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Effect of salinity of water in lime-fly ash treated sand

Effect of salinity of water in lime-fly ash treated sand emdadul.buet@gmail.com Department of Civil Ensuring sustainable development of coastal areas need improvement of road Engineering, Bangladesh embankment infrastructure. Being a byproduct of industry, fly ash may be considered University of Engineering and Technology, Dhaka 1000, as environment friendly and low cost material for this purpose. However, scarcity of Bangladesh fresh water in coastal areas may compel to use saline water. To investigate the effects of sodium chloride content of mixing water on fly ash and lime mixed compacted sand, a series of the unconfined compression tests have been conducted on 50 mm diameter and 100 mm high specimens. Lime content was varied over a range of 1–5% of dry sand weight and fly ash contents were 9, 15 and 30% of dry sand weight. Besides, 0, 4 and 8% of sodium chloride were mixed with tap water, which were used for prepar- ing specimens at 10% moisture content by compaction method. The specimens were cured for 7, 15, 30 and 60 days by spraying method. Experiment results show that, the unconfined compression strength of fly ash and lime mixed compacted sand increases with the increase in sodium chloride content. However, the long term effect of using saline water in fly ash and lime mixed compacted sand should be investigated, which is out of scope of this study. Keywords: Unconfined compressive strength, Lime, Fly ash, Salt Introduction Fly ash is largely used as construction materials as well as for soil improvement over the world [1]. In every day enormous amount of fly ash is produced from coal based power plants and other industrial units. Disposal of fly ash is an environmental concern [2]. Indeed, utilization of industrial by-products brings the environment and economi- cal benefits [ 3]. Lots of researches have been done on utilizing lime and fly ash for soil improvement as it was done for making durable and economic concrete. Different out - comes were exposed, (i) utilization of lime and fly ash increases the shear strength of soil [1, 3], (ii) maximum strength and stiffness of lime and fly ash treated soil observed on the dry side of optimum moisture content [3], (iii) curing temperature (till 35 °C) increases the tensile and compressive strength, for further increment of temperature no signifi - cant influence found. Temperature mainly works as a catalyzer of pozzolanic reactions [1] and (iv) increase of quantity of lime and fly ash increases the strength [ 4, 5]. However, few research works have been done on the effect of salt content in water on soil improve - ment by mixing lime and fly ash, though many researches have been conducted on effect of salt water on compressive strength of concrete. For concrete, strength increases with © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Karim et al. Geo-Engineering (2017) 8:15 Page 2 of 12 increase of salt content in water [6], [7]). However, some researchers found that com- pressive strength of concrete (cube specimen) decreases with the increase of salt content in water [8, 9]. Some researchers found that concrete compressive strength for 28 days increases with salt content of water whereas salt content has no effect on long term strength of concrete [10]. In case of Bangladesh, salinity problem in coastal area is tremendous. About 2.85 mil- lion hectares of coastal areas [11] consists of 19 districts and accommodates more than 35 million people [12]. All the coastal lands are not being used for crop production due to soil salinity. Each and every year the road damages and embankment collapses due to incessant rain or flood. In this research, the main target is to use lime and fly ash for soil improvement in coastal areas using saline water. Material Sand Sand sample was collected from Mawa, Padma river bank. Collected sand was oven dried before grain size analysis. The result of grain size of sand is shown in Fig.  1. Refer- ring the Fig.  1, the fines content (passes sieve 200) is near about 3% and the fineness modulus (FM) is 1.30. According to the unified soil classification system, the sample is poorly graded sand (SP). To investigate the shape of the sample, scanning electron microscopic (SEM) was performed on sand. The image is exhibited in Fig.  2. The shape of sand particles is sub-angular and specific gravity is 2.67. 10 1 0.1 0.01 Diameter (mm) Fig. 1 Grain size distribution of studied sand Percent Finer Karim et al. Geo-Engineering (2017) 8:15 Page 3 of 12 Fig. 2 Scanning electron microscopic view of sand particles Lime Lime stones were bought from the local market of Dhaka, Bangladesh. It was in cobble size. Before using, lime stones were crushed to form powder. In powder form it is easier to make a homogenous mixture with sand and fly ash. The specific gravity of lime was 2.57. Fly ash Fly ash was collected from Bashundhara Cement Company. The properties of fly ash vary with source [4, 7, 10, 13, 14]. The variation is mainly due to variation of calcium content. Higher calcium content increases the self-hardening value of fly ash [5]. Lower calcium content of fly ash was suggested to use for geotechnical purpose (i.e. soil improvement, filling material). Fly ash was used in this study was classified as class F, because it has no calcium determined by scanning electron microscopy (SEM) with energy disper- sive X-ray (SEM/EDX) test. The scanning electron microscopic (SEM) view of fly ash is exhibited in Fig.  3. The shape of fly ash particles is spherical. The specific gravity of fly ash was 2.18. Salt and water In Bangladesh the food salt is produced from sea water by evaporation process. Con- sequently, the food salt was opted to prepare saline water (representative of sea water). The salt was bought from the local grocery shop of Dhaka, Bangladesh. What is more, normal tap water was used to prepare the saline water. The pH value of tap water was 7.48 and for dissolving 4% (4 g/L) and 8% (8 g/L) of salt into the tap water the pH were increased to 7.51 and 7.60 respectively. Experimental program In the lime-fly ash treated sand, lime content was 1, 2, 3 and 5% of dry sand weight and fly ash content was 9, 15 and 30% of dry sand weight. The average salt content in sea water is 3–5% [15] and sodium chloride (NaCl) is predominant [16]. In order to investi- gate the effect of sodium chloride, three NaCl solution in tap water with 0, 4 and 8% (0, Karim et al. Geo-Engineering (2017) 8:15 Page 4 of 12 Fig. 3 Scanning electron microscopic view of fly ash particles 40 and 80 g/L) NaCl were used for preparing specimen at 10% moisture content by wet compaction method. The dry density was maintained at 1.283, 1.467 and 1.558  g/cm . The required amount of tamping for target density was measured by trial method. Each specimen was prepared within 30 min. The size of the specimen was 50 mm in diameter and 100 mm in height. The prepared specimen was kept in 76 mm inner diameter hol - low pipe as shown in Fig. 4; thereafter it was preserved in the curing box. 50 mm diam- eter specimen was kept in 76  mm hollow pipe so that it can get more surface area for curing to ensure lime, fly ash and salt water reaction in whole specimen. A wet geotextile containing same NaCl solution was placed above hollow pipes and a polythene sheet was used with the lid. Lid locks were used so that the moisture content does not decrease rapidly (see Fig.  4). Curing was done by spraying same NaCl solution 3 or 4 times in a week. 3 or 4 time spraying was found favorable to maintain high moisture content in the specimens. Temperature accelerates the reaction of sand-lime-fly ash mixture. With high curing temperature it is possible to get higher strength within a short time than that of low temperature and long time curing [1]. The temperature in boxes was around 25 to 28 °C. The specimens were cured for 7, 15, 30 and 60 days arbitrarily. Polythene sheet Lid 76mm dia. Wet Geotextile Lid lock hollow Pipe Surface area of specimen 50mm dia. Specimen Temperature 25°C to 28°C Fig. 4 Specimens in the curing box Karim et al. Geo-Engineering (2017) 8:15 Page 5 of 12 Unconfined compression test After curing, each specimen was submerged for 24  h in the same NaCl solution to get better saturation ratio. In such way it is possible to get the saturation ratio near about 0.89 [4]. Saturation ratio was not determined in this study. Since, for each specimen the dominant material (sand) and submerging method was same, it may be assumed that saturation ratio would be nearly same. However, density, fly ash content and lime con - tent were different. The unconfined compression test was conducted on submerged specimen at an axial strain rate of 1.2% per minute [17] (see Fig.  5). The unconfined compressive strength (q ) is peak stress. Axial stress verses axial strain graphs of sand treated with 1% lime and 9% fly ash at 0, 4 and 8% salt content after 30 days curing are plotted in Fig. 6. In this three specimens brittle shear failure was observed (as in Fig. 5) and in other specimens the same behavior was observed. Results and discussion Eec ff t of lime and fly ash It is important to understand the reactions in lime-fly ash treated sand. Fly ash having no calcium can not increase shear strength of sand. Silica and alumina of fly ash (glassy portion) react with dissolved lime to form calcium silicate hydrate (C–S–H) and calcium aluminate hydrate (C–A–H). In the normal condition the following hydration reactions occur [18]: 1. CaO + H O → Ca(OH) (Porlandite) 2 2 Fig. 5 Submerged specimen for unconfined compression test Karim et al. Geo-Engineering (2017) 8:15 Page 6 of 12 Sand + 1% Lime + 9% Fly Ash 30 days, (0% Salt) Sand + 1% Lime + 9% Fly Ash 30 days, (4% Salt) Sand +1% Lime + 9% Fly Ash 30 days, (8% Salt) 01234 5 Axial Strain (%) Fig. 6 Axial strain verses axial stress graph 2. SiO  + Ca(OH)  + H O → CaSiO ·2H O (CSH) 2 2 2 2 2 3. Al O  + Ca(OH)  + H O → CaO·Al O3·2H O (CAH) 2 3 2 2 2 2 4. SiO  + Al O  + Ca(OH)  + H O → CaSiO ·Al O ·H O (CAS) 2 2 3 2 2 2 2 3 2 In Fig. 7, the unconfined compressive strength (q ) data of two constant dry densities (1.283 and 1.467 g/cm ) containing equal amount of fly ash (30%) and salt (0%) but dif - ferent percent (1, 2, 3 and 5%) of lime content is exhibited. It can be observed that the q is the function of lime content and dry density. With the increase in lime content the 30% Fly Ash, 0% Salt, 30 days curing g/cm 1.283 g/cm3 200 g/cm 1.467 g/cm3 34.7 15.6 1234 5 Lime Content (%) Fig. 7 Eec ff t of lime content on lime and fly ash treated sand Unconfined Compressive Strength (kPa) Axial Stress (kN/m ) 57.3 kPa 95.5 kPa Karim et al. Geo-Engineering (2017) 8:15 Page 7 of 12 q increases at constant fly ash content. However, at higher density rate of increase is higher. At 1% lime content the fly ash was not fully consumed by lime, at 2, 3 and 5% lime content more fly ash was consumed, and consequently the q increased. This con - sumption reduces the pH value with time. Figure  8 traces the pH value verses curing time graph. With long time reaction the p value decreases. The SEM micrograph of lime and fly ash is shown in Fig.  9. Here the needle shaped crystal formation is found on spherical fly ash particles. That could be C–S–H or C–A–H. In Fig.  10, influence of fly ash on compressive strength of lime-fly ash treated sand is shown. At constant lime content, unconfined compressive strength of treated sand increased with increase of fly ash content. At higher dry density, q is greater. It could be a reason that at higher density the lime and fly ash get closer and accelerate the pozzo - lonic reaction therefore the strength increases with the increase of density. 0% Salt Sand+Lime (1%) Fly Ash (9%) Sand+Lime (3%) Fly Ash (15%) Sand+Lime (1%) Fly Ash (15%) Curing days Fig. 8 pH value verses curing days Fig. 9 Scanning electron microscopic view of lime and fly ash after curing P value Karim et al. Geo-Engineering (2017) 8:15 Page 8 of 12 Lime 3%, 0% Salt, 30 days curing 1.283 g/cm3 g/cm 80 3 g/cm 1.467 g/cm3 05 10 15 20 25 30 35 Fly Ash Content (%) Fig. 10 Eec ff t of fly ash content on lime and fly ash treated sand Eec ff t of salt content in water To investigate the effect of salt content in water on fly ash treated sample which was pre - pared with sand and 10% fly ash (no lime), three specimens at 0, 4 and 8% salt content were prepared and cured with same salt containing water solution for 30 days. When the specimens were put into water the total specimens collapsed. No significant effect of salt content is observed. Without lime, fly ash alone could not contribute to the strength of treated sand. Fly ash had no lime content. It was F class fly ash. Some lime-fly ash treated sand specimens were prepared using 3% lime and 9, 15, and 30% fly ash. 0, 4 and 8% salt content was used in mixing water solution. The specimens were cured for 30  days. Unconfined compression test results for different percents of fly ash content and salt content are shown in Fig.  11. It is clearly seen that unconfined compressive strength increased with the increase of salt content of mixing water. This increase is due to increase in pH of the mixture by sodium chloride. Davidson et al. [19] proposed that the presence of NaOH increase the pH value. 2NaCl + Ca OH → CaCl + 2NaOH ( ) The higher pH value increases the dissolubility of silicates to interact with calcium and create pozzolanic process to produce cement. Also a calcium-sodium silicate gel improves the cementation faster than a calcium silicate gel [6, 19]. Porosity and bv ‑ alue correction for best fit curve In lime-fly ash treated sand, the porosity is a function of sand, lime and fly ash content. The relation was proposed by Consoli et al. [20] as shown in Eq. 1. Unconfined Compressive Strength (kPa) Karim et al. Geo-Engineering (2017) 8:15 Page 9 of 12 Sand+3%Lime+9%Fly ash Sand+3%Lime+15%Fly ash Sand+3%Lime+30%Fly ash Lime 3%, 30 days curing 0246 810 Salt Content (%) Fig. 11 Eec ff t of salt content on lime and fly ash treated sand � � � � � �        � � � �  � �  γ V γ V γ V  S FA L  d S d S d S  � � � � � �         L 100 L 100 L 100   1+ 1+ 1+       100 100 100       η = 100− 100 + + /V         G G G S S S   S   FA   L        (1) where, η = porosity of specimen, FA = fly ash content, L  = lime content, γ  = dry den- sity specimen of Vs = volume of specimen, G , G , G , specific gravity of sand, fly ash S S S S FA L and lime, respectively. Using this equation Consoli et  al. [20] proposed η/L ratio [L , iv iv volumetric lime content] later Consoli et al. [4] used an exponent for L and proposed iv 0.12 η/L to best fit, which is more reliable. In Fig.  12, unconfined compressive strength iv 0.12 verses η/L for all lime-fly ash treated sand of 30 days age specimens are exhibited. The iv 0.12 unconfined compressive strength increases with the reduction of η/L . At higher den- iv 0.12 0.12 sity (lower η/L ) the salt effect is as significant as that of low density (higher η/L ). iv iv In Fig.  12, the best fitted curves of 0, 4 and 8% salt content specimens were tried to bring closer by multiplying the q of each specimens. Therefore by back calculation the b-value was determined. The b-value correction is shown in Fig.  13. By multiplying the q with b-value all trend curves come closer. Here the b-values were used to normal- ize all the trend curves which finally fall in a single trend curve (see Fig.  14). This curve can be used for determining the unconfined compressive strength of lime-fly ash treated sand at different percent of salt contents in mixing water. Here Eqs.  2 and 3 are for 4 and 8% salt content respectively are also given below: Unconfined Compressive Strength (kPa) Karim et al. Geo-Engineering (2017) 8:15 Page 10 of 12 Lime-fly ash treated sand, after curing 30 days 8% Salt R² = 0.851 0% Salt R² = 0.897 0% Salt 4% Salt 4% Salt 8% Salt R² = 0.864 20 30 40 50 60 0.12 η/(L ) (%) 0.12 Fig. 12 Unconfined compressive strength verses η/L graph iv 0.8 Eq. 2 -0.812 0.6 y = 9.744x R² = 0.9981 0.4 Eq. 3 0.2 -1.249 y = 39.719x 4% Salt R² = 0.9986 8% Salt 20 30 40 50 60 0.12 η/(L ) (%) Fig. 13 b-value graph −0.812 y = 9.744x (for 4% salt content) (2) −1.249 y = 39.719x (for 8% salt content) (3) 0.12 where, y = b, x = η/L (%) and for 0% salt water the b-value is 1. iv Unconfined Compressive Strength (kN/ m ) b-value Karim et al. Geo-Engineering (2017) 8:15 Page 11 of 12 -6.945 y = 8E+12x R² = 0.9075 Best fit curve 0% Salt 4% Salt 8% Salt 20 30 40 50 60 0.12 η/(L ) (%) Fig. 14 Best fit normalized curve of unconfined compressive strength for different porosities, lime content and salt contents Conclusion A series of unconfined compression tests was conducted on specimens containing dif - ferent percents of lime and fly ash mixed with sand. Here, for preparing and curing the specimens 0, 4 and 8% percent salt (NaCl) solution were used. The following outcomes were found from the study, 1. With the increase in lime content the unconfined compressive strength of treated sand increased. 2. Salt content of water causes increase of compressive strength of lime-fly ash treated sand. 3. Compressive strength of lime-fly ash treated sand increases with the increase of fly ash content. 4. For fine sand, a correlation among unconfined compressive strength, porosity, volu - metric lime content and salt content in water is developed. 5. Fly ash of F class does not have any effect on compressive strength of treated soil without using lime. Authors’ Contributions MEK has performed experiments, analyse data and written the manuscript. MJA and MSH has supervised the research and revised the manuscript. All authors read and approved the final manuscript. Acknowledgements Writers wish to express their gratitude to “Introduction of Quality Test Protocols for Road and Market Rehabilitation” under Coastal Climate Resilient Infrastructure Project (CCRIP) (Package No: CCRIP-S-05(C), LGED, GOB) for their financial support. And thanks to Prof. Dr. Md. Tarek Uddin for his suggestions. Competing interests The authors declare that they have no competing interests. Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Unconfined Compressive Strength * b (kN/ m ) Karim et al. Geo-Engineering (2017) 8:15 Page 12 of 12 Received: 21 December 2016 Accepted: 27 July 2017 References 1. Consoli NC, Rocha CG, Silvani C (2014) Eec ff t of curing temperature on the strength of sand, coal fly ash, and lime blends. J Mater Civ Eng 26(8):1–7 2. Lokeshappa B, Dikshit AK (2011) Disposal and management of flyash. 2011 International Conference on Life Science and Technology, vol. 3. IACSIT Press, Singapore, pp 11–14 3. Consoli NC, Marques Prietto PD, Carraro JA, Heineck KS (2001) Behavior of compacted soil-fly ash-carbide lime mixtures. J Geotech Geoenviron Eng 127(9):774–782 4. Consoli NC, Rosa AD, Saldanha BR (2011) Variables governing strength of compacted soil-fly ash–lime mixtures. J Mater Civ Eng 23(4):432–440 5. Das SK, Yudhbir (2005) Geotechnical characterization of some indian fly ashes. J Mater Civ Eng 17(5):544–552 6. Davoudi MH, Kabir E (2011) Interaction of lime and sodium chloride in a low plasticity fine grain soils. J Appl Sci 11(2):330–335 7. Olutoge FA, Amusan GM (2014) The effect of sea water on compressive strength of concrete. Int J Eng Sci Invent 3(7):23–31 8. Islam MM, Islam MS (2013) Eec ff t of sea water on the performance of fly ash concrete under freezing-thawing cyclic action. J Mater Civ Eng 41(2):139–159 9. Mbadikea EM, Elinwab AU (2011) Eec ff t of salt water in the production of concrete. Niger J Technol 30(2):105–110 10. Mohammed TU, Hidenori H, Toru Y (2004) Performance of seawater-mixed concrete in the tidal environment. Cem Concr Res 34(4):593–601 11. Haque SA (2006) Salinity problems and crop production in coastal regions of Bangladesh. Pak J Bot 38(5):1359–1365 12. Mahmuduzzaman M, Ahmed ZU, Nuruzzaman AK, Ahmed FR (2014) Causes of salinity intrusion in coastal belt of Bangladesh. Int J Plant Res 4(4A):8–13 13. Winter MG, Clarke BG (eds) (2002) Improved use of pulverized fuel ash as general fill. Proc Inst Civ Eng Geotech Eng 155(2):1331–1341 14. Yudhbir HY, Honjo Y (1991) Application of geotechnical engineering to environmental control. Proceedings of 9th Asian regional conference on soil mechanics and foundation engineering, vol. 2. Bangkok, pp 431–469 15. Emmanuel AO, Oladipo FA (2012) Investigation of salinity effect of compression strength of reinforced concree. J Sustain Dev 5(6):74–82 16. Akinkurolere OO, Jiang C, Shobola OM (2007) The influence of salt water on the compressive strength of concrete. J Eng Appl Sci 2:412–415 17. ASTM-D2166 (2002) Standard test method for unconfined compressive strength of cohesive soil. ASTM International 18. Abdel Hadi NARM (2008) Stabilization of the phosphatic wastes using high calcium ash in Jordan. Can J Civ Eng 35(11):1193–1199 19. Davidson LK, Demeril T, Handy RL (1965) Soil Pulverization and Lime Migration in SOil Lime Stabilization. The National Academies of Sciences Engineering Medicine, Washington, DC, pp 103–126 20. Consoli NC, Johann AD, Gauer EA, Santos VR, Moretto RL, Corte MB (2012) Key parameters for tensile and compres- sive strength of silt–lime mixtures. Géotech Lett 2(3):81–85 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Geo-Engineering Springer Journals

Effect of salinity of water in lime-fly ash treated sand

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2017 The Author(s)
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Abstract

emdadul.buet@gmail.com Department of Civil Ensuring sustainable development of coastal areas need improvement of road Engineering, Bangladesh embankment infrastructure. Being a byproduct of industry, fly ash may be considered University of Engineering and Technology, Dhaka 1000, as environment friendly and low cost material for this purpose. However, scarcity of Bangladesh fresh water in coastal areas may compel to use saline water. To investigate the effects of sodium chloride content of mixing water on fly ash and lime mixed compacted sand, a series of the unconfined compression tests have been conducted on 50 mm diameter and 100 mm high specimens. Lime content was varied over a range of 1–5% of dry sand weight and fly ash contents were 9, 15 and 30% of dry sand weight. Besides, 0, 4 and 8% of sodium chloride were mixed with tap water, which were used for prepar- ing specimens at 10% moisture content by compaction method. The specimens were cured for 7, 15, 30 and 60 days by spraying method. Experiment results show that, the unconfined compression strength of fly ash and lime mixed compacted sand increases with the increase in sodium chloride content. However, the long term effect of using saline water in fly ash and lime mixed compacted sand should be investigated, which is out of scope of this study. Keywords: Unconfined compressive strength, Lime, Fly ash, Salt Introduction Fly ash is largely used as construction materials as well as for soil improvement over the world [1]. In every day enormous amount of fly ash is produced from coal based power plants and other industrial units. Disposal of fly ash is an environmental concern [2]. Indeed, utilization of industrial by-products brings the environment and economi- cal benefits [ 3]. Lots of researches have been done on utilizing lime and fly ash for soil improvement as it was done for making durable and economic concrete. Different out - comes were exposed, (i) utilization of lime and fly ash increases the shear strength of soil [1, 3], (ii) maximum strength and stiffness of lime and fly ash treated soil observed on the dry side of optimum moisture content [3], (iii) curing temperature (till 35 °C) increases the tensile and compressive strength, for further increment of temperature no signifi - cant influence found. Temperature mainly works as a catalyzer of pozzolanic reactions [1] and (iv) increase of quantity of lime and fly ash increases the strength [ 4, 5]. However, few research works have been done on the effect of salt content in water on soil improve - ment by mixing lime and fly ash, though many researches have been conducted on effect of salt water on compressive strength of concrete. For concrete, strength increases with © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Karim et al. Geo-Engineering (2017) 8:15 Page 2 of 12 increase of salt content in water [6], [7]). However, some researchers found that com- pressive strength of concrete (cube specimen) decreases with the increase of salt content in water [8, 9]. Some researchers found that concrete compressive strength for 28 days increases with salt content of water whereas salt content has no effect on long term strength of concrete [10]. In case of Bangladesh, salinity problem in coastal area is tremendous. About 2.85 mil- lion hectares of coastal areas [11] consists of 19 districts and accommodates more than 35 million people [12]. All the coastal lands are not being used for crop production due to soil salinity. Each and every year the road damages and embankment collapses due to incessant rain or flood. In this research, the main target is to use lime and fly ash for soil improvement in coastal areas using saline water. Material Sand Sand sample was collected from Mawa, Padma river bank. Collected sand was oven dried before grain size analysis. The result of grain size of sand is shown in Fig.  1. Refer- ring the Fig.  1, the fines content (passes sieve 200) is near about 3% and the fineness modulus (FM) is 1.30. According to the unified soil classification system, the sample is poorly graded sand (SP). To investigate the shape of the sample, scanning electron microscopic (SEM) was performed on sand. The image is exhibited in Fig.  2. The shape of sand particles is sub-angular and specific gravity is 2.67. 10 1 0.1 0.01 Diameter (mm) Fig. 1 Grain size distribution of studied sand Percent Finer Karim et al. Geo-Engineering (2017) 8:15 Page 3 of 12 Fig. 2 Scanning electron microscopic view of sand particles Lime Lime stones were bought from the local market of Dhaka, Bangladesh. It was in cobble size. Before using, lime stones were crushed to form powder. In powder form it is easier to make a homogenous mixture with sand and fly ash. The specific gravity of lime was 2.57. Fly ash Fly ash was collected from Bashundhara Cement Company. The properties of fly ash vary with source [4, 7, 10, 13, 14]. The variation is mainly due to variation of calcium content. Higher calcium content increases the self-hardening value of fly ash [5]. Lower calcium content of fly ash was suggested to use for geotechnical purpose (i.e. soil improvement, filling material). Fly ash was used in this study was classified as class F, because it has no calcium determined by scanning electron microscopy (SEM) with energy disper- sive X-ray (SEM/EDX) test. The scanning electron microscopic (SEM) view of fly ash is exhibited in Fig.  3. The shape of fly ash particles is spherical. The specific gravity of fly ash was 2.18. Salt and water In Bangladesh the food salt is produced from sea water by evaporation process. Con- sequently, the food salt was opted to prepare saline water (representative of sea water). The salt was bought from the local grocery shop of Dhaka, Bangladesh. What is more, normal tap water was used to prepare the saline water. The pH value of tap water was 7.48 and for dissolving 4% (4 g/L) and 8% (8 g/L) of salt into the tap water the pH were increased to 7.51 and 7.60 respectively. Experimental program In the lime-fly ash treated sand, lime content was 1, 2, 3 and 5% of dry sand weight and fly ash content was 9, 15 and 30% of dry sand weight. The average salt content in sea water is 3–5% [15] and sodium chloride (NaCl) is predominant [16]. In order to investi- gate the effect of sodium chloride, three NaCl solution in tap water with 0, 4 and 8% (0, Karim et al. Geo-Engineering (2017) 8:15 Page 4 of 12 Fig. 3 Scanning electron microscopic view of fly ash particles 40 and 80 g/L) NaCl were used for preparing specimen at 10% moisture content by wet compaction method. The dry density was maintained at 1.283, 1.467 and 1.558  g/cm . The required amount of tamping for target density was measured by trial method. Each specimen was prepared within 30 min. The size of the specimen was 50 mm in diameter and 100 mm in height. The prepared specimen was kept in 76 mm inner diameter hol - low pipe as shown in Fig. 4; thereafter it was preserved in the curing box. 50 mm diam- eter specimen was kept in 76  mm hollow pipe so that it can get more surface area for curing to ensure lime, fly ash and salt water reaction in whole specimen. A wet geotextile containing same NaCl solution was placed above hollow pipes and a polythene sheet was used with the lid. Lid locks were used so that the moisture content does not decrease rapidly (see Fig.  4). Curing was done by spraying same NaCl solution 3 or 4 times in a week. 3 or 4 time spraying was found favorable to maintain high moisture content in the specimens. Temperature accelerates the reaction of sand-lime-fly ash mixture. With high curing temperature it is possible to get higher strength within a short time than that of low temperature and long time curing [1]. The temperature in boxes was around 25 to 28 °C. The specimens were cured for 7, 15, 30 and 60 days arbitrarily. Polythene sheet Lid 76mm dia. Wet Geotextile Lid lock hollow Pipe Surface area of specimen 50mm dia. Specimen Temperature 25°C to 28°C Fig. 4 Specimens in the curing box Karim et al. Geo-Engineering (2017) 8:15 Page 5 of 12 Unconfined compression test After curing, each specimen was submerged for 24  h in the same NaCl solution to get better saturation ratio. In such way it is possible to get the saturation ratio near about 0.89 [4]. Saturation ratio was not determined in this study. Since, for each specimen the dominant material (sand) and submerging method was same, it may be assumed that saturation ratio would be nearly same. However, density, fly ash content and lime con - tent were different. The unconfined compression test was conducted on submerged specimen at an axial strain rate of 1.2% per minute [17] (see Fig.  5). The unconfined compressive strength (q ) is peak stress. Axial stress verses axial strain graphs of sand treated with 1% lime and 9% fly ash at 0, 4 and 8% salt content after 30 days curing are plotted in Fig. 6. In this three specimens brittle shear failure was observed (as in Fig. 5) and in other specimens the same behavior was observed. Results and discussion Eec ff t of lime and fly ash It is important to understand the reactions in lime-fly ash treated sand. Fly ash having no calcium can not increase shear strength of sand. Silica and alumina of fly ash (glassy portion) react with dissolved lime to form calcium silicate hydrate (C–S–H) and calcium aluminate hydrate (C–A–H). In the normal condition the following hydration reactions occur [18]: 1. CaO + H O → Ca(OH) (Porlandite) 2 2 Fig. 5 Submerged specimen for unconfined compression test Karim et al. Geo-Engineering (2017) 8:15 Page 6 of 12 Sand + 1% Lime + 9% Fly Ash 30 days, (0% Salt) Sand + 1% Lime + 9% Fly Ash 30 days, (4% Salt) Sand +1% Lime + 9% Fly Ash 30 days, (8% Salt) 01234 5 Axial Strain (%) Fig. 6 Axial strain verses axial stress graph 2. SiO  + Ca(OH)  + H O → CaSiO ·2H O (CSH) 2 2 2 2 2 3. Al O  + Ca(OH)  + H O → CaO·Al O3·2H O (CAH) 2 3 2 2 2 2 4. SiO  + Al O  + Ca(OH)  + H O → CaSiO ·Al O ·H O (CAS) 2 2 3 2 2 2 2 3 2 In Fig. 7, the unconfined compressive strength (q ) data of two constant dry densities (1.283 and 1.467 g/cm ) containing equal amount of fly ash (30%) and salt (0%) but dif - ferent percent (1, 2, 3 and 5%) of lime content is exhibited. It can be observed that the q is the function of lime content and dry density. With the increase in lime content the 30% Fly Ash, 0% Salt, 30 days curing g/cm 1.283 g/cm3 200 g/cm 1.467 g/cm3 34.7 15.6 1234 5 Lime Content (%) Fig. 7 Eec ff t of lime content on lime and fly ash treated sand Unconfined Compressive Strength (kPa) Axial Stress (kN/m ) 57.3 kPa 95.5 kPa Karim et al. Geo-Engineering (2017) 8:15 Page 7 of 12 q increases at constant fly ash content. However, at higher density rate of increase is higher. At 1% lime content the fly ash was not fully consumed by lime, at 2, 3 and 5% lime content more fly ash was consumed, and consequently the q increased. This con - sumption reduces the pH value with time. Figure  8 traces the pH value verses curing time graph. With long time reaction the p value decreases. The SEM micrograph of lime and fly ash is shown in Fig.  9. Here the needle shaped crystal formation is found on spherical fly ash particles. That could be C–S–H or C–A–H. In Fig.  10, influence of fly ash on compressive strength of lime-fly ash treated sand is shown. At constant lime content, unconfined compressive strength of treated sand increased with increase of fly ash content. At higher dry density, q is greater. It could be a reason that at higher density the lime and fly ash get closer and accelerate the pozzo - lonic reaction therefore the strength increases with the increase of density. 0% Salt Sand+Lime (1%) Fly Ash (9%) Sand+Lime (3%) Fly Ash (15%) Sand+Lime (1%) Fly Ash (15%) Curing days Fig. 8 pH value verses curing days Fig. 9 Scanning electron microscopic view of lime and fly ash after curing P value Karim et al. Geo-Engineering (2017) 8:15 Page 8 of 12 Lime 3%, 0% Salt, 30 days curing 1.283 g/cm3 g/cm 80 3 g/cm 1.467 g/cm3 05 10 15 20 25 30 35 Fly Ash Content (%) Fig. 10 Eec ff t of fly ash content on lime and fly ash treated sand Eec ff t of salt content in water To investigate the effect of salt content in water on fly ash treated sample which was pre - pared with sand and 10% fly ash (no lime), three specimens at 0, 4 and 8% salt content were prepared and cured with same salt containing water solution for 30 days. When the specimens were put into water the total specimens collapsed. No significant effect of salt content is observed. Without lime, fly ash alone could not contribute to the strength of treated sand. Fly ash had no lime content. It was F class fly ash. Some lime-fly ash treated sand specimens were prepared using 3% lime and 9, 15, and 30% fly ash. 0, 4 and 8% salt content was used in mixing water solution. The specimens were cured for 30  days. Unconfined compression test results for different percents of fly ash content and salt content are shown in Fig.  11. It is clearly seen that unconfined compressive strength increased with the increase of salt content of mixing water. This increase is due to increase in pH of the mixture by sodium chloride. Davidson et al. [19] proposed that the presence of NaOH increase the pH value. 2NaCl + Ca OH → CaCl + 2NaOH ( ) The higher pH value increases the dissolubility of silicates to interact with calcium and create pozzolanic process to produce cement. Also a calcium-sodium silicate gel improves the cementation faster than a calcium silicate gel [6, 19]. Porosity and bv ‑ alue correction for best fit curve In lime-fly ash treated sand, the porosity is a function of sand, lime and fly ash content. The relation was proposed by Consoli et al. [20] as shown in Eq. 1. Unconfined Compressive Strength (kPa) Karim et al. Geo-Engineering (2017) 8:15 Page 9 of 12 Sand+3%Lime+9%Fly ash Sand+3%Lime+15%Fly ash Sand+3%Lime+30%Fly ash Lime 3%, 30 days curing 0246 810 Salt Content (%) Fig. 11 Eec ff t of salt content on lime and fly ash treated sand � � � � � �        � � � �  � �  γ V γ V γ V  S FA L  d S d S d S  � � � � � �         L 100 L 100 L 100   1+ 1+ 1+       100 100 100       η = 100− 100 + + /V         G G G S S S   S   FA   L        (1) where, η = porosity of specimen, FA = fly ash content, L  = lime content, γ  = dry den- sity specimen of Vs = volume of specimen, G , G , G , specific gravity of sand, fly ash S S S S FA L and lime, respectively. Using this equation Consoli et  al. [20] proposed η/L ratio [L , iv iv volumetric lime content] later Consoli et al. [4] used an exponent for L and proposed iv 0.12 η/L to best fit, which is more reliable. In Fig.  12, unconfined compressive strength iv 0.12 verses η/L for all lime-fly ash treated sand of 30 days age specimens are exhibited. The iv 0.12 unconfined compressive strength increases with the reduction of η/L . At higher den- iv 0.12 0.12 sity (lower η/L ) the salt effect is as significant as that of low density (higher η/L ). iv iv In Fig.  12, the best fitted curves of 0, 4 and 8% salt content specimens were tried to bring closer by multiplying the q of each specimens. Therefore by back calculation the b-value was determined. The b-value correction is shown in Fig.  13. By multiplying the q with b-value all trend curves come closer. Here the b-values were used to normal- ize all the trend curves which finally fall in a single trend curve (see Fig.  14). This curve can be used for determining the unconfined compressive strength of lime-fly ash treated sand at different percent of salt contents in mixing water. Here Eqs.  2 and 3 are for 4 and 8% salt content respectively are also given below: Unconfined Compressive Strength (kPa) Karim et al. Geo-Engineering (2017) 8:15 Page 10 of 12 Lime-fly ash treated sand, after curing 30 days 8% Salt R² = 0.851 0% Salt R² = 0.897 0% Salt 4% Salt 4% Salt 8% Salt R² = 0.864 20 30 40 50 60 0.12 η/(L ) (%) 0.12 Fig. 12 Unconfined compressive strength verses η/L graph iv 0.8 Eq. 2 -0.812 0.6 y = 9.744x R² = 0.9981 0.4 Eq. 3 0.2 -1.249 y = 39.719x 4% Salt R² = 0.9986 8% Salt 20 30 40 50 60 0.12 η/(L ) (%) Fig. 13 b-value graph −0.812 y = 9.744x (for 4% salt content) (2) −1.249 y = 39.719x (for 8% salt content) (3) 0.12 where, y = b, x = η/L (%) and for 0% salt water the b-value is 1. iv Unconfined Compressive Strength (kN/ m ) b-value Karim et al. Geo-Engineering (2017) 8:15 Page 11 of 12 -6.945 y = 8E+12x R² = 0.9075 Best fit curve 0% Salt 4% Salt 8% Salt 20 30 40 50 60 0.12 η/(L ) (%) Fig. 14 Best fit normalized curve of unconfined compressive strength for different porosities, lime content and salt contents Conclusion A series of unconfined compression tests was conducted on specimens containing dif - ferent percents of lime and fly ash mixed with sand. Here, for preparing and curing the specimens 0, 4 and 8% percent salt (NaCl) solution were used. The following outcomes were found from the study, 1. With the increase in lime content the unconfined compressive strength of treated sand increased. 2. Salt content of water causes increase of compressive strength of lime-fly ash treated sand. 3. Compressive strength of lime-fly ash treated sand increases with the increase of fly ash content. 4. For fine sand, a correlation among unconfined compressive strength, porosity, volu - metric lime content and salt content in water is developed. 5. Fly ash of F class does not have any effect on compressive strength of treated soil without using lime. Authors’ Contributions MEK has performed experiments, analyse data and written the manuscript. MJA and MSH has supervised the research and revised the manuscript. All authors read and approved the final manuscript. Acknowledgements Writers wish to express their gratitude to “Introduction of Quality Test Protocols for Road and Market Rehabilitation” under Coastal Climate Resilient Infrastructure Project (CCRIP) (Package No: CCRIP-S-05(C), LGED, GOB) for their financial support. And thanks to Prof. Dr. Md. Tarek Uddin for his suggestions. Competing interests The authors declare that they have no competing interests. Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Unconfined Compressive Strength * b (kN/ m ) Karim et al. Geo-Engineering (2017) 8:15 Page 12 of 12 Received: 21 December 2016 Accepted: 27 July 2017 References 1. Consoli NC, Rocha CG, Silvani C (2014) Eec ff t of curing temperature on the strength of sand, coal fly ash, and lime blends. J Mater Civ Eng 26(8):1–7 2. Lokeshappa B, Dikshit AK (2011) Disposal and management of flyash. 2011 International Conference on Life Science and Technology, vol. 3. IACSIT Press, Singapore, pp 11–14 3. Consoli NC, Marques Prietto PD, Carraro JA, Heineck KS (2001) Behavior of compacted soil-fly ash-carbide lime mixtures. J Geotech Geoenviron Eng 127(9):774–782 4. Consoli NC, Rosa AD, Saldanha BR (2011) Variables governing strength of compacted soil-fly ash–lime mixtures. J Mater Civ Eng 23(4):432–440 5. Das SK, Yudhbir (2005) Geotechnical characterization of some indian fly ashes. J Mater Civ Eng 17(5):544–552 6. Davoudi MH, Kabir E (2011) Interaction of lime and sodium chloride in a low plasticity fine grain soils. J Appl Sci 11(2):330–335 7. Olutoge FA, Amusan GM (2014) The effect of sea water on compressive strength of concrete. Int J Eng Sci Invent 3(7):23–31 8. Islam MM, Islam MS (2013) Eec ff t of sea water on the performance of fly ash concrete under freezing-thawing cyclic action. J Mater Civ Eng 41(2):139–159 9. Mbadikea EM, Elinwab AU (2011) Eec ff t of salt water in the production of concrete. Niger J Technol 30(2):105–110 10. Mohammed TU, Hidenori H, Toru Y (2004) Performance of seawater-mixed concrete in the tidal environment. Cem Concr Res 34(4):593–601 11. Haque SA (2006) Salinity problems and crop production in coastal regions of Bangladesh. Pak J Bot 38(5):1359–1365 12. Mahmuduzzaman M, Ahmed ZU, Nuruzzaman AK, Ahmed FR (2014) Causes of salinity intrusion in coastal belt of Bangladesh. Int J Plant Res 4(4A):8–13 13. Winter MG, Clarke BG (eds) (2002) Improved use of pulverized fuel ash as general fill. Proc Inst Civ Eng Geotech Eng 155(2):1331–1341 14. Yudhbir HY, Honjo Y (1991) Application of geotechnical engineering to environmental control. Proceedings of 9th Asian regional conference on soil mechanics and foundation engineering, vol. 2. Bangkok, pp 431–469 15. Emmanuel AO, Oladipo FA (2012) Investigation of salinity effect of compression strength of reinforced concree. J Sustain Dev 5(6):74–82 16. Akinkurolere OO, Jiang C, Shobola OM (2007) The influence of salt water on the compressive strength of concrete. J Eng Appl Sci 2:412–415 17. ASTM-D2166 (2002) Standard test method for unconfined compressive strength of cohesive soil. ASTM International 18. Abdel Hadi NARM (2008) Stabilization of the phosphatic wastes using high calcium ash in Jordan. Can J Civ Eng 35(11):1193–1199 19. Davidson LK, Demeril T, Handy RL (1965) Soil Pulverization and Lime Migration in SOil Lime Stabilization. The National Academies of Sciences Engineering Medicine, Washington, DC, pp 103–126 20. Consoli NC, Johann AD, Gauer EA, Santos VR, Moretto RL, Corte MB (2012) Key parameters for tensile and compres- sive strength of silt–lime mixtures. Géotech Lett 2(3):81–85

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