Basically concrete mixture is composed of cement, aggregates, admixtures and water. This article will discuss on cement in concrete.
Portland cement is the most common type of cement in general use. It is basic ingredient of concrete, mortar and plaster. English engineer Joseph Aspdin patented Portland cement in 1824.
It is made by heating limestone (calcium) with clay until all water molecules are gone (calcination) and finely grinding it. This product (called clinker) is mixed with a source of sulfate (most commonly gypsum) which regulates setting. The strength of cement is related to its fineness or specific surface. Cement is a mixture of oxides of calcium, silicon and aluminium.
When portland cement and similar materials are mixed with water, the resulting powder will become a hydrated solid over time.
The water molecules react with the cement, creating crystalline structures, which grow out from the cement molecules and bond the other components together, eventually creating a stone-like material.
The basic of the chemistry of cement are mostly understood, but the variations in the raw materials make 100% control of industrial process nearly impossible.
For these reasons, frequent controls are required for the production of concrete and admixture have to be adjusted to the varying raw materials used in the concrete, depending on the source.
The most common types of portland cement are:
Type I: Portland Cement – General use
Type II: Composite Cement (>65% portland) – Moderate resistance to sulphates
Type III: Blast furnace cement – High early strength
Type IV: Pozzolan cement -Low hydration heat
Type V: Composite cement- High resistance to sulfates.
Again, concrete is a construction material that consists of cement (commonly portland cement), aggregate (generally gravel and sand), water and admixture. Concrete solidifies and hardens after mixing and placement due to a chemical process known as hydration.