基于NMR技术的多因素耦合作用下水工混凝土损伤特征研究

Research on the damage characteristics of hydraulic concrete under multi-factor coupling based on NMR technology

为研究西北地区水工混凝土在多因素耦合作用下的损伤特征,根据现场调研结果设计了室内加速试验,得到了干湿-冻融-盐侵作用下各试件质量损失率、抗压强度、相对动弹性模量的变化规律;通过核磁共振扫描结果分析了各试件T_(2)谱的演化规律,并以灰色系统理论计算出了试件相对动弹性模量与T_(2)图谱之间的关联度。研究结果表明:随着试验的进行,冻融-干湿-盐侵对试件造成的损伤效应不断积累,试件各项参数持续下降,最终失效;核磁共振扫描所得T_(2)谱总面积随试验进行不断增大,其中峰1、峰2面积占T_(2)谱总面积的比例不断减小,而峰3所占比例不断增大;试件相对动弹性模量与T_(2)图谱中峰1、峰2的关联度最高,可根据T_(2)图谱中峰1、峰2的分布情况对试件损伤程度作初步判断。在试验中发现聚丙烯纤维能削弱冻融-干湿-盐侵对混凝土的破坏作用,可在水工混凝土设计中掺入聚丙烯纤维以延长输水建筑物的使用寿命。

In order to understand the damage characteristics of hydraulic concrete in Northwest China under the coupling action of multiple factors,indoor accelerated tests are designed according to the field investigation.And the variation rules of mass loss rate,compressive strength and relative dynamic elastic modulus of each specimen under the action of dry-wet-freeze-thaw-salt invasion are obtained.The evolution law of T_(2) spectrum of each specimen is analyzed by NMR scanning results,and the correlation between the relative dynamic elastic modulus of specimen and T_(2) spectrum is computed by the grey system theory.The results show that with the progress of the test,the damage effect caused by freeze-thaw-dry-wet-salt invasion on the specimen continues to accumulate,the parameters of the specimen continue to decline,and finally cause failure;The total area of T_(2) spectrum obtained by NMR scanning increased with the experiment,and the proportion of peak 1 and peak 2 to the total area of T_(2) spectrum decreased,while the proportion of peak 3 increased.The relative dynamic modulus of the specimen has a high correlation with the change of peak 1 and peak 2 in the T_(2) map,and the damage degree of the specimen can be preliminarily judged according to the distribution of peak 1 and peak 2 in the T_(2) map.It is found that polypropylene fiber can reduce the damage of freezing-thaw-dry-wet-salt invasion to concrete,and polypropylene fiber can be incorporated into hydraulic concrete to prolong the service life of water conveying buildings.