Study On Mix Design And Mechanical Properties Of CMA Concrete

In the remote Tibetan and pastoral areas in the northwest of China,the environment is bad and the building materials are seriously deficient.In these areas,the transportation and cost must be considered in civil engineering construction,so it is particularly important to obtain materials from nearby.In the local area,cattle manure,as an important resource for residents to use as fuel,produces a lot of waste cattle manure ash.Cattle manure ash(CMA)is pure and relatively stable.The use of waste CMA to replace part of cement in concrete can not only improve the shortage of building materials,but also solve the environmental problems caused by improper treatment of CMA.The systematic study on the mechanical properties of CMA concrete can provide a theoretical basis for the engineering application of CMA.In this paper,the properties of CMA prepared under different combustion conditions are compared.It is found that the physical and chemical properties of CMA obtained by burning at 650 ℃ for two hours are the best,which can be used for subsequent tests.According to the relevant specifications,the mix proportion of CMA concrete is designed.A total of 42 groups of CMA concrete blocks with 5%,10%,15% single and 10%,20% and30% double admixtures of C20,C25 and C30 strength grades were made,of which 21 groups were used for compressive and splitting tensile tests.The mesostructure of CMA concrete block was studied by industrial CT,and the influence of mesostructure on its mechanical properties was analyzed.The conclusions are as follows:(1)The compressive strength and splitting tensile strength of single and double mixed concrete decrease with the increase of ash content.Among the single mixed concrete,the concrete with 5% CMA has the best compression and splitting tensile effects.Among the double mixed concrete,the concrete with 5% CMA and fly ash has the best compression and splitting tensile effects.When the amount of single and double admixtures is the same,the mechanical properties of single concrete are better.The compressive strength and splitting tensile strength of concrete with 15% of CMA and fly ash are the lowest,but they can still meet the requirements of the strength grade.(2)Using industrial CT to study the micro structure of CMA concrete,the number of pores in the scanning layer of CMA concrete increases with the increase of ash content,and the number of macropores increases gradually.The higher the ash content of CMA concrete is,the more its porosity is.The higher the strength grade of concrete is,the smaller the overall porosity of specimens is: the porosity of C30 concrete is less than that of C25 concrete,while the porosity of C25 concrete is less than that of C20 concrete.(3)The porosity of CMA concrete is inversely proportional to its compressive strength,with the increase of porosity,the compressive strength of CMA concrete decreases.Theporosity of concrete with 10% CMA is smaller than that with 5% CMA and fly ash,but the compressive strength of single mixed concrete is higher than that of double mixed concrete.Although the compressive and splitting tensile strength of CMA concrete decreases with the increase of ash content,it still meets the requirements of the strength grade.At the same time,the research on the pore problem of CMA concrete will have an important guiding significance for the study of the performance improvement of CMA concrete,especially the thermal physical properties.