Research For The Performance Of The Lightweight Aggregate Concrete Based On The Absorption And Desorption Characteristic Of Ceramsite

A water absorption and desorption characteristic of ceramsite with different type and prewetting degree in concrete with the same total water to cement ratio (TWC) were compared and analyzed. The cement hydration degree, pore structure and compressive strength of lightweight aggregate concrete (LWAC) using ceramsite with different type and prewetting degree were investigated. By the tests above, the water absorption and desorption characteristic of ceramsite was discussed, and theoretical models used to predict the properties of LWAC were proposed. The main test methods and conclusions can be drawn as follows:1. The water absorption and desorption characteristics of ceramsite in pure water respectively obtained from the volumetric flask test and U-shaped tube test have good correlation. The water absorption and desorption characteristic of ceramsite in LWAC is measured by using a U-shaped tube test device, and the result shows that the ceramsite content has little impact on the water absorption and desorption property of ceramsite. When the type of ceramsite is the same, the water-absorbing ability of ceramsite decrease and the desorbing ability increase with the increasing of prewetting degree of ceramsite. When the prewetting degree is the same, the ceramsite with higher water absorption capacity has stronger water-absorbing and desorbing ability.2. With MATLAB and lstOpt softwares, the water absorption and desorption characteristic model of ceramsite considering age, water absorption rate and net water-cement ratio (NWC) was obtained by fitting the test data, and verified by the test data of former scholars. The calculated model of effective water-cement ratio including age and water absorption and desorption was deduced according to the U-shaped tube test results.3. The hydration degree of LWAC was studied by measuring the chemical combined water content. For the same TWC, the hydration reaction rate and hydration degree decrease with the increase of the water absorption rate and prewetting degree of ceramsite, and then the time to reaching the maximal hydration degree was prolonged, and the number of internal not hydration of cement particle also increases. The paper performed a regression analysis to build and verify a calculation model of hydration degree as a function of effective water to cement ratio (EWC) and age by using lstOpt software.4. The microstructure of LWAC was studied by using a nitrogen adsorption method. The large pore volume decreases and the gel pore volume increases with the increase of age. For the same TWC, the large pore volume decreases with the increase of prewetting degree, and the average pore diameter reduces with the increase of age and the decrease of prewetting degree.5. The compressive strength of LWAC was studied, and a compressive strength calculated model considering the hydration degree and the strength of ceramsite was built and verified. Compared with the existing Bowromi formula, the formula in this paper is more suitable for predicting the LWAC strength.6. Based on above research, the EWC of LWAC can be deduced by the water absorption and desorption characteristic of ceramsite in concrete, and can the properties of LWAC such as the hydration degree and compressive strength can be predicted.The research comes from the National Natural Science Foundation named "The mechanism research of the tensile creep of lightweight aggregate concrete".