Effects Of Curing Conditions On Temperature Field And Microscopic Properties Of Negative Temperatue Concrete

In cold areas,the excessive temperature difference between hydration heat inside the concrete and surrounding temperature will lead to concrete cracks in the structure and seriously affecting the structure of the safety and durability.So it is important to study the development scheme of the interior temperature field and properties of negative temperature concrete used for construction.The temperature field and performance of negative temperature concrete under different curing conditions were systematically studied by adopting the structural member test and theoretical analysis method in this paper.Such scheme of concrete structures with different dimension when exposed to constant negative temperature of-15?,-20?,and-30?respectively were studied.The effect of different curing conditions on the temperature field of these negative temperature concretes was also investigated.Results revealed that the cooling rate of concrete specimen under benzene board cover was the slowest,while the geotextile cover the second and the direct exposure to air the fastest.Under the same condition,the time concrete contained antifreeze needed to reach the lowest temperature was longer than that of concrete without antifreeze.Moreover,concrete specimen with the larger size featured a slower cooling rate.The lower the curing temperature,the greater the cooling rate of the specimen center.The finite element software MIDAS/Civil was used to analyze the numerical conditions under the corresponding conditions.Finite element analysis(FEA)results showed good agreement with the measured results,which can simulate the interior temperature field of concrete structures during construction and curing process.Through FEA simulation,a more accurate temperature change in concrete can be obtained and thus a better heat-storage curing method can be suggested.Using method of loss of weight and mercury intrusion,the hydration degree and pore structure of the negative temperature concrete of different ages under different curing temperature,water binder ratio,anti-freezing admixture were analyzed in this paper.The results showed that the greater the water binder ratio,the greater the volume of chemical combined water under the same conditions.With the increase of age,the influence of water binder ratio on hydration degree also rises,raising porosity,cumulative mercury volume and relative amount of pores.The admixture of anti-freezing increases the chemical combined water of paste,slightly increasing the porosity and the volume of pore size less than 100 nm.The lower the early curing temperature,the lower the chemical combined water of cement paste,while the porosity,the total pore volume,the average pore size and the critical pore size decrease at different levels.