To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 ...To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 kPa) and the plains(Beijing, 101 kPa). Air content, slump, compressive strength and pore structure of the three air-entrained concretes were tested in these two places. It is found that the air content of concrete under low atmospheric pressure(LAP) is 4%-36% lower than that of concrete under normal atmospheric pressure(NAP), which explaines the decrease of slump for air-entrained concrete under LAP. Pore number of hardened concrete under LAP is reduced by 48%-69%. While, the proportion of big pores(pore diameter >1 200 μm) and air void spacing factor are increased by 1.5%-7.3% and 51%-92%, respectively. The deterioration of pore structure results in a 3%-9% reduction in the compressive strength of concrete. From the results we have obtained, it can be concluded that the increase of critical nucleation energy of air bubbles and the decrease of volumetric compressibility coefficient of air in the concrete are responsible for the variation of air content and pore structure of concrete under LAP.展开更多
The experimental study of air-entrained concrete specimens subjected to different cycles of freeze-thaw was completed. The dynamic modulus of elasticity, weight loss, the cubic compressive strength, compressive streng...The experimental study of air-entrained concrete specimens subjected to different cycles of freeze-thaw was completed. The dynamic modulus of elasticity, weight loss, the cubic compressive strength, compressive strength, tensile strength and cleavage strength of air-entrained concrete were measured after 0, 100, 200, 300, 400 cycles of freeze-thaw. The experimental results showed that the dynamic modulus of elasticity and strength decreased as the freeze-thaw was repeated. The influences of freeze-thaw cycles on the mechanical properties, the dynamic modulus of elasticity and weight loss were analyzed according to the experimental results. It can serve as a reference for the maintenance, design and the life prediction of dams, hydraulic structures, offshore structures, concrete roads and bridges in northern cold regions.展开更多
通过低气压试验箱模拟高原不同海拔地区气压环境,研究了低气压环境对引气混凝土含气量及气泡稳定性的影响。结果表明：环境气压的降低能够显著削弱引气剂的引气能力,混凝土含气量随环境气压降低呈线性减少,当环境气压降低至50 k Pa时,...通过低气压试验箱模拟高原不同海拔地区气压环境,研究了低气压环境对引气混凝土含气量及气泡稳定性的影响。结果表明：环境气压的降低能够显著削弱引气剂的引气能力,混凝土含气量随环境气压降低呈线性减少,当环境气压降低至50 k Pa时,混凝土含气量比常压环境下降低约28%～52%。低气压环境使引气混凝土气泡稳定性变差,在搅拌结束50～55 min内,低压引气混凝土含气量经时损失较大,且气泡间距系数明显增大;延长振捣时间会使低压引气混凝土损失更多气泡,从而导致含气量降低幅度以及间距系数的增大程度均大于常压引气混凝土。展开更多
基金Funed by the National Key R&D Program of China(No.2017YFB0309903)
文摘To study the effect of atmospheric pressure on the properties of fresh and hardened airentrained concrete, three kinds of air entraining agents were used for preparing air-entrained concrete in the plateaus(Lhasa, 61 kPa) and the plains(Beijing, 101 kPa). Air content, slump, compressive strength and pore structure of the three air-entrained concretes were tested in these two places. It is found that the air content of concrete under low atmospheric pressure(LAP) is 4%-36% lower than that of concrete under normal atmospheric pressure(NAP), which explaines the decrease of slump for air-entrained concrete under LAP. Pore number of hardened concrete under LAP is reduced by 48%-69%. While, the proportion of big pores(pore diameter >1 200 μm) and air void spacing factor are increased by 1.5%-7.3% and 51%-92%, respectively. The deterioration of pore structure results in a 3%-9% reduction in the compressive strength of concrete. From the results we have obtained, it can be concluded that the increase of critical nucleation energy of air bubbles and the decrease of volumetric compressibility coefficient of air in the concrete are responsible for the variation of air content and pore structure of concrete under LAP.
基金supported by part of the Key Project of the China Postdoctoral Science Foundation(Nos.20080430183 and 200801386)the Promotional Foundation for Excellent Middle-aged or Young Scientists of Shandong Province(No.2008BS08001)National Basic Research Program(No.2007CB714202)
文摘The experimental study of air-entrained concrete specimens subjected to different cycles of freeze-thaw was completed. The dynamic modulus of elasticity, weight loss, the cubic compressive strength, compressive strength, tensile strength and cleavage strength of air-entrained concrete were measured after 0, 100, 200, 300, 400 cycles of freeze-thaw. The experimental results showed that the dynamic modulus of elasticity and strength decreased as the freeze-thaw was repeated. The influences of freeze-thaw cycles on the mechanical properties, the dynamic modulus of elasticity and weight loss were analyzed according to the experimental results. It can serve as a reference for the maintenance, design and the life prediction of dams, hydraulic structures, offshore structures, concrete roads and bridges in northern cold regions.
文摘通过低气压试验箱模拟高原不同海拔地区气压环境,研究了低气压环境对引气混凝土含气量及气泡稳定性的影响。结果表明：环境气压的降低能够显著削弱引气剂的引气能力,混凝土含气量随环境气压降低呈线性减少,当环境气压降低至50 k Pa时,混凝土含气量比常压环境下降低约28%～52%。低气压环境使引气混凝土气泡稳定性变差,在搅拌结束50～55 min内,低压引气混凝土含气量经时损失较大,且气泡间距系数明显增大;延长振捣时间会使低压引气混凝土损失更多气泡,从而导致含气量降低幅度以及间距系数的增大程度均大于常压引气混凝土。
