Influence of Initial Temperature of Fresh Concrete on Compressive Strength of Concrete

Abstract

This paper aims to evaluate the influence of initial temperature of fresh concrete on compressive strength and degree of reactions of binder in concrete with and without fly ash. The aggregates are cooled before being used to mix the concrete to achieve the temperatures of fresh concrete of 18°C, 25°C, and 30°C. After 24 hours in the mould, the concrete specimens are continually cured in water at 28 ± 2°C. Test results indicate that the compressive strength of the concrete at an early age decreases when the initial temperature of the fresh concrete decreases. However, the compressive strength of concrete at 91 days increases in the case of low initial temperature of fresh concrete. The effect of initial cooling is more obvious in concrete with higher fly ash content. The bound water, degree of reactions, and C-S-H content, the paste samples were analyzed by TGA. The lower initial temperature of fresh concrete leads to a lower rate of the degree of reaction and produces less amount of C-S-H at an early age. The degree of reaction of the binder at an early age affects early strength and long-term pozzolanic reaction that causes long-term strength. A lower initial temperature of fresh concrete reduces the early hydration of cement and delays the start of the pozzolanic reaction, resulting in an enhancement of the compressive strength at later ages. The degree of reaction and C-S-H content correlated well with the compressive strength of the concrete at early and long-term ages.

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“…Subsequently, there was a period of conditional isothermal exposure lasting 3-4 hours. Following this, during the evening and nighttime hours, there was a gradual decrease in temperature, decreasing at a rate of 4-5°C per hour until it reached 33-35°C [17]. It should be noted that when measuring temperature gradients in building blocks, the maximum jump was 65 degrees.…”