低气压环境对混凝土含气量及气孔结构影响研究

Effect of Air Pressure Environment on Air Content and Air Void Structures of Concrete

通过低气压试验箱模拟高原不同海拔地区气压环境，研究了低气压对引气混凝土含气量及气孔结构的影响。试验结果表明：环境气压的降低将显著削弱引气剂的引气能力，当搅拌气压降低至50kPa时，混凝土含气量降低约20％～49％；混凝土含气量随环境气压降低呈线性减少，初始含气量越高，随环境气压降低含气量减少速率越大；混凝土塌落度越大，其抵抗因环境气压降低造成含气量降低的能力越强；低气压下搅拌后硬化的混凝土气孔结构参数整体要劣于常压下搅拌的硬化混凝土，具体表现为气泡间距系数偏大，单位体积气泡数量较少，气泡比表面积以及气泡平均直径增大的特点，但总体上看，当混凝土含气量达到一定值后，低气压下硬化混凝土的气泡间距系数可达到在200～300μm之间。

The effects of low air pressure on air content and air void structures of air-entraining concrete are studied using low-pressure test chamber to stimulate the environmental air pressures in different altitude regions. The result indicates that （ 1 ） the reduce of air pressure of environment has a significant impact on the performance of air-entraining agents, the air content of concrete falls by roughly 20% -49% when the mixing pressure decreases to 50 kPa; （2） the air content of concrete decreases linearly with the drop of air pressure of environment, the higher the initial air content is, the faster the air content decreases with the drop of air pressure ; （3） the concrete with higher slump shows more resistance to drop of air-content due to decrease of air pressure ; （4） the air void parameters of the hardened concrete mixed under low-pressure are worse than those of the hardened concrete mixed under ordinary pressure, i. e. , the spacing factor of air void increases, the number of bubble in unit volume of concrete is less, and the specific surface area and the average diameter of bubble are larger, but overall, the bubble spacing factor of the hardened concrete under low-pressure can reach 200 - 300 μm when the air content of concrete reaches a certain value.