用电阻率法确定混凝土结构形成的发展阶段及结构形成动力学参数

Determination and Kinetics Parameters of Structure Formation Periods of Concrete by Electrical Resistivity Measurement

测定和分析了水灰比为0.4和0.5的不同骨料掺量(Va)的混凝土早龄期(24 h)水化期间电阻率发展的特性。根据电阻率微分曲线上的特征峰值点将混凝土分为:溶解和结晶期、诱导和凝结期、硬化加速期、硬化减速期4个结构形成发展阶段。相同水灰比、不同骨料掺量的混凝土电阻率微分曲线上的前2个特征峰值点对应的时间几乎相等,骨料含量高(Va=70%)的混凝土的第3个特征峰值点对应的时间延长,这与其界面过渡区面积较大有关。不同水灰比、相同骨料掺量的混凝土的电阻率微分曲线表明,水灰比为0.4时混凝土的3个特征峰值点对应的时间都提前,这与低水灰比基体材料的结构密实速度较快有关。混凝土电阻率随时间对数的发展在硬化后表现出线性关系,混凝土电阻率时间对数曲线斜率越大,说明单位体积混凝土中的骨料量较多,或者净浆基体的水泥颗粒较多。

The electrical resistivity of concretes with various aggregate volume fractions （Va） at water-cement ratios of 0.4 and 0.5 during 24 h were analyzed. The different structure formation periods are dissolution and precipitation period, induction and setting period, accelerating period, and decelerating period, which are identified from the three critical peak points on the differential electrical resistivity curve. The durations at which the first two peaks occurred were similar, and the third point, which was caused by a larger transitional zone to be filled for a higher Va used, was delayed. The time to reach the same critical point on the differential electrical resistivity curve was earlier for a lower water-cement ratio concrete when the same Va was used. A logarithmic equation was proposed to predict the electrical resistivity development with time after hardening period, and the physical meaning of parameter Kc was the slope of electrical resistivity for concrete system after hardening. Kc is a function of its aggregate volume and the slope of its matrix paste in a concrete. The higher aggregate volume and more cement particles in unit volume concrete both can result in a higher rate of electrical resistivity development of concrete.