Research On Dynamic Compressive Properities Of Ceramsite Concrete Affected By Freeze-Thaw Cycle Conditions

With the large-scale use of concrete materials and the improvement of energy-saving and environmental protection requirements,ceramsite concrete has been widely used in engineering.The concrete structure in cold regions is often damaged by freezing and impact loading.Therefore,it is of great engineering significance to study the influence of freeze-thaw cycle(FTC)conditions on the dynamic compressive properties of ceramsite concrete.In this paper,static and dynamic mechanical properties tests and theoretical analysis were carried out on ceramsite concrete samples with a volume content of 40% and mortar concrete samples as a control group.The effects of freeze-thaw cycle temperature and cycles on mechanical properties were studied.The major contributes as follows:1.The influence of FTC conditions on concrete damage.In this paper,two sizes of samples(?70mm × 35 mm cylinder and 150 mm × 150 mm × 100 mm cuboid)were produced.The effects of different cycles on the sample’s properties were studied when the temperature of FTC was constant period(+ 10 °C ～-20 °C)and cycles were taken as 0,10,20 and 30,respectively.When the freezethaw cycles were unchanged(10 times),the highest temperature was +10 °C,the lowest temperature was-20 °C,-30 °C,-40 °C,-50 °C,-60 °C,respectively,the effect of different FTC temperature on samples were studied.The change of the weight and the ultrasonic velocity can characterize the damage of samples by the FTC.Whether it is increasing the cycles or lowering the minimum cycle temperature,it will cause more damage to the both types of concrete.The weight loss rate and the modulus of elasticity change of the mortar concrete are significantly smaller than those of ceramsite concrete.When the minimum temperature of the cycle is higher than-30 °C,the mass of the mortar concrete is little lost.2.The quasi-static compression test shows that with the decrease of the minimum temperature of the FTC and the increase of the freeze-thaw cycles,the damage of the sample is intensified,the frost resistance is weakened,the static compressive strength is reduced,and the ceramsite concrete is more obvious.It has similarity with the change trend of the elastic modulus,and the strain corresponding to the maximum stress increases,and the deformation resistance increases.3.The dynamic compression tests were carried out on the concrete of two sizes(?70mm×35mm cylinder and 150mm×150mm×100mm rectangular parallelepiped)by the single and beam of SHPB respectively,shows that with the increase of the loading strain rate,the compressive strength of mortar concrete and ceramsite concrete increases with obvious strain rate effect.Whether it is increasing the cycles or lowering the minimum cycle temperature,the strength of mortar concrete and ceramsite concrete will decrease,and corresponding strain increases with the decrease of compressive strength.Under similar conditions,the effect of lowering the minimum temperature of the FTC and increasing the cycles of FTC on the compressive strength of ceramsite concrete is similar.4.The study of constitutive relations shows that the damage evolution of ceramsite concrete is a rate-related process.The damage evolution of concrete is the same as the viscoelastic process of concrete,which is regarded as a stress-promoting thermal activation process.This paper uses the improved standard linear solids model characterizes the nonlinear viscoelastic properties of the material.The damage during the FTC is always caused by local tensile failure.Therefore,only the damage caused by tensile stress is used to characterize the damage of concrete caused by FTC.The constitutive relationship of the ceramsite concrete finally established has a good agreement with the experimental data,and the correlation coefficient is more than 95.5%.