Chemical Kinetics Analysis of Strength Development of Mortar Containing Fly Ash Based on Various Curing Temperatures

Abstract

Due to large size and high internal temperature of hydraulic dams, the strength development process of damming materials is often faster than those under standard curing conditions. In order to further study the strength development features of damming materials under internal temperature conditions, two kinds of fly ash mortars were investigated, of which fly ash content is 40% and 30%. The compressive strength of mortars under three curing temperatures containing 20, 30 and 38°C was tested at 3 days, 7 days, 14 days, 28 days, 56 days and 90 days, respectively. Then chemical kinetics equation was employed to describe the strength development features under different temperature conditions. The results show that the compressive strength of fly ash mortar increases with the increase of curing temperature in the range of 20 to 38 °C. The main reason is that the chemical reaction rate of cementitious materials is accelerated by increasing curing temperature. For example, the hydration rate at 30° is 1.6 to 1.9 times of that at 20°, and the hydration rate at 38° is 3.1 to 3.9 times of that at 20°. In addition, the hydration rate of mortar with higher fly ash content is accelerated more. It can be seen that the apparent activation energy of mortar containing 40% of fly ash is 1.2 times of that with 30% of fly ash, and its chemical reaction barrier is higher. Therefore, the equivalent age of mortar with 40% of fly ash is longer and its compressive strength is improved more greatly under temperature-raising conditions.