Influence Of Ice Crystals Filled In Capillaries On Performance Of Hybrid Aggregates Concrete

In the artificial freezing method,the ambient temperature of the working face is generally about-10℃,which leads to the formation of ice crystals in the free water in the capillary pores of concrete,thus affecting the strength and stiffness of concrete.If it can be guaranteed that the concrete is not frozen for the first 3 days after the concrete is poured,the capillary ice crystals can strengthen the strength and stiffness;otherwise,they can deteriorate the strength.Capillary ice crystals can fill the interior pores of lightweight aggregate concrete at low temperatures,increase the effective bearing area,reduce stress concentration,and thereby increase the strength of the concrete.However,in the curing stage,the free water inside the lightweight aggregate concrete freezes under low temperature environment,which will slow down the hydration reaction process,and the strength is reduced compared with the normal temperature environment.In order to reduce the deteriorating effect of capillary ice crystals on concrete,this article takes the all-lightweight concrete as the benchmark,and uses ordinary aggregates to replace the equivalent volume of sand aggregate,sand lightweight concrete,gravel lightweight concrete and hybrid aggregates lightweight concrete can be collectively referred to as mixed aggregate concrete or semi-light concrete to improve its low temperature resistance.Specifically,in this paper,icicle simulation experiments are carried out to analyze the thermal properties of concrete,compare and analyze the effect of low temperature curing on the mechanical properties of different concrete,and reveal the damage mechanism of capillary ice crystals on mixed aggregate concrete.(1)The physical and mechanical properties of icicles formed by the freezing of tap water tend to be stable after freezing for a period of time,and the freezing temperature has a significant effect on the density,strength and stiffness of the ice;(2)Through the adiabatic temperature rise test and thermal conductivity test of the mixed aggregate concrete,it is found that the mixed aggregate concrete will generate a large amount of heat within 30 hours of pouring,and its thermal conductivity is far less than that of ordinary concrete.And the dry apparent density of concrete has a significant influence on its thermal conductivity;(3)After low temperature maintenance,the mechanical properties of mixed aggregate concrete are tested,and the degree of icing inside the concrete is different at different low temperature conditions.It is found that different maintenance temperatures and aggregate composition have a significant effect on the mechanical properties of concrete.And it is also found that the concrete is converted to normal temperature after low temperature maintenance,the strength of the concrete will increase.The drying effect will accelerate the increase of the strength of the concrete;(4)After freezing at low temperature,the mechanical properties of all-lightweight concrete are tested.It is found that freezing at low temperature can obviously improve the strength of concrete,and the strength of concrete will increase with the increase of the volume ratio of ice crystals.The strengthening effect of capillary ice crystals on concrete is significantly different at different freezing temperatures.The research results can provide a theoretical basis for the strength prediction of concrete during the freezing method construction,and provide a reference for the evaluation of the concrete strength loss after the freezing method construction is completed.