Humidity Diffusion Test And Simulation Study Of Lightweight Aggregate Concrete

With the development of the industrialization of prefabricated buildings,lightweight aggregate concrete(LWAC)is also used in the exterior wall design of the integration of structure and heat preservation.However,there are more connected pores in LWAC than in ordinary concrete,the existence of pores in LWAC will lead to the difference of moisture transfer between LWAC and ordinary concrete,and the distribution of moisture content and moisture field will affect the strength of LWAC at early age?volume deformation and durability.Throughout the domestic and foreign scholars,most of the researches are on the internal relative humidity change of ordinary concrete,but the relative humidity transfer and humidity field of LWAC are very few.Based on this,in order to clearly understand the moisture diffusion and humidity field distribution of LWAC,this paper explores the relationship between moisture diffusion and humidity field distribution and time and space of LWAC from the second law of Fick,and the comparative tests of various factors are designed to measure the physical performance parameters and relative humidity of concrete,the test results are compared and analyzed.In addition,based on theory and experiment,by the established moisture diffusion model of LWAC,the moisture field of LWAC at early age(test after demolding)and LWAC at non-early age(After the test piece is demolded,for 28 days of soaking water and then tested)were simulated by finite element method and finite difference method,respectively,which can make the theory?experiment and simulation combine with each other.The main work accomplished in this paper is as follows:(1)Through Fick's second law,in the process of moisture diffusion of LWAC at early age,the self-drying action source term is added,and the mathematical model of moisture diffusion of LWAC is established at early age;In the process of moisture diffusion of LWAC at non-early age,the mathematical model of moisture diffusion of LWAC is established by using the classical Fick's second law at non-early age.(2)LWAC specimens were prepared by using crushed shale ceramsite as lightweight coarse aggregate,the specimen size is 100 mm × 100 mm × 400 mm,among them,the water-cement ratio is 0.35 and 0.45,the bulk density of the coarse aggregate is 900 and 500,and the coarse aggregate volume ratio is 40% and 20%,which are tested in the same environment to explore the effect of water-cement ratio,coarse aggregate density grade and coarse aggregate volume ratio on humidity diffusion of LWAC,and to fit the the relationship with time between the relative humidity of LWAC in early age and non-early age.(3)The concrete parameters obtained from the moisture diffusion test of early age LWAC are modeled by ABAQUS finite element mass diffusion module,which can obtain the change of normalized concentration distribution with time in concrete by introduced of normalized concentration variable;the relative parameters of concrete obtained from moisture diffusion test of LWAC at non-early age are substituted into program language,and calculated by MATLAB software,which can obtain the variation of relative humidity with time LWAC at non-early age.By comparing and analyzing with the test,it is found that the simulated value is in good agreement with the experimental value.