KINETICS PARAMETERS OF STRUCTURE FORMATION OF CONCRETE BY ELECTRICAL RESISTIVITY MEASUREMENT

摘要

The electrical resistivity of concretes with various aggregate volume fractions (Va) at water/cement (W/C) ratios of 0.4 and 0.5 during 24 hours were measured by a non-contact electrical resistivity setup.The four structure formation periods are the dissolution and precipitation period, the setting period, the accelerating period, and the 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 was delayed which was caused by a larger transitional zone to be filled for a higher Va used.The time to reach the same critical point on the differential electrical resistivity curve was earlier for a lower W/C ratio concrete when the same Va was used.A logarithmic equation p(t)=Kc·ln(D·t) =Km·Ka·In(D·t) is proposed to express the electrical resistivity development with time after the decelerating period, with the physical meaning of the parameter Kc being the slope of the electrical resistivity for the concrete system after hardening.Ka is a function of its aggregate volume fraction and represents impact factor of the aggregate in unit volume concrete.Km is firstly defined as the structure formation factor of the matrix and represents the rate of densification of the matrix during hydration, which is independent of Va.The mixture with lower W/C has a higher Kin, and D is the average reaction rate of the cement particle hydration during a particular period.Both the higher aggregate volume and an increase in cement particles in unit volume concrete will result in a higher rate of electrical resistivity development in the concrete.