不同密度等级泡沫混凝土的性能和孔结构

泡沫混凝土的密度等级对其性能有显著影响。笔者制备了干密度在300～1 000 kg/m~3范围内的泡沫混凝土,对其浆体流动度、抗压强度、吸水率和干燥收缩进行了测试,利用X射线计算机断层扫描成像(X-ray computed tomography, X-CT)对试件的孔结构进行表征。结果显示:随着泡沫混凝土密度等级增加,其浆体流动度先增大后减小,密度为600 kg/m~3时流动度最大;抗压强度随密度等级增加而逐渐增大,并与密度等级之间存在指数关系;干燥收缩和吸水率均随密度等级增加逐渐减小,这是由于其内部孔隙率降低、封闭孔增多所致。X-CT分析结果显示,密度低于600 kg/m~3的泡沫混凝土内部孔隙分布不均,试件表面的大孔较多,这是由于浆体与泡沫的体积比过低、浆体无法均匀地包裹在泡沫表面所致。

Properties and pore structure of foam concrete with different density

Density of foam concrete has a significant impact on its performance. In this study, foam concrete with dry density of 300 kg/m³ to 1 000 kg/m³ was prepared to test the slurry fluidity, compressive strength, water absorption, and drying shrinkage; and pore structures of the specimens were characterized by X-CT(X-ray computed tomography). The results showed that the fluidity of the slurry firstly increased and then decreased with the increase of the foam concrete density, and reached a maximum at 600 kg/m³. The compressive strength of the foam concrete increased gradually and there was an exponential relationship between it and the density grade. The drying shrinkage and water absorption were all gradually reduced with the increase of the density due to the decrease of internal porosity and the increase of closed pores. X-CT analysis showed that the pores in the foamed concrete with a density less than 600 kg/m³ were unevenly distributed, and there were more large pores on the surface of the specimen compared with the bulk. It is presumed that the volume ratio of the cement paste to the foam is too low for the paste to uniformly wrap the bubbles on the surface of the foam concrete.