The Importance of Sand in Concrete

Components of Concrete

• The major components of concrete are cement (typically Portland cement); sand; gravel or stones; and water. The larger stones and gravel are called coarse aggregate and the sand is referred to as fine aggregate. Air may also be considered a component of concrete. Air bubbles are formed in finished concrete through the addition of special additives to the mixture. Sand typically makes up about 25 percent of a wet concrete mixture.

Function of Aggregate

• The total aggregate in a concrete mixture comprises up to three-quarters of the mixture; the Portland cement is approximately 10 to 15 percent. The coarse aggregate is the volume of finished concrete, and the sand fills in the spaces between the larger stones of the coarse aggregate. The cement in its wet form should coat the individual pieces of aggregate and as the cement dries and hardens, it locks the gravel and sand into a matrix of small-to-larger aggregate pieces, giving strength to the concrete.

Properties of Sand

• Sand for concrete can be classified as soft or sharp sand. Soft sand has a smooth surface on the individual granules. It is natural sand formed by erosion factors such as water movement on a beach. Sharp sand granules have a rough surface. This sand is the result of manufacturing by crushing larger forms of aggregate. The most important factor concerning sand used in concrete is that it must be clean sand. Impurities in the sand such as silt or organic matter will weaken the final hardened concrete.

Technical

• The aggregate--including the sand--used in large commercial or government projects such as road building must meet rigid standards for size and cleanliness. Government inspectors will take core samples of the concrete to determine if the sand and other aggregate is of the proper size and composition. The strongest concrete comes from aggregate labeled as well-graded. This means the sand and coarse aggregate mixture is composed of granules and gravel of different sizes so the concrete mixture has uniform voids between the aggregate particles. The voids fill with cement to give the concrete a uniform structure.