| The main purpose of this study is to investigate the system performance,including engineering properties,durability and transportation parameters of new MgO activated slag-bentonite?MSB?and ECC cutoff wall.This study is finanically supported by National Key Research and Development Programme?Grant No.2018YFC1803100 and 2018YFC1802300?,National Natural Science Foundation of China?Grant No.51278100?,Jiangsu Provincial Key Research and Development Programme?No.BE2017715?,China Scholarship Council Sponsored Program?No.201606090130?,the Colleges and Universities in Jiangsu Province Plans to Graduate Research and Innovation?KYLX160242?,and the Scientific Research Foundation of Graduate School of Southeast University?Grant No.YBJJ1735?.Main findings are incorporated as follows:?1?The development of cutoff wall materials based on MSB is systematically researched.According to the lab-scale tests,the engineering properties and hydration mechanism are observed in this study.The good workability is observed for the MSB cutoff wall.The unconfined compressive strength meets the design requirements of over 100 kPa after curing 28 days.The hydraulic conductivity of MSB cutoff wall meets the common limitation(1×10-7cm/s)as exposed to tap water and pollutant solution.Further,the MSB cutoff wall reduces approximately 84.7%-85.1%in CO2 emissions and 15.3%-16.9%cost as compared to the conventional backfill made from the OPC-bentonite mixture.The thermodynamic analysis and micro-mechanical analysis indicate that the main hydraulic products of MSB cutoff wall are C-S-H and Ht.?2?The development of cutoff wall materials based on ECC is systematically researched.According to the lab-scale tests,the effects of MgO and natural sand on mechanical performance and micro-mechanics of ECC are observed in this study.The increased MgO proportion in ECC reduces the unconfined compressive strength but enhance the permeability.The optimal content of 6%MgO can reach the largest tensile capacity and ultimate tensile strength.The decreasing sand particle roundness and sphericity lead to enhancements in compressive strength,ultimate tensile strength and tensile strain capacity of ECC.The higher MgO content tends to reduce matrix fracture toughness Km,Young's modulus Em,enhance the matrix/fiber interface zone,and then weakes the ?0 and Jtip.The lower roundness and sphericity lead to increments in the fiber-bridging capacity ?0,crack tip toughness Jtip as well as complementary energy Jb',which resultes in a better tensile performance of ECC in terms of tensile strength,ultimate tensile strain and crack control capacity.The 6%MgO-ECC pose the greatest engendering properties and eco-friendly than ECC and natural sand ECC.?3?The durability of MSB and ECC cutoff wall is researched in this study.The mass loss of MSB cutoff wall is larger than a cement-based cutoff wall as suffered wetting-drying cycles.Few cracks occur after 4th cycles and a small amount of peeling and cavitation are observed after 6th cycles,and the pH of MSB cutoff wall arranged from 9.6 to 10.5.It is found that the durability of MSB cutoff wall is less than the cement-based cutoff wall.The increased bentonite contented decrease the durability,while the increased GGBS-MgO content enhances the durability.The mass and unconfined compressive strength of MgO-ECC is increased as exposed to tap water but decreased in AMD solution.The tensile capacity decreases 29.8%-35.2%for AMD and tap water exposure condition.The AMD solution can restrict the self-healing ratio for 2-3 cycles.The mainly self-healing products are C-S-H,CaCO3,AFt,and Ht.?4?The transportation parameters of MSB and ECC cutoff wall as exposed to Pb-Zn and AMD solution are investigated.For the MSB cutoff wall,the effective dispersion coefficient,retardation factor,and distribution coefficient are 8.79×10-10-9.32×10-10 m2/s,9.98-10.72 and 3.12-3.38 mL/kg for Pb solution,respectively.The effective dispersion coefficient,retardation factor,and distribution coefficient are 6.70×10-10-7.23×10-10 m2/s,10.60-10.95 and 3.31-3.44 mL/kg for Zn solution,respectively.Further,the effective dispersion coefficient and distribution coefficient are 1.03×10-10m2/s and 0.189 mL/g for ECC,5.38×10-11 m2/s and 0.186 mL/g for MgO-ECC,respectively.?5?The MSB cutoff wall is applied to the real demonstration engineering projects.The results of lab-scale MSB cutoff wall with the in-situ contaminated soil show that the pH,unconfined compressive strength and hydraulic conductivity are 10.5-10.8,400-680kPa and 3.2×10-7-3.8×10-8cm/s,respectively.The filed-scale results show that the pH,unconfined compressive strength and hydraulic conductivity are lower than the cement-based cutoff wall.The fixed ratio of heavy metal and PAHs are higher than the cement-based cutoff wall. |
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