引气剂对冻融循环前后砂浆毛细吸水规律的影响

Effect of Air Entraining Agent on Capillary Water Absorption of Mortar before and after Freeze-Thaw Cycle

摘要:

通过称重法研究了引气剂掺量对冻融循环前后砂浆毛细吸水规律的影响，并借助低场核磁共振和扫描电子显微镜从微观角度讨论了其影响机理.结果表明：在冻融循环作用前，砂浆的毛细吸水性系数随着引气剂掺量的增加而降低，气孔切断了毛细孔的连通性，导致水分传输通道更为曲折；在冻融循环作用后，砂浆试件的吸水曲线均呈现双线性特征；冻融损伤裂纹可以快速吸水并向毛细孔和气孔中传导水分，导致砂浆试件的前期吸水加速，该现象在低引气剂掺量砂浆中更为显著；随着裂纹充水度的提高，砂浆试件的后续吸水主要通过毛细孔及气孔进行，吸水速度下降；砂浆冻融循环前后的毛细吸水性系数与毛细孔体积占比均存在明显的线性相关性.

Abstract:

The influence of air entraining agent content on the capillary water absorption test of mortar before and after freeze-thaw cycle was conducted by weighing method， and its mechanism was investigated from the microscopic point of view by low field nuclear magnetic resonance and scanning electron microscopy. The results show that the capillary water absorption coefficient of mortar decreases with the increase of air entrainment without freeze-thaw cycle. The air voids cut off the connectivity of pores， resulting in increase of the tortuosity of water transport channel. After freeze-thaw cycle， the water absorption curves of mortar specimens show bilinear characteristics. Freeze-thaw damage cracks can quickly absorb water and transmit water to the pores and air voids， resulting in acceleration of early water absorption of mortar specimens， which is more significant in low air entrainment mortar. As the moisture in the crack increases gradually， the subsequent water absorption of mortar specimen is mainly through the capillary pores and air voids， and the water absorption rate decreases. There is an obvious linear correlation between the capillary water absorption coefficient of mortar and the volumetric percentage of capillary pores of air entrained mortar with and without freeze-thaw cycle.