Concrete Countertops and Acid Stain Source

The importance of concrete in modern society cannot be underestimated. Just look around you and you will find concrete structures everywhere such as buildings, roads, bridges and dams. There’s no escaping the impact of concrete.

Concrete is a composite material made up of a filler and a binder. The binder (cement paste) “glues” the filler together to form a synthetic material. The constituents used for the binder are cement and water, while the filler can be fine or course aggregates. Cement, as it is commonly known, is a mixture of compounds made by burning limestone and clay together at very high temperatures ranging from 1400 to 1600 deg c. The production of Portland cement begins with the quarrying of limestone, CaCO3. Huge machines break the limestone into small pieces and is then mixed with clay, sand, and iron ore and ground together to forma powder.

The mixture is then heated in kilns that are rotating steel cylinders on a slight incline. The kilns may be up to 6 meters in diameter and 180 meters in length. The mixture enters the kiln at the high end and and slowly moves along the length of the kiln due to the constant rotation and angle of the kiln. At the low end of the kiln, fuel is injected and burned thus providing the heat needed to make the materials react. It can take as much as 2 hours for the mixture to pass through the kiln., this depending on the size of the kiln. As the mixture moves down the

cylinder, it progresses through four stages of transformation. Initially, any free water in the powder is lost by evaporation. Next, decomposition occurs from the loss of bound water and carbon dioxide. This is called calcination. The third stage is called clinkering. During this stage, the calcium silicates are formed. The final stage is the cooling stage. The marble sized pieces produced by the kiln are referred to as clinker. The clinker is cooled, ground and mixed with a small amount of gypsum (regulates setting) to produce the general purpose of Portland cement. Water is the key ingredient, which when mixed with cement, forms a paste that binds the aggregate together. The water causes the hardening of the concrete through a process called hydration. Hydration is a chemical reaction in which the major compound in cement form chemical bond with water molecules and become hydrates or hydration products.

Too much water reduces concrete strength. Aggregates are solid bodies held together by the cement. 70 to 80% of concrete is aggregate. Characteristics desired determine types of aggregate. Concrete is non combustible and able to withstand high temperatures. Concrete does not need to dry out to harden. When concrete dries it actually stoops getting stronger. Only the calcium silicates contribute to the strength in concrete. Tri calcium silicate is responsible for most early strength. Dicalcium silicate reacts more slowly, contributes to strength at later times.