基于MRI探究冷却方式和骨料粒径对水泥砂浆微观结构的影响  

Investigating the Effects of Cooling Methods and Aggregate Sizes on the Microstructure of Cement Mortars Based on MRI

作　　者：李贤 陈亮亮 毕靖 LI Xian;CHEN Liangliang;BI Jing(Broadvision Engineering Consultants Co.,Ltd.,Kunming 650011,China;School of Civil Engineering,Guizhou University,Guiyang 550025,China)

机构地区：[1]云南省交通规划设计研究院股份有限公司,云南昆明650011 [2]贵州大学土木工程学院,贵州贵阳550025

出　　处：《昆明理工大学学报（自然科学版）》2024年第3期55-64,共10页Journal of Kunming University of Science and Technology(Natural Science)

基　　金：国家自然科学基金项目(52164001);云南省科技厅重点研发计划项目(202103AA080013).

摘　　要：为研究冷却方式和骨料粒径(AS)对水泥砂浆试样的微观孔隙分布特征以及损伤的影响,将AS分别为0.63~1.25 mm、1.25~2.5 mm、2.5~5.0 mm、5.0~10.0 mm的水泥砂浆试样加热到400℃后分别放置在空气和水中冷却.采用低场核磁共振(Nuclear Magnetic Resonance,NMR)和数字声波仪分别测试了T_(2)谱、核磁共振成像(Magnetic Resonance Imaging,MRI)和纵波波速,研究了冷却方式和AS对水泥砂浆试样孔径分布及几何平均孔隙半径、孔隙体积、纵波及损伤程度的影响,并深入探究了MRI像素特征值(均值ω、标准差δ和熵)与损伤度之间的联系.结果表明:高温作用后孔隙几何平均半径、孔隙体积、ω、δ、均增大,但受冷却方式及AS影响,变化幅值有所区别:一方面,水冷对试验样损伤度大于气冷,高温水冷后毛细孔T_(2)峰面积、孔隙几何平均半径、孔隙体积、ω的增加幅值均大于气冷;另一方面,水冷作用下胶凝孔T_(2)峰面积减少,而气冷下的孔隙几何平均半径和初始情况下的δ几乎不受AS影响.同时,AS与毛细孔T_(2)峰面积、水冷下的孔隙几何平均半径、孔隙体积的增加量呈负相关,与ω、气冷作用下的成正相关.试样高温后MRI的亮斑在既有光斑上扩展、联通形成更亮更大的光斑,并且MRI像素值服从正态分布.损伤度与ω和存在指数函数关系(R^(2)为0.91和0.76),可用ω来表征多孔介质的损伤程度.To study the effects of cooling methods and aggregate sizes(AS)on the microscopic pore distribution characteristics and damage of cement mortar samples,the cement mortar samples with AS of 0.63-1.25 mm,1.25-2.5 mm,2.5-5.0 mm,and 5.0-10.0 mm were heated to 400℃and then placed in air and water for cooling,respectively.Low-field nuclear magnetic resonance(NMR)and digital acoustic wave instruments were used to test the T_(2) spectrum,nuclear magnetic resonance imaging(MRI),and P-wave velocity,respectively.The effects of cooling methods and AS were studied on the pore size distribution,geometric mean pore radius,pore volume,P-wave,and damage degree of cement mortar samples.The relationship between the eigenvalues of MRI pixel values(meanω,standard deviationδ,and entropy)and the degree of damage was deeply explored.The results show that the pore geometric mean radius,pore volume,ω,δ,and all increased after high temperature,but the amplitude of change was different due to the effect of the cooling method and AS:On the one hand,the damage degree of water cooling was greater than that of air cooling.After high-temperature water cooling,the increased amplitude of T_(2) peak area of pores,pore geometric mean radius,pore volume,andωwere all greater than that of air cooling.On the other hand,the T_(2) peak area of the gel pore decreased under water cooling,while the geometric mean radius and initialδof the pore under air cooling were almost unaffected by the aggregate size.At the same time,the aggregate size was negatively correlated with the T_(2) peak area of capillary pores,the geometric mean radius of pores under water cooling,and the increase of pore volume,and positively correlated withωand under air cooling.After high temperature,the bright spots of MRI expanded on the existing spots and connected to form brighter and larger spots,and the MRI pixel values were normally distributed.There is an exponential functional relationship between the damage degree andωand(R^(2) were 0.91 and 0.76,respectively),andωcan

关 键 词：核磁共振成像(MRI) 骨料粒径 冷却方式 孔径分布 损伤度 水泥砂浆 

分 类 号：TQ177.62[化学工程—硅酸盐工业]