Study On The Road Performance And Solidifying Mechanism Of Waste Marine Clay Modified With Composite Soil Stabilizer

The coastal area of Zhejiang Province is distributed with deep marine clay layer,and its poor engineering properties make it difficult to directly use the engineering waste soil generated in the area for practical construction.In recent years,the rapid development of soil stabilization technology provides a feasible way for the road resource utilization of such waste soil,which can help the green and high-quality development of transportation infrastructure.This paper proposes a comprehensive solidification program of"pretreatment before solidification"to improve the work ability and road mechanics of the waste marine clay generated during the construction of highway bridge pile foundations.The selection of materials from the perspective of"treating waste with waste",i.e.,replacement of cement and lime in the traditional solidification program.In this paper,the development tests of pretreatment agents and soil stabilizers were carried out and the road performance test of the corresponding solidified soil was conducted,the conclusions are as follows:（1）The single/multi-mixing tests were conducted to investigate the effects of quicklime and ground calcium carbonate powder（GCCP）on engineering indicators of waste marine clay such as dewatering rate,liquid-plastic limit and compaction characteristics,and to establish the relationship among these indicators and air-drying time.The results show that:the optimal ratio of pretreatment agent is 3%of quicklime and 3%of GCCP;after modified by the pretreatment agent,the soil becomes loose and easy to break,which meets the prior requirements of stabilizing.（2）The single admixture optimization test was carried out to improve the existing cement-lime based stabilizer（WSS-I）using alkali-activated modifier.The results showed that:when the mixing ratio of WSS-I and alkali-activated modifier are 6:4,the water stability coefficient and strength of the solidified soil is the highest,so this ratio is used as the optimal ratio to form a cement-lime-alkali-activated composite curing agent,named WSS-II;WSS-II stabilizer is better than cement,and pretreatment is beneficial to the strength of solidified soil;when the amount of WSS-II is 1%to 2%,solidified soil can be used as a high-grade highway roadbed filling material,and when the amount of3%to 5%,it can be used as a highway（sub）base paving material.（3）The controlled variable tests were carried out to determine the optimal ratios of alkali-activated binders using slag and fly ash with carbide slag.After that,the effect of poor construction conditions on the solidified effect was investigated.The results showed that:the optimal ratio of the two curing agents is 3:2 for the slag:carbide slag and 6:5 for the fly ash:carbide slag,respectively;the effect of slag-carbide slag binder was better than fly ash-carbide slag binder,but there was still a gap compared with cement;improper control of moisture content of the mixture,long delay time and low temperature curing all had a strong negative impact on the alkali-activated binders.（4）Based on the Taguchi optimization method,the effects of nano-Si O₂,nano-Ca CO₃,nano-Al₂O₃,slag-carbide slag mass ratio and curing temperature on the performance of alkali-activated soil stabilizer were investigated,and the contribution of each factor to the soil strength was determined by ANOVA.The results show that the optimal ratio of soil stabilizer is 0.3%of nano-Si O₂,0.75%of nano-Ca CO₃,0.4%of nano-Al₂O₃,and 1.5 of slag-carbide slag mass ratio,named NAAS;the contribution of slag-carbide slag mass ratio and nano-Si O₂content is higher in standard maintenance,and the contribution of nano-Al₂O₃and nano-Si O₂content are higher in low temperature maintenance.（5）The micro-morphology and mineral phase composition of different soils were analyzed by X-ray diffraction and scanning electron microscopy.The results show that the flocculation effect and ion-exchange effect of the pretreatment agent changed the contact form between clay minerals;C-S-H,C-A-H,and AFm were generated in both WSS-II treated soil and NAAS treated soil,which improved the macroscopic mechanical strength of the waste marine clay;the two curing agents differed significantly in the early morphology and later evolution of hydrates due to different reaction mechanisms;the composite nanomaterials in NAAS enhanced the alkali-activated procession and promoted the diverse generation of C-A-S-H and AFm phase under low-temperature curing condition.