新拌修补砂浆与基体水分交换行为及其对复合体性能的影响

Moisture Exchange Between Fresh Repair Mortar and Old Mortar and Its Effect on Performance of Composite

在基体上浇筑新拌砂浆是常见的修补与加固措施.当新拌砂浆与基体含水状态差异较大时,会发生水分交换改变修补砂浆配合比,并影响修补砂浆水化进程、微观特征、渗透性以及修补材料与基体间的粘结性能.对此,利用称重法研究了新拌普通砂浆、应变硬化水泥基复合材料(SHCC)与不同初始含水饱和度旧砂浆基体(0、30%、70%和100%)粘结时的水分交换过程,分析了修补砂浆类型和基体初始含水饱和度对水分交换速度、修补砂浆最终水胶比等的影响.通过力学试验、低场核磁共振技术和称重法进一步研究了水分交换对标准养护后修补砂浆与基体粘结强度、修补砂浆微结构和吸水性能的影响规律.结果表明:在水分交换早期,非饱和基体单位面积吸水质量与时间平方根存在良好的线性关系.基体含水饱和度为0时,SHCC或普通砂浆与基体间的界面剪切强度最高.SHCC作为修补材料与基体间的界面剪切强度普遍大于普通砂浆.随着基体饱和度的增大,普通砂浆的孔隙率、小孔体积分数、毛细吸水系数逐渐增大,中孔和大空隙的体积分数逐渐减小.随着基体饱和度的增大,SHCC孔隙率、中孔和大空隙的体积分数逐渐减小,小孔体积分数和毛细吸水系数变化幅度较小.

Pouring fresh mortar on the substrate is a common repair and reinforcement measure.The water exchange occurs when the moisture degree of the new mortar and the old mortar is different,thus changing the mixing ratio of the repair material,and affecting the hydration process,microscopic characteristics,permeability and bonding performance between the repair material and the old mortar.In this paper,the water exchange process among fresh ordinary mortar,strain hardening cementitious composites(SHCC),and old mortar with different moisture degrees(i.e.,0%,30%,70%and 100%)was investigated by a weighing method.The influences of the type of fresh repair mortar and the initial moisture degree of the old mortar on the rate of water exchange and the final water-binder ratio of the repair mortar were analyzed.The effect of the water exchange on the bond strength between the repair mortar and the old mortar,the microstructure of the repair mortar and the water absorption properties was investigated via the mechanical tests,low field nuclear magnetic resonance and weighing method.The results show that there is a good linear relationship between the mass of water absorbed per unit area of the unsaturated matrix and the square root of time in the early stage of water exchange.The shear strength between SHCC or ordinary mortar and substrate is maximum at 0%moisture degree of the substrate.The shear strength between SHCC as a repair material and the substrate is greater than that of ordinary mortar.The porosity,micropores volume fraction and capillary absorption coefficient of ordinary mortar gradually increase and the volume fraction of mesopores and large voids gradually decrease as the moisture of old mortar increases.The volume fraction of SHCC porosity,mesopores and large voids gradually decrease as the moisture degree of old mortar increases,and the volume fraction of micropores and capillary absorption coefficient change slightly.