Evaluation of the reliability and life span for cement materials by electric property measurements

选取硬化石膏和硅酸盐水泥作为混凝土的简单模型，找出其力学强度和介电强度分布的相似性。两种强度均采用威布尔统计量进行评估，两种强度分布均采用双参数威布尔函数。两幅图均表现出较好的吻合性，与半水粉末在振荡硬化过程中的含水量无关。在掺水量为70wt%的硬化石膏板上，力学强度和介电强度分布图均为两条斜率不同的直线，但两者吻合较好。结果表明，硬化石膏或硅酸盐水泥的力学强度分布可以用介质强度分布来评价，而介质强度分布是通过击穿试验容易得到的。硅酸盐水泥浆体的低频阻抗随养护时间的延长而增大，且受NaCl加入量的影响较大。NaCl的污染会引起碱集料反应，引起混凝土的突然断裂或死亡。反应性骨料（热玻璃）水泥浆体中加入少量NaCl，养护3天后异常阻抗增大。经过365天的养护，发现了在NaCl加入凡人和活性骨料时碱骨料发生反应的证据。通过对人体阻抗的连续监测，可以对碱集料反应进行预测，如果早期观察到阻抗的异常增加，则可对碱集料反应进行预警。提出了一种同时获得多个试件强度分布的替代方法。该方法利用试样的弹性模量常数，同时增加试样的弯曲应力，并通过电导的变化来监测试样的断裂数。

Hardened gypsum and portland cement are chosen as a simple model of concrete and analogy beween the mechanical and dielectric strength distributions are found out. Both strength is evaluated in terms of Weibull statistics and the two-parameter Weibull function was adopted for both strength distribution. Both plots shows good coincidence independent of the water content during shaking of hemihydrate powder for hardening. At the hardened gypsum sheets which are made by shaking with 70wt% of water, both plots for mechanical and dielectric strength distribution show two straight lines with different slopes, however, both plots shows in good agreement. From the results, it is concluded that the mechanical strength distribution of hardened gypsum or Portland cement can be evaluated by using the dielectric strength distribution, which is casily obtained by breakdown testing.The low frequency impedance of Portland cement paste or mortal increased with an increasc in curing time and it is strongly affected by the addition of NaCl. The contamination of NaCl would induce the alkaliaggregate reaction ane it induces a sudden fracture of concrete or mortal. When small amount of NaCl is added to cement paste with reactive aggregate (Pyrex glass), the impedance in anomalous increases after 3 days curing. After 365 days curing, the evidence of alkali aggregate reaction is found out at NaCl added mortal with reactive aggregate. By the continuous monitoring of impedance of mortal, the alkali aggregate reaction can be foresee and if the anomalous increase in impedance is observed in early times, the alkali aggregated reaction is apprehensive.An alternative method to obtain a strength distribution of many test pieces at one time is proposed. In this method, bending stress of all subjected samples is simultaneously increased utilizing their elastic modules constancy and the fractured sample number is monitored by the change in electric conductance.