8.12 : Accelerated Curing of Concrete

Accelerating concrete curing is achieved by applying heat and additional moisture. This process accelerates the hydration of the cement, resulting in an earlier strength gain in the concrete. Steam curing is a method wherein the concrete products are either transported through a chamber on a conveyor belt or encased in plastic, allowing steam at atmospheric pressure to circulate freely around them. This process begins with a phase of moist curing that typically lasts between 3 to 5 hours, after which the temperature is gradually increased at a rate of 40 to 60 degrees Fahrenheit per hour until it reaches a maximum of 150 to 180 degrees Fahrenheit. The concrete is then allowed to soak up the residual heat and moisture without adding more heat. A cooling down period follows, where the temperature is allowed to decrease. High-pressure steam curing is primarily used for curing smaller precast concrete products such as hollow concrete masonry blocks. Alternatively, concrete is heated by applying alternating current via external electrodes, reinforcing steel, or electric blankets wrapped around the concrete. Other techniques involve using infrared heaters or circulating hot oil around the steel forms. For concrete exposed to freezing temperatures, insulating blankets or layers of porous materials like hay or straw are used to prevent heat loss and facilitate curing.