Experiment And Analysis Of Concrete After Thermal Cycles

Concrete structure is always exposed to heating and cooling cycles in its lifetime,no matter civil buildings,road engineering,industry structure or national defence construction.Previous researches show that a single exposure cycle of elevated temperature and cooling down has negligible effects on concrete mechanical properties provided that the highest temperature does not exceed about 200?.However,during their whole lifetime of service some industrial structures,such as chimneys,vessel containments and supporting structures of thermal facilities,etc.,are always exposed to large amount of thermal cycles which may dramatically deteriorates the mechanical properties of concrete.The deterioration processes of concrete under positive thermal cycles are researched in this paper,which is mainly based on those structures in severe circumstances.The content primarily includes the following aspects:1.Experimental study on mechanical behavior of concrete under thermal cycles with the highest temperature below 200? is presented.In particular,the mechanical properties and cracking performance of concrete are investigated regarding prismatic testing specimens subjected to different numbers(ranging from 1 to 50)of thermal cycles.Crack evolution is photographically recorded,and the stress versus strain curves under uniaxial compression are measured.2.This paper presents another experiment on cement past and mortar specimens subjected to different numbers of thermal cycles.The exterior crack evolution is photographically recorded,and the micro properties are detected with SEM.Rupture strength of specimens with the size of 40×40×160 are measured after different times of thermal cycles.The components of concrete which is assumed as three-phase composite are studied in the macro and micro scope.The mechanism of concrete deterioration process under positive thermal cycles is better understood in this way.3.Numerical simulation as a sufficient modeling tool is properly used in this paper.The modeled concrete and meso-scale concrete models are employed to reveal the principles and mechanism of the fracture process under uniaxial compression and positive thermal cycles.The cement matrix,aggregate,ITZ are separately partitioned,temperature coupled displacement analysis is employed in the numerical simulations.With the comparison and analysis of experiment and numerical simulation,concrete properties under positive thermal cycles are well researched.In addition it provides design approach for concrete structures under this special circumstance.