Concrete curing is a process in which the cement and the water in concrete bond and harden through a chemical reaction called hydration. As they bond, the cement and water bind the aggregate and the sand to form a strong foundation structure. Proper curing is critical to the strength and durability of concrete.
When a slab-on-grade foundation is curing, it's important to provide enough time for hydration to take place. Hot, dry conditions make water evaporate more quickly from the slab surface, which can cause concrete to harden more quickly, ultimately leading to a weaker material that's at greater risk of curling and cracking. The surface of the slab must be kept moist to prevent water from evaporating too quickly. Inadequate hydration reduces the slab foundation's strength, durability, impermeability, resistance to abrasion, and resistance to freeze-thaw cycles.
There are several ways to keep the slab surface moist during the curing process. One method is to apply curing blankets for a minimum of three days. Curing blankets are burlap sheets that cover the slab. The sheets should be wetted periodically to keep the concrete surface moist. However, they shouldn't be applied until the concrete has cured enough to resist surface damage.
If the slab cures unevenly, it can result in a phenomenon called slab curling, in which the slab surface cures faster and therefore shrinks more quickly than the slab core. When the slab surface shrinks and pulls inward, the slab tries to curl upward and usually cracks instead.
Often, when weather conditions are hot and dry, excess water is added to the mix to make it easier to work with and to extend the working time. However, the excess water can cause the slab to curl unevenly and increase the likelihood of slab curling. An effective way to reduce the water content while maintaining workability is to add a plasticizer to the mix. Plasticizers increase the strength, fluidity and workability of the concrete mix without having to add water.
A proper curing process leads to a slab-on-grade foundation that's strong, durable and wear-resistant. Curing helps concrete attain its optimum strength, maximizing the foundation's life span.
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