大气压强对混凝土引气剂引气效果的影响

Effect of Atmospheric Pressure on Air-Entraining Performance of Air-Entraining Agent of Concrete

通过对比北京、楚雄和日喀则3地不同气压条件下2种混凝土引气剂(AES、303R)溶液中气泡尺寸与发育情况、引气水泥净浆孔径分布特征与引气水泥净浆、砂浆的表观密度,研究了大气压强对混凝土引气剂工作性能的影响机理.结果表明:随着环境气压的降低,2种引气剂溶液中的气泡尺寸均有所增大;气泡初始直径越大,其吞噬、合并周围小气泡的速度越快,稳定性越差;在相同气压条件下,303R溶液中的气泡尺寸较AES溶液更小,稳定性与高原低气压适应性更强;随着环境气压的降低,硬化水泥净浆的表观密度减小,内部大孔比例增加;3地水泥净浆在100~1000 nm半径范围内累计孔体积的排序为日喀则>楚雄>北京;随着环境气压的降低,水泥砂浆的表观密度有小幅增加,含气量减小2.1%(相当于混凝土1.2%)以内.

The foaming performances of two air-entraining agents(AEA),including AES and 303R,in Beijing,Chuxiong,and Shigatse were respectively investigated to study the effect of air pressure on air entrainment of cement-based materials.The foaming performances were assessed by size and development of bubbles in water solution,pore size distribution in hardened cement paste,and apparent densities of hardened cement paste and mortar.The results show that as the atmospheric pressure decreases,initial air bubbles in both two AEA solutions become larger.Larger initial bubbles are less stable as they engulfed surrounding small bubbles more quickly.Bubbles foamed by 303R are obviously smaller than those foamed by AES,indicating that 303R has superiorities in bubble stability and adaptability to plateau environments.As the atmospheric pressure decreases,the apparent density of hardened cement paste decreases,and the percentage of large pores increases.The ranking about cumulative volume of pores with radius between 1001000 nm is Shigaste>Chuxiong>Beijing.Additionally,the apparent density of cement mortar slightly increases,indicating a little air content reduction,as the atmospheric decreases.However,the air content of mortar reduction is no more than 2.1%(equivalent to 1.2%for concrete).