Study On Cracking Of Cement Paste Ring With Pre-crack Using Electrical Resistivity Method

Early cracking of concrete reduces the durability of concrete, the cracking problem has become the hot research problem. At present, there are many ways to study cracking problem, but a standard method has not yet be formed, based on the test of cement paste ring with pre-crack, this paper proposes a fast prediction method of cracking time of cement paste ring with pre-crack- electrical resistivity method.This paper studied influence of water cement ratio, cement grade on cracking time of cement paste ring with pre-crack, using test of cement paste ring with pre-crack. With the same grade of cement, effects of different water cement ratio on the cracking time of cement paste ring has the same trend, that is, the lower the water cement ratio, the earlier cement paste ring cracking time. The cracking time curve of cement paste ring of P?C32.5 is above that of P?O42.5, namely, with the same water cement ratio of cement paste cement ring, the higher the cement grade, the earlier cracking time.The effects of water cement ratio, cement grade of cement paste on electrical resistivity curve and electrical resistivity differential curve in 1440 min(24 h) was studied by using the electrical resistivity method. Under the same conditions of cement grade, the electrical resistivity curve of cement paste of low water cement ratio is always above that of cement paste of high water cement ratio, and the time correspond to points, which are the three maxima points of the rate of change of electrical resistivity curve. Under the same conditions of water cement ratio, the electrical resistivity of P?O42.5 in the early hydration is less than that of P?C32.5, but electrical resistivity of cement paste in the later hydration process of P?O42.5 is higher than that of P?C32.5, and the time correspond to points of P?O42.5, which are the three maxima points of the rate of change of electrical resistivity curve, appears earlier than that of P?C32.5.Based on the test of cement paste ring with pre-crack and test of electrical resistivity, it is found that the higher electrical resistivity, the earlier cracking time. The relationship between cracking time tcr and electrical resistivity at 24 h is built, and it is proposed that electrical resistivity at 24 h can be used to predict the cracking time of cement paste ring.ANSYS thermal-structure coupling field was used to simulate the humidity field time-history of cement, then to get the stress field time-history. Comparing with the actual tensile strength, the cracking time can be got. It provides a kind of method to research the cracking problem for reference.