轻骨料预湿程度对混合骨料混凝土抗冻性能影响

Effect of Lightweight Aggregate Pre-Wetting on Frost-Resistance of Combined Aggregate Concrete

研究了轻骨料预湿程度对不同水胶比混合骨料混凝土28 d和90 d抗冻性能以及界面区微观结构的影响。结果表明:风干轻骨料自身的多孔结构在混凝土内部起到了"引气"的作用,同时其强烈的吸水作用使得界面层厚度约为预湿轻骨料的2倍,结构也较致密,故其配制的混凝土抗冻性最优。随着轻骨料预湿程度的增加,骨料引气及吸水作用均减弱,故混凝土抗冻性逐渐降低,但预湿轻骨料后期较强的返水作用可使其附近水泥石中的有害孔含量减少,显微硬度提高,界面结构得到持续改善,特别是当水胶比较低时对提高混凝土长期抗冻性能有利。当水胶比较高时,由于水泥石结构比较疏松,此时轻骨料在冻压下导致内部较高的含水率对混凝土抗冻性的不利影响更为突出。即使饱和预湿的轻骨料配制的低水胶比混合骨料混凝土,其抗冻性仍优于同条件下的普通混凝土。

The frost-resistance of combined aggregate concrete prepared with different pre-wetting degrees of lightweight aggregate （LWA） and water-binder ratios at 28 d and 90 d was investigated. The microstructure of LWA and the interfacial zone were examined, and the effect of LWA pre-wetting on frost-resistance of concrete was analyzed. The results show that the porous air-dry LWA can play the role of＂air-entraining＇, and the strong water absorbing effect can make the thickness of interfacial zone of about two times of that ofprewetted LWA, as well as the densification of the interracial paste. The frost-resistance of concrete prepared with air-dry LWA was superior. The air-entraining and water-absorbing effect of LWA both decreased with the increase of LWA pre-wetting degree, thus leading to the gradual decrease of concrete frost-resistance. However, the strong water-releasing effect of pre-wetted LWA in later age could improve the interracial structure that decreased the volume content of harmful pores and increased the micro-hardness of the interracial paste, which could favor the long term frost-resistance of concrete, especially for concrete with a lower water binder ratio. For concrete with a higher water-binder ratio, the high water content of pre-wetted LWA had a negative effect on the concrete frost-resistance, which may be due to the loose cement paste structure and frost-heave force. Even for the saturation pre-wetted LWA, the frost-resistance of combined aggregate concrete was better than that of ordinary concrete at a lower water binder ratio.