Effect Of Low Humidity And Low Atmospheric Pressure On The Properties Of Concrete

As we all know,there are three factors in curing condition:temperature, humidity and curing time. If the curing conditions of concrete are not abundant, the later mechanical properties and durability of concrete will decrease.In Qinghai and Plateau regions, positive and negative temperature alternate frequently, the climate is drought and windy,and the water evaporates fast.So,in Qinghai and Plateau regions,the curing problem must be pay more attention.In this paper,the relative standard atmospheric pressure in the curing conditions includes75% and 50%;the relative humidity in the curing conditions includes 60% and 30%.Therefore we can compose four curing modes: P 50H30,P50 H60,P75H30,P75H60.By changing the relative standard atmospheric pressure and the relative humidity,we study the diversification in the mechanical properties and durability of concrete.Based on these four curing modes( P50H30,P50H60,P75H30,P75H60),when the relative standard atmospheric pressure is constant and the relative humidity is decreasing, pore structure in the concrete deteriorates,at the sametime the porosity and aperture size decrease.And the the mechanical properties and durability of concrete become worse. When the relative humidity is constant and The relative standard atmospheric pressure decrease,the concrete appears the same conversation.When the curing mode is P50H30,and fly ash added increase from 0% to 15%,then from 15% to 30%,the compressive strength and the flexural strength of concrete are descended;the impermeability is increased and frost-salt resistance is increased.When the fly ash(the amounts is 15%) and the air-entraining agent are added in the concrete,the compressive strength is decreased and the the impermeability and frost-salt resistance are increased.As the example of concrete with the fly ash(the amounts is 15%) and the airentraining agent adding,the curing period is 28 d,before nonstandard curing the standard curing time includes 0d,3d,7d.The compressive strength is descended by 34% and the impermeability is decreased by 38% with 0d of the standard curing time;but when the standard curing time is 7d,the compressi ve strength is descended by 10% and the the impermeability is decreased by 13%.