低气压对浇筑期泡沫混凝土性能和孔结构的影响

Effect of Low Air Pressure on Performance and Pore Structure of Foamed Concrete in Pouring Period

泡沫混凝土具有轻质性、强度可调节性,固化后自立性好,隔热性及耐久性佳,已成功应用在软基换填、地下空洞与溶洞填筑、保温隔热等工程中,尤其是高速公路路堤填筑工程,如道路改扩建、桥背填土、地铁空间上覆减荷等。泡沫混凝土在浇筑至固化成型这段时期内,若受低气压这一不利环境因素的影响,会导致固化成型后泡沫混凝土的性能退化和劣化。然而,目前尚缺少关于泡沫混凝土在浇筑期受低气压影响后的宏观性能和孔结构的研究。为了研究浇筑期泡沫混凝土受低气压影响后的服役性能,文中设计低气压环境模拟箱对比研究了低气压(50、60和80 kPa)下泡沫混凝土的宏观性能和孔结构的演变规律。结果表明:随着浇筑期气压的降低,泡沫混凝土的干密度、抗压强度不断减小,吸水率不断增大,其中50 kPa下泡沫混凝土的干密度为常压(101 kPa)下的63.9%,抗压强度为常压下的15.8%;60 kPa时泡沫混凝土的体积吸水率达到最大值,为38.7%;随着气压降低,泡沫混凝土的等效孔径、孔隙分布分维不断增大,50 kPa下的大孔(直径>500μm)数量比常压下的增加了24%,不规则大孔和连通孔增多,小孔分布愈加不均匀;在1.0~1.1的孔隙圆度范围内,气孔数量占比随着气压降低而逐渐减小。

Due to its advantages of light weight,adjustable strength,self-supporting after curing,good heat insulation and durability,etc.,foamed concrete has been successfully used in soft foundation replacement,underground cavity and cavity filling,heat insulation and some other projects,especially in highway embankment filling projects,such as road reconstruction and expansion,bridge backfilling,subway space overlay’s load reduction,etc.If the foamed concrete is affected by such adverse environmental factor as low air pressure in the period from pouring to curing,performance degradation and deterioration of the cured foamed concrete may occur.However,there is a lack of research on the macroscopic properties and pore structure of foamed concrete after being affected by low air pressure in the pouring period.In order to investigate the service performance of foamed concrete after being affected by low air pressure in the pouring period,a simulation box of low air pressure environment was designed,and the evolution of macroscopic performance and pore structure of the foamed concrete at low air pressure(50,60 and 80 kPa)were comparatively explored.The results show that the dry density and compressive strength of the foamed concrete decrease continuously,while the water absorption increases continuously as the air pressure decreases in the pouring period.Concretely,the dry density of the foamed concrete at 50 kPa is 63.9%of that at atmospheric pressure(101 kPa),the compressive strength is 15.8%of that at atmospheric pressure,and the water absorption of the foamed concrete reaches the maximum of 38.7%at 60 kPa.As the air pressure decreases,the equivalent pore size and the fractal dimension of pore distribution of foamed concrete both increase continuously.The number of large pores(more than 500μm in diameter)at 50 kPa increases by 24%as comparing with that at atmospheric pressure,the number of irregular large pores and connected pores increases,and the distribution of small pores becomes more and more uneven.Moreover,in the range of pore roundness from 1.0 to 1.1,the percentage of pore number of the foamed concrete decreases gradually with the decrease of air pressure.