利用低场磁共振弛豫测孔技术预测水泥基材料的水分渗透率  

Prediction of Water Permeability for Cement-based Material from the Pore Size Distribution Achieved by Low-field Nuclear Magnetic Resonance Relaxation Technique

作　　者：谢恩慧 周春圣[1] XIE Enhui;ZHOU Chunsheng(School of Civil Engineering,Harbin Institute of Technology,Harbin 150090,China)

机构地区：[1]哈尔滨工业大学土木工程学院,哈尔滨150090

出　　处：《硅酸盐学报》2020年第11期1808-1816,共9页Journal of The Chinese Ceramic Society

基　　金：国家自然科学基金面上项目(51578194)。

摘　　要：为深入揭示水泥基材料渗透率与孔结构间的关系,以不同水灰比、不同温度水养的白水泥砂浆为研究对象,利用低场磁共振与压汞技术分别测试了砂浆在饱水与干燥状态下的孔径分布,并利用稳态渗透法测试其水分渗透率。结果表明:砂浆在饱水与干燥状态下的孔结构差异显著,临界孔径相差1个数量级左右,原因在于水化硅胶钙(C-S-H)凝胶具有显著的水敏性。经历56 d 80℃热水养护后,由于C-S-H凝胶高温老化加速,饱水砂浆的孔隙率及临界孔径显著增大,孔结构明显粗化,水分渗透率增大,对耐久性不利。干燥预处理对压汞测试所得孔结构的影响可能远超高温老化,在分析孔结构变化时必须考虑水敏性的影响,否则可能得出错误结论。将孔隙视作不同大小的毛细管束,经典Kozeny-Carman模型可基于低场磁共振测试所得饱水孔径分布曲线来准确预测水分渗透率,将比例系数取为1.09所得理论值与实测值的相对误差在[–42.7%,71.1%]范围内,预测精度接近极低渗透率测试的误差水平。In order to clarify the relationship between the permeability of cement-based material and its pore structure, several mortars at different water to cement ratios and curing temperatures were investigated through the measurements of their pore structures by the low-field nuclear magnetic resonance(LF-NMR) and mercury intrusion porosimetry(MIP). Their permeability coefficients to water were also measured based on the Darcy law. The results show that the pore size distribution of water-saturated mortar is obviously different from that at totally dry state, whose critical diameter is larger by roughly 1 order of magnitude. This great gap is rooted to the essential water permeability for hydrated calcium silicate(C-S-H) and thus cement-based material, making their nanoscale pore structure highly depend on water contents. Furthermore, the total porosity and critical pore size both remarkably increase after curing in hot water of 80 ℃ for 56 d, which therefore increases the water permeability. These effects are brought by the chemical aging of C-S-H gels, which harms the durability performance of cement-based material. When investigating the evolution of pore structure through common MIP, the effect of drying preconditioning on pore structure should be taken into account because it is much greater than the effect of chemical aging at elevated temperature. If treating all the pores as bundles of capillary tubes, the classical Kozeny-Carman theory is able to predict the water permeability of mortars according to the pore structure achieved through LF-NMR at water-saturated state. The relative prediction error of the Kozeny-Carman theory with a linear coefficient of 1.09 is as low as within [–42.7%, 71.1%], which is similar to the experimental error of extremely low water permeability.

关 键 词：水泥砂浆 水分渗透率 孔结构 低场磁共振 水敏性 

分 类 号：TU528.1[建筑科学—建筑技术科学]