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Abstract
applied sciences Article Article Article Industrial Low-Clinker Precast Elements Using Industrial Low-Clinker Precast Elements Using Industrial Low-Clinker Precast Elements Using Recycled Aggregates Recycled Aggregates Recycled Aggregates 1 , 1 2 2 Carlos Thomas * , Ana I. Cimentada , Blas Cantero , Isabel F. Sáez del Bosque 1, 1 1, 2 1 2 2 2 Carlos Thomas *, Ana I. Cim Care lnt osad Thom a , Blas C as *, An anter a I o. Cim , Isae bnt elad F. Sáe a , Blas C z del Bo ant ser que o , I and sabel F. Sáez del Bosque and and Juan A. Polanco 1 1 Juan A. Polanco Juan A. Polanco LADICIM (Laboratory of Materials Science and Engineering), University of Cantabria E.T.S. de Ingenieros 1 1 LADICIM (Laboratory of Mat eLADICIM rials Science (Lab anoratory of Mat d Engineeringe ), Un rials Science iversity of C and Engineer antabria Ein .T.S. g), Un de In iver gesity nier of C os antabria E.T.S. de Ingenieros de Caminos, Canales y Puertos, Av. Los Castros 44, 39005 Santander, Spain; de Caminos, Canales y Puertos, de Caminos, C Av. Los Castros 44, 39005 anales y Puertos, Santander, Spain; Av. Los Castros 44, 39005 Santander, Spain; anaisabel.cimentada@unican.es (A.I.C.); polancoa@unican.es (J.A.P.) anaisabel.cimentada@unican.es (A anaisabel .I.C.); pol .cima en nc toa@ ada@ uu nn ican ican .es (J .es (A .A.I .P.) .C .); polancoa@unican.es (J.A.P.) School of Civil Engineering, University of Extremadura, Institute for Sustainable Regional 2 2 School of Civil Engineering, U n School of iversity of Civ Ext il Engineering, remadura, Inst Uitute fo niversity of r Susta Ext inable Regional remadura, InstDevelopment itute for Sustainable Regional Development Development (INTERRA), Avda. de la Universidad, s/n, 10003 Cáceres, Spain; bcanteroch@unex.es (B.C.); (INTERRA), Avda. de la Universidad, (INTERRA) s/n, 10 , Avda. de 003 Cáceres, Sp la Universidad, ain; bcanteroch@unex.es (B.C.) s/n, 10003 Cáceres, Spain; bcanteroch@unex.es (B.C.) ; ; cmedinam@unex.es (I.F.S.d.B.) cmedinam@unex.es (I.F.S.d.B.)cm edinam@unex.es (I.F.S.d.B.) * Correspondence: thomasc@unican.es * Correspondence: thomasc@u * Correspondence: nican.es thomasc@unican.es Received: 31 August 2020; Accepted: 21 Received: 31 Sept August 2020; Accepted: 21 ember 2020; Published: 23 Se Sep pttember 2020; ember 2020 Published: 23 September 2020 Received: 31 August 2020; Accepted: 21 September 2020; Published: 23 September 2020 Abstract: Increasing amounts of Abstrasu ct: stainable concre Increasing amotes are unts of being sustainable concre used as society becomes tes are beingmore used as society becomes more Abstract: Increasing amounts of sustainable concretes are being used as society becomes more aware aware of the environment. Thi aware of s pa the envi per attempts to ronment. Thi evalua s pa te the properti per attempts to es of eva precast concrete luate the properties of precast concrete of the environment. This paper attempts to evaluate the properties of precast concrete elements elements formed with recyelements cled coarse for aggr med with egate rec and low ycled clinke coarser content cem aggregate aned low nt using clinke recry content cem cled ent using recycled formed with recycled coarse aggregate and low clinker content cement using recycled additions. additions. To this end, six different mix propor additions. To this end, six tions were different mix propor characterized: a re tions were ference concr charaecttee; 2 rize d: a reference concrete; 2 To this end, six di erent mix proportions were characterized: a reference concrete; 2 concretes with concretes with 25%wt. and 50 concretes wi %wt. subst ti h tuti 25on of %wt. coarse and 50%wt. aggreg subst ate made using mixed itution of coarse agconstr gregate made using mixed uction construction 25%wt. and 50%wt. substitution of coarse aggregate made using mixed construction and demolition and demolition wastes; and others with and demolition wastes; recycled cem an e d others with nt with low clink recycle er cont d ce e m nt e.nt The compress with low clink ive er content. The compressive wastes; and others with recycled cement with low clinker content. The compressive strength, strength, the elastic modulus, a strength, the nd the dura elasti bilic modulus, a ty indicator decrea nd the dura se with the proporti bility indicator decrea ons of recycl se wied th the proportions of recycled the elastic modulus, and the durability indicator decrease with the proportions of recycled aggregate aggregate replacing aggregat aggr e, eg and ate r it eis p acc lacing ent a uat ggr ed w egatie, th t and he in it corp is acc orat ention uat o ed w f recyc ith t led he ce inm corp entorat . ion of recycled cement. replacing aggregate, and it is accentuated with the incorporation of recycled cement. However, all the However, all the precast elements te However, all the prec sted show go ast od elements te performanc sted show e with s go light r od pe edurfcor tioma n in nc th e w e ith slight reduction in the precast elements tested show good performance with slight reduction in the mechanical properties. mechanical properties. To confirm the mechanical p appropriate roperties. To behavio confirm the ur of New Jersey pre appropriate be chavio ast bar ur r of iersNew Jersey pre , a test cast barriers, a test To confirm the appropriate behaviour of New Jersey precast barriers, a test that simulated the impact that simulated the impact of that sim a vehicu le w lated the imp as carried out act of . a vehicle was carried out. of a vehicle was carried out. Keywords: recycled concrete; Keywor low ds: clinker c recyclede conc ment; pr rete; eclow ast; m clinker c echanical ement; pr propertec ies;ast p; m hyseica chanic l al properties; physical Keywords: recycled concrete; low clinker cement; precast; mechanical properties; physical properties; properties; New Jersey barrproperties; New Jer iers sey barriers New Jersey barriers 1. Introduction 1. Introduction 1. Introduction Construction and demolition w Constarst uct e i(C onDW) and demo is non- lithaz ion w ardo ast use , (C inert DW) waisst non- e generat hazardo ed in us a , inny ert waste generated in any Construction and demolition waste (CDW) is non-hazardous, inert waste generated in any construction, rehabilitation or demol construction, reha ition work. Th bilitation or demol e industrial iand construction sectors genera tion work. The industrial and construction sectors genera te te construction, rehabilitation or demolition work. The industrial and construction sectors generate ǂ ǂǂ ǂ practically the same amount of non-h practically th azardo e same us w amo aste u(ind nt of non-h ustry 37, azardo 417 k u and s wacon ste (ind struct ustry ion 35 37, ,8 469 kt 17 k ) and construction 35,869 kt ) practically the same amount of non-hazardous waste (industry 37,417 kt and construction 35,869 kt ) in Spain [1]. The European Commi in Spain [1 ssion ]. The Eu estimates tha ropean t the vol Commi u ssi me of on esti CDW compri mates that the vol ses one thi ume of rd of CDW compri all ses one third of all in Spain [1]. The European Commission estimates that the volume of CDW comprises one third of all waste generated in the Eurowaste gene pean Union rat , which consti ed in the Euro tupean Union tes the largest wa , which consti ste stream [ tutes the la 2]. Recycling thi rgest was ste stream [ 2]. Recycling this waste generated in the European Union, which constitutes the largest waste stream [2]. Recycling this CDW would lead to more sust CDW would ainable growth, replac lead to more ing sust a linear economy based on use ainable growth, replacing a linear economy based on use of materials of materials CDW would lead to more sustainable growth, replacing a linear economy based on use of materials with a more circular econwit omh y. Th a miso i res cir imcpuolrt arant eco , as nom aggre y. Th gat is i ess are im t pohrt e sec ant, oas nd-m aggre ostg -use ated s r are aw t he second-most-used raw with a more circular economy. This is important, as aggregates are the second-most-used raw material material by humans, behind ma ote nrly ia wa l byte hu r [3 ma ]. T nsh, be ere hi isnd Europe only wa an le tegis r [3lat ]. T ioh n t ero e e isn Europe courage an rec leygis clin lat g ion to encourage recycling by humans, behind only water [3]. There is European legislation to encourage recycling CDW [4] CDW [4] and many countries h CDW [4] ave specific norms fo and many countries h r the use o ave fspecific norms fo recycled aggregat r t es he use o (RA) for f re co cy ncrete cled ag gregates (RA) for concrete and many countries have specific norms for the use of recycled aggregates (RA) for concrete [5–8]. [5–8]. In addition, the use of [5–8]. In RA could addition, the use lead to cheaper concrete of RA could [9]. lead to cheaper concrete [9]. In addition, the use of RA could lead to cheaper concrete [9]. Several studies have corroborated that Several studies have corr the inclusionoborated that of RA produ the incl ces conu crseio ten w ofit R h a A l porw od eru ces concrete with a lower Several studies have corroborated that the inclusion of RA produces concrete with a lower density density and increased hete dreongseity a neityn [10 d in–12 crea ]. seRd he A noterrm ogalelnei y ha ty [10 s a hi –12g].h eR r po A no rosrim tya tha lly ha n na s atu hi ragl her porosity than natural and increased heterogeneity [10–12]. RA normally has a higher porosity than natural aggregate aggregate (NA) [13]. In a fresh st aggreg ate, at S e ( ilv N a et A) a [1l3] . [. In 11] co a fr nclude esh stat d that e, Silv recycle a et al. d [ aggr 11] co egate concr ncluded that ete (RAC) recycled aggregate concrete (RAC) (NA) [13]. In a fresh state, Silva et al. [11] concluded that recycled aggregate concrete (RAC) is is less workable and, to achieve is lessa work workaabil ble it and, y eq t uoi ac valent to hieve that o a workfabil NA, RA ity eq could be uivalent to pre-sat that o ufrated, NA, RA could be pre-saturated, less workable and, to achieve a workability equivalent to that of NA, RA could be pre-saturated, or water added during mixing or wa ter ad to compensate [1 ded during mixing 4]. However to co , mpensate [1 the incorpor4]. However ation of com, pthe incorpor letely ation of completely or water added during mixing to compensate [14]. However, the incorporation of completely saturated Appl. Sci. 2020, 10, x; doi: FOR PEER RE Appl. Sci. VIEW 2020 www.mdpi.com/ , 10, x; doi: FOR PEER REVIEW www.mdpi.com/journal/applsci journal/applsci Appl. Sci. 2020, 10, 6655; doi:10.3390/app10196655 www.mdpi.com/journal/applsci Appl. Sci. 2020, 10, 6655 2 of 14 aggregates might cause an excessive water supply [15,16]. Once the RAC hardens, these aggregates make the concrete more susceptible to detrimental environmental e ects, resulting in a lower durability [17,18], which should be taken into consideration. Consequently, Annex 15 of the Spanish Instruction for Structural Concrete EHE-08 [19] and other studies [14,20] propose solutions, such as increasing the cement content, reducing the water/cement ratio, or increasing the coating thickness in the case of reinforced concrete. Generally, it is known that the incorporation of RA into concrete reduces its mechanical properties [21,22], due to the presence of contaminants such as plastics, glass, adhered mortar, etc., ref. [23] and the type of source material (crushed concrete, ceramic or mixed) of the RA [24–26]. The elastic modulus of RAC is lower than that of conventional concrete [15], reaching 45% less for 100% replacement [25]. The results obtained in the characterization of RAC with intermediate replacements present greater variation of results [20]. Other authors have demonstrated the viability of other types of recycled aggregates from waste, such as steel slag [27]. Moreover, the RA a ects the fatigue behavior of the concrete [28–32], showing a greater loss of properties than with the static properties. Further research has evaluated the recycling of concrete which incorporates RA [33,34]. With regard to precast concrete elements, it should be noted that, according to the ANDECE (National Association of the Prefabricated Concrete Industry, based in Spain), although the initial cost of elements is higher, the final cost is lower [35]. Other studies such as López-Mesa et al. [36] indicate an almost 18% higher cost of precast slabs versus in situ slabs; although the former have a lower environmental impact and the quality may be higher. Normally, precast elements have a quality seal guaranteeing their properties. Due to a manufacturing process with complete exhaustive control, precast slabs can be: tailored with special properties more easily as they are not manufactured on site; designed with flexibility dicult to achieve in-situ; and incorporate RA in their fabrication. In the case of precast elements using RA, a lower density and strength is observed [37]. Poon et al. [37] investigated the factors that a ect the properties of precast concrete blocks with RA, concluding that the compressive strength increases with the reduction in the aggregate/cement ratio (A/C), and that the water absorption of concrete blocks is significantly related to the absorption capacity of the aggregate. Katz [21] investigated the use of precast elements at di erent ages to produce RA for new precast elements, concluding that the mechanical properties (strength, modulus of elasticity, etc.) when using this type of aggregate in concrete, resemble those when using lightweight aggregates, such as those manufactured using fly ash. This paper presents the e ect on physical and mechanical properties of six types of mixes with di erent degrees of substitution. The physical properties and durability of these concretes will be analyzed first, then the mechanical properties will be assessed. Finally, the behavior of precast elements will be addressed. 2. Materials and Methodology The natural siliceous aggregate used in this study is present in three di erent sizes: 6/0 mm (NS), 12/6 mm (NG-M), and 22/12 mm (NG-C). Mixed recycled aggregates (MRA) were used by substituting NG-M for MRA-M and NG-C for MRA-C. These MRA were obtained from CDW and were principally made up of concrete and mortars ( 45%), unbound aggregate, and natural stone ( 45%). Figure 1 shows the di erent size grading for each aggregate. Appl. Sci. 2020, 10, 6655 3 of 14 Appl. Sci. 2020, 10, x FOR PEER REVIEW 3 of 14 100% NS 80% NG-M NG-C MRA-M MRA-C 60% 40% 20% 0% 0.01 0.1 1 10 100 Sieve size (log scale) [mm] Figure 1. Grading of the aggregates. Figure 1. Grading of the aggregates. Table 1 displays physical and mechanical properties: where SSS is the saturated dry surface Table 1 displays physical and mechanical properties: where SSS is the saturated dry surface density according to EN 1097-6 [38]; A is the water absorption by weight according to EN 1097-6 [38]; density according to EN 1097-6 [38]; A is the water absorption by weight according to EN 1097-6 [38]; LA is the Los Angeles index according to EN 1097-2 [39]; and FI is the flakiness index according to LA is the Los Angeles index according to EN 1097-2 [39]; and FI is the flakiness index according to EN 933-3 [40]. EN 933-3 [40]. The conventional cement (OPC) was CEM I 42.5 R, and the low clinker content cement (RC) was Table 1. Physical and mechanical properties of the aggregates. constituted of 75% CEM I 42.5 R and 25% ceramic waste from CDW. The tests performed with the Aggregates cement revealed a compressive strength 20% higher in the case of OPC. Property NS NG-M NG-C MRA-M MRA-C Table 1. Physical and mechanical properties of the aggregates. 2.76 2.74 2.74 2.42 2.45 SSS [g/cm ] A [%] 1.18 0.88 0.78 6.28 5.27 Aggregates LA [%] - 16 18 32 36 Property NS NG-M NG-C MRA-M MRA-C FI [%] - 21 25 10 10 SSS [g/cm ] 2.76 2.74 2.74 2.42 2.45 A [%] 1.18 0.88 0.78 6.28 5.27 The conventional cement (OPC) was CEM I 42.5 R, and the low clinker content cement (RC) was LA [%] - 16 18 32 36 constituted of 75% CEM I 42.5 R and 25% ceramic waste from CDW. The tests performed with the FI [%] - 21 25 10 10 cement revealed a compressive strength 20% higher in the case of OPC. Mixing the aggregates in di erent proportions with the two existing types of cement produced Mixing the aggregates in different proportions with the two existing types of cement produced six concrete mixtures, as shown in Table 2. HP signifies a combination of natural aggregates and six concrete mixtures, as shown in Table 2. HP signifies a combination of natural aggregates and conventional cement. HPR is a mixture of natural aggregates and low clinker content cement. HR25 conventional cement. HPR is a mixture of natural aggregates and low clinker content cement. HR25 and HR50 were fabricated with conventional cement and substitutions of NA by 25%wt. and 50%wt. and HR50 were fabricated with conventional cement and substitutions of NA by 25%wt. and 50%wt. proportions of RA, respectively. Finally, HRR25 and HRR50 were obtained by amalgamating low proportions of RA, respectively. Finally, HRR25 and HRR50 were obtained by amalgamating low clinker content cement with natural aggregates, substituted by 25%wt. and 50%wt. of recycled clinker content cement with natural aggregates, substituted by 25%wt. and 50%wt. of recycled aggregates accordingly. aggregates accordingly. Table 2. Concrete mix proportions (by m ). Concrete: HP HPR HR25 HR50 HRR25 HRR50 NS (6/0 mm) [kg]: 732 732 719 705 719 705 NG-M (12/6 mm) [kg]: 382 382 284 184 284 184 NG-C (22/12 mm) [kg]: 766 766 568 369 568 369 MRA-M (12/6 mm) [kg]: - - 89 178 89 178 MRA-C (22/12 mm) [kg]: - - 178 356 178 356 Cement [kg]: 400 - 400 400 - - Passing [%wt.] Appl. Sci. 2020, 10, 6655 4 of 14 Table 2. Concrete mix proportions (by m ). Concrete: HP HPR HR25 HR50 HRR25 HRR50 NS (6/0 mm) [kg]: 732 732 719 705 719 705 NG-M (12/6 mm) [kg]: 382 382 284 184 284 184 NG-C (22/12 mm) [kg]: 766 766 568 369 568 369 MRA-M (12/6 mm) [kg]: - - 89 178 89 178 MRA-C (22/12 mm) [kg]: - - 178 356 178 356 Cement [kg]: 400 - 400 400 - - Low clinker content cement [kg]: - 400 - - 400 400 Water [kg]: 193 193 202 211 202 211 Superplasticizer [kg]: 6.2 6.2 6.2 6.2 6.2 6.2 Water/cement ratio 0.48 0.48 0.50 0.53 0.50 0.53 2.1. Physical and Mechanical Properties Densities were obtained according to EN-12390-7 [41]. Sub-specimens (10Ø 10 cm) obtained by cutting 10Ø 20 cm cylindrical specimens were used. The porosity coecient is the result of comparing the absorbed water and specimen volume, while the absorption coecient is the result of comparing the absorbed water and specimen weight. Compressive strength was determined using 10Ø 20 cm cylindrical specimens according to EN-12390-3 [42], with an application strength rate of 0.5 MPa/s. Elastic modulus was determined with 10Ø 20 cm cylindrical specimens according to EN-12390-13 [43], at a strength rate of 0.5 MPa/s. 2.2. Durability A water penetration test was performed according to EN-12390-8 [44]. Sub-specimens (10Ø 10 cm) obtained by cutting 10Ø 20 cm cylindrical specimens were used. The samples were subjected to a pressure of 5 bar for 72 h. After 72 h water penetration under pressure, it was necessary to analyze how deep the water reached. To be able to observe the interior of the sample, it had to be opened. During this research, the Brazilian method (or indirect tensile strength method) was used to open the sample and analyze its interior. In general, when a cylindrical specimen is subjected to tension along its generatrix, it breaks into two halves, which allows the interior to be analyzed. Once the specimen had been opened, it was possible to measure the penetration depth of the water into the porous concrete. This technique also provided another interesting result: the indirect tensile strength of the concrete. For the determination of oxygen permeability, UNE-83981 [45] was taken as a reference. The 10Ø 20 cm cylindrical specimens were cut to discard the upper and lower face obtaining a new sample of 10Ø 10 cm. Silicone was impregnated perimetrically in the samples so that the oxygen could only pass longitudinally. A regulated oxygen pressure was applied on the upper face. Digital flow meters registered the oxygen escaping from the lower face. 2.3. Precast Element Preparation Two di erent types of precast elements were manufactured: unreinforced concrete ditches and steel-reinforced New Jersey barriers. Both were manufactured with an industrial concrete mixer, poured in metallic molds and vibrated by hand (Figure 2). In the case of reinforced concrete, reinforcements were set into the mold before the pouring of concrete. In both cases, precast elements were unmolded and cured at ambient temperature. Appl. Sci. 2020, 10, x FOR PEER REVIEW 4 of 14 Concrete: HP HPR HR25 HR50 HRR25 HRR50 Low clinker content cement [kg]: - 400 - - 400 400 Water [kg]: 193 193 202 211 202 211 Superplasticizer [kg]: 6.2 6.2 6.2 6.2 6.2 6.2 Water/cement ratio 0.48 0.48 0.50 0.53 0.50 0.53 2.1. Physical and Mechanical Properties Densities were obtained according to EN-12390-7 [41]. Sub-specimens (10Ø × 10 cm) obtained by cutting 10Ø × 20 cm cylindrical specimens were used. The porosity coefficient is the result of comparing the absorbed water and specimen volume, while the absorption coefficient is the result of comparing the absorbed water and specimen weight. Compressive strength was determined using 10Ø × 20 cm cylindrical specimens according to EN-12390-3 [42], with an application strength rate of 0.5 MPa/s. Elastic modulus was determined with 10Ø × 20 cm cylindrical specimens according to EN- 12390-13 [43], at a strength rate of 0.5 MPa/s. 2.2. Durability A water penetration test was performed according to EN-12390-8 [44]. Sub-specimens (10Ø × 10 cm) obtained by cutting 10Ø × 20 cm cylindrical specimens were used. The samples were subjected to a pressure of 5 bar for 72 h. After 72 h water penetration under pressure, it was necessary to analyze how deep the water reached. To be able to observe the interior of the sample, it had to be opened. During this research, the Brazilian method (or indirect tensile strength method) was used to open the sample and analyze its interior. In general, when a cylindrical specimen is subjected to tension along its generatrix, it breaks into two halves, which allows the interior to be analyzed. Once the specimen had been opened, it was possible to measure the penetration depth of the water into the porous concrete. This technique also provided another interesting result: the indirect tensile strength of the concrete. For the determination of oxygen permeability, UNE-83981 [45] was taken as a reference. The 10Ø × 20 cm cylindrical specimens were cut to discard the upper and lower face obtaining a new sample of 10Ø × 10 cm. Silicone was impregnated perimetrically in the samples so that the oxygen could only pass longitudinally. A regulated oxygen pressure was applied on the upper face. Digital flow meters registered the oxygen escaping from the lower face. 2.3. Precast Element Preparation Two different types of precast elements were manufactured: unreinforced concrete ditches and steel-reinforced New Jersey barriers. Both were manufactured with an industrial concrete mixer, poured in metallic molds and vibrated by hand (Figure 2). In the case of reinforced concrete, reinfo Appl. Sci. rcemen 2020, 10 ts were set int , 6655 o the mold before the pouring of concrete. In both cases, precast elements 5 of 14 were unmolded and cured at ambient temperature. Appl. Sci. 2020, 10, x FOR PEER REVIEW 5 of 14 2.4. Precast Element Mechanical Characterization Concrete ditches have approximate measurements of 50 × 50 × 15 cm. In order to characterize concrete ditches, the tests were carried out by bending. The horizontality of the set was verified, and force was applied by a roller (10Ø × 22 cm) in the central section with a displacement rate of 0.1 mm/s Figure 2. Precast element manufacturing sequence. (Figure 3). Figure 2. Precast element manufacturing sequence. New Jersey barriers have a section with approximate measurements of 47 × 80 cm and a length 2.4. Precast Element Mechanical Characterization of 100 cm. In order to characterize New Jersey barriers, a small crane was used to support the precast element on steel beams. These steel beams were placed at one end to correct the inclination of the Concrete ditches have approximate measurements of 50 50 15 cm. In order to characterize concr face on wh ete ditches, ich the test was to be perfo the tests were carried rmed, out by achiev bending. ing hori The zont horizontality ality on that fof ace (F the ig set ure was 3). verified, The test consisted in applying a stress with a roller (3Ø × 40 cm). The time of the test was very short (0.1–0.2 and force was applied by a roller (10Ø 22 cm) in the central section with a displacement rate of 0.1 s) to si mmmul /s (Figur ate an e i 3m ). pact. The strength and displacement data of the actuator were recorded during the test. Figure 3. Precast element characterization (concrete ditches left, New Jersey barriers right). Figure 3. Precast element characterization (concrete ditches left, New Jersey barriers right). New Jersey barriers have a section with approximate measurements of 47 80 cm and a length of 3. Results and Discussion 100 cm. In order to characterize New Jersey barriers, a small crane was used to support the precast element 3.1. Physion cal steel Proper beams. ties These steel beams were placed at one end to correct the inclination of the face on which the test was to be performed, achieving horizontality on that face (Figure 3). The test Figure 4 shows the relative and saturated densities of the concretes. As demonstrated, the consisted in applying a stress with a roller (3Ø 40 cm). The time of the test was very short (0.1–0.2 s) density decreases as the percentage of NA replaced by RA increases. This is due to the lower density to simulate an impact. The strength and displacement data of the actuator were recorded during of RA. It also becomes clear that the use of this RC does not affect density significantly. the test. 2.65 3. Results and Discussion OPC-Relative 2.6 RC-Relative 3.1. Physical Properties OPC-Saturated RC-Saturated 2.55 Figure 4 shows the relative and saturated densities of the concretes. As demonstrated, the density decreases as the percentage of NA replaced by RA increases. This is due to the lower density of RA. 2.5 It also becomes clear that the use of this RC does not a ect density significantly. 2.45 2.4 2.35 y = 2.61 - 0.00273x R = 0.852 y = 2.56 - 0.00183x R = 0.565 y = 2.45 - 0.00167x R = 0.789 2.3 y = 2.44 - 0.00203x R = 0.833 2.25 0 1020 304050 RA content [%] Figure 4. Density vs. RA content. Figure 5a shows porosity, and Figure 5b shows the absorption coefficient vs. substitution of NA by RA. A decrease in both properties is found in the concretes containing OPC as the percentage of Density [g/cm ] Appl. Sci. 2020, 10, x FOR PEER REVIEW 5 of 14 2.4. Precast Element Mechanical Characterization Concrete ditches have approximate measurements of 50 × 50 × 15 cm. In order to characterize concrete ditches, the tests were carried out by bending. The horizontality of the set was verified, and force was applied by a roller (10Ø × 22 cm) in the central section with a displacement rate of 0.1 mm/s (Figure 3). New Jersey barriers have a section with approximate measurements of 47 × 80 cm and a length of 100 cm. In order to characterize New Jersey barriers, a small crane was used to support the precast element on steel beams. These steel beams were placed at one end to correct the inclination of the face on which the test was to be performed, achieving horizontality on that face (Figure 3). The test consisted in applying a stress with a roller (3Ø × 40 cm). The time of the test was very short (0.1–0.2 s) to simulate an impact. The strength and displacement data of the actuator were recorded during the test. Figure 3. Precast element characterization (concrete ditches left, New Jersey barriers right). 3. Results and Discussion 3.1. Physical Properties Figure 4 shows the relative and saturated densities of the concretes. As demonstrated, the density decreases as the percentage of NA replaced by RA increases. This is due to the lower density Appl. Sci. 2020, 10, 6655 6 of 14 of RA. It also becomes clear that the use of this RC does not affect density significantly. 2.65 OPC-Relative 2.6 RC-Relative OPC-Saturated RC-Saturated 2.55 2.5 2.45 2.4 2.35 2 y = 2.61 - 0.00273x R = 0.852 y = 2.56 - 0.00183x R = 0.565 y = 2.45 - 0.00167x R = 0.789 2.3 y = 2.44 - 0.00203x R = 0.833 2.25 0 1020 304050 RA content [%] Figure 4. Density vs. RA content. Figure 4. Density vs. RA content. Figure 5a shows porosity, and Figure 5b shows the absorption coecient vs. substitution of NA Figure 5a shows porosity, and Figure 5b shows the absorption coefficient vs. substitution of NA Appl. Sci. 2020, 10, x FOR PEER REVIEW 6 of 14 by RA. A decrease in both properties is found in the concretes containing OPC as the percentage of by RA. A decrease in both properties is found in the concretes containing OPC as the percentage of replacement of aggregate increases. However, in the case of concrete made with RC, both properties replacement of aggregate increases. However, in the case of concrete made with RC, both properties increase as the percentage of RA increases. This may be because this type of cement interacts more increase as the percentage of RA increases. This may be because this type of cement interacts more with RAs of di erent nature, making it dicult to fill all the gaps amongst aggregates. Alternatively, with RAs of different nature, making it difficult to fill all the gaps amongst aggregates. Alternatively, it may be because the RA is able to absorb more water during kneading, causing a small deficit in this it may be because the RA is able to absorb more water during kneading, causing a small deficit in type of cement, which is very susceptible to variations in the water dosage. It is possible that there this type of cement, which is very susceptible to variations in the water dosage. It is possible that may be another reason that has not been identified. there may be another reason that has not been identified. 12 5 OPC RC OPC RC 4.5 3.5 2 2 y = 10.1 - 0.0561x R = 0.61 y = 4.3 - 0.0225x R = 0.55 2 2 y = 8.03 + 0.0206x R = 0.136 y = 3.41 + 0.0125x R = 0.236 5 2.5 0 102030 4050 0 102030 40 50 RA content [%] RA content [%] (b) (a) Figure 5. Porosity (a) and absorption coecient (b) vs. RA content. Figure 5. Porosity (a) and absorption coefficient (b) vs. RA content. 3.2. Compressive Strength and Modulus of Elasticity 3.2. Compressive Strength and Modulus of Elasticity Figure 6a shows the compressive strength-strain curves for each concrete at 160 days. Several Figure 6a shows the compressive strength-strain curves for each concrete at 160 days. Several studies [25,46,47] show that the concrete’s compressive strength decreases with the degree of substitution studies [25,46,47] show that the concrete’s compressive strength decreases with the degree of of RA for NA, but in strain terms, concretes show similar values around 2500 m/m for the failure. substitution of RA for NA, but in strain terms, concretes show similar values around 2500 µm/m for The exception is the HRR50 mix, which exceeds the values of the rest by almost 1000 m/m. Figure 6b the failure. The exception is the HRR50 mix, which exceeds the values of the rest by almost 1000 shows the same mixtures but at an age of 365 days. The decrease in strength may also be due to µm/m. Figure 6b shows the same mixtures but at an age of 365 days. The decrease in strength may also be due to the randomness of the type of RA and its distribution into the mortar matrix, which causes greater uncertainty than conventional mixtures. 30 30 HP HP HPR HPR 20 HR25 HR25 HRR25 HRR25 HR50 HR50 HRR50 HRR50 10 10 0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Strain [μm/m] Strain [μm/m] (a) (b) Figure 6. Compressive strength-strain at 160 (a) and 365 (b) days. Table 3 shows the different values of compressive strength obtained at different ages. Compressive strength [MPa] Porosity [%] Density [g/cm ] Compressive strength [MPa] Absorption coefficient [% wt.] Appl. Sci. 2020, 10, x FOR PEER REVIEW 6 of 14 replacement of aggregate increases. However, in the case of concrete made with RC, both properties increase as the percentage of RA increases. This may be because this type of cement interacts more with RAs of different nature, making it difficult to fill all the gaps amongst aggregates. Alternatively, it may be because the RA is able to absorb more water during kneading, causing a small deficit in this type of cement, which is very susceptible to variations in the water dosage. It is possible that there may be another reason that has not been identified. OPC RC OPC RC 4.5 3.5 2 2 y = 10.1 - 0.0561x R = 0.61 y = 4.3 - 0.0225x R = 0.55 2 2 y = 8.03 + 0.0206x R = 0.136 y = 3.41 + 0.0125x R = 0.236 5 2.5 0 102030 4050 0 102030 40 50 RA content [%] RA content [%] (b) (a) Figure 5. Porosity (a) and absorption coefficient (b) vs. RA content. 3.2. Compressive Strength and Modulus of Elasticity Figure 6a shows the compressive strength-strain curves for each concrete at 160 days. Several studies [25,46,47] show that the concrete’s compressive strength decreases with the degree of substitution of RA for NA, but in strain terms, concretes show similar values around 2500 µm/m for Appl. Sci. 2020, 10, 6655 7 of 14 the failure. The exception is the HRR50 mix, which exceeds the values of the rest by almost 1000 µm/m. Figure 6b shows the same mixtures but at an age of 365 days. The decrease in strength may a the lso be due t randomness o the ra of the ndom type ness of of RA the type of RA and its distribution and iinto ts distri thebution i mortar n matrix, to the morta which r m causes atrix, gr whi eater ch causes greater uncertainty than conventional mixtures. uncertainty than conventional mixtures. HP HP HPR HPR 20 20 HR25 HR25 HRR25 HRR25 HR50 HR50 HRR50 HRR50 0 0 0 500 1000 1500 2000 2500 3000 3500 4000 0 500 1000 1500 2000 2500 3000 3500 4000 Strain [μm/m] Strain [μm/m] (a) (b) Figure 6. Compressive strength-strain at 160 (a) and 365 (b) days. Figure 6. Compressive strength-strain at 160 (a) and 365 (b) days. Table 3 shows the di erent values of compressive strength obtained at di erent ages. Table 3 shows the different values of compressive strength obtained at different ages. Table 3. Compressive strength at di erent ages. Compressive Strength [MPa] Concrete: 28 days 160 days 365 days D [%] 36 28 HP 51.2 53.5 56.8 +10.9 HPR 46.1 50.2 46.6 +1.1 HR25 51.7 47.0 45.1 12.8 HR50 51.2 48.8 42.1 17.7 HRR25 45.0 47.5 43.7 2.9 HRR50 41.2 47.5 42.4 +2.9 Table 4 displays the modulus of elasticity, and shows that when using RC, the decrease in the elastic modulus is around 4%. The substitution of 25% by RA implies a decrease in elastic modulus of 5.6%, while the substitution of OPC in this case does not seem to have an influence. In the case of replacing 50% of aggregate by RA, the influence of the substitution of OPC by RC is meaningful, decreasing the elastic modulus by 15%. As for the loss of elastic modulus over time, a greater influence of the cement is observed than the type of aggregate, with a limit that tends to an asymptotic value of around 27 GPa. Table 4. Modulus of elasticity. Modulus of Modulus of Elasticity at % of the Initial Concrete: Substitution [%] Elasticity [GPa] 365 days [GPa] Elastic Modulus HP 0 35.5 31.7 89.3 HPR 0 34.1 29.5 86.5 HR25 25 33.9 30.8 90.8 HR50 50 31.9 29.3 91.8 HRR25 25 34.2 27.9 81.6 HRR50 50 27.8 27.4 98.6 Compressive strength [MPa] Porosity [%] Compressive strength [MPa] Absorption coefficient [% wt.] Appl. Sci. 2020, 10, 6655 8 of 14 Some organizations such as EHE-08, ACI, and Eurocode present their expressions to predict elastic modulus at 28 days from the compressive strength. In Expressions (1)–(3): E is elastic modulus at 28 days [GPa] and f is the compressive strength at 28 days [MPa]. EHE-08 [48] E = 8.5 f (1) ACI [49] E = 4.7 f (2) Eurocode 2 [50] 0.3 E = 22( f /10) (3) These expressions can be used to obtain the predictions and comparisons, with the experimental results shown in Table 5. The ACI method fits quite well in most cases but predicts higher values when the percentage of substitution is 50%. The EHE-08 method is safer, although when the substitution is 50% and the OPC is replaced by RC, higher values are produced due to the heterogeneity of the RA a ecting the compressive strength. These types of expressions only satisfactorily fit ordinary concrete models. Appl. Sci. 2020, 10, x FOR PEER REVIEW 8 of 14 Table 5. Elastic modulus obtained with di erent expressions. Table 5. Elastic modulus obtained with different expressions. Elastic Modulus [GPa] Elastic Modulus [GPa] Concrete: Concrete: Experimental EHE-08 ACI Eurocode 2 D [%] Experimental EHE-08 ACI Eurocode 2 ∆experimen experimental tal−EHE-08 [%] EHE-08 HP 35.5 31.6 33.6 35.9 12.5 HP 35.5 31.6 33.6 35.9 12.5 HPR 34.1 30.5 31.9 34.8 11.9 HPR 34.1 30.5 31.9 34.8 11.9 HR25 33.9 31.7 33.8 36.0 7.1 HR25 33.9 31.7 33.8 36.0 7.1 HR50 31.9 31.6 33.6 35.9 1.1 HR50 31.9 31.6 33.6 35.9 1.1 HRR25 34.2 30.2 31.5 34.5 13.1 HRR25 34.2 30.2 31.5 34.5 13.1 HRR50 27.8 29.4 30.2 33.6 -5.3 HRR50 27.8 29.4 30.2 33.6 -5.3 Figure 7 shows that from approximately 48 MPa, concrete with RA achieved the same Figure 7 shows that from approximately 48 MPa, concrete with RA achieved the same compressive compressive strength as concrete with OPC. RA concrete increases its elastic modulus significantly. strength as concrete with OPC. RA concrete increases its elastic modulus significantly. This might This might be due to the addition of a new variable, such as RA compared with OPC, which is much be due to the addition of a new variable, such as RA compared with OPC, which is much more more standardized throughout its production process. standardized throughout its production process. y = 1.15 * e^(0.123x) R = 0.984 y = 12.3 * e^(0.0452x) R = 0.985 OPC RC 26 28 30 32 34 Modulus of elasticity [GPa] Figure 7. Compressive strength vs. modulus of elasticity. Figure 7. Compressive strength vs. modulus of elasticity. 3.3. Oxygen and Water Permeability Figure 8a shows the oxygen permeability and Figure 8b shows the maximum penetration of water vs. percentage of substitution, respectively. The oxygen permeability coefficient increases with the substitution of the NA by RA. This behavior has been reported in some studies, such as Ismail et al. [51], Medina et al. [52], and Thomas et al. [14]. This increase is higher in concrete with RC than OPC; the type of cement being used is an important factor. The penetration of water increases with the increase in RA substitution. With these results, only HP and HPR comply with the standard EHE-08 [48] for structural concrete in the case of IIIa, IIIb, IV, etc. environment exposition, which requires an average penetration depth of 30mm, and maximum penetration depth of 50 mm. Penetration of water is related to typology and distribution of the RA, and its impurities with high absorption coefficients. Compressive strength [MPa] Appl. Sci. 2020, 10, 6655 9 of 14 3.3. Oxygen and Water Permeability Figure 8a shows the oxygen permeability and Figure 8b shows the maximum penetration of water vs. percentage of substitution, respectively. Appl. Sci. 2020, 10, x FOR PEER REVIEW 9 of 14 -17 60 5 10 -17 4 10 OPC RC -17 3 10 -17 2 10 Appl. Sci. 2020, 10, x FOR PEER REVIEW 9 of 14 OPC RC -17 y = 1.51e-17 + 1.66e-19x R = 0.94 60 -17 5 10 1 10 y = 46.8 + 0.06x R = 0.182 y = 47.5 + 0.22x R = 0.976 y = 8.32e-18 + 7.28e-19x R = 0.987 -17 4 10 0 30 0 10203040 50 0 10 OPC 203 RC 04050 RA content [%] RA content [%] -17 3 10 (a) (b) Figure 8. Oxygen permeability coecient (a) and water penetration depth (b). Figure 8. Oxygen permeability coefficient (a) and water penetration depth (b). -17 2 10 OPC RC The oxygen permeability coefficient increases with the substitution of the NA by RA. This behavior Figure 9 shows cross-sections of concrete where different colors can be seen. These are caused y = 1.51e-17 + 1.66e-19x R = 0.94 has been repo-1r 7ted in some studies, such as Ismail et al. [51], Medina et al. [52], and Thomas et al. [14]. 1 10 y = 46.8 + 0.06x R = 0.182 by the RC in HPR and HRR50 mixtures, and some kind of RA and impurities (such as wood or fired This increase is higher in concrete with RC than OPC; the type of cement being used is an important 2 factor. y = 47.5 + 0.22x R = 0.976 y = 8.32e-18 + 7.28e-19x R = 0.987 clay) in HRR50 mix. The penetration of water increases with the increase in RA substitution. With these results, 0 10203040 50 0 10 20304050 only HP and HPR comply with the standard EHE-08 [48] for structural concrete in the case of IIIa, IIIb, RA content [%] RA content [%] IV, etc. environment exposition, which requires an average penetration depth of 30mm, and maximum (b) (a) penetration depth of 50 mm. Penetration of water is related to typology and distribution of the RA, Figure 8. Oxygen permeability coefficient (a) and water penetration depth (b). and its impurities with high absorption coecients. Figure 9 shows cross-sections of concrete where di erent colors can be seen. These are caused by Figure 9 shows cross-sections of concrete where different colors can be seen. These are caused the RC in HPR and HRR50 mixtures, and some kind of RA and impurities (such as wood or fired clay) by the RC in HPR and HRR50 mixtures, and some kind of RA and impurities (such as wood or fired in HRR50 mix. clay) in HRR50 mix. Figure 9. Concrete specimen sections. 3.4. Testing Precast Elements Figure 10a shows the results of flexural tests on concrete ditches. It can be observed that the concrete composed of RC and RA (HRR50) behaves similarly to HP concrete, which is consistent with the results of splitting tensile strength shown in Table 6. Figure 10b shows the results of the impact test on reinforced precast New Jersey barriers, in which the force applied by the test machine and the position of the actuator are recorded. As expected, the concrete with OPC and NA displayed superior mechanical behavior than concrete with RC and RA. HRR50 could resist only 60% of the force, and Figure 9. Concrete specimen sections. Figure 9. Concrete specimen sections. 66% of the displacement that HP resisted. 3.4. Testing Precast Elements Figure 10a shows the results of flexural tests on concrete ditches. It can be observed that the concrete composed of RC and RA (HRR50) behaves similarly to HP concrete, which is consistent with the results of splitting tensile strength shown in Table 6. Figure 10b shows the results of the impact test on reinforced precast New Jersey barriers, in which the force applied by the test machine and the position of the actuator are recorded. As expected, the concrete with OPC and NA displayed superior mechanical behavior than concrete with RC and RA. HRR50 could resist only 60% of the force, and 66% of the displacement that HP resisted. Oxygen permeability coefficient [m ] Oxygen permeability coefficient [m ] Water penetration depth [mm] Water penetration depth [mm] Appl. Sci. 2020, 10, 6655 10 of 14 3.4. Testing Precast Elements Figure 10a shows the results of flexural tests on concrete ditches. It can be observed that the concrete composed of RC and RA (HRR50) behaves similarly to HP concrete, which is consistent with the results of splitting tensile strength shown in Table 6. Figure 10b shows the results of the impact test on reinforced precast New Jersey barriers, in which the force applied by the test machine and the position of the actuator are recorded. As expected, the concrete with OPC and NA displayed superior mechanical behavior than concrete with RC and RA. HRR50 could resist only 60% of the force, and 66% of the displacement that HP resisted. Appl. Sci. 2020, 10, x FOR PEER REVIEW 10 of 14 Appl. Sci. 2020, 10, x FOR PEER REVIEW 10 of 14 HP HRR50 HP HP HRR50 HRR50 400 HP HRR50 0 0 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0 Displacement [mm] Displacement [mm] 0 0.5 1 1.5 2 2.5 0 0.5 1 1.5 2 2.5 3 3.5 4 (b) (a) Displacement [mm] Displacement [mm] (b) (a) Figure 10. Figure 10.Mechanical Mechanicalcharacterization of characterization of pre precast cast elem elements: ents: Bending test o Bending test on n dit ditches ches ((a a)), , iimpact mpact ttest est o on n barriers ( barriers (b b). ). Figure 10. Mechanical characterization of precast elements: Bending test on ditches (a), impact test on barriers (b). Table 6. Splitting tensile strength. Table 6. Splitting tensile strength. Splitting Tensile Strength [MPa] Table 6. Splitting tensile strength. Splitting Tensile Strength [MPa] HP HPR HR25 HR50 HRR25 HRR50 HP HPR HR25 HR50 HRR25 HRR50 Splitting Tensile Strength [MPa] 3.36 3.51 3.48 - 3.30 3.58 3.36 3.51 3.48 - 3.30 3.58 HP HPR HR25 HR50 HRR25 HRR50 Figure 11 shows the results of the test performed with both types of precast elements. Different 3.36 3.51 3.48 - 3.30 3.58 sections of cracks in OPC and RC concrete ditches, and the fissure produced in a New Jersey barrier Figure 11 shows the results of the test performed with both types of precast elements. Different Figure 11 shows the results of the test performed with both types of precast elements. Di erent are visual results of the tests. sections of cracks in OPC and RC concrete ditches, and the fissure produced in a New Jersey barrier sections of cracks in OPC and RC concrete ditches, and the fissure produced in a New Jersey barrier are visual results of the tests. are visual results of the tests. Figure 11. Precast test and cracking. Figure 11. Precast test and cracking. Figure 11. Precast test and cracking. Equation (4) indicates whether a New Jersey barrier could withstand the perpendicular impact of a vehicle. Velocity and mass are variables, and it would be necessary to incorporate a restitution Equation (4) indicates whether a New Jersey barrier could withstand the perpendicular impact coefficient in order to avoid the elastic impact. of a vehicle. Velocity and mass are variables, and it would be necessary to incorporate a restitution This coefficient relates the velocity before impact with the velocity after collision, considering coefficient in order to avoid the elastic impact. the barrier is without velocity before and after impact. This coefficient relates the velocity before impact with the velocity after collision, considering the barrier is without velocity before and after impact. 𝑉 −𝑉 𝑉 𝐶 =− ;𝑤ℎ𝑒𝑛 𝑉 ,𝑉 =0 → 𝐶 =− (4) 𝑉 −𝑉 𝑉 𝑉 −𝑉 𝑉 𝐶 =− ;𝑤ℎ𝑒𝑛 𝑉 ,𝑉 =0 → 𝐶 =− (4) 𝑉 −𝑉 𝑉 García and Cabreiro [53] proposed a method for obtaining the coefficient of restitution based on experimental processes in “Use of dynamic models in the investigation of road accidents” (text in Spanish), García and Cabreiro [53] proposed a method for obtaining the coefficient of restitution based on for which they suggested two equations: experimental processes in “Use of dynamic models in the investigation of road accidents” (text in Spanish), for which they suggested two equations: (.·) 𝐶 =0.45 · 𝑒 , For v < 54 km/h (5) (.·) 𝐶 =0.45 · 𝑒 , For v < 54 km/h (5) Force a Fo ppl rcei a ed ppl [ki N ed ] [kN] Force applied [kN] Force applied [kN] Appl. Sci. 2020, 10, 6655 11 of 14 Equation (4) indicates whether a New Jersey barrier could withstand the perpendicular impact of a vehicle. Velocity and mass are variables, and it would be necessary to incorporate a restitution coecient in order to avoid the elastic impact. This coecient relates the velocity before impact with the velocity after collision, considering the barrier is without velocity before and after impact. V V V 1 f 2 f f C = ; when V , V = 0 ! C = (4) R 2i R 2 f V V V 1i 2i i García and Cabreiro [53] proposed a method for obtaining the coecient of restitution based on experimental processes in “Use of dynamic models in the investigation of road accidents” (text in Spanish), for which they suggested two equations: ( 0.040278v) C = 0.45e , For v < 54 km/h (5) ( 0.015278v) C = 0.45e , For v 54 km/h (6) Appl. Sci. 2020, 10, x FOR PEER REVIEW 11 of 14 With Equations (4)–(6), considering the maximum force that a barrier resists, and the duration of (.·) 𝐶 =0.45 · 𝑒 , For v ≥ 54 km/h (6) the impact as 0.1 s, Equations (7) and (8) are obtained, shown in Figure 12. With Equations (4)–(6), considering the maximum force that a barrier resists, and the duration 0.1F of the impact as 0.1 s, Equations (7) and (8) are obtained, shown in Figure 12. m = , For v < 54 km/h (7) i ( 0.040278v) 0.45e + 1 3.6 .· 𝑚= , For v < 54 km/h (7) (. · ) ·(.· ) 0.1F m = , For v 54 km/h (8) v .· ( 0.015278v) 0.12e + 1 𝑚= , For v ≥ 54 km/h 3.6 (8) (. · ) ·(.· ) 20 HP HRR50 0 20 40 60 80 100 120 140 Speed [km/h] Figure 12. Simulated behavior of reinforced barriers. Figure 12. Simulated behavior of reinforced barriers. These curves are conservative, as the barrier can withstand strains that absorb energy before These curves are conservative, as the barrier can withstand strains that absorb energy before cracking, and the parapet would not always be immobile (they are only anchored to the ground cracking, and the parapet would not always be immobile (they are only anchored to the ground on on viaducts). viaducts). 4. Conclusions 4. Conclusions Characterization tests on concrete specimens and precast elements have been carried out Characterization tests on concrete specimens and precast elements have been carried out using using low-clinker cements and recycled aggregates, obtaining the following conclusions. Firstly, low-clinker cements and recycled aggregates, obtaining the following conclusions. Firstly, the the physical-mechanical properties of mixed recycled aggregates are suitable for the manufacture of physical-mechanical properties of mixed recycled aggregates are suitable for the manufacture of concrete and precast elements when the medium and coarse fraction is used. Secondly, the use of mixed recycled aggregates causes a loss of density and compressive strength slightly higher than that which occurs when using recycled concrete aggregates. Recycled concretes made from low-clinker cement are slightly more porous than concretes made with ordinary Portland cement. Finally, regarding the mechanical properties of recycled concrete, a loss of around 10% of the compressive strength is observed when using low-clinker cement. In addition, recycled concrete made with ordinary Portland cement evolves slightly more when over 1 year of curing has elapsed. Author Contributions: For research articles with several authors, a short paragraph specifying their individual contributions must be provided. The following statements should be used “conceptualization, C.T., A.I.C.， J.A.P.; methodology, C.T., A.I.C., J.A.P., I.F.S.d.B., B.C.; validation, C.T., I.F.S.d.B., B.C.; formal analysis, C.T.; investigation, C.T., A.I.C., J.A.P.; resources, C.T., J.A.P.; writing—original draft preparation, C.T., I.F.S.d.B., B.C.; writing—review and editing C.T. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by SODERCAN, S.A. (SODERCAN/FEDER) and BIA2013-48876-C3-2-R awarded by the Ministry of Science and Innovation. Acknowledgments: The authors would like to express our gratitude to Jaime de la Fuente and César Medina for their support and participation in part of the project. Mass [t] Appl. Sci. 2020, 10, 6655 12 of 14 concrete and precast elements when the medium and coarse fraction is used. Secondly, the use of mixed recycled aggregates causes a loss of density and compressive strength slightly higher than that which occurs when using recycled concrete aggregates. Recycled concretes made from low-clinker cement are slightly more porous than concretes made with ordinary Portland cement. Finally, regarding the mechanical properties of recycled concrete, a loss of around 10% of the compressive strength is observed when using low-clinker cement. In addition, recycled concrete made with ordinary Portland cement evolves slightly more when over 1 year of curing has elapsed. Author Contributions: Conceptualization, C.T., A.I.C., J.A.P.; methodology, C.T., A.I.C., J.A.P., I.F.S.d.B., B.C.; validation, C.T., I.F.S.d.B., B.C.; formal analysis, C.T.; investigation, C.T., A.I.C., J.A.P.; resources, C.T., J.A.P.; writing—original draft preparation, C.T., I.F.S.d.B., B.C.; writing—review and editing C.T. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by SODERCAN, S.A. (SODERCAN/FEDER) and BIA2013-48876-C3-2-R awarded by the Ministry of Science and Innovation. Acknowledgments: The authors would like to express our gratitude to Jaime de la Fuente and César Medina for their support and participation in part of the project. Conflicts of Interest: Authors declare no conflict of interest. References 1. Instituto Nacional de Estadística (INE). Estadísticas Sobre Generación de Residuos. Available online: https://www.ine.es (accessed on 23 September 2020). 2. UE Comisión Europea. 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Journal
Applied Sciences – Multidisciplinary Digital Publishing Institute
Published: Sep 23, 2020