Study On Water Absorption Test Evaluating The Internal Damage Of Concrete Caused By Freeze-Thaw Cycles

Concrete is widely used in construction all over the world due to its high strength and easy access.In the seasonal frozen region,the damage of concrete generally caused by the freeze-thaw cycles which leads to the development of micro-cracks in concrete;more seriously,the micro-cracks cause the concrete destroyed.There are many tests are widely used for evaluating the internal damage in concrete caused by freeze-thaw cycles: dynamic elastic modulus method,charge passed method(rapid chloride penetration test)and resistivity method(electrical surface resistivity test).These tests are difficult in operation,long in testing time,and has some serious requirements for the size of the specimen.However,the water absorption test does not has these defects.Considering that,the rate of water absorption of concrete was introduced to evaluate the damage caused by freeze-thaw cycles in concrete in this study.The main contents and research results of this paper are as follows:(1)the failure mechanism of concrete caused by freezing thawing cycles was summarized,based on that the principles of three testing methods(dynamic modulus method,charge passed method and resistivity method)of concrete internal damage test and characteristics of various experimental methods on concrete internal damage were discussed were analyzed.The result shows that the rapid chloride ion penetration method and electricity surface resistivity method might not represent the internal damage effectively.(2)based on Darcy's law,dynamic theoretical model of capillary action and freeze-thaw cycle failure mechanism,the relationship between concrete moisture absorption and internal micro cracks in concrete was analyzed,and the damage state of concrete can be represented by the rate of water absorption.Besides that,the result shows that rate of water absorption is inversely proportion to resistivity(resistivity method),and proportional to charge passed(rapid chloride penetration test).(3)a total of 18 concrete cylinders were tested for the dynamic elastic modulus test,the electrical surface resistance test,the rapid chlorine ion penetration test and the water absorption test in the laboratory and after concrete cylinders were subjected to freeze-thaw cycles(100 to 300 cycles)to better represent the field concrete.The test results show that the dynamic elastic modulus of concrete may not evaluate the internal damage in concrete very effectively;for the same internal damage state,the resistivity of the concrete would be different because of different aggregate types and volume,the additive,the mix ratio and other different surface resistivity tests,indicating that the resistivity of concrete for different materials can not be directly conducted to evaluate the internal damage of concrete;the test results of water absorption test and rapid chlorine ion penetration test are basically consistent with the evaluation of concrete internal damage,which shows that the test of water absorption test can be conducted to evaluate the damage caused by freeze-thaw cycles.