Experimental Study On Reinforcing The Organic Soil Based On The Filling Function Of Ettringite

The method of cement-soil mixing is widely applied in ground improvement due to its high velocity,high efficiency and lower cost.However,stabilization of organic soil is more challenging than that of inorganic soils due to the tendency of humic acids to hinder the hydration processes and related reactions required for the development of strength.In order to solidify the organic soils effectively,a series of laboratory tests were carried out in this study to explore new stabilization agents and determine the optimal dosage.The research contents and conclusions can be drawn as follows:(1)The cement hydration progress is seriously retarded by the fulvic acid,so the cement admixed cement fail to reach a high strength.When the fulvic acid is added in water,it dissolves immediately and attached with cement particles and soil particles.On the one hand,the cement could not hydrate as usual,the hydration products fail to produce.On the other hand,the pozzolanic reaction between cement particles and soil particles can not happen.So there is little strength forming during the process.(2)The method based on the filling function of ettringite is feasible to solidify the organic soil.The new curing agent combined with C,PG and CAC can solidify soil contained organic matter between 5%and 10%more effectively than using cement only.The 14d strength using the new curing agent could reach 1.2MPa.The adding of PG and CAC increase the strength of cement solidified the organic soil obviously.The main mechanism is the formation of ettringite,it could fill the large porosity of organic soil effectively.So the strength gets improved as a result of the decreasing of porosity.(3)The SEM images matched with EDS present the main production of the new curing agent is ettringite.After the adding of CAC,the formation of ettingite is accelerated and the ettringite is formed by cluster.After the 90 days curing time,the ettringte is developed entirely and they interwaved with each other to form the high strength of cement-soil mixing.The XRD results indicate the presence of the new mineral ettringite.The MIP results indicate that the porosity is decreased by the adding of PG and CAC,which contribute to the improvement of strength.(4)The elementary composition of the new curing agent has the optimal ratio between aluminum,calcium and sulfate,the ratio CaO/Al2O3 is determined by 2.3-4 and the ratio SO3/(Al2O3·CaO)is determined by 8-12 based on the experiment results.The empirical equation between UCS,water-cement ratio and organic content is established.It is allowable to use the moisture content,organic content and target strength to determine the content of the new curing agent.