基于低场核磁共振的水泥砂浆终凝前水化特征研究

Hydration and water distribution characteristics of cement mortar beforefinalsetting based on low-field NMR

为探究水泥砂浆终凝前的水化及水分布特征,减少水化过程对水泥基材料性能的不利影响,采用低场核磁共振(NMR)设备实时观测水泥砂浆凝固过程中孔径和水分分布变化,并基于核磁共振T2谱定量表征了水泥砂浆水化程度以及水化速率,揭示了水泥砂浆终凝前微观孔隙结构、水分分布及水化反应规律。研究结果表明:毛细孔随水化程度的提高逐渐转变为更小孔径的过渡孔和胶凝孔;试件内部孔隙中存在水的传输及转移,前3 h内物理束缚水主要转化为沁水覆盖在试件表面,部分传输到胶凝孔中;3 h后,有更多小孔隙生成,在毛细孔压力作用下,毛细孔中的水传输到过渡孔和胶凝孔中;水化程度随水化时间增加而逐渐增大,但水化速率以倒“S”形变化,初始阶段逐渐减小,当减小到休眠阶段后基本保持不变,随后又加速反应一段时间后保持稳定。

In order to explore the hydration and water distribution characteristics of cement mortar before final setting and reduce the adverse effects of hydration process on the properties of cement-based materials,low-field nuclear magnetic resonance equipment was used to observe the pore size variation and water distribution during the solidification process of cement mortar in real time,and quantitatively characterized the hydration degree and hydration rate of cement mortar based on nuclear magnetic resonance T 2 spectrum,which effectively reveals the microscopic pore structure,water distribution and hydration reaction law of cement mortar before final setting.The results showed that the capillary pores gradually changed into transition pores and gel pores of smaller pore size with the increasing of hydration degree.Water transmission and transfer in the internal pores of the specimen were observed.In the first 3 hours,the physical bound water was mainly converted into bled water covering on the surface of the specimen,and some of it was transmitted to the gel pores.After 3 hours,more small pores were generated.Under the action of capillary pressure,the water in the capillary pores was transmitted to the transition pores and gel pores.In addition,the hydration degree gradually increased with the increase of hydration time.While,the hydration rate changed in an inverted S shape,in which it gradually decreased at the initial stage,and remained basically unchanged when it decreased to the dormant stage,and then reacted fast for a period of time and finally to be stable.