Study On Durability And Reinforcement Mechanism Of Desulfurization Gypsum & Fly Ash Composite Cement Soil

The research of durability and reinforcement mechanism for cement soil is a key problem to spread and application in northern cold areas. In view of lower strength and poor durability of common cement soil, meanwhile, in order to solve massive industrial waste like fly ash and desulfurization gypsum produced by coal-fired power plant in our region, a new type of composite cement soil material was prepared by adding coal-fired power plant industrial waste like fly ash and desulfurization gypsum. And then, their mechanics properties, durability, damage characteristics and reinforcement mechanism were researched by testing in the laboratory, which provide theoretical basis and test data for them widely used in Inner Mongolia area.Firstly, the strength prediction model for composite cement soil was built, and the best mix proportion for the components material of composite cement soil was proposed.(1)The unconfined compressive strength tests of common cement soil were carried out considering different cement mixing ratios, different curing ages, different specification and molding methods, and its characteristics were basically mastered. The cement soil is prepared of typical silty soil which is distributed in the Tu Mo Chuan branch one of Yellow River irrigation located in Inner Mongolia area.(2)Either fly ash or desulfurization gypsum incorporated into common cement soil, the influence law of strength affected by the mixing amount of fly ash or desulfurization gypsum was researched.(3)Through orthogonal testing and additional testing, the influence law of strength affected by the combining admixture of fly ash and desulfurization gypsum were researched, the best mix proportion for the components material of composite cement soil was proposed and verified, and the strength prediction model was built.Secondly, a completely new nonlinear elastic constitutive model for composite cement soil was built, and its deformation and failure characteristics were analyzed.(1)According to the characteristics of whole stress-strain curve for composite cement soil under uniaxial compression condition, using growth function logistic to fit upward section of the curve and using composite hyperbolic function to fit downward section of the curve, the author was first put forward nonlinear elastic constitutive model for composite cement soil which was better than traditional CSDC-2002 model.(2)According to the characteristics of deviator stress- axial strain curve for composite cement soil under triaxial compression condition, nonlinear elastic model named “three-segment method”by the author, and its complete derivation process or parameter calculation process was given.(3)The relationship between deformation modulus or failure strain with unconfined compressive strength was researched; meanwhile, the failure model of composite cement soil under uniaxial compression or triaxial compression condition was analyzed.Thirdly, the durability of composite cement soil material was evaluated, and comparative analysis with common cement soilˊs durability was made.(1)Drying-wetting and freezing-thawing cycle test showed that resistant to drying-wetting cycle capacity and frost resistance for composite cement soil was better than common cement soil.(2)Three-temperature freezing-thawing cycle test showed that the integral displacement of composite cement soil was shorter than common cement soil; when the soil materialˊwater content in the base is close to optimum water content, congruent composite cement soil sampleˊs integral displacement is the minimum and frost resistance is the best.Fourthly, the analysis method of microstructure for composite cement soil was innovated; also, its reinforcement mechanism and damage characteristics were researched.(1)The making sample method that cement soil sample is observed by atomic force microscope(AFM) was put forward and used in practice; the microstructure of non-conducting composite cement soil sample is also observed by field emission environment scanning electron microscope.(2)Based on microstructure analysis, reinforcement mechanism of composite cement soil was explored; besides, based on uniaxial compression damage test, damage evolution law was analyzed; the elastic-plastic damage model of composite cement soil under uniaxial compression condition was deducted and built.