4.0/). Infrastructures 2021, 6, 121. https://doi.org/10.3390/infrastructures6090121 https://www.mdpi.com/journal/infrastructures Infrastructures 2021, 6, x FOR PEER REVIEW 2 of 15 Infrastructures 2021, 6, 121 2 of 15 and the first UHPC pedestrian bridge, with a span of 60 m, was built in Quebec, Canada [4]. The first UHPC bridge in the US was constructed in 2006 in Wappello County, Iowa, UHPC bridge in the US was constructed in 2006 in Wappello County, Iowa, and another and another UHPC bridge was built in Buchanan County, Iowa, in 2008 [5,6]. UHPC bridge was built in Buchanan County, Iowa, in 2008 [5,6]. UHPC is a dense flowable mix which is mainly composed of fine masonry sands (no UHPC is a dense flowable mix which is mainly composed of fine masonry sands coarse aggregates) and steel fibers with a high-range water reducer to produce a very low (no coarse aggregates) and steel fibers with a high-range water reducer to produce a very water/cement ratio of around 0.25. UHPC typically exhibits a compressive strength low water/cement ratio of around 0.25. UHPC typically exhibits a compressive strength greater than 150 MPa (21.7 ksi) and a sustained post-cracking tensile strength greater than greater than 150 MPa (21.7 ksi) and a sustained post-cracking tensile strength greater 5 MPa (0.72 ksi) [7]. It is common to include a high proportion of silica fume up to 10 than 5 MPa (0.72 ksi) [7]. It is common to include a high proportion of silica fume up to percent relative to the weight of cement. UHPC displays a discontinuous pore structure 10 percent relative to the weight of cement. UHPC displays a discontinuous pore structure that enhances its durability. The most common steel fiber used in UHPC constructions is that enhances its durability. The most common steel fiber used in UHPC constructions is a a 0.2 mm diameter by 13 mm long straight fiber with a specified minimum tensile strength 0.2 mm diameter by 13 mm long straight fiber with a specified minimum tensile strength of 2000 MPa (290 ksi) [8]. of 2000 MPa (290 ksi) [8]. This paper presents the laboratory test results, design, construction, and monitoring This paper presents the laboratory test results, design, construction, and monitoring of a new bridge using a unique UHPC technology which utilizes two different lengths of of a new bridge using a unique UHPC technology which utilizes two different lengths of steel fibers, 16.3 mm and 19.5 mm, at a 1:2 ratio by weight. Lengths of steel fibers were steel fibers, 16.3 mm and 19.5 mm, at a 1:2 ratio by weight. Lengths of steel fibers were optimized to increase both the tensile strength and the toughness. This unique UHPC mix optimized to increase both the tensile strength and the toughness. This unique UHPC was used to build a pi-girder bridge in Buchanan County, Iowa. After the bridge was mix was used to build a pi-girder bridge in Buchanan County, Iowa. After the bridge was constructed, the bridge joints were monitored three times over four years using strain constructed, the bridge joints were monitored three times over four years using strain sensors attached on both sides of each joint. sensors attached on both sides of each joint. 2. Background 2. Background Over Overthe thepast past15 15years, years,as asshown shownin in F Figur igur e e1 1,, t the he n number umberof of U UHPC HPC p prrojects ojectscompleted completed each year has been steadily increasing [9]. As depicted in Figure 2, UHPC has been applied each year has been steadily increasing [9]. As depicted in Figure 2, UHPC has been applied in over 250 bridges in the US, mainly as precast concrete deck panels and the composite in over 250 bridges in the US, mainly as precast concrete deck panels and the composite connections between precast deck panels and supporting girders [9]. Until recently, UHPC connections between precast deck panels and supporting girders [9]. Until recently, materials were predominantly used for field-cast connections between prefabricated bridge UHPC materials were predominantly used for field-cast connections between elements [10]. Steel fibers cost $615/m when they are added 3 at 1.5% by volume, which prefabricated bridge elements [10]. Steel fibers cost $615/m when they are added at 1.5% represents about half of the total cost of UHPC at $1110/m [3]. Due to the high 3 cost of by volume, which represents about half of the total cost of UHPC at $1110/m [3]. Due to steel fibers in UHPC materials, UHPC has been more commonly used as a deck overlay the high cost of steel fibers in UHPC materials, UHPC has been more commonly used as rather than for building new bridges [11]. As a result, to date, only three bridges have a deck overlay rather than for building new bridges [11]. As a result, to date, only three been constructed in the US using UHPC materials, all in Iowa. An increased tensile bridges have been constructed in the US using UHPC materials, all in Iowa. An increased bond strength of a specially formulated UHPC overlay on existing bridge decks has been tensile bond strength of a specially formulated UHPC overlay on existing bridge decks reported [12]. has been reported [12]. Figure 1. Number of UHPC projects each year [9]. Figure 1. Number of UHPC projects each year [9]. Infrastructures 2021, 6, 121 3 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 3 of 15 Figure 2. Use of UHPC materials in bridge components in the United States [9]. Figure 2. Use of UHPC materials in bridge components in the United States [9]. Grouts have a significant impact on a bridge’s deck-level connection performance. To Grouts have a significant impact on a bridge’s deck-level connection performance. improve the structural performance of the connections between bridge decks, UHPC grout To improve the structural performance of the connections between bridge decks, UHPC with a lower shrinkage and enhanced bonding strength has been adopted [13]. Due to grout with a lower shrinkage and enhanced bonding strength has been adopted [13]. Due UHPC grouting material’s improved shear bearing capacity, the beam stress is effectively to UHPC grouting material’s improved shear bearing capacity, the beam stress is reduced and the development of oblique cracks is inhibited [14]. To better comprehend the effectively reduced and the development of oblique cracks is inhibited [14]. To better behavior of precast deck connections for accelerated construction, a new connection detail comprehend the behavior of precast deck connections for accelerated construction, a new to connect a precast column to a cap beam was analyzed using nonlinear finite element connection detail to connect a precast column to a cap beam was analyzed using nonlinear analysis [15]. Furthermore, small-scale direct shear tests and large-scale double shear push- finite element analysis [15]. Furthermore, small-scale direct shear tests and large-scale off tests were performed on innovative connections constructed using UHPC materials. The double shear push-off tests were performed on innovative connections constructed using novel connection details were reported to have the potential to meet the existing strength UHPC materials. The novel connection details were reported to have the potential to meet limit requirements outlined in the AASHTO bridge design specification [16]. the existing strength limit requirements outlined in the AASHTO bridge design UHPC does not exhibit a significant amount of drying shrinkage because a large specification [16]. amount of steel fibers in the HPC help reduce the shrinkage cracking and redistribute UHPC does not exhibit a significant amount of drying shrinkage because a large the shrinkage strains [17]. UHPC materials have less propensity for shrinkage cracking amount of steel fibers in the HPC help reduce the shrinkage cracking and redistribute the and shrinkage cracking occurs in the form of microcracks due to the steel fibers [18]. For shrinkage strains [17]. UHPC materials have less propensity for shrinkage cracking and the creep and shrinkage models for AASHTO LRFD, UHPC materials provide superior shrinkage cracking occurs in the form of microcracks due to the steel fibers [18]. For the mechanical properties, a low water content, and a high volume of fiber reinforcement, creep and shrinkage models for AASHTO LRFD, UHPC materials provide superior which can enhance creep and shrinkage behavior compared to conventional concretes [19]. mechanic Full-depth al p application roperties, a low water co of UHPC at the ntent, punching and a hi shear gh volu area me of in flat fi slabs ber rei transferr nforcement, ed the which can failure mode enhance creep and sh from a brittle punching rinkage beha shear failur vior compa e to a ductile red to conventi punchingona shear l concretes -flexural [1 failur 9]. Fu eland l-dep impr th ap oved plicat both ion of cracking UHPCstr atength the pu and nchpunching ing shear a shear rea in str fl ength at slab [20 s t]. ransferred the failure m It is possible ode from to a br constr ittle punchin uct a 300 foot g she (91.4 ar fail m) ure to a UHPC du gir ctider le pu with nching shear-flexural a weight per unit length that is similar to that of an existing 200 feet (61 m) long conventional concrete failure and improved both cracking strength and punching shear strength [20]. girder [21]. This innovative slender and longer girder design will provide aesthetic value It is possible to construct a 300 foot (91.4 m) UHPC girder with a weight per unit and more of the open space that is critically needed for smart cities. The adoption of length that is similar to that of an existing 200 feet (61 m) long conventional concrete girder UHPC materials in rehabilitating bridges and constructing primary bridge components [21]. This innovative slender and longer girder design will provide aesthetic value and is progressing rapidly in the world because of UHPC’s unique characteristics of higher more of the open space that is critically needed for smart cities. The adoption of UHPC strength and longer durability than regular concretes [22]. materials in rehabilitating bridges and constructing primary bridge components is progressing rapidly in the world because of UHPC’s unique characteristics of higher 3. Materials and Specimen Preparation strength and longer durability than regular concretes [22]. Table 1 summarizes the optimum mix design for the proposed UHPC material, which was developed by performing compressive and indirect tensile tests of numerous spec- 3. Materials and Specimen Preparation imens. Short steel fibers prevent microcracks whereas long fibers prevent macro-cracks Table 1 summarizes the optimum mix design for the proposed UHPC material, which through their bridging effect [9]. Our unique UHPC material contained longer steel fibers was developed by performing compressive and indirect tensile tests of numerous Infrastructures 2021, 6, 121 4 of 15 with lengths of 0.63 in (16.3 mm) and 0.78 in (19.5 mm) mixed at a respective ratio of 1.6% and 3.2% by weight, and they significantly increased flexural tensile strength. The water to cement (w/c) ratio of the UHPC was 0.23, which is the lowest amount of water needed for cement hydration. To improve the workability, based on the observations of the dry mixing condition, a slightly higher amount of superplasticizer (0.7% by weight) was used. Table 1. Mix design of UHPC. Percent 3 3 3 Constituents lb/yd (kg/m ) lb/ft by Weight Sand 1462 (867) 54.1 35.30% Cement 1329 (789) 45.9 32.10% Water 311 (184) 11.5 7.50% Superplasticizer 31 (18) 1.15 0.70% 16.3 mm fiber 66 (39) 2.4 1.60% 19.5 mm fiber 131 (78) 4.8 3.20% Defoamer 1 (0.5) 0.04 0.02% Shrinkage-reducing agent 13 (8) 0.48 0.30% Premix * 797 (473) 29.5 19.30% Total 4142 (2457) 153.4 100% * Silica fume, ground quartz, and other performance enhancers. First, all dry materials, namely cement, sand, and premix, were mixed in a 2-cubic concrete mixer at a speed of 20 rpm for 5 min. The water and other liquid additives such as superplasticizer and defoamer were then added and mixed for an additional 4 min. Finally, after the mix was evenly mixed, steel fibers were added to produce the laboratory mix. During the mixing process, extra amounts of water and superplasticizer were added to improve workability of the mix. For example, 0.9 kg of extra water and 0.74 kg of superplasticizer were added to the laboratory mix, resulting in higher w/c ratios (to 0.27 from the original w/c ratio of 0.23). 3.1. Compressive Strengths Both laboratory and field mix 3 6 inch (7.6 15.2 cm, diameter height) cylindrical specimens were tested for compressive strength using an Instron Prism 5500 (1.1 MN Capacity). The test results of both laboratory and field mixes are summarized in Table 2. As can be seen from plots of average compressive strengths with standard deviations shown in Figure 3, the wet-cured laboratory mix satisfied the target compressive strength of 180 MPa after 28 days, whereas the field mix slightly missed the target. As shown in Figure 3, the wet-cured laboratory mix achieved a very significant early gain in compressive strength of 87.9 MPa after one day, continued to gain strength until 14 days, and remained at a similar level after 28 days. The wet-cured field specimens exhibited similar levels of strength gain as those of wet-cured laboratory mix. Table 2. Compressive strength and standard deviation results of lab and field mix specimens. Average and Standard Deviation of Compression Strength in MPa Batch Day 1 Day 2 Day 4 Day 7 Day 14 Day 18 Day 28 Lab mix (1 cf) 87.9/10.8 114.3/15.4 133/3.2 155.8/3.4 174.4/5.3 n.a. 180/3.7 Field mix (5.5 cy) n.a. n.a. n.a. 154.5/8.4 144/2.5 181/5.0 174.2/21.9 Infrastructures 2021, 6, 121 5 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 5 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 5 of 15 Figure 3. Averages and standard deviations of compressive strengths of laboratory and field mixes Figure Figure 3. 3. A Aver verages ages and and standar standard dev d deviations iations of com of compr press essive ive streng strengths ths of la ofboratory laboratory and fi and eld m field ixmixes es for 66 UHPC specimens. for 66 UHPC specimens. for 66 UHPC specimens. 3.2. Indirect Tensile Strength 3.2. Indirect Tensile Strength 3.2. Indirect Tensile Strength For the laboratory mix (not the field mix) 3 by 6 in (7.6 × 15.2 cm, diameter × height) For the laboratory mix (not the field mix) 3 by 6 in (7.6  15.2 cm, diameter  height) For the laboratory mix (not the field mix) 3 by 6 in (7.6 × 15.2 cm, diameter × height) cylindrical specimens were prepared for indirect tensile strength testing. The average cylindrical specimens were prepared for indirect tensile strength testing. The average cylindrical specimens were prepared for indirect tensile strength testing. The average indirect tensile strengths and standard deviations are plotted in Figure 4. The wet-cured indir indir ect ect tensile strengths tensile strengths and stan and standar dard ddeviat deviations ions ar ar e plotted e plotted in in Figur Figur e 4. The e 4. The wet-cured wet-cur ed laboratory mix specimens achieved the highest indirect tensile strength of 18.3 MPa after laboratory laboratory m mix ix specimen specimens s achieve achieved d the thehighest highest in indir direct tensi ect tensile le strength of 18 strength of .3 18.3 MPa MPa after after 7 days and maintained the same strength after 14 days. 7 days and maintained the same strength after 14 days. 7 days and maintained the same strength after 14 days. 18.4/2.27 20 18.3/2.99 18.3/2.99 18.4/2.27 14.0/0.49 14.0/0.49 12.7/0.59 11.7/0.79 12.7/0.59 11.7/0.79 Day 1 Day 2 Day 4 Day 7 Day 14 Day 1 Day 2 Day 4 Day 7 Day 14 Curing Days Curing Days Laboratory Mix Laboratory Mix Figure 4. Averages and standard deviations of indirect tensile strengths of laboratory mixes. Figure 4. Averages and standard deviations of indirect tensile strengths of laboratory mixes. Figure 4. Averages and standard deviations of indirect tensile strengths of laboratory mixes. 4. Design of the Hawkeye UHPC Bridge 4. Design of the Hawkeye UHPC Bridge 4. Design of the Hawkeye UHPC Bridge As shown in Figure 5, the Hawkeye Bridge is 52′ (15.8 m) long and 32′-5” (10 m) wide 0 0 00 As shown in Figure 5, the Hawkeye Bridge is 52′ (15.8 m) long and 32′-5” (10 m) wide As shown in Figure 5, the Hawkeye Bridge is 52 (15.8 m) long and 32 -5 (10 m) wide with an innovative pi-girder design, where each girder is 52′ (15.8 m) long, 5′-3” (1.6 m) 0 0 00 with an innovative pi-girder design, where each girder is 52′ (15.8 m) long, 5′-3” (1.6 m) with an innovative pi-girder design, where each girder is 52 (15.8 m) long, 5 -3 (1.6 m) wide, and 2′-4” (0.7 m) deep. The Hawkeye Bridge was designed using the load factors 0 00 wide, and 2′-4” (0.7 m) deep. The Hawkeye Bridge was designed using the load factors wide, and 2 -4 (0.7 m) deep. The Hawkeye Bridge was designed using the load factors and load combinations of the AASHTO-LRFD standard. Service load stress checking was applied to precast girders and ultimate strength design was applied to the girder deck and INDIRECT TENSILE STRENGTH (MPa) INDIRECT TENSILE STRENGTH (MPa) Infrastructures 2021, 6, x FOR PEER REVIEW 6 of 15 and load combinations of the AASHTO-LRFD standard. Service load stress checking was Infrastructures 2021, 6, 121 6 of 15 applied to precast girders and ultimate strength design was applied to the girder deck and abutment. Each of six girders was post-tensioned. Five crossbeams were installed and post-tensioned at 12′-9” (3.9 m) spacing to ensure a proper lateral load distribution. The shear abutment. bulbs were then filled with U Each of six girders was post-tensioned. HPC materia Five ls to i crossbeams mprove the connecti were installed and vity between post- 0 00 tensioned at 12 -9 (3.9 m) spacing to ensure a proper lateral load distribution. The shear girders. bulbs were then filled with UHPC materials to improve the connectivity between girders. Figure 5. Plan view and cross-section of Hawkeye Bridge design. Figure 5. Plan view and cross-section of Hawkeye Bridge design. The original pi-girder design was developed by the Massachusetts Institute of Technology (MIT, Cambridge, MA, USA) with a 33” tall girder covered with a 3” top-slab throughout the mid span and a 6” thick slab at the ends of the girder [23]. The girders were prestressed, which allowed reinforcing steel to be eliminated. For the Hawkeye Infrastructures 2021, 6, 121 7 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 7 of 15 The original pi-girder design was developed by the Massachusetts Institute of Tech- Infrastructures 2021, 6, x FOR PEER REVIEW 7 of 15 00 00 nology (MIT, Cambridge, MA, USA) with a 33 tall girder covered with a 3 top-slab throughout the mid span and a 6 thick slab at the ends of the girder [23]. The girders Bridge, the shape of the pi girders was optimized for UHPC to minimize the cross-section were prestressed, which allowed reinforcing steel to be eliminated. For the Hawkeye Bridge, the shape of the pi girders was optimized for UHPC to minimize the cross-section while exploiting the superior properties of UHPC materials. The very high tensile and Bridge, the shape of the pi girders was optimized for UHPC to minimize the cross-section while exploiting the superior properties of UHPC materials. The very high tensile and compressive strengths of UHPC allowed a thinner slab and slimmer girders, making it while exploiting the superior properties of UHPC materials. The very high tensile and compressive strengths of UHPC allowed a thinner slab and slimmer girders, making it possible to combine slab and girder in a single piece. Compared to the MIT’s pi-girder compressive strengths of UHPC allowed a thinner slab and slimmer girders, making it possible to combine slab and girder in a single piece. Compared to the MIT’s pi-girder design, as shown in Figure 6, the height of a UHPC girder for the Hawkeye Bridge was possible to combine slab and girder in a single piece. Compared to the MIT’s pi-girder design, as shown in Figure 6, the height of a UHPC girder for the Hawkeye Bridge was reduced from 33”to 28” while the thickness of the slab was increased from 4” to 4.5”. Each design, as shown in Figure 6, the height of a UHPC girder for the Hawkeye Bridge was reduced from 33”to 00 28” wh 00 ile the thickness of the slab was increased from0 4” to 4.5” 0 00 . Each girder was post-tensioned rather than prestressed. To provide a more stable structure, reduced from 33 to 28 while the thickness of the slab was increased from 4 to 4.5 . Each girder was post-tensioned rather than prestressed. To provide a more stable structure, UHPC girders were laterally post-tensioned at the jobsite through the crossbeams. girder was post-tensioned rather than prestressed. To provide a more stable structure, UHPC girders were laterally post-tensioned at the jobsite through the crossbeams. UHPC girders were laterally post-tensioned at the jobsite through the crossbeams. Figure 6. Hawkeye Bridge pi-girder cross-section design. Figure 6. Hawkeye Bridge pi-girder cross-section design. Figure 6. Hawkeye Bridge pi-girder cross-section design. 5. Construction of the Hawkeye UHPC Bridge 5. Construction of the Hawkeye UHPC Bridge 5. Construction of the Hawkeye UHPC Bridge As shown in Figure 7, after demolishing the unstable existing bridge, construction of As shown in Figure 7, after demolishing the unstable existing bridge, construction of As shown in Figure 7, after demolishing the unstable existing bridge, construction of the substructure of the new UHPC bridge started in May 2015. First, six H-shaped steel the substructure of the new UHPC bridge started in May 2015. First, six H-shaped steel the substructure of the new UHPC bridge started in May 2015. First, six H-shaped steel piles were driven into the soil, approximately 12 ft (3.7 m) deep. Concrete stub abutments piles were driven into the soil, approximately 12 ft (3.7 m) deep. Concrete stub abutments piles were driven into the soil, approximately 12 ft (3.7 m) deep. Concrete stub abutments were constructed on top of the pile foundation. All pictures in this section were captured were constructed on top of the pile foundation. All pictures in this section were captured were constructed on top of the pile foundation. All pictures in this section were captured by the authors. by the authors. by the authors. Figure 7. Existing unstable bridge (left) and construction of substructure of new UHPC bridge (right). Figure 7. Existing unstable bridge (left) and construction of substructure of new UHPC bridge (right). Figure 7. Existing unstable bridge (left) and construction of substructure of new UHPC bridge (right). On 23 June 2015, construction of the first UHPC girder commenced at the yard of On 23 June 2015, construction of the first UHPC girder commenced at the yard of Buchanan County Office, Iowa. Due to dry, hot weather conditions, an additional 10% of Buchanan County Office, Iowa. Due to dry, hot weather conditions, an additional 10% of superplasticizer was added to the mix to increase the workability. Table 3 summarizes the superplasticizer was added to the mix to increase the workability. Table 3 summarizes the final mix design for the ready-mix UHPC along with mixing instructions in the field. final mix design for the ready-mix UHPC along with mixing instructions in the field. Initially, we added cement to the wet sand and it created many cement balls because of Initially, we added cement to the wet sand and it created many cement balls because of the quick hydration of cement by the moisture in the wet sand. To prevent the creation of the quick hydration of cement by the moisture in the wet sand. To prevent the creation of Infrastructures 2021, 6, 121 8 of 15 On 23 June 2015, construction of the first UHPC girder commenced at the yard of Buchanan County Office, Iowa. Due to dry, hot weather conditions, an additional 10% of superplasticizer was added to the mix to increase the workability. Table 3 summarizes the final mix design for the ready-mix UHPC along with mixing instructions in the field. Initially, we added cement to the wet sand and it created many cement balls because of the quick hydration of cement by the moisture in the wet sand. To prevent the creation of cement balls, we mixed cement with less reactive premix and then added the wet sand in a ready-mix truck. Table 3. Mixing proportions and mixing instructions for UHPC. Mixing Orders UHPC MIX Total (lb/5.5 CY) Mixing Instruction 1 Premix 4386 2 Cement 7310 Mix for 10 min 3 Wet sand (MC = 4.2%) 8041 Mix for 5 min 4 Water 1710 Rotate at 10 RPM 5 Shrinkage reducer 73 Mix for 5 min 6 Defoamer 5 Add at 10 RPM 7 Superplasticizer 140 Mix for 5 min at maximum speed 8 Steel fiber (0.63 inch long) 362 Add for 20 min at 10 RPM 9 Steel fiber (0.78 inch long) 723 Mix for 2 min at maximum speed For the first batch, bolts at the bottom of formwork were pulled out of the form due to the lateral pressure and leaking concrete mix. Therefore, as shown in Figure 8a, a special wooden girder form was fabricated to ensure the strength needed to resist the lateral pressure generated by the weight of the flowable UHPC mix. It took 11 cubic yards (8.4 m ) of UHPC mix to fill a form, where each ready-mix truck produced 5.5 cubic yards. Compared to the laboratory mix, only 82% superplasticizer was needed for the ready-mix truck due to its better mixing capability. As shown in Figure 8b, steel fibers were delivered to the ready-mix truck using a vibrating mesh and a conveyor belt. As shown in Figure 8c, flowable UHPC mix was poured into a form and the surface was leveled. Since the flowable UHPC mix set very quickly as it came out of the ready-mix truck, another batch of mix had to be discarded. After removing the formwork, the UHPC girder was steam-cured by placing heated water hoses to provide sufficient heat and water with a gradual heat application rate set at 10–15 C/hr. As shown in Figure 8d, each girder was post-tensioned using seven 0.6 (1.5 cm) diameter longitudinal strands with a total force of 300 kips (2.67 MN) to achieve a gauge pressure of 6500 psi (44.8 MPa) at both bottom ends. Strands were pulled up to 80% of the ultimate tensile strength, resulting in a 6 inch elongation. On 9 September 2015, six steam-cured girders were installed at the jobsite. As shown in Figure 8e, each of five transverse crossbeams was post-tensioned using three 0.6 (1.5 cm) diameter strands with a total force of 105.3 kips (0.468 MN), where 35.1 kips (0.156 MN) was applied to each strand to achieve a gauge pressure of 4500 psi (31.0 MPa). Once all three strands were post-tensioned, a duct was grouted and a cap was installed. As shown in Figure 8f, the unique Hawkeye Bridge was successfully constructed using innovative UHPC materials. Infrastructures 2021, 6, x FOR PEER REVIEW 9 of 15 Infrastructures 2021, 6, 121 9 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 9 of 15 (a) Girder formwork (b) Adding premix/steel fibers to ready-mix truck (a) Girder formwork (b) Adding premix/steel fibers to ready-mix truck (c) UHPC pouring (d) Longitudinal post-tensioning of girder (c) UHPC pouring (d) Longitudinal post-tensioning of girder (e) Transverse post-tensioning of crossbeam (f) Completed Hawkeye Bridge (e) Transverse post-tensioning of crossbeam (f) Completed Hawkeye Bridge Figure 8. Figure 8. U UH HPC mixing, PC mixing, pouring, pouring, and and c o cns ons trtr uc uc tion process tion process of Hawkeye Br of Hawkeye Br idge. idge. Figure 8. UHPC mixing, pouring, and construction process of Hawkeye Bridge. 6 6.. M Mo oni nito torrii ng ng o o ff Br Br id id gg ee De De ck ck Jo Jo in in tst s 6. Monitoring of Bridge Deck Joints As shown in Figure 9, each SenSpot strain sensor consists of two parts: a strain gauge As shown in Figure 9, each SenSpot strain sensor consists of two parts: a strain gauge As shown in Figure 9, each SenSpot strain sensor consists of two parts: a strain gauge with a precision of 1 microstrain and a wireless transmitter. The wireless transmitter with with a a pr precisi ecision on of of 1 1 micr microstra ostrainin and and a a wi wireless reless transmi transmitter tter. The wi . The wireless reless transmi transmitter tter converts analog strain measurements from the strain gauge to digitized data and sends converts converts an analog alog str strain ainmeasur measurements fr ements from om th thee str strain aingauge gauge to to digitized digitized d data ata and and sen sends ds them wirelessly to the remote transmission gateway, which then sends the data to a them wirelessly to the remote transmission gateway, which then sends the data to a remote them wirelessly to the remote transmission gateway, which then sends the data to a remote cloud server through a cellular service. The wireless transmitter can transmit cloud remote clo serveru thr d serve ough r a thro cellular ugh service. a cellular The serv wireless ice. The wi transmitter reless transmi can transmit tter ca digital n tra strain nsmit digital strain data every six seconds or at longer intervals. The sensors are expected to last data every six seconds or at longer intervals. The sensors are expected to last for a minimum digital strain data every six seconds or at longer intervals. The sensors are expected to last for a minimum of 10 years without a battery replacement. of 10 years without a battery replacement. for a minimum of 10 years without a battery replacement. Figure 9. Installed strain gauge and wireless transmitter. Figure 9. Installed strain gauge and wireless transmitter. Figure 9. Installed strain gauge and wireless transmitter. 6.1. Installation of Strain Gauges 6.1. Installation of Strain Gauges As shown in Figure 10a, the gaps between precast girders were stuffed with rubber As shown in Figure 10a, the gaps between precast girders were stuffed with rubber pad and shear bulbs were then filled UHPC materials. To monitor the short-term pad and shear bulbs were then filled UHPC materials. To monitor the short-term Infrastructures 2021, 6, 121 10 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 10 of 15 6.1. Installation of Strain Gauges As shown in Figure 10a, the gaps between precast girders were stuffed with rubber pad and shear bulbs were then filled UHPC materials. To monitor the short-term performance performance of the bridge deck joints, as shown in Figure 10b, six sensors were installed of the bridge at tdeck he left joints, and rias ght shown sides (in L and Figu R) re of 10 th b, ree jo six sensors ints from wer the ed e installed ge to the center at the left of the brid and ge right sides(1, 2, (L and and R) 3). ofTwo strain se three joints nsors we from there edge attached to the atcenter the bottom of of the bridge each of (1, three joints usi 2, and 3). ng a superglue. Silicon was then applied around the strain gauges for protection from Two strain sensors were attached at the bottom of each of three joints using a superglue. moisture. Silicon was then applied around the strain gauges for protection from moisture. (a) Bridge joints filled with UHPC materials 3L 3R 2L 1L 1R 2R (b) SenSpot strain sensors installed on three joints from edge (1L, 1R, 2L, 2R, 3L, and 3R) Figure 10. Six SenSpot strain sensors installed on three joints. Figure 10. Six SenSpot strain sensors installed on three joints. 6.2. Loading Tests 6.2. Loading Tests Loading tests Load wer ing t e e performed sts were peusing rformead us standar ing a dsttandem-axial andard tandem dump -axial d truck umpadopted truck adopted 0 00 0 by Buchanan by Buch County anan , Iowa, County, Iow which is a, which 26 -8 i (8.1 s 26m) ′-8” (8 long .1 m) and lo8 ng a (2.4 nd m) 8′ ( wide 2.4 mwith ) wida e w wheel ith a wheel 0 00 0 00 base of 18′-8” (5.7 m) and a tandem axle spacing of 4′-6” (1.4 m). The loading truck was base of 18 -8 (5.7 m) and a tandem axle spacing of 4 -6 (1.4 m). The loading truck was driven at a crawl speed of 2–3 mph. As shown in Figure 11, the gross weight of the loading driven at a crawl speed of 2–3 mph. As shown in Figure 11, the gross weight of the loading truck was 50,000 lb (22.6 ton) with a rear tandem axle load of 40,000 lb (18.1 ton) and a truck was 50,000 lb (22.6 ton) with a rear tandem axle load of 40,000 lb (18.1 ton) and a front front single axle load of 10,000 lb (4.5 ton). The dump truck was driven on top of each joint single axle load of 10,000 lb (4.5 ton). The dump truck was driven on top of each joint in Infrastructures 2021, 6, 121 11 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 11 of 15 in such a way that the rightmost wheels were placed on top of a joint. First, the truck was such a way that the rightmost wheels were placed on top of a joint. First, the truck was driven 10 times on top of the rightmost joint. The truck was then moved laterally by about driven 10 times on top of the rightmost joint. The truck was then moved laterally by about six feet and driven 10 times on top of the second joint; this was repeated on the third joint six feet and driven 10 times on top of the second joint; this was repeated on the third joint located at the center of the bridge. located at the center of the bridge. Figure 11. A heavy tandem-axial dump truck loading on bridge joints. Figure 11. A heavy tandem-axial dump truck loading on bridge joints. To evaluate the short-term performance of the bridge joints after construction, strain To evaluate the short-term performance of the bridge joints after construction, strain data were collected from both sides of each joint. Figure 12a shows example strain data data were collected from both sides of each joint. Figure 12a shows example strain data collected from the left and right sides of joint 3 two years after construction. It shows three collected from the left and right sides of joint 3 two years after construction. It shows three sets of strain data collected on zero, two and four years after construction while a truck sets of strain data collected on zero, two and four years after construction while a truck was driven was dri on ven on top of top of the joint. the jo Ain close-up t. A close-up vi view ofew of the thir the thi d loadi rd l ng oaset dinis g set i shown s shown in Figur in Fi e 12 gure b, 12b, where the highest strain value from sensors 19 and 21 were 10 and 13 microstrains, where the highest strain value from sensors 19 and 21 were 10 and 13 microstrains, respec- respectively. The highest strain value from each sensor was selected to represent peak tively. The highest strain value from each sensor was selected to represent peak loading when loadin the g when the truck was pla truck was placed right c on ed top right of on top of the joint. the joint. Figur Figue re13 13shows showsa aplot plotof ofstrain straindata datacollected collected from three joi from three joints nts at at t thr hee ree time time-points: -points: (1) right after construction, (2) two years after construction, and (3) four years after con- (1) right after construction, (2) two years after construction, and (3) four years after struction. As can be seen from Figure 13, the first loading test right after construction in construction. As can be seen from Figure 13, the first loading test right after construction 2015 resulted in relatively high strain values, particularly the 36 microstrains at joint 1. It in 2015 resulted in relatively high strain values, particularly the 36 microstrains at joint 1. can be postulated that these high strain values were due to not well-seated bridge girders It can be postulated that these high strain values were due to not well-seated bridge and incomplete curing of the UHPC filling materials at the joints. However, it should girders and incomplete curing of the UHPC filling materials at the joints. However, it be noted that strain data collected from the left and right sides of each joint were quite should be noted that strain data collected from the left and right sides of each joint were similar. Strain data collected in the second and the fourth years after construction were quite similar. Strain data collected in the second and the fourth years after construction lower, ranging between 10 and 20 microstrains. Overall, the two sensors installed on both were lower, ranging between 10 and 20 microstrains. Overall, the two sensors installed on sides of the same joint exhibited similar peak strains, which confirmed that the stresses both sides of the same joint exhibited similar peak strains, which confirmed that the applied to the joint were evenly distributed across the joint. stresses applied to the joint were evenly distributed across the joint. Infrastructures 2021, 6, x FOR PEER REVIEW 12 of 15 Infrastructures 2021, 6, 121 12 of 15 (a) Sample strain data collected from three loading trials at joint 3 (b) Detailed sample strain data collected from joint 3 on the third loading trial Figure 12. Example strain data collected from joint 3 two years after construction. − Figure 12. Example strain data collected from joint 3 two years after construction. Infrastructures 2021, 6, 121 13 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 13 of 15 40 8 J1 Left J1 Right J2 Left J2 Right 35 7 7 J3 Left J3 Right Difference Joint1 Difference Joint2 30 6 Difference Joint3 25 5 5 20 4 15 3 10 2 5 1 1 11 0 0 0 Year since construction Figure 13. Strain data collected from left and right sides of each of three joints at 0, 2, and 4 years after construction. Figure 13. Strain data collected from left and right sides of each of three joints at 0, 2, and 4 years after construction. 7. Summary and Conclusions 7. Summary and Conclusions In the past 15 years, UHPC materials have been applied in over 250 bridges in the In the past 15 years, UHPC materials have been applied in over 250 bridges in the US, US, mostly as precast concrete deck panels and field-cast connections between mostly as precast concrete deck panels and field-cast connections between prefabricated prefabricated bridge elements. This paper presents the laboratory test results, design, field bridge elements. This paper presents the laboratory test results, design, field construction, construction, and monitoring and monitoring of a new of a new bridge using brid a unique ge usin UHPC g a un technology ique UHPC t which echnolog utilizes y which two ut difilfer ize ent s tw lengths o different of steel leng fibers ths of st of 16.3 eel f mm ibers of and 19.5 16.3mm mm and at a 1:219 ratio .5 mm at by weight. a 1:2 rat Lengths io by of steel fibers were optimized to increase both tensile strength and the toughness. This weight. Lengths of steel fibers were optimized to increase both tensile strength and the t unique oughness UHPC . This un material ique U was HPC mat used to eribuild al was a used t pi-girder o build bridge a piin -gir Buchanan der bridge in County Buchan , Iowa. an County, Iowa. Af After the bridge was ter the bridge wa constructed, the s constructe bridge joints d, the b werr eid monitor ge joints edwere moni three times tored three over four years using sensors attached to both sides of each of three joints. times over four years using sensors attached to both sides of each of three joints. First, laboratory testing of the UHPC material was performed to determine com- First, laboratory testing of the UHPC material was performed to determine pressive and indirect tensile strengths. The compressive strength satisfied the target compressive and indirect tensile strengths. The compressive strength satisfied the target compressive strength of 200 MPa (29,000 psi) after 28 days, with a very significant early compressive strength of 200 MPa (29,000 psi) after 28 days, with a very significant early gain in the compressive strength of 87.9 MPa (12,750 psi) in one day. The indirect tensile gain in the compressive strength of 87.9 MPa (12,750 psi) in one day. The indirect tensile strength of UHPC materials achieved 18.3 MPa (2654 psi) in 7 days, which is significantly strength of UHPC materials achieved 18.3 MPa (2,654 psi) in 7 days, which is significantly higher than that of regular concretes. higher than that of regular concretes. A pi-girder design with a box-shaped joint between girders was adopted to reduce A pi-girder design with a box-shaped joint between girders was adopted to reduce construction cost and protect the post-tensioned bottom flange from potential environmen- construction cost and protect the post-tensioned bottom flange from potential tal damage. The proposed UHPC material was produced with local cement and aggregates environmental damage. The proposed UHPC material was produced with local cement using a regular ready-mix truck. Flowable ready-mix UHPC materials were poured into a and aggregates using a regular ready-mix truck. Flowable ready-mix UHPC materials prefabricated form and a total of six UHPC girders were steam-cured using heated water were poured into a prefabricated form and a total of six UHPC girders were steam-cured hoses at the Buchanan County yard. All precast pi-girders were post-tensioned using using heated water hoses at the Buchanan County yard. All precast pi-girders were post- longitudinal strands at both bottom ends. Six precast UHPC girders were installed at the tensioned using longitudinal strands at both bottom ends. Six precast UHPC girders were jobsite using a crane and laterally post-tensioned through the crossbeams. installed at the jobsite using a crane and laterally post-tensioned through the crossbeams. During the construction process, we learned the following lessons through wasting During the construction process, we learned the following lessons through wasting batches of UHPC mixes: batches of UHPC mixes: We observed many cement balls due to quick hydration of cement with wet cement. • We observed many cement balls due to quick hydration of cement with wet cement. Because UHPC does not use coarse aggregates, the chance of forming cement balls Because UHPC does not use coarse aggregates, the chance of forming cement balls is is very high. We solved the cement ball problem by separating cement from wet very high. We solved the cement ball problem by separating cement from wet sand sand by mixing cement with less reactive premix first before adding wet sand to the by mixing cement with less reactive premix first before adding wet sand to the ready- ready-mix truck. mix truck. Strain (µs) Difference Infrastructures 2021, 6, 121 14 of 15 Bolts used to tie wood formwork panels at the bottom were separated due to the lateral pressure from the flowable UHPC mix. We solved this problem by doubling the number of bolts at the bottom of the formwork. Due to the use of a high amount of superplasticizer with minimum water, there was a very narrow time window between flowing and setting of UHPC mix. There- fore, we optimized the mixing time so that UHPC mix did not start setting in the ready-mix truck. To evaluate a short-term performance of the bridge joints after construction, strain data were collected from each of three joints. High strain values were observed right after construction due to unsettled bridge girders and incomplete curing of the UHPC filling materials at the joints. However, strain data collected from the left and right sides of each joint were very similar. Strain data collected in the second and fourth years after construction were lower, ranging between 10 and 20 microstrains, and the differences between strains from left and right sides of each joint were 7 microstrains or less. Based on similar peak strains from both sides of each joint four years after construction, it can be concluded that the joints between girders have been performing well. Hawkeye bridge was successfully constructed utilizing innovative UHPC materials and has been performing satisfactorily. The adoption of UHPC materials in rehabilitating bridges and constructing primary bridge components is progressing rapidly in the world because of UHPC’s unique charac- teristics of the higher strength and longer durability than regular concretes. This innovative slender and longer girder design is aesthetically pleasing and provides more open space, which should be a preferred bridge design in smart cities. Author Contributions: The authors confirm contribution to the paper as follows: study conception and design: H.L., B.-S.K. and B.K., data collection, processing and analysis: H.K., X.H., B.M., draft manuscript preparation: H.K., X.H., B.M., H.L., laboratory tests: H.K., G.-S.R., K.-T.K., field construction and documentation: H.K., C.J., B.-S.K. and B.K. All authors have read and agreed to the published version of the manuscript. Funding: This research received an external funding from Korea Agency for Infrastructure Technol- ogy Advancement (KAIA). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: No new data were created or analyzed in this study. Data sharing is not applicable to this article. Conflicts of Interest: The authors declare no conflict of interest. Disclaimer Notice: The contents of this paper reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. The opinions, findings, and conclusions expressed in this paper are those of the authors and not necessarily those of the sponsors. The sponsors assume no liability for the contents or use of the information contained in this document. References 1. Lorea, C. CO Emission from Cement Industry, What’s the Best Estimate? 2021. Available online: https://www.linkedin.com/ pulse/co2-emission-from-cement-industry-whats-best-estimate-claude-lorea (accessed on 19 July 2021). 2. Sheheryar, M.; Rehan, R.; Nehdi, M.L. Estimating CO2 Emission Savings from Ultrahigh Performance Concrete: A System Dynamics Approach. Materials 2021, 14, 995. [CrossRef] [PubMed] 3. Wille, K.; Boisvert-Cotulio, C. Development of Non-Proprietary Ultra-High Performance Concrete for Use in the Highway Bridge Sector; Report No. PB2013-110587; NTIS: Springfield, VA, USA, 2013. 4. Blais, Y.P.; Couture, M. Precast, Prestressed Pedestrian Bridge World’s First Reactive Powder Concrete Structure. PCI J. 1997, 44, 60–72. [CrossRef] 5. David, G.; Micheal, A.; Maher, K.T. Ultra-High-Performance Concrete Optimization of Double-Tee Bridge Beams. In ASPIRE Concrete Bridge Magazine; Winter, 2020; pp. 26–32. Available online: http://aspirebridge.com/magazine/2020Winter/CBP-UHPC. pdf (accessed on 19 July 2021). Infrastructures 2021, 6, 121 15 of 15 6. Russell, H.G.; Graybeal, B.A. Ultra High Performance Concrete: A State of the Art Report for the Bridge Community; FHWA-HRT-13-060; Federal Highway Administration: Washington, DC, USA, June 2013. 7. Graybeal, B.A. Ultra-High Performance Concrete; FHWA-HRT-11-038; Federal Highway Administration: Washington, DC, USA, March 2011. 8. Ryu, G.S.; Kang, S.T.; Park, J.J.; Koh, K.T.; Kim, S.W. Mechanical Behavior of UHPC according to Hybrid use of Steel Fibers. Adv. Mater. Res. 2011, 287–290, 453–457. [CrossRef] 9. FHWA North American Deployments of UHPC in Highway Bridge Construction. Available online: https://highways.dot.gov/ research/structures/ultra-high-performance-concrete/deployments (accessed on 19 July 2021). 10. Haber, Z.B. Improving Bridge Preservation with UHPC; No. FHWA-HRT-21-002; Federal Highway Administration, Office of Infrastructure Research and Development: Washington, DC, USA, 2021. 11. Sritharan, S.; Doiron, G.; Bierwagen, D.; Keierleber, B.; Abu-Hawash, A. First Application of UHPC Bridge Deck Overlay in North America. J. Transp. Res. Board 2018, 2672, 40–47. [CrossRef] 12. Graybeal, B.A.; Haber, Z.B. Ultra-High-Performance Concrete for Bridge Deck Overlays; FHWA-HRT-17-097; Federal Highway Administration: Washington, DC, USA, 2018. 13. Varga, I.D.L.; Haber, Z.B.; Graybeal, B.A. Enhancing Shrinkage Properties and Bond Performance of Prefabricated Bridge Deck Connection Grouts: Material and Component Testing. J. Mater. Civ. Eng. 2018, 30, 04018053. [CrossRef] 14. Zhang, S.; Du, S.; Ang, Y.; Lu, Z. Study on Performance of Prestressed Concrete Hollow Slab Beams Reinforced by Grouting with Ultra-High Performance Concrete. Case Stud. Constr. Mater. 2021, 15, e00583. 15. Shafieifar, M.; Farzad, M.; Azizinamini, A. New Connection Detail to Connect Precast Column to Cap Beam using Ultra-High- Performance Concrete in Accelerated Bridge Construction Applications. Transp. Res. Rec. 2018, 2672, 207–220. [CrossRef] 16. Haber, Z.B.; Graybeal, B.A.; Nakashoji, B. Ultimate Behavior of Deck-to-girder Composite Connection Details using UHPC. J. Bridge Eng. 2020, 25, 04020038. [CrossRef] 17. Haber, Z.B.; Varga, I.D.; Graybeal, B.A.; Nakashoji, B.; El-Helou, R. Properties and Behavior of UHPC-Class Materials; FHWA-HRT- 18-036; Federal Highway Administration: Washington, DC, USA, 2018. 18. De la Varga, I.; Spragg, R.P.; El-Helou, R.G.; Graybeal, B.A. Shrinkage Cracking Propensity of UHPC. In International Interactive Symposium on Ultra-High Performance Concrete; Iowa State University Digital Press: Ames, IA, USA, 2019; Volume 2. 19. Mohebbi, A.; Haber, Z.; Graybeal, B.A. Evaluation of AASHTO Provisions for Creep and Shrinkage of Prestressed UHPC Girders. In International Interactive Symposium on Ultra-High Performance Concrete; Iowa State University Digital Press: Ames, IA, USA, 2019; Volume 2. 20. Qi, J.; Cheng, Z.; Zhou, K.; Zhu, Y.; Wang, J.; Bao, Y. Experimental and Theoretical Investigations of UHPC-NC Composite Slabs Subjected to Punching Shear-Flexural Failure. J. Build. Eng. 2021, 44, 102662. [CrossRef] 21. El-Helou, R.G.; Graybeal, B.A. The Ultra Girder: A design Concept for a 300-foot Single Span Prestressed Ultra-High Performance Concrete Bridge Girder. In International Interactive Symposium on Ultra-High Performance Concrete; Iowa State University Digital Press: Ames, IA, USA, 2019; Volume 2. 22. Graybeal, B.A.; Brühwiler, E.; Kim, B.S.; Toutlemonde, F.; Voo, F.L.; Zaghi, A. International perspective on UHPC in bridge engineering. J. Bridge Eng. 2020, 25, 04020094. [CrossRef] 23. Soh, M. Model-Based Design of a Ultra High Performance Concrete Prototype Highway Bridge Girder. Ph.D. Thesis, Mas- sachusetts Institute of Technology, Cambridge, MA, USA, 2003. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Infrastructures Multidisciplinary Digital Publishing Institute

Construction and Performance Monitoring of Innovative Ultra-High-Performance Concrete Bridge

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infrastructures Article Construction and Performance Monitoring of Innovative Ultra-High-Performance Concrete Bridge 1 1 1 1 , 2 2 Haena Kim , Byungkyu Moon , Xinyu Hu , Hosin (David) Lee *, Gum-Sung Ryu , Kyung-Taek Koh , 2 2 3 Changbin Joh , Byung-Suk Kim and Brian Keierleber Iowa Technology Institute, University of Iowa, Iowa City, IA 52242, USA; haena612@gmail.com (H.K.); byungkyu-moon@uiowa.edu (B.M.); xinyu-hu@uiowa.edu (X.H.) Department of Infrastructure Safety Research, Korea Institute of Civil Engineering and Building Technology, Goyang, Gyeonggi 10223, Korea; ryu0505@kict.re.kr (G.-S.R.); ktgo@kict.re.kr (K.-T.K.); cjoh@kict.re.kr (C.J.); bskim@kict.re.kr (B.-S.K.) Buchanan County, 1511 First Street Independence, Iowa City, IA 50644, USA; bkeierleber@co.buchanan.ia.us * Correspondence: hosin-lee@uiowa.edu; Tel.: +1-801-512-4202 Abstract: The application of Ultra-High-Performance Concrete (UHPC) materials in rehabilitating bridges and constructing primary bridge components is increasing rapidly across the world because of their superior strength and durability characteristics when compared to regular concretes. However, there have been few new bridges constructed using UHPC materials with regular formworks, ready- mix trucks, and construction equipment. This paper presents a comprehensive report encompassing the design, construction, and performance monitoring of a new bridge constructed in Iowa using a unique UHPC technology that includes steel fibers of two different lengths embedded in the concrete. By using optimized lengths of steel fibers, both the tensile strength and the toughness were increased. The UHPC material was produced with local cement and aggregates in the US Citation: Kim, H.; Moon, B.; Hu, X.; using typical ready-mix concrete equipment. This paper discusses the experience gained from Lee, H.; Ryu, G.-S.; Koh, K.-T.; Joh, C.; the design and construction process including mix design, batching, delivery of steel fibers to the Kim, B.-S.; Keierleber, B. Construction ready-mix concrete batch unit, and post-tensioning of precast slabs at the jobsite. For four years and Performance Monitoring of after construction, the joints of the bridge decks were monitored using strain sensors mounted on Innovative Ultra-High-Performance both sides of the deck joints. The strain values were quite similar between the two sides of each Concrete Bridge. Infrastructures 2021, 6, 121. https://doi.org/10.3390/ joint, indicating a good load transfer between precast bridge girders. A bridge was successfully infrastructures6090121 constructed using a unique UHPC technology incorporating two different lengths of steel fibers and utilizing local cement and aggregates and a ready-mix truck, and has been performing satisfactorily Academic Editor: Moncef L. Nehdi with a good load transfer across post-tensioned precast girder joints. Received: 23 July 2021 Keywords: UHPC; strain gauge; field construction; post-tensioning; monitoring; bridge; joint; Accepted: 24 August 2021 steel fibers Published: 30 August 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in 1. Introduction published maps and institutional affil- Concrete is the most commonly used building material in the world. A total of iations. 4.1 billion tons of cement were used in 2019, contributing approximately 7% of global CO emissions, assuming 0.9 pounds of CO generated for the manufacturing of 1 pound of cement [1]. The proposed Ultra-High-Performance Concrete (UHPC)’s significantly higher strength allows for the use of a slender member with smaller cross-sections and with a Copyright: © 2021 by the authors. longer service life, which will reduce the amount of CO emissions associated with building Licensee MDPI, Basel, Switzerland. concrete bridges [2]. This article is an open access article Concrete technology has evolved through the optimization of mix ingredients to distributed under the terms and improve strength, workability, and durability. In the 1980s, High-Performance Concretes conditions of the Creative Commons (HPCs) were developed, with significantly improved durability and compressive strengths Attribution (CC BY) license (https:// ranging from 48 to 117 MPa [3]. In the 1990s, UHPC was introduced in France and the first creativecommons.org/licenses/by/ UHPC pedestrian bridge, with a span of 60 m, was built in Quebec, Canada [4]. The first 4.0/). Infrastructures 2021, 6, 121. https://doi.org/10.3390/infrastructures6090121 https://www.mdpi.com/journal/infrastructures Infrastructures 2021, 6, x FOR PEER REVIEW 2 of 15 Infrastructures 2021, 6, 121 2 of 15 and the first UHPC pedestrian bridge, with a span of 60 m, was built in Quebec, Canada [4]. The first UHPC bridge in the US was constructed in 2006 in Wappello County, Iowa, UHPC bridge in the US was constructed in 2006 in Wappello County, Iowa, and another and another UHPC bridge was built in Buchanan County, Iowa, in 2008 [5,6]. UHPC bridge was built in Buchanan County, Iowa, in 2008 [5,6]. UHPC is a dense flowable mix which is mainly composed of fine masonry sands (no UHPC is a dense flowable mix which is mainly composed of fine masonry sands coarse aggregates) and steel fibers with a high-range water reducer to produce a very low (no coarse aggregates) and steel fibers with a high-range water reducer to produce a very water/cement ratio of around 0.25. UHPC typically exhibits a compressive strength low water/cement ratio of around 0.25. UHPC typically exhibits a compressive strength greater than 150 MPa (21.7 ksi) and a sustained post-cracking tensile strength greater than greater than 150 MPa (21.7 ksi) and a sustained post-cracking tensile strength greater 5 MPa (0.72 ksi) [7]. It is common to include a high proportion of silica fume up to 10 than 5 MPa (0.72 ksi) [7]. It is common to include a high proportion of silica fume up to percent relative to the weight of cement. UHPC displays a discontinuous pore structure 10 percent relative to the weight of cement. UHPC displays a discontinuous pore structure that enhances its durability. The most common steel fiber used in UHPC constructions is that enhances its durability. The most common steel fiber used in UHPC constructions is a a 0.2 mm diameter by 13 mm long straight fiber with a specified minimum tensile strength 0.2 mm diameter by 13 mm long straight fiber with a specified minimum tensile strength of 2000 MPa (290 ksi) [8]. of 2000 MPa (290 ksi) [8]. This paper presents the laboratory test results, design, construction, and monitoring This paper presents the laboratory test results, design, construction, and monitoring of a new bridge using a unique UHPC technology which utilizes two different lengths of of a new bridge using a unique UHPC technology which utilizes two different lengths of steel fibers, 16.3 mm and 19.5 mm, at a 1:2 ratio by weight. Lengths of steel fibers were steel fibers, 16.3 mm and 19.5 mm, at a 1:2 ratio by weight. Lengths of steel fibers were optimized to increase both the tensile strength and the toughness. This unique UHPC mix optimized to increase both the tensile strength and the toughness. This unique UHPC was used to build a pi-girder bridge in Buchanan County, Iowa. After the bridge was mix was used to build a pi-girder bridge in Buchanan County, Iowa. After the bridge was constructed, the bridge joints were monitored three times over four years using strain constructed, the bridge joints were monitored three times over four years using strain sensors attached on both sides of each joint. sensors attached on both sides of each joint. 2. Background 2. Background Over Overthe thepast past15 15years, years,as asshown shownin in F Figur igur e e1 1,, t the he n number umberof of U UHPC HPC p prrojects ojectscompleted completed each year has been steadily increasing [9]. As depicted in Figure 2, UHPC has been applied each year has been steadily increasing [9]. As depicted in Figure 2, UHPC has been applied in over 250 bridges in the US, mainly as precast concrete deck panels and the composite in over 250 bridges in the US, mainly as precast concrete deck panels and the composite connections between precast deck panels and supporting girders [9]. Until recently, UHPC connections between precast deck panels and supporting girders [9]. Until recently, materials were predominantly used for field-cast connections between prefabricated bridge UHPC materials were predominantly used for field-cast connections between elements [10]. Steel fibers cost $615/m when they are added 3 at 1.5% by volume, which prefabricated bridge elements [10]. Steel fibers cost $615/m when they are added at 1.5% represents about half of the total cost of UHPC at $1110/m [3]. Due to the high 3 cost of by volume, which represents about half of the total cost of UHPC at $1110/m [3]. Due to steel fibers in UHPC materials, UHPC has been more commonly used as a deck overlay the high cost of steel fibers in UHPC materials, UHPC has been more commonly used as rather than for building new bridges [11]. As a result, to date, only three bridges have a deck overlay rather than for building new bridges [11]. As a result, to date, only three been constructed in the US using UHPC materials, all in Iowa. An increased tensile bridges have been constructed in the US using UHPC materials, all in Iowa. An increased bond strength of a specially formulated UHPC overlay on existing bridge decks has been tensile bond strength of a specially formulated UHPC overlay on existing bridge decks reported [12]. has been reported [12]. Figure 1. Number of UHPC projects each year [9]. Figure 1. Number of UHPC projects each year [9]. Infrastructures 2021, 6, 121 3 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 3 of 15 Figure 2. Use of UHPC materials in bridge components in the United States [9]. Figure 2. Use of UHPC materials in bridge components in the United States [9]. Grouts have a significant impact on a bridge’s deck-level connection performance. To Grouts have a significant impact on a bridge’s deck-level connection performance. improve the structural performance of the connections between bridge decks, UHPC grout To improve the structural performance of the connections between bridge decks, UHPC with a lower shrinkage and enhanced bonding strength has been adopted [13]. Due to grout with a lower shrinkage and enhanced bonding strength has been adopted [13]. Due UHPC grouting material’s improved shear bearing capacity, the beam stress is effectively to UHPC grouting material’s improved shear bearing capacity, the beam stress is reduced and the development of oblique cracks is inhibited [14]. To better comprehend the effectively reduced and the development of oblique cracks is inhibited [14]. To better behavior of precast deck connections for accelerated construction, a new connection detail comprehend the behavior of precast deck connections for accelerated construction, a new to connect a precast column to a cap beam was analyzed using nonlinear finite element connection detail to connect a precast column to a cap beam was analyzed using nonlinear analysis [15]. Furthermore, small-scale direct shear tests and large-scale double shear push- finite element analysis [15]. Furthermore, small-scale direct shear tests and large-scale off tests were performed on innovative connections constructed using UHPC materials. The double shear push-off tests were performed on innovative connections constructed using novel connection details were reported to have the potential to meet the existing strength UHPC materials. The novel connection details were reported to have the potential to meet limit requirements outlined in the AASHTO bridge design specification [16]. the existing strength limit requirements outlined in the AASHTO bridge design UHPC does not exhibit a significant amount of drying shrinkage because a large specification [16]. amount of steel fibers in the HPC help reduce the shrinkage cracking and redistribute UHPC does not exhibit a significant amount of drying shrinkage because a large the shrinkage strains [17]. UHPC materials have less propensity for shrinkage cracking amount of steel fibers in the HPC help reduce the shrinkage cracking and redistribute the and shrinkage cracking occurs in the form of microcracks due to the steel fibers [18]. For shrinkage strains [17]. UHPC materials have less propensity for shrinkage cracking and the creep and shrinkage models for AASHTO LRFD, UHPC materials provide superior shrinkage cracking occurs in the form of microcracks due to the steel fibers [18]. For the mechanical properties, a low water content, and a high volume of fiber reinforcement, creep and shrinkage models for AASHTO LRFD, UHPC materials provide superior which can enhance creep and shrinkage behavior compared to conventional concretes [19]. mechanic Full-depth al p application roperties, a low water co of UHPC at the ntent, punching and a hi shear gh volu area me of in flat fi slabs ber rei transferr nforcement, ed the which can failure mode enhance creep and sh from a brittle punching rinkage beha shear failur vior compa e to a ductile red to conventi punchingona shear l concretes -flexural [1 failur 9]. Fu eland l-dep impr th ap oved plicat both ion of cracking UHPCstr atength the pu and nchpunching ing shear a shear rea in str fl ength at slab [20 s t]. ransferred the failure m It is possible ode from to a br constr ittle punchin uct a 300 foot g she (91.4 ar fail m) ure to a UHPC du gir ctider le pu with nching shear-flexural a weight per unit length that is similar to that of an existing 200 feet (61 m) long conventional concrete failure and improved both cracking strength and punching shear strength [20]. girder [21]. This innovative slender and longer girder design will provide aesthetic value It is possible to construct a 300 foot (91.4 m) UHPC girder with a weight per unit and more of the open space that is critically needed for smart cities. The adoption of length that is similar to that of an existing 200 feet (61 m) long conventional concrete girder UHPC materials in rehabilitating bridges and constructing primary bridge components [21]. This innovative slender and longer girder design will provide aesthetic value and is progressing rapidly in the world because of UHPC’s unique characteristics of higher more of the open space that is critically needed for smart cities. The adoption of UHPC strength and longer durability than regular concretes [22]. materials in rehabilitating bridges and constructing primary bridge components is progressing rapidly in the world because of UHPC’s unique characteristics of higher 3. Materials and Specimen Preparation strength and longer durability than regular concretes [22]. Table 1 summarizes the optimum mix design for the proposed UHPC material, which was developed by performing compressive and indirect tensile tests of numerous spec- 3. Materials and Specimen Preparation imens. Short steel fibers prevent microcracks whereas long fibers prevent macro-cracks Table 1 summarizes the optimum mix design for the proposed UHPC material, which through their bridging effect [9]. Our unique UHPC material contained longer steel fibers was developed by performing compressive and indirect tensile tests of numerous Infrastructures 2021, 6, 121 4 of 15 with lengths of 0.63 in (16.3 mm) and 0.78 in (19.5 mm) mixed at a respective ratio of 1.6% and 3.2% by weight, and they significantly increased flexural tensile strength. The water to cement (w/c) ratio of the UHPC was 0.23, which is the lowest amount of water needed for cement hydration. To improve the workability, based on the observations of the dry mixing condition, a slightly higher amount of superplasticizer (0.7% by weight) was used. Table 1. Mix design of UHPC. Percent 3 3 3 Constituents lb/yd (kg/m ) lb/ft by Weight Sand 1462 (867) 54.1 35.30% Cement 1329 (789) 45.9 32.10% Water 311 (184) 11.5 7.50% Superplasticizer 31 (18) 1.15 0.70% 16.3 mm fiber 66 (39) 2.4 1.60% 19.5 mm fiber 131 (78) 4.8 3.20% Defoamer 1 (0.5) 0.04 0.02% Shrinkage-reducing agent 13 (8) 0.48 0.30% Premix * 797 (473) 29.5 19.30% Total 4142 (2457) 153.4 100% * Silica fume, ground quartz, and other performance enhancers. First, all dry materials, namely cement, sand, and premix, were mixed in a 2-cubic concrete mixer at a speed of 20 rpm for 5 min. The water and other liquid additives such as superplasticizer and defoamer were then added and mixed for an additional 4 min. Finally, after the mix was evenly mixed, steel fibers were added to produce the laboratory mix. During the mixing process, extra amounts of water and superplasticizer were added to improve workability of the mix. For example, 0.9 kg of extra water and 0.74 kg of superplasticizer were added to the laboratory mix, resulting in higher w/c ratios (to 0.27 from the original w/c ratio of 0.23). 3.1. Compressive Strengths Both laboratory and field mix 3 6 inch (7.6 15.2 cm, diameter height) cylindrical specimens were tested for compressive strength using an Instron Prism 5500 (1.1 MN Capacity). The test results of both laboratory and field mixes are summarized in Table 2. As can be seen from plots of average compressive strengths with standard deviations shown in Figure 3, the wet-cured laboratory mix satisfied the target compressive strength of 180 MPa after 28 days, whereas the field mix slightly missed the target. As shown in Figure 3, the wet-cured laboratory mix achieved a very significant early gain in compressive strength of 87.9 MPa after one day, continued to gain strength until 14 days, and remained at a similar level after 28 days. The wet-cured field specimens exhibited similar levels of strength gain as those of wet-cured laboratory mix. Table 2. Compressive strength and standard deviation results of lab and field mix specimens. Average and Standard Deviation of Compression Strength in MPa Batch Day 1 Day 2 Day 4 Day 7 Day 14 Day 18 Day 28 Lab mix (1 cf) 87.9/10.8 114.3/15.4 133/3.2 155.8/3.4 174.4/5.3 n.a. 180/3.7 Field mix (5.5 cy) n.a. n.a. n.a. 154.5/8.4 144/2.5 181/5.0 174.2/21.9 Infrastructures 2021, 6, 121 5 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 5 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 5 of 15 Figure 3. Averages and standard deviations of compressive strengths of laboratory and field mixes Figure Figure 3. 3. A Aver verages ages and and standar standard dev d deviations iations of com of compr press essive ive streng strengths ths of la ofboratory laboratory and fi and eld m field ixmixes es for 66 UHPC specimens. for 66 UHPC specimens. for 66 UHPC specimens. 3.2. Indirect Tensile Strength 3.2. Indirect Tensile Strength 3.2. Indirect Tensile Strength For the laboratory mix (not the field mix) 3 by 6 in (7.6 × 15.2 cm, diameter × height) For the laboratory mix (not the field mix) 3 by 6 in (7.6  15.2 cm, diameter  height) For the laboratory mix (not the field mix) 3 by 6 in (7.6 × 15.2 cm, diameter × height) cylindrical specimens were prepared for indirect tensile strength testing. The average cylindrical specimens were prepared for indirect tensile strength testing. The average cylindrical specimens were prepared for indirect tensile strength testing. The average indirect tensile strengths and standard deviations are plotted in Figure 4. The wet-cured indir indir ect ect tensile strengths tensile strengths and stan and standar dard ddeviat deviations ions ar ar e plotted e plotted in in Figur Figur e 4. The e 4. The wet-cured wet-cur ed laboratory mix specimens achieved the highest indirect tensile strength of 18.3 MPa after laboratory laboratory m mix ix specimen specimens s achieve achieved d the thehighest highest in indir direct tensi ect tensile le strength of 18 strength of .3 18.3 MPa MPa after after 7 days and maintained the same strength after 14 days. 7 days and maintained the same strength after 14 days. 7 days and maintained the same strength after 14 days. 18.4/2.27 20 18.3/2.99 18.3/2.99 18.4/2.27 14.0/0.49 14.0/0.49 12.7/0.59 11.7/0.79 12.7/0.59 11.7/0.79 Day 1 Day 2 Day 4 Day 7 Day 14 Day 1 Day 2 Day 4 Day 7 Day 14 Curing Days Curing Days Laboratory Mix Laboratory Mix Figure 4. Averages and standard deviations of indirect tensile strengths of laboratory mixes. Figure 4. Averages and standard deviations of indirect tensile strengths of laboratory mixes. Figure 4. Averages and standard deviations of indirect tensile strengths of laboratory mixes. 4. Design of the Hawkeye UHPC Bridge 4. Design of the Hawkeye UHPC Bridge 4. Design of the Hawkeye UHPC Bridge As shown in Figure 5, the Hawkeye Bridge is 52′ (15.8 m) long and 32′-5” (10 m) wide 0 0 00 As shown in Figure 5, the Hawkeye Bridge is 52′ (15.8 m) long and 32′-5” (10 m) wide As shown in Figure 5, the Hawkeye Bridge is 52 (15.8 m) long and 32 -5 (10 m) wide with an innovative pi-girder design, where each girder is 52′ (15.8 m) long, 5′-3” (1.6 m) 0 0 00 with an innovative pi-girder design, where each girder is 52′ (15.8 m) long, 5′-3” (1.6 m) with an innovative pi-girder design, where each girder is 52 (15.8 m) long, 5 -3 (1.6 m) wide, and 2′-4” (0.7 m) deep. The Hawkeye Bridge was designed using the load factors 0 00 wide, and 2′-4” (0.7 m) deep. The Hawkeye Bridge was designed using the load factors wide, and 2 -4 (0.7 m) deep. The Hawkeye Bridge was designed using the load factors and load combinations of the AASHTO-LRFD standard. Service load stress checking was applied to precast girders and ultimate strength design was applied to the girder deck and INDIRECT TENSILE STRENGTH (MPa) INDIRECT TENSILE STRENGTH (MPa) Infrastructures 2021, 6, x FOR PEER REVIEW 6 of 15 and load combinations of the AASHTO-LRFD standard. Service load stress checking was Infrastructures 2021, 6, 121 6 of 15 applied to precast girders and ultimate strength design was applied to the girder deck and abutment. Each of six girders was post-tensioned. Five crossbeams were installed and post-tensioned at 12′-9” (3.9 m) spacing to ensure a proper lateral load distribution. The shear abutment. bulbs were then filled with U Each of six girders was post-tensioned. HPC materia Five ls to i crossbeams mprove the connecti were installed and vity between post- 0 00 tensioned at 12 -9 (3.9 m) spacing to ensure a proper lateral load distribution. The shear girders. bulbs were then filled with UHPC materials to improve the connectivity between girders. Figure 5. Plan view and cross-section of Hawkeye Bridge design. Figure 5. Plan view and cross-section of Hawkeye Bridge design. The original pi-girder design was developed by the Massachusetts Institute of Technology (MIT, Cambridge, MA, USA) with a 33” tall girder covered with a 3” top-slab throughout the mid span and a 6” thick slab at the ends of the girder [23]. The girders were prestressed, which allowed reinforcing steel to be eliminated. For the Hawkeye Infrastructures 2021, 6, 121 7 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 7 of 15 The original pi-girder design was developed by the Massachusetts Institute of Tech- Infrastructures 2021, 6, x FOR PEER REVIEW 7 of 15 00 00 nology (MIT, Cambridge, MA, USA) with a 33 tall girder covered with a 3 top-slab throughout the mid span and a 6 thick slab at the ends of the girder [23]. The girders Bridge, the shape of the pi girders was optimized for UHPC to minimize the cross-section were prestressed, which allowed reinforcing steel to be eliminated. For the Hawkeye Bridge, the shape of the pi girders was optimized for UHPC to minimize the cross-section while exploiting the superior properties of UHPC materials. The very high tensile and Bridge, the shape of the pi girders was optimized for UHPC to minimize the cross-section while exploiting the superior properties of UHPC materials. The very high tensile and compressive strengths of UHPC allowed a thinner slab and slimmer girders, making it while exploiting the superior properties of UHPC materials. The very high tensile and compressive strengths of UHPC allowed a thinner slab and slimmer girders, making it possible to combine slab and girder in a single piece. Compared to the MIT’s pi-girder compressive strengths of UHPC allowed a thinner slab and slimmer girders, making it possible to combine slab and girder in a single piece. Compared to the MIT’s pi-girder design, as shown in Figure 6, the height of a UHPC girder for the Hawkeye Bridge was possible to combine slab and girder in a single piece. Compared to the MIT’s pi-girder design, as shown in Figure 6, the height of a UHPC girder for the Hawkeye Bridge was reduced from 33”to 28” while the thickness of the slab was increased from 4” to 4.5”. Each design, as shown in Figure 6, the height of a UHPC girder for the Hawkeye Bridge was reduced from 33”to 00 28” wh 00 ile the thickness of the slab was increased from0 4” to 4.5” 0 00 . Each girder was post-tensioned rather than prestressed. To provide a more stable structure, reduced from 33 to 28 while the thickness of the slab was increased from 4 to 4.5 . Each girder was post-tensioned rather than prestressed. To provide a more stable structure, UHPC girders were laterally post-tensioned at the jobsite through the crossbeams. girder was post-tensioned rather than prestressed. To provide a more stable structure, UHPC girders were laterally post-tensioned at the jobsite through the crossbeams. UHPC girders were laterally post-tensioned at the jobsite through the crossbeams. Figure 6. Hawkeye Bridge pi-girder cross-section design. Figure 6. Hawkeye Bridge pi-girder cross-section design. Figure 6. Hawkeye Bridge pi-girder cross-section design. 5. Construction of the Hawkeye UHPC Bridge 5. Construction of the Hawkeye UHPC Bridge 5. Construction of the Hawkeye UHPC Bridge As shown in Figure 7, after demolishing the unstable existing bridge, construction of As shown in Figure 7, after demolishing the unstable existing bridge, construction of As shown in Figure 7, after demolishing the unstable existing bridge, construction of the substructure of the new UHPC bridge started in May 2015. First, six H-shaped steel the substructure of the new UHPC bridge started in May 2015. First, six H-shaped steel the substructure of the new UHPC bridge started in May 2015. First, six H-shaped steel piles were driven into the soil, approximately 12 ft (3.7 m) deep. Concrete stub abutments piles were driven into the soil, approximately 12 ft (3.7 m) deep. Concrete stub abutments piles were driven into the soil, approximately 12 ft (3.7 m) deep. Concrete stub abutments were constructed on top of the pile foundation. All pictures in this section were captured were constructed on top of the pile foundation. All pictures in this section were captured were constructed on top of the pile foundation. All pictures in this section were captured by the authors. by the authors. by the authors. Figure 7. Existing unstable bridge (left) and construction of substructure of new UHPC bridge (right). Figure 7. Existing unstable bridge (left) and construction of substructure of new UHPC bridge (right). Figure 7. Existing unstable bridge (left) and construction of substructure of new UHPC bridge (right). On 23 June 2015, construction of the first UHPC girder commenced at the yard of On 23 June 2015, construction of the first UHPC girder commenced at the yard of Buchanan County Office, Iowa. Due to dry, hot weather conditions, an additional 10% of Buchanan County Office, Iowa. Due to dry, hot weather conditions, an additional 10% of superplasticizer was added to the mix to increase the workability. Table 3 summarizes the superplasticizer was added to the mix to increase the workability. Table 3 summarizes the final mix design for the ready-mix UHPC along with mixing instructions in the field. final mix design for the ready-mix UHPC along with mixing instructions in the field. Initially, we added cement to the wet sand and it created many cement balls because of Initially, we added cement to the wet sand and it created many cement balls because of the quick hydration of cement by the moisture in the wet sand. To prevent the creation of the quick hydration of cement by the moisture in the wet sand. To prevent the creation of Infrastructures 2021, 6, 121 8 of 15 On 23 June 2015, construction of the first UHPC girder commenced at the yard of Buchanan County Office, Iowa. Due to dry, hot weather conditions, an additional 10% of superplasticizer was added to the mix to increase the workability. Table 3 summarizes the final mix design for the ready-mix UHPC along with mixing instructions in the field. Initially, we added cement to the wet sand and it created many cement balls because of the quick hydration of cement by the moisture in the wet sand. To prevent the creation of cement balls, we mixed cement with less reactive premix and then added the wet sand in a ready-mix truck. Table 3. Mixing proportions and mixing instructions for UHPC. Mixing Orders UHPC MIX Total (lb/5.5 CY) Mixing Instruction 1 Premix 4386 2 Cement 7310 Mix for 10 min 3 Wet sand (MC = 4.2%) 8041 Mix for 5 min 4 Water 1710 Rotate at 10 RPM 5 Shrinkage reducer 73 Mix for 5 min 6 Defoamer 5 Add at 10 RPM 7 Superplasticizer 140 Mix for 5 min at maximum speed 8 Steel fiber (0.63 inch long) 362 Add for 20 min at 10 RPM 9 Steel fiber (0.78 inch long) 723 Mix for 2 min at maximum speed For the first batch, bolts at the bottom of formwork were pulled out of the form due to the lateral pressure and leaking concrete mix. Therefore, as shown in Figure 8a, a special wooden girder form was fabricated to ensure the strength needed to resist the lateral pressure generated by the weight of the flowable UHPC mix. It took 11 cubic yards (8.4 m ) of UHPC mix to fill a form, where each ready-mix truck produced 5.5 cubic yards. Compared to the laboratory mix, only 82% superplasticizer was needed for the ready-mix truck due to its better mixing capability. As shown in Figure 8b, steel fibers were delivered to the ready-mix truck using a vibrating mesh and a conveyor belt. As shown in Figure 8c, flowable UHPC mix was poured into a form and the surface was leveled. Since the flowable UHPC mix set very quickly as it came out of the ready-mix truck, another batch of mix had to be discarded. After removing the formwork, the UHPC girder was steam-cured by placing heated water hoses to provide sufficient heat and water with a gradual heat application rate set at 10–15 C/hr. As shown in Figure 8d, each girder was post-tensioned using seven 0.6 (1.5 cm) diameter longitudinal strands with a total force of 300 kips (2.67 MN) to achieve a gauge pressure of 6500 psi (44.8 MPa) at both bottom ends. Strands were pulled up to 80% of the ultimate tensile strength, resulting in a 6 inch elongation. On 9 September 2015, six steam-cured girders were installed at the jobsite. As shown in Figure 8e, each of five transverse crossbeams was post-tensioned using three 0.6 (1.5 cm) diameter strands with a total force of 105.3 kips (0.468 MN), where 35.1 kips (0.156 MN) was applied to each strand to achieve a gauge pressure of 4500 psi (31.0 MPa). Once all three strands were post-tensioned, a duct was grouted and a cap was installed. As shown in Figure 8f, the unique Hawkeye Bridge was successfully constructed using innovative UHPC materials. Infrastructures 2021, 6, x FOR PEER REVIEW 9 of 15 Infrastructures 2021, 6, 121 9 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 9 of 15 (a) Girder formwork (b) Adding premix/steel fibers to ready-mix truck (a) Girder formwork (b) Adding premix/steel fibers to ready-mix truck (c) UHPC pouring (d) Longitudinal post-tensioning of girder (c) UHPC pouring (d) Longitudinal post-tensioning of girder (e) Transverse post-tensioning of crossbeam (f) Completed Hawkeye Bridge (e) Transverse post-tensioning of crossbeam (f) Completed Hawkeye Bridge Figure 8. Figure 8. U UH HPC mixing, PC mixing, pouring, pouring, and and c o cns ons trtr uc uc tion process tion process of Hawkeye Br of Hawkeye Br idge. idge. Figure 8. UHPC mixing, pouring, and construction process of Hawkeye Bridge. 6 6.. M Mo oni nito torrii ng ng o o ff Br Br id id gg ee De De ck ck Jo Jo in in tst s 6. Monitoring of Bridge Deck Joints As shown in Figure 9, each SenSpot strain sensor consists of two parts: a strain gauge As shown in Figure 9, each SenSpot strain sensor consists of two parts: a strain gauge As shown in Figure 9, each SenSpot strain sensor consists of two parts: a strain gauge with a precision of 1 microstrain and a wireless transmitter. The wireless transmitter with with a a pr precisi ecision on of of 1 1 micr microstra ostrainin and and a a wi wireless reless transmi transmitter tter. The wi . The wireless reless transmi transmitter tter converts analog strain measurements from the strain gauge to digitized data and sends converts converts an analog alog str strain ainmeasur measurements fr ements from om th thee str strain aingauge gauge to to digitized digitized d data ata and and sen sends ds them wirelessly to the remote transmission gateway, which then sends the data to a them wirelessly to the remote transmission gateway, which then sends the data to a remote them wirelessly to the remote transmission gateway, which then sends the data to a remote cloud server through a cellular service. The wireless transmitter can transmit cloud remote clo serveru thr d serve ough r a thro cellular ugh service. a cellular The serv wireless ice. The wi transmitter reless transmi can transmit tter ca digital n tra strain nsmit digital strain data every six seconds or at longer intervals. The sensors are expected to last data every six seconds or at longer intervals. The sensors are expected to last for a minimum digital strain data every six seconds or at longer intervals. The sensors are expected to last for a minimum of 10 years without a battery replacement. of 10 years without a battery replacement. for a minimum of 10 years without a battery replacement. Figure 9. Installed strain gauge and wireless transmitter. Figure 9. Installed strain gauge and wireless transmitter. Figure 9. Installed strain gauge and wireless transmitter. 6.1. Installation of Strain Gauges 6.1. Installation of Strain Gauges As shown in Figure 10a, the gaps between precast girders were stuffed with rubber As shown in Figure 10a, the gaps between precast girders were stuffed with rubber pad and shear bulbs were then filled UHPC materials. To monitor the short-term pad and shear bulbs were then filled UHPC materials. To monitor the short-term Infrastructures 2021, 6, 121 10 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 10 of 15 6.1. Installation of Strain Gauges As shown in Figure 10a, the gaps between precast girders were stuffed with rubber pad and shear bulbs were then filled UHPC materials. To monitor the short-term performance performance of the bridge deck joints, as shown in Figure 10b, six sensors were installed of the bridge at tdeck he left joints, and rias ght shown sides (in L and Figu R) re of 10 th b, ree jo six sensors ints from wer the ed e installed ge to the center at the left of the brid and ge right sides(1, 2, (L and and R) 3). ofTwo strain se three joints nsors we from there edge attached to the atcenter the bottom of of the bridge each of (1, three joints usi 2, and 3). ng a superglue. Silicon was then applied around the strain gauges for protection from Two strain sensors were attached at the bottom of each of three joints using a superglue. moisture. Silicon was then applied around the strain gauges for protection from moisture. (a) Bridge joints filled with UHPC materials 3L 3R 2L 1L 1R 2R (b) SenSpot strain sensors installed on three joints from edge (1L, 1R, 2L, 2R, 3L, and 3R) Figure 10. Six SenSpot strain sensors installed on three joints. Figure 10. Six SenSpot strain sensors installed on three joints. 6.2. Loading Tests 6.2. Loading Tests Loading tests Load wer ing t e e performed sts were peusing rformead us standar ing a dsttandem-axial andard tandem dump -axial d truck umpadopted truck adopted 0 00 0 by Buchanan by Buch County anan , Iowa, County, Iow which is a, which 26 -8 i (8.1 s 26m) ′-8” (8 long .1 m) and lo8 ng a (2.4 nd m) 8′ ( wide 2.4 mwith ) wida e w wheel ith a wheel 0 00 0 00 base of 18′-8” (5.7 m) and a tandem axle spacing of 4′-6” (1.4 m). The loading truck was base of 18 -8 (5.7 m) and a tandem axle spacing of 4 -6 (1.4 m). The loading truck was driven at a crawl speed of 2–3 mph. As shown in Figure 11, the gross weight of the loading driven at a crawl speed of 2–3 mph. As shown in Figure 11, the gross weight of the loading truck was 50,000 lb (22.6 ton) with a rear tandem axle load of 40,000 lb (18.1 ton) and a truck was 50,000 lb (22.6 ton) with a rear tandem axle load of 40,000 lb (18.1 ton) and a front front single axle load of 10,000 lb (4.5 ton). The dump truck was driven on top of each joint single axle load of 10,000 lb (4.5 ton). The dump truck was driven on top of each joint in Infrastructures 2021, 6, 121 11 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 11 of 15 in such a way that the rightmost wheels were placed on top of a joint. First, the truck was such a way that the rightmost wheels were placed on top of a joint. First, the truck was driven 10 times on top of the rightmost joint. The truck was then moved laterally by about driven 10 times on top of the rightmost joint. The truck was then moved laterally by about six feet and driven 10 times on top of the second joint; this was repeated on the third joint six feet and driven 10 times on top of the second joint; this was repeated on the third joint located at the center of the bridge. located at the center of the bridge. Figure 11. A heavy tandem-axial dump truck loading on bridge joints. Figure 11. A heavy tandem-axial dump truck loading on bridge joints. To evaluate the short-term performance of the bridge joints after construction, strain To evaluate the short-term performance of the bridge joints after construction, strain data were collected from both sides of each joint. Figure 12a shows example strain data data were collected from both sides of each joint. Figure 12a shows example strain data collected from the left and right sides of joint 3 two years after construction. It shows three collected from the left and right sides of joint 3 two years after construction. It shows three sets of strain data collected on zero, two and four years after construction while a truck sets of strain data collected on zero, two and four years after construction while a truck was driven was dri on ven on top of top of the joint. the jo Ain close-up t. A close-up vi view ofew of the thir the thi d loadi rd l ng oaset dinis g set i shown s shown in Figur in Fi e 12 gure b, 12b, where the highest strain value from sensors 19 and 21 were 10 and 13 microstrains, where the highest strain value from sensors 19 and 21 were 10 and 13 microstrains, respec- respectively. The highest strain value from each sensor was selected to represent peak tively. The highest strain value from each sensor was selected to represent peak loading when loadin the g when the truck was pla truck was placed right c on ed top right of on top of the joint. the joint. Figur Figue re13 13shows showsa aplot plotof ofstrain straindata datacollected collected from three joi from three joints nts at at t thr hee ree time time-points: -points: (1) right after construction, (2) two years after construction, and (3) four years after con- (1) right after construction, (2) two years after construction, and (3) four years after struction. As can be seen from Figure 13, the first loading test right after construction in construction. As can be seen from Figure 13, the first loading test right after construction 2015 resulted in relatively high strain values, particularly the 36 microstrains at joint 1. It in 2015 resulted in relatively high strain values, particularly the 36 microstrains at joint 1. can be postulated that these high strain values were due to not well-seated bridge girders It can be postulated that these high strain values were due to not well-seated bridge and incomplete curing of the UHPC filling materials at the joints. However, it should girders and incomplete curing of the UHPC filling materials at the joints. However, it be noted that strain data collected from the left and right sides of each joint were quite should be noted that strain data collected from the left and right sides of each joint were similar. Strain data collected in the second and the fourth years after construction were quite similar. Strain data collected in the second and the fourth years after construction lower, ranging between 10 and 20 microstrains. Overall, the two sensors installed on both were lower, ranging between 10 and 20 microstrains. Overall, the two sensors installed on sides of the same joint exhibited similar peak strains, which confirmed that the stresses both sides of the same joint exhibited similar peak strains, which confirmed that the applied to the joint were evenly distributed across the joint. stresses applied to the joint were evenly distributed across the joint. Infrastructures 2021, 6, x FOR PEER REVIEW 12 of 15 Infrastructures 2021, 6, 121 12 of 15 (a) Sample strain data collected from three loading trials at joint 3 (b) Detailed sample strain data collected from joint 3 on the third loading trial Figure 12. Example strain data collected from joint 3 two years after construction. − Figure 12. Example strain data collected from joint 3 two years after construction. Infrastructures 2021, 6, 121 13 of 15 Infrastructures 2021, 6, x FOR PEER REVIEW 13 of 15 40 8 J1 Left J1 Right J2 Left J2 Right 35 7 7 J3 Left J3 Right Difference Joint1 Difference Joint2 30 6 Difference Joint3 25 5 5 20 4 15 3 10 2 5 1 1 11 0 0 0 Year since construction Figure 13. Strain data collected from left and right sides of each of three joints at 0, 2, and 4 years after construction. Figure 13. Strain data collected from left and right sides of each of three joints at 0, 2, and 4 years after construction. 7. Summary and Conclusions 7. Summary and Conclusions In the past 15 years, UHPC materials have been applied in over 250 bridges in the In the past 15 years, UHPC materials have been applied in over 250 bridges in the US, US, mostly as precast concrete deck panels and field-cast connections between mostly as precast concrete deck panels and field-cast connections between prefabricated prefabricated bridge elements. This paper presents the laboratory test results, design, field bridge elements. This paper presents the laboratory test results, design, field construction, construction, and monitoring and monitoring of a new of a new bridge using brid a unique ge usin UHPC g a un technology ique UHPC t which echnolog utilizes y which two ut difilfer ize ent s tw lengths o different of steel leng fibers ths of st of 16.3 eel f mm ibers of and 19.5 16.3mm mm and at a 1:219 ratio .5 mm at by weight. a 1:2 rat Lengths io by of steel fibers were optimized to increase both tensile strength and the toughness. This weight. Lengths of steel fibers were optimized to increase both tensile strength and the t unique oughness UHPC . This un material ique U was HPC mat used to eribuild al was a used t pi-girder o build bridge a piin -gir Buchanan der bridge in County Buchan , Iowa. an County, Iowa. Af After the bridge was ter the bridge wa constructed, the s constructe bridge joints d, the b werr eid monitor ge joints edwere moni three times tored three over four years using sensors attached to both sides of each of three joints. times over four years using sensors attached to both sides of each of three joints. First, laboratory testing of the UHPC material was performed to determine com- First, laboratory testing of the UHPC material was performed to determine pressive and indirect tensile strengths. The compressive strength satisfied the target compressive and indirect tensile strengths. The compressive strength satisfied the target compressive strength of 200 MPa (29,000 psi) after 28 days, with a very significant early compressive strength of 200 MPa (29,000 psi) after 28 days, with a very significant early gain in the compressive strength of 87.9 MPa (12,750 psi) in one day. The indirect tensile gain in the compressive strength of 87.9 MPa (12,750 psi) in one day. The indirect tensile strength of UHPC materials achieved 18.3 MPa (2654 psi) in 7 days, which is significantly strength of UHPC materials achieved 18.3 MPa (2,654 psi) in 7 days, which is significantly higher than that of regular concretes. higher than that of regular concretes. A pi-girder design with a box-shaped joint between girders was adopted to reduce A pi-girder design with a box-shaped joint between girders was adopted to reduce construction cost and protect the post-tensioned bottom flange from potential environmen- construction cost and protect the post-tensioned bottom flange from potential tal damage. The proposed UHPC material was produced with local cement and aggregates environmental damage. The proposed UHPC material was produced with local cement using a regular ready-mix truck. Flowable ready-mix UHPC materials were poured into a and aggregates using a regular ready-mix truck. Flowable ready-mix UHPC materials prefabricated form and a total of six UHPC girders were steam-cured using heated water were poured into a prefabricated form and a total of six UHPC girders were steam-cured hoses at the Buchanan County yard. All precast pi-girders were post-tensioned using using heated water hoses at the Buchanan County yard. All precast pi-girders were post- longitudinal strands at both bottom ends. Six precast UHPC girders were installed at the tensioned using longitudinal strands at both bottom ends. Six precast UHPC girders were jobsite using a crane and laterally post-tensioned through the crossbeams. installed at the jobsite using a crane and laterally post-tensioned through the crossbeams. During the construction process, we learned the following lessons through wasting During the construction process, we learned the following lessons through wasting batches of UHPC mixes: batches of UHPC mixes: We observed many cement balls due to quick hydration of cement with wet cement. • We observed many cement balls due to quick hydration of cement with wet cement. Because UHPC does not use coarse aggregates, the chance of forming cement balls Because UHPC does not use coarse aggregates, the chance of forming cement balls is is very high. We solved the cement ball problem by separating cement from wet very high. We solved the cement ball problem by separating cement from wet sand sand by mixing cement with less reactive premix first before adding wet sand to the by mixing cement with less reactive premix first before adding wet sand to the ready- ready-mix truck. mix truck. Strain (µs) Difference Infrastructures 2021, 6, 121 14 of 15 Bolts used to tie wood formwork panels at the bottom were separated due to the lateral pressure from the flowable UHPC mix. We solved this problem by doubling the number of bolts at the bottom of the formwork. Due to the use of a high amount of superplasticizer with minimum water, there was a very narrow time window between flowing and setting of UHPC mix. There- fore, we optimized the mixing time so that UHPC mix did not start setting in the ready-mix truck. To evaluate a short-term performance of the bridge joints after construction, strain data were collected from each of three joints. High strain values were observed right after construction due to unsettled bridge girders and incomplete curing of the UHPC filling materials at the joints. However, strain data collected from the left and right sides of each joint were very similar. Strain data collected in the second and fourth years after construction were lower, ranging between 10 and 20 microstrains, and the differences between strains from left and right sides of each joint were 7 microstrains or less. Based on similar peak strains from both sides of each joint four years after construction, it can be concluded that the joints between girders have been performing well. Hawkeye bridge was successfully constructed utilizing innovative UHPC materials and has been performing satisfactorily. The adoption of UHPC materials in rehabilitating bridges and constructing primary bridge components is progressing rapidly in the world because of UHPC’s unique charac- teristics of the higher strength and longer durability than regular concretes. This innovative slender and longer girder design is aesthetically pleasing and provides more open space, which should be a preferred bridge design in smart cities. Author Contributions: The authors confirm contribution to the paper as follows: study conception and design: H.L., B.-S.K. and B.K., data collection, processing and analysis: H.K., X.H., B.M., draft manuscript preparation: H.K., X.H., B.M., H.L., laboratory tests: H.K., G.-S.R., K.-T.K., field construction and documentation: H.K., C.J., B.-S.K. and B.K. All authors have read and agreed to the published version of the manuscript. Funding: This research received an external funding from Korea Agency for Infrastructure Technol- ogy Advancement (KAIA). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: No new data were created or analyzed in this study. Data sharing is not applicable to this article. Conflicts of Interest: The authors declare no conflict of interest. Disclaimer Notice: The contents of this paper reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. The opinions, findings, and conclusions expressed in this paper are those of the authors and not necessarily those of the sponsors. The sponsors assume no liability for the contents or use of the information contained in this document. References 1. Lorea, C. CO Emission from Cement Industry, What’s the Best Estimate? 2021. Available online: https://www.linkedin.com/ pulse/co2-emission-from-cement-industry-whats-best-estimate-claude-lorea (accessed on 19 July 2021). 2. Sheheryar, M.; Rehan, R.; Nehdi, M.L. 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Journal

Infrastructures – Multidisciplinary Digital Publishing Institute

Published: Aug 30, 2021

Keywords: UHPC; strain gauge; field construction; post-tensioning; monitoring; bridge; joint; steel fibers

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