Study On The Mixture Ratio Of Silt Cement Based Composite Curing Agent And Properties Of Solidified Soil

With the development of dredging projects such as river and lake management and channel dredging,the output of silt is increasing day by day.Silt has high water content,low strength,high viscosity and a lot of pollutants.If it cannot be timely and effectively treated,it will not only occupy land resources,but also cause serious secondary pollution to the environment.Silt solidification is one of the best technologies for the utilization of silt resources.The selection of curing agent can effectively improve the performance of silt,improve the mechanical strength of silt,and stabilize the pollutants in silt.In this paper,cement was selected as the curing agent,fly ash,polycarboxylic acid superplasticizer,calcium aluminate and calcium-bentonite were selected as additives to solidify silt,and the optimal ratio was determined to obtain cement-based composite reinforcement materials(referred to as composite curing agent).The microstructure of composite solidified soil(silt added with composite solidifying agent)was described by SEM test.Response surface test was used to explore the effects and laws of silt water content,silt organic matter content and content of curing agent on the strength of solidified soil.The total nitrogen,total phosphorus,chemical oxygen demand,electrical conductivity and potential of hydrogen values of the cement solidified soil(silt added with cement)and the leaching liquid of the composite solidified soil were compared and analyzed.The main content includeds the following aspects:(1)The changes and laws of unconfined compressive strength,water content,electrical conductivity and potential of hydrogen of cured soil under different curing materials and curing ages were investigated,and the optimal ratio of composite curing agent was obtained.The results show that cement,fly ash,polycarboxylic acid superplasticizer,calcium-bentonite and calcium aluminate all had the optimal content range(cement was 10%?30%,fly ash was 5%?15%,polycarboxylic acid superplasticizer was 0.1%?0.2%,calcium bentonite was 2%?8%,calcium aluminate was 1%?4%).The optimal combination of compound curing agent was:cement:fly ash:polycarboxylic acid superplasticizer:calcium aluminate:calcium bentonite was 22:5:0.2:2:6.(2)The effects of silt organic matter content and silt moisture content on the strength of solidified soil were investigated.The results showed that the strength loss rate of cement-cured soil was 39.49%and that of composite solidified soil was 17.1%when the content of humus increases to 10%at the curing age of 28 days.When the silt moisture content increasededs to 70%,the strength loss rate of cement-cured soil was 37.17%,and the strength loss rate of compound solidified soil was 16.05%,indicated that compound curing agent can better eliminated the influence of organic matter and water content changes on unconfined compressive strength of solidified soil than cement.Used response surface analysis method,the interaction rules of the content of composite curing agent,the content of silt organic matter and the silt moisture content on the unconfined compressive strength of solidified soil were deeply analyzed,and the strength prediction model of the three was established at the curing ages of 14 days and 28 days.(3)The environmental characteristics of solidified soil under different contents of cement and composite curing agent and different curing ages were studied,and the variation rules of total phosphorus value,total nitrogen value,chemical oxygen demand value,electrical conductivity value and potential of hydrogen value of solidified soil leaching liquid were emphatically analyzed.The results showed that the solidification technology can stabilize the pollutants in the silt to some extent.The values of chemical oxygen demand,total nitrogen,total phosphorus,potential of hydrogen and conductivity of the leaching solution of the composite solidified soil showed a general downward trend with the increase of the content of the composite solidifying agent and the curing age,which was less than that of the cement-solidified soil,indicated that the composite solidifying agent had a better effect than cement in reducing alkalinity and stabilizing organic matter and nitrogen and phosphorus pollutants in the silt.(4)SEM was used to study the microstructure of the composite solidified soil,and the formation of hydrated substances in the composite solidified soil was analyzed.SEM images showed that the composite curing agent was helpful to improve the microstructure of the silt.Compared with the original silt,the particles of the composite solidified soil had an obvious solidarity effect.With the increase in the content of curing agent,the gel materials such as reticular and coarse bar bodies were generated,which increased the strength of the solidified soil.