不同湿度环境下内养护混凝土气体传输性能试验研究

Gas transportation properties of internal cured concrete under different moisture conditions

采用预湿轻骨料作为内养护材料代替普通粗、细骨料拌制混凝土,既可以缓解混凝土早期自收缩和开裂的问题,又能减轻混凝土的自重。然而,预湿轻骨料的内养护效率受混凝土自身水胶比和外界养护环境的影响较大。开展了不同水胶比、不同湿度环境(饱和石灰水养护、喷雾养护、密封养护以及干燥养护)下普通混凝土及内养护混凝土氧气扩散和渗透性能试验。从混凝土的骨料界面过渡区结构、内部相对湿度、水化程度、混凝土孔隙率和孔隙迂曲度等方面,研究了水胶比、养护环境以及内养护材料对混凝土气体传输性能的影响,分析了不同养护环境下轻骨料的内养护效率,以及不同湿度养护条件下混凝土中气体的传输机制。结果表明:高水胶比混凝土的氧气扩散系数及渗透系数均显著高于低水胶比混凝土的;预湿轻骨料的掺入降低了混凝土的氧气扩散性能,提高了其氧气渗透性能;随着养护环境湿度的减小,混凝土的氧气扩散系数和渗透系数增加;预湿轻骨料在低水胶比、密封养护条件下内养护效率较高。

The internal curing concrete with coarse/fine aggregate replaced by pre-wet lightweight aggregate(LWA) can not only mitigate the early age autogenous shrinkage and cracking, but also reduces the weight of concrete. However, the internal curing efficiency of pre-wet lightweight aggregate is largely influenced by water-to-cement ratio and curing condition of the concrete. In this study, oxygen diffusivity and permeability tests on ordinary concrete and internal curing concrete with different water-to-cement ratios under different curing conditions(i.e. saturated lime water curing, moist curing, sealed curing and drying) were carried out. Besides, the influences of water-to-cement ratio, curing condition and internal curing material on oxygen transport in concrete were explained by considering the structure of interfacial transition zone, internal relative humidity, degree of hydration, porosity and pore tortuosity of concrete. The internal curing efficiency of lightweight aggregate and the gas transmission mechanism in concrete under different curing conditions were analyzed. The results show that the oxygen diffusivity and permeability of specimens with a high water-to-cement ratio are significantly higher than those of the specimens with a low water-to-cement ratio. The inclusion of LWA decreases the oxygen diffusivity of the specimens, but may increase the oxygen permeability of the specimens. As the ambient humidity decreases, the oxygen diffusivity and permeability of the concrete mixtures increase. The internal curing efficiency of the pre-wet lightweight aggregate is higher when the concrete has a low water-to-cement ratio and is under the sealed curing condition.