Modern structural concrete is a composite building material that has changed over time and continues to evolve. It is a mixture of cement, water, and aggregate that can be molded into various shapes and sizes. The first concrete structures were built by Nabataean or Bedouin merchants around 6500 BC. C.
They discovered the advantages of hydraulic lime, or cement that hardens under water, and used it to build kilns to supply mortar for the construction of houses with rubble walls, concrete floors, and underground waterproof cisterns. The mixing consistency of modern concrete is fluid and homogeneous, allowing it to be poured with reinforcing materials such as reinforcing bars embedded to provide tensile strength. This results in reinforced concrete, which is more fire resistant than those built with steel frames due to its lower thermal conductivity. A small proportion of gypsum is added to slow the rate of hydration and keep the concrete workable longer.
Polymer concretes are often used for the repair and construction of other applications, such as drains. Cement is more expensive than lime-based cements, but polymer concretes have advantages; they have significant tensile strength even without reinforcement and are largely impermeable to water. Traditional concrete can be stressed when exposed to moisture and higher concentrations of atmospheric CO2. When making concrete, it is important to keep the mixture as dry or low as possible since excess water introduces voids and weaknesses in the concrete. This process of mixing concrete for the first time is called design mixture.
It is essential for professionals to understand the drying time of field concrete, especially in above-ground slabs or suspended slabs that are going to receive moisture-sensitive flooring materials.