For long lasting strong concrete it is vitally important to control how concrete is exposed to water. Portland cement concrete, the most commonly used building material is composed of four basic ingredients; Portland cement, small aggregate(sand), large aggregate(stone) and water. While all are important in the initial mix and curing process, the introduction of water throughout the life of the concrete can have undesired effects on the concrete. The amount of water added to the initial concrete mix is very important. For strong concrete a cement to water ratio of .4 is recommended. This means for every 100 pounds of cement in the mix, 40 pounds of water should be used. For sidewalks and residential driveways, .4 to .5 is sometimes used, but higher amounts of water can result in a more porous surface which can lead to problems later on.