Early Strength And Freezing Resistance Experimental Study Of Air-entrained Concrete Under -3? Sustained Preservation Of The Environment

This topic is the National Natural Science Foundation “Research on initial strength increasing law and miscrostructure of concrete in permafrost of ice-water-ice medium” of main content. The strength of concrete pile in permafrost is often less than the design requirements, this is due to the cement hydration process reflect the growth of strength of concrete process, while the hydration process associates with temperature, cement hydration speed is caused by negative temperature slowly, resulting in different the strength of concrete under standard curing conditions. If it constructs referring to the strength of concrete under the standard curing conditions, it will be bound to give engineering quality planteded security risk. In addition, insufficient freezing resistance is the main reason why caused durability of concrete damage in cold regions, thus,an important aspect of solving the problem is to study the frost resistance of concrete materials.Based on the problems above, this paper focuses on different water-cement ratio air-entrained concrete(0.24,0.31,0.38) to study the growth of early strength, the variation of pore structure, freezing resistance and other aspects under-3?sustained preservation of the environment. The principal conclusions are as follows:(1) Through testing the pore structure of concrete in different water-cement ratio, different gas content and different ages under-3?sustained preservation of the environment, research indicates: With the increase of water-cement ratio, the porosity of hardened concrete decreases, the average pore diameter of bubbles decreases, the spacing factor of bubbles decreases and the specific surface area increases. With the gas content increasing, the porosity of the hardened concrete increases, the specific surface area increases, the average pore diameter of bubbles first decreases and then gradually increases, when the gas content is lower than(3.5 ± 0.5)%, the spacing factor of bubbles decreases, but it is more than(3.5 ± 0.5)%, the spacing factor of bubbles unchanges. With the ages increasing, the porosity of hardened concrete increases, the average pore diameter of bubbles decreases, the spacing factor of bubbles decreases and the specific surface area increases. It is the same in the pore structure under the standard curing, but the pore structure is roughed under-3?sustained preservation of the environment.(2) The compressive strength of concrete at 28 d under the standard curing is the same at 84 d under-3?sustained preservation of the environment, Therefore, the compressive strengthof concrete under-3?sustained preservation of the environment needs more time to reach under the standard curing. The porosity of hardened concrete increase every 1%, the compressive strength will be reduced by 3% to 5%.(3) In this experiment, freezing resistance of concrete under the standard curing is stronger than-3?sustained preservation of the environment at the same strength, Therefore, in the actual construction process, especially for the pile of concrete in the permafrost, it is necessary to consider the impact of the strength, but also square up the factor of freezing resistance.