基于核磁共振技术对水泥砂浆高温后孔隙结构及水分迁移特征的研究

Study on Pore Structure and Water Migration Characteristics of Cement Mortar after High Temperature Based on NMR Technology

为研究高温后水泥砂浆内部水分迁移特征,将水泥砂浆试件300、400、500℃高温处理后表面镀蜡(留有一个上表面),随后将试件未镀蜡一端置于液面下2 cm进行自渗吸试验。采用核磁共振(NMR)技术T_(2)谱及核磁共振成像研究高温作用后水泥砂浆试件水分迁移情况及特征。结果表明,随着处理温度升高,试件胶凝孔和气孔或裂隙占比增大,而毛细孔占比逐渐降低,试件吸水质量减小,吸水质量前24 h内快速增加,随后减缓并趋于稳定。同时,高温作用影响毛细管吸水率,当处理温度小于等于400℃时,高温可增大毛细管吸水率;当处理温度大于400℃时,高温反而削弱毛细管吸水率。通过引入毛细吸收系数S来表征毛细管吸水率,S在6 h前大于10,而在6 h后减小超过2个数量级。另外,水分迁移存在优先孔径,在毛细孔中迁移的优先孔径为10~480 nm,在气孔或者裂隙中迁移的优先孔径为1680~16800 nm,且随浸水时间增加,水分更倾向由大孔传输到较小孔隙中。最后,通过核磁共振成像可实时观测到水分迁移位置由外到内,迁移速度与试件处理温度呈正相关。

In order to study the characteristics of water migration in cement mortar after high temperature,the surface of cement mortar samples was coated with wax(leaving an upper surface)after being treated at 300,400,500℃.Then the non-waxed end of samples was placed 2 cm below the liquid surface for self-imbibition test.The water migration state and characteristics of cement mortar samples after high temperature were studied by nuclear magnetic resonance(NMR)technology T_(2) spectrum and NMR imaging.The results show that with the increase of treatment temperature,the proportion of gel pores and air-voids or cracks in samples increases,while the proportion of capillary pores gradually decreases,and the water absorption mass of samples decreases.The water absorption mass increases rapidly in the first 24 h,then slows down and tends to be stable.The high temperature affects the capillary water absorption.When the treatment temperature is less than or equal to 400℃,the high temperature could increase the capillary water absorption.When the treatment temperature is greater than 400℃,the capillary water absorption is weakened.By introducing the capillary absorption coefficient S to characterize the capillary water absorption,S is greater than 10 before 6 h and decreases by more than two orders of magnitude after 6 h.There is a preferential pore size for water migration.The preferential pore size for migration in capillary pores is 10~480 nm,and the preferential pore size for pores or cracks is 1680~16800 nm.With the increase of immersion time,water tends to transfer from large pores to smaller pores.Finally,the migration position of water can be observed in real time from outside to inside by NMR imaging,and the migration speed is positively correlated with the temperature of samples.