A high-density, alkali-resistant concrete will withstand moisture infiltration better. Because concrete is a porous substance, reinforcing bars within the concrete may corrode if proper precautions are not followed. Corrosion of these bars will decrease their strength and could lead to collapse of the structure. Alkali-resistant concrete can be identified by its gray color and increased density. This type of concrete contains sodium carbonate as a drying agent that prevents it from becoming too dry. The dried powder helps create a solid surface that resists penetration by water and other substances that could otherwise cause concrete to deteriorate. Concrete that has not been properly cured can contain saltwater that can dissolve some of the cement particles. If this occurs in an area that contacts soil, it may become infested with algae. This is because the oxygen needed for this process comes from air that can reach the soil through the concrete slab. Without oxygen, the water becomes anaerobic, which means there are no bacteria present to break down the organic material in the soil. As you can see, alkali-resistant concrete is better because it is more durable. However, this type of concrete cannot be dyed like porous concrete can. Therefore, it will always be white or off-white rather than colored like regular concrete.