Pouring concrete is a process that requires attention during every step. The final step in pouring concrete is curing. The curing process is where the concrete builds up its strength. Concrete is already wet when you begin pouring it, but it must be kept damp during the curing process.
Concrete is a mixture of aggregate, binder material, additives and water. Aggregate consists of gravel, sand or crushed stone. The binder is the cement added to the mixture to allow it to harden. An additive is part of the mixture when you want the concrete mixture to set up a certain way, primarily used in winter to prevent the concrete from freezing before it cures. The concrete mixture contains 6 percent air, 11 percent cement, 41 percent crushed stone or gravel, 26 percent sand and 16 percent of water. The concrete is very wet at this point.
You need a good, level foundation before you begin pouring the concrete. The foundation must be tapped down to make it solid, and plastic must be placed over the dirt so the ground will not draw the water out of the concrete. A good layer of sand, about 2 inches, must be placed over the plastic. If you pour a large patio or driveway, you need reinforced bars placed on top of the sand to prevent the concrete from cracking. Using three people to pour the concrete allows you to each work the concrete efficiently. While two people spread the concrete mixture, the third person can screed, which is a 10-foot straightedge used to push the concrete around like a bulldozer. The concrete is very wet at this point.
After the concrete is placed and smoothed out, the curing process or strengthening process begins. If the weather is too hot or too cold, the concrete will not cure at the proper rate. The concrete company can place additives in the concrete mixture to prevent the concrete from drying out too quickly or freezing too quickly. Curing takes approximately five to seven days. During the curing process, the concrete must be kept damp, not excessively wet. Cover the concrete with roofing black paper or burlap. You must spray a light mist over the concrete at least two times every 24-hour period.
Problems can occur if the concrete is not mixed with the proper amount of water, too much water or not kept damp during the curing process. If too much water is in the mixture, the water will bleed to the surface causing the concrete to peel off the top, called "scaling." If the concrete begins to prematurely crack, the concrete did not cure properly and lost its strength when drying. The cracking is caused when the concrete hardens too quickly, which does not allow the cement to combine with the aggregate.