Effect Of Aggregate On Thermal Expansion Coefficient And Thermal Shock Cracking Of Concrete

In the high-altitude and high-altitude regions such as Tibet,the daily average temperature difference is large,the solar radiation causes the sunny surface temperature of the concrete structure to be higher than the shady surface,so that the daily average temperature difference of the sunny surface can reach 40-60°C,thus causing the sunny surface's the violent repeated expansion and contraction causes cracking damage.In order to study the damage law of such phenomena,starting with aggregate,the mineral composition,porosity and grain size of granite,quartzite,limestone and basalt aggregates are determined,and the thermal expansion coefficients of aggregate and concrete were measured by improved thermal expansion coefficient measuring instrument,and the correlation degree of each influencing factor was analyzed by grey correlation.At the same time,the prediction program of thermal expansion coefficient of concrete is compiled by using MATLAB software.Then,the mechanical properties and microstructural changes of concrete with different aggregates during thermal shock are studied.Studies have shown that the composition and content of aggregated minerals of aggregates have a greater influence on the thermal expansion coefficient of aggregates than their grain size.The grey correlation coefficient order of granite thermal expansion coefficient is mica content ratio > quartz content ratio > feldspar content ratio > average grain size.Although the mica content in granite is small,it has a great influence on the thermal expansion coefficient of granite,indicating the influence of the composition of rock minerals is large;the gray correlation degree of thermal expansion coefficient order of quartzite is quartz content ratio > average grain size > proportion of feldspar content > proportion of mica content.For concrete,the influence of aggregate on the thermal expansion coefficient of concrete is weaker than that of cement stone.The influence of water-cement ratio on the thermal expansion coefficient of concrete is the most direct and direct,while the degree of influence for concrete coefficient of thermal expansion is weakened in order of the thermal expansion coefficient of aggregate,aggregate dosage and aggregate porosity.The thermal shock stability test results of aggregates with different thermal expansion coefficients indicate that the greater the difference between the thermal expansion coefficient of aggregate and cement stone,the greater the compressive strength and relative dynamic elastic modulus loss of concrete,in a word,the greater the difference of the thermal expansion coefficient of aggregate and cement stone,the worse its ability to withstand thermal shock damage.The study of concrete microstructure shows that the thermal shock damage of concrete is mainly caused by the generation,expansion and connectivity of microcracks induced by thermal shock in the transition zone of aggregate interface.The thermal shock stability of the four aggregate concrete decreases in the order of granite,basalt,quartzite and limestone.