What Is Concrete Made Of?
Concrete
The word concrete is derived from the Latin word “concretus” (which means compact or condensed). Concrete is a mixture of cement, preferably Portland cement, gravel or crushed stone, known as coarse aggregate, sand, water and chemical admixtures. When mixed with water, the fluid mixture can be given any desired shape by pouring into molds or designs. It solidifies gradually creating a robust material very akin to stone. The process of solidification is known as hydration. Water acts like a re-agent by reacting with the cement and making it function like an adhesive to bond with the other components. Concrete is used in the construction of pavements, architectural structures like roofs, pillars, poles, walls, foundations, highways, roads, runways, bridges, flyovers or overpasses, parking structures, bricks and fences and too many to list. The diagram below clearly depicts an approximate mixture ratio of the components in concrete.
The measure of compressive strength of concrete is done in MPa (Mega pascal) scale. In layman’s term it is the measure of how much force can be applied to the concrete structure before it mutilates. One MPa is equal to one million pascals (Pa), which is equivalent to one million Newtons per square meter. A concrete structure with higher MPa value would be more resilient and stronger.
Concrete can be made really strong by re-enforcing, pre-stressing and air en training the concrete mixture as discussed below –
- Re-enforced concrete – Developed by casting concrete around steel rods and bars which strengthens the concrete. All massive structures like bridges, skyscrapers, overpasses need this concrete.
- Pre-stressed concrete – Concrete is cast around steel cables stretched by hydraulic jacks. When the concrete hardens after hydration hydraulic the jacks are removed and the concrete gets compressed by the cables.
- Air entrained concrete – Special chemicals of the kinds of soap like resinous or fatty material added to the concrete during its mixing creates micro air bubbles inside it. The air bubbles act like shock absorbers when the water dries out.
Concrete can be made resistant to cold weather by following some basic rules before and after the preparation and installation. It should have a low water to cement ratio. It should not have a slump of more than 4 inches, which is a measure of stiffness of the concrete. It should be created by using six bags or 4000 PSI mix, which is using a minimum of 6 bags (564 lbs) of cement per cubic yard. Air entrained concrete must be used for cold weathers. The concrete slabs must have a slope of at least 1/8th inch so that water can’t freeze its surface. It should be sealed by using a breathable sealant or water repellent containing silanes or siloxanes
Various types of concrete installation are as follows –
- Steel Rebar (Re-enforcing bar) – Concrete is poured over a wire mesh made up of steel rebars. The rebar mesh might also have similar structures attached to it for desired shape achieved by using plywood coverings.
- Gravel compacted – Once poured, high speed vibratory compactors are used to compact the gravels in the fluid concrete.
- Concrete pouring – Concrete is poured in a timely manner and spread accordingly to attain uniformity in the construction.
- Concrete Masonry/Pre-cast concrete – Pre-molded concrete blocks are created in large numbers and transported to the construction site.