The Effect of Initial Curing Temperature and Duration on the 28-Day Compressive Strength of Concrete

Abstract

The objective of this study was to determine the effect of initial curing temperature and duration on the 28-day compressive strength of concrete. To determine the relationship between initial curing temperature and duration on compressive strength, concrete cylinders were initially cured at six temperatures for three different initial curing durations. The six different initial curing temperatures used were 60 ⁰F, 68 ⁰F, 78 ⁰F, 84 ⁰F, 90 ⁰F, and 100 ⁰F, while the three initial curing durations used were 24 hours, 48 hours, and 72 hours. After the initial curing duration was complete, the cylinders were moved to final curing in a moist cure room that maintained a temperature of at 73.5 ± 3.5 ⁰F, until testing at 28 days. Eight different concretes were produced to have elevated fresh concrete temperatures to simulate summer placement conditions. The effects of Type I and Type III portland cement and fly ash, slag cement, and silica fume were assessed. Using an initial curing temperature of 68 ⁰F as a basis of comparison, the relative 28-day compressive strength differences were recorded for each initial curing temperature. An acceptable limit of ±10% was used to evaluate the strength differences. The results confirmed that as initial curing temperature increases, the 28-day compressive strength of the concrete decreases. When initially cured at a temperature of 100 ⁰F, a maximum reduction of 23% in the 28-day compressive strength was observed. It is critical to maintain an initial curing temperature from 60 ⁰F to 80 ⁰F to remain within the chosen acceptable limit of ±10% for relative strength differences for concrete from the same batch. Additionally, it was concluded that within an initial curing temperature range from 60 ⁰F to 80 ⁰F, an increase to 72 hours in initial curing duration will not significantly affect the 28-day compressive strength of the concrete.