Study On Heat And Moisture Properties Of Lightweight Aggregate Concrete Based On Micromechanics Homogenization Method

Lightweight aggregate concretes(LWACs)are more and more applied to industrial and civil buildings and other projects because of its light weight,good thermal insulation and anti-seismic performance.Compared to the ordinary concrete,LWACs contain more inside pores,the existence of pores provides a transmission channel for moisture and heat transfer.The heat and moisture transfer in concrete has a great influence on the durability design of concrete,but at present,there is not much research on the moisture diffusion of LWACs.The performance of concrete is studied from two aspects: macro scale and meso scale.There are many limits to research concrete in macro perspective and the macroscopic behavior of materials is the result of the evolution of microscopic properties.More and more researchers begin to proceed from the angle of view and try to establish the relationship between microstructure and macroscopic properties of materials.Based on the above problems,this paper use shale ceramsite as lightweight aggregate to prepare the concrete,as one hand,using two-phases homogenization model to theoretically analyze the relationship between the whole concrete's physical parameters(diffusion coefficient and thermal conductivity)and each component's physical parameters in LWAC,on the other hand,analyze the moisture and thermal conductivity of LWAC by experiments;at the same time,using finite element software to simulate the moisture transfer in concrete and compared with the experiment.In addition,this article also through the reverse method,by the data of the whole and the matrix properties,combine with the inversion method to get the relative performance parameters of the lightweight aggregate which is not easy to get from experiment,and then according to the matrix and lightweight aggregate performance parameters combine with the theoretical formula to get new concrete which is required,so as to provide the basis for the design of concrete durability.(1)By introducing the method of micromechanics homogenization,treat cement mortar as matrix phase,lightweight aggregate is inclusion phase,get the thermal and physical properties expression of lightweight aggregate concrete by the volume ratio of coarse aggregate.(2)The experiment design five kinds of concrete proportion and choose three environment conditions to start the test,there are two dimensions of the specimen,100 mm ×100mm × 400mm(concrete prism)and 300 mm ×300mm × 40mm(concrete board);use the concrete prism to do water vapor transport experiment under the different environment,and use the concrete board to do the thermal conductivity experiment under different water content.Theoretically analyzed the experiment result and found it can be well matched with the micro theoretical formula.Combine the inversion of aggregate physical parameter with cement mortar matrix to get the physical parameters of concrete with different volume ratio,find the theoretical value is less than the experimental value.(3)Using the experiment data(mass increment,moisture diffusion coefficient,porosity,etc)to establish finite element model by ABAQUS mass diffusion module,get the result about moisture-distribution in concrete along with time history,compared with the experimental results,the simulation results are accordant with the experimental values.