Accelerating strength gain aims to create a favorable temperature for hydration to occur.
This method is useful in cold weather or when early strength gain is important. There are two methods of curing:
Maximum temperatures range from 104°to 212°F (40° to 100°C), with the optimum being in the 150°to 175°F (65°to 80°C) range. The higher the initial temperature of the curing environment, the lower the ultimate strength. This means that the temperature used will be a compromise between the rate of strength gain and the ultimate strength.
During curing, the concrete is taken through a curing cycle consisting of the following stages:
High pressure steam:
This method is used for small manufactured units. The curing is done in autoclaves at temperatures in the 325°to 375°F range and pressures of 80 to 170 psi. This environment changes the chemistry of the hydration producing a concrete that has the following modified properties:
In these cases care needs to be taken to ensure that temperatures do not rise excessively.
Electrical, oil and infrared curing
These methods are used primarily in the precast concrete industry. Electrical methods include a variety of techniques such as using the concrete itself as a conductor, using the steel as the conductors, and heated steel forms. The last method is the most common at present.
Hot oil may also be circulated through steel forms to heat the concrete. Infra-red rays may also be used to heat concrete under a covering or steel forms.