Investigation Of Mechanical Properties And Durability Of Different Calcium-based Geopolymer Stabilized Silty Soft Soil

Silty soft soil is extensively distributed in the southeastern coastal regions of China.A foundation of silty soft soil generally has difficulty meeting construction requirements due to its characteristics of high water content,poor shear strength,and high compressibility.In order to address the problem of high carbon emission and high energy consumption of traditional stabilizer,the geopolymer cementitious material is used as replacement for Ordinary Portland cement（OPC）to stabilize silty soft soil.This study compared the mechanical properties,durability,and microstructure of silty soft soil stabilized by low-calcium geopolymers,high-calcium geopolymers and OPC via unconfined compressive strength（UCS）testing,scanning electron microscopy（SEM）,and X-ray diffraction（XRD）.The detailed conclusions can be summarized as follows:（1）A relatively high A/P（alkaline activator/precursor）ratio,Na₂Si O₃/Na OH ratio,and Na OH concentration were beneficial to the strength development of CMK-treated samples but were unfavorable for GGBS-treated samples.The optimum A/P ratio and Na₂Si O₃/Na OH ratio for the CMK-treated samples were 1.5 and 75:25,and those for the GGBS-treated samples were 1.0 and 25:75.The recommended Na OH concentration for practical applications is 12 M.（2）The increase in precursor content increases the strength of all the treated samples.The CMK-treated samples showed a lower strength than the OPC-and GGBS-treated samples,ang the GGBS-treated samples showed a higher strength than the OPC-treated samples when the precursor content is higher than 20%.The increase in water content decreases the strength of all the treated samples.Increasing the temperature accelerated cementitious product formation and shortened the curing time,especially for the CMK-treated samples.As the curing time increased,the strength of the CMK-treated samples increased linearly,while the strength of the OPC-and GGBS-treated samples increased logarithmically,and a reduction was found in the strength of the GGBS-treated samples at later stages of curing.（3）Among the three kinds of stabilized soil,the high-calcium geopolymer stabilized soil shows the best dry-wetting cycle properties,whereas the low-calcium geopolymer stabilized soil shows the worst dry-wetting cycle properties,and the dry-wetting cycle properties of all samples improve with the increase of precursor content.The sulfate environment has little effect on the strength development of low-calcium geopolymer stabilized soil,and promotes the strength development of high-calcium geopolymer stabilized soil,whereas is not conducive to the development of OPC stabilized soil,which indicates that the geopolymer stabilized soil has excellent sulfate resistance.（4）The stabilization effect of CMK,GGBS,and OPC for silty soft soil are mainly attributed the dense gels network structure formed.The hydration products of the OPC-treated samples are C-S-H gels,ettringite（AFt）,and Ca（OH）_2,whereas C-（A）-S-H gels were found in the GGBS-treated samples,and N-A-S-H gels were found in the CMK-treated samples.In this paper,the industrial solid wastes were used to prepare geopolymer to replace cement on soft soil foundation treatment,which can not only solve the problem of solid waste stacking and pollution,but also can play a role in certain value.This study provided a theoretical basis for the practical application of geopolymer on silty soft soil stabilization.