Experimental Study On Effect Of Ceramic Powder Admixture On Properties Of Recycled Concrete

Recycled concrete as a new green building material has been widely used in engineering.However,due to the surface structure defects of recycled coarse aggregate,many properties of recycled concrete are inferior to ordinary concrete.In addition,the amount of ceramic waste is increasing every year in China,while abundant active silica of waste ceramics and other chemical components can react with pozzolanic ash.After grinding,the waste ceramics have the potential to be used as admixtures in concrete.If waste ceramics can be treated as admixtures and applied in recycled concrete,some mechanical and durability properties of recycled concrete can be improved,it is undoubtedly the best solution to the problems of resource depletion and environmental protection.In order to explore the feasibility of ceramic powder used in recycled concrete,the effect of ceramic powder admixture on compressive strength and durability of recycled concrete was studied in this paper.The main contents of the study are as follows:1.The orthogonal test was designed to study the effect of water-binder ratio,recycled coarse aggregate substitution rate and ceramic powder content on the compressive strength of recycled concrete.By means of range analysis,orthogonal test hierarchy analysis and variance analysis,the primary and secondary order and the optimal level of the influence of various factors on the compressive strength are obtained.The results show that the increase of water-binder ratio and the replacement ratio of recycled coarse aggregate will decrease the compressive strength of concrete at different ages.The addition of ceramic powder can reduce the early compressive strength of recycled concrete,but it can improve the compressive strength of recycled concrete in the later stage.When the curing age is 28 d and 56 d,the compressive strength of the recycled concrete with 20% ceramic powder content in the treatment group will be greater than that of the treatment group without ceramic powder.2.The influence of the replacement ratio of recycled coarse aggregate and the content of ceramic powder on the carbonation durability of concrete was investigated by designing the rapid carbonization test.The change law of concrete quality,dynamic elastic modulus and carbonation depth was analyzed under different carbonation age.Finally,the microstructure of concrete before and after carbonization was analyzed by SEM scanning electron microscope.The results show that after the recycled coarse aggregate replaced the ordinary coarse aggregate,the higher the replacement rate of recycled coarse aggregate,the worse the carbonization resistance of concrete.The addition of ceramic powder can improve the dynamic elastic modulus of concrete,but the higher the content of ceramic powder,the greater the mass increase rate and carbonation depth of concrete,so the addition of ceramic powder has a negative effect on the carbonation resistance of concrete.In addition,with the prolongation of carbonation time,the carbonation rate of concrete decreases gradually,and the change rate of each carbonation measurement index tends to be more and more gentle.3.The change law that free chloride ion concentration and chloride diffusion coefficient in different depth of concrete of the replacement ratio of recycled coarse aggregate and the content of ceramic powder was studied by using chlorine salt solution immersion test.Furthermore,the influence of various factors on chloride corrosion resistance of concrete was evaluated.Finally,the microstructure of concrete after chloride immersion was analyzed by SEM scanning electron microscope.The results show that the higher the replacement ratio of recycled coarse aggregate,the worse the corrosion resistance of concrete.Although proper incorporation of ceramic powder will improve the free chloride ion concentration on the surface layer of concrete(0~15mm),if the depth of concrete is more than 15 mm,it will not have obviously significant effect on the increase of the free chloride ion concentration of concrete.In addition,when the amount of ceramic powder is added to 0%~20%,the chloride diffusivity of concrete will decreases with the increase of ceramic powder content.Therefore,the incorporation of ceramic powder plays a positive role in concrete resistance to chloride ion erosion.Because carbonation will increase the free chloride concentration and chloride diffusion coefficient of concrete,so the more the prolongation of carbonation time,the worse the corrosion resistance of concrete.