Lu Xiaochun, Tong Fuguo, Zha Xinyuan, Liu Gang
College of Hydraulic & Environmental Engineering, China Three Gorges University, Yichang, 443000, China.
Sci Rep. 2021 Nov 5;11(1):21720. doi: 10.1038/s41598-021-00447-8.
Concrete age is the time since the moment water is added to the cement, and the age of concrete comprehensively reflects the physical properties of the concrete when curing under standard conditions. For concrete under nonstandard conditions, its physical properties are directly related to both its age and temperature history. The equivalent age of concrete is the time at which concrete under nonstandard conditions reaches the same state as concrete under standard conditions. Most equivalent methods, such as the Nurse-Saul function and the Arrhenius function, are based on a maturity index. However, the accuracy of these methods breaks down when the curing temperature range is wide. In this paper, the electrical resistivity of concrete is used as the index to determine the equivalent age of concrete. This method is based on the assumption that concrete with the same mixture proportions has the same electrical resistivity when the maturity of the concrete is the same, regardless of the curing history. The proposed method is advantageous because it can be performed in real time and is nondestructive. To constantly measure the electrical resistivity of concrete, an automatic data acquisition system is developed to monitor the electrical resistivity of concrete and reduce the error caused by polarization as much as possible. Then, a model for predicting the electrical resistivity of concrete under different curing temperatures is proposed to conveniently calculate the equivalent coefficient. Finally, the results calculated by the proposed equivalent method are compared with those of the standard method (Nurse-Saul equation), and the results of the proposed model are found to be more reasonable.
实际龄期是指从向水泥中加水的时刻起所经历的时间，混凝土的龄期全面反映了其在标准条件下养护时的物理性能。对于非标准条件下的混凝土，其物理性能直接与其龄期和温度历程相关。混凝土的等效龄期是指非标准条件下的混凝土达到与标准条件下的混凝土相同状态时所对应的时间。大多数等效方法，如Nurse-Saul函数和Arrhenius函数，都是基于成熟度指标。然而，当养护温度范围较宽时，这些方法的准确性会降低。在本文中，将混凝土的电阻率用作确定混凝土等效龄期的指标。该方法基于这样的假设：对于相同配合比的混凝土，当其成熟度相同时，无论养护历程如何，其电阻率相同。所提出的方法具有优势，因为它可以实时进行且无损。为了持续测量混凝土的电阻率，开发了一个自动数据采集系统来监测混凝土的电阻率，并尽可能减少极化引起的误差。然后，提出了一个用于预测不同养护温度下混凝土电阻率的模型，以便方便地计算等效系数。最后，将所提出的等效方法计算结果与标准方法（Nurse-Saul方程）的结果进行比较，发现所提出模型的结果更合理。
