Maturity Method To Predict The Strength Of Concrete In Winter Construction

Due to large ambient temperature fluctuations in winter, same condition curing concrete cubes to monitor strength of engineering concrete are not reliable. In this case, simple and effective maturity methods are adopted to get strength developing law of engineering concrete in the course of winter construction. Many scholars studied maturity methods and have achieved some results, it is necessary to improve accuracy and temperature scope of current maturity equations. The main purpose of this study is to establish maturity equation in positive, low positive and negative temperature range, and build relationship among strength of concrete, maturity, variation of electrical resistivity and ultrasonic velocity with age in order to provide double protection for improving the accuracy and reliability of predicting strength of concrete.Firstly, according ASTM C1074-11 testing method for cement mortar to determine the apparent activation energy in the positive temperature range 20~50℃,low positive temperature range 0~20℃and negative temperature range-10~0℃.This paper studied the effects of temperature, water-cement ratio, fly ash and admixture on the apparent activation energy. The results show that the apparent activation energy decreased with the increase of temperature.The apparent activation energy changed with water-cement ratio did not show obvious regularity. Fly ash increases the apparent activation energy, and calcium nitrite reduces the apparent activation energy.Next, considering the effect of capillary supercooled water freezeing on the energy convertion of chemical reaction system, F-P maturity equation within negative temperature range was amended. And then based on ASTM C1074-11 testing method and the rate constant at diffenent temperatures, the reference temperature of N-S maturity equation in the three temperature range above were revised.This paper studied the effects of temperature, water-cement ratio, fly ash and admixture on the reference temperature. The results show that the reference temperature increased with the increase of temperature, while the reference temperature is not affected by fly ash, admixture and water-cement ratio. Comparing forecast accuracy between F-P maturity equation and N-S maturity equation in the three temperature range. It turned out that forecasting performance of modified F-P maturity equation is better than revised N-S maturity equation in the positive and negative temperature range, while modified N-S maturity equation can get better predictive results than modified F-P equation in the low positive temperature range.Finally, modified F-P and N-S maturity equation of concrete are established by the relevant data obtained through ASTM C1074-11 mortar testing method. And then the fuction relationship among strength of concrete, maturity, variation of electrical resistivity and ultrasonic velocity with age was founded in order to predict the concrete strength by these nondestructive testing method in the filed.