Concrete is a mixture of fine and/or coarse aggregates, and a paste made from Portland cement, trapped or entrained air, and water. The chemical reaction of the cement with the water glues the aggregates together to form a solid rocky material. Reducing the water in the mixture makes the concrete stronger and more resistant to carbonation. Carbonation increases concrete drying, shrinking, and cracking, and reduces the alkalinity that protects embedded steel from corrosion. Admixtures can be added during concrete batching to change the concrete's setting or hardening time, water and entrained air quantity, and workability. Entrained air and a low water to cement ratio makes cured concrete more resistant to the destructive effects of freezing and thawing. Air spaces provide cavities for water to enter after it is displaced by freezing thus preventing breakup of the concrete.