Concrete can be made from many materials, depending on the form of construction and types of design work involved.
Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement that hardens over time.
In modern construction, concrete develops structural strength after all the ingredients have been combined and water has been added. As a building material, concrete can be cast in almost any shape desired by an architect or engineer including plain concrete for basement floors or foundation walls to precast architectural elements such as panels and lintels. It can also be used to make hollow blocks as well as both concave and convex curved surfaces through slip forming.
Concrete has many uses-in foundations, as a structural element in buildings, as piping for water and sewage, in roadways, steel bars, ball mill, as well as many other existing structures and ready mix plant places where strength, resistance to wear or to the hot weather elements are needed. Concrete is also used in making pavements for highways and other projects. As used by ancient romans, concrete continues to be used on all types: fine and coarse, in mix proportions and water form.
Concrete is made by mixing specific materials such as an aggregate consisting of large chunks of rocks with sand and small gravel mixed together with cement. The mixture forms what is called a mortar which becomes hard when it combines with water inside the concrete blocks or items that are being moulded into shape.The most common type of aggregate consists of broken pieces of rock, pebbles or crushed stones that ranged between 1/4 inch to 3/8 inch (6 mm) in size. It has sharp edges which tend to cut the bonding agent. Fine aggregate, on the other hand, contains particles that are smaller than 1/4 inch (6 mm). It generally consists of crushed stone dust which, when mixed with water has less tendency to erode the cementing material. Coarse and fine aggregates for concrete are usually selected according to the nature of the job they will perform within concrete structures.
Concrete is made in different ways without changing its basic composition. It can be cast against formwork or poured in place; it can also be precast into blocks, beams, panels, walls and other shapes. Concrete can also be used in combination with steel reinforcing bars or mesh placed either within or outside of the concrete forms during casting to produce reinforced concrete. This type is especially strong and is used in many forms of construction work.
Concrete that allows the passage of water through it is called permeable concrete. It can contain high cement ratio or low water cement ratio and great quantities of large aggregate and other materials, be made thin and still resist strong compression or tensile stresses. Since the small stones or pieces of gravel cannot move apart, water that falls onto its surface passes into it by way of channels among the larger stones and porous concrete . If this does not happen, all the parts stick together under the action of water to form a block called impermeable concrete which stops up all openings through which water could pass; this type has little use for anything except as road surfacing raw materials in the cement industry.
Normal concrete hardness varies depending on how hard or fine each component is but generally ranges between 2200 psi (15.5 MPa) in the lower end to 8000 psi (55 MPa) in the higher end.
The four basic ingredients in modern concrete are cement, aggregate, water and admixtures. Cement is composed of fine powder and larger chunks or rocks. The main components of the aggregate are large chunks of rocks with sand and small gravel properly mixed together with cement for cement production to make high-quality concrete mixes and ready-mix suppliers for construction companies.
It also contains raw materials or basic components called admixtures which when added to the concrete mix causes the concrete to harden over time because it reacts with water in a chemical process, allowing the concrete to cure and harden into a stone-like material.
This results in hardened concrete. Some of the concrete basics are that water is the main solvent that reacts with the cement in a process called hydration which forms a new material called calcium silicate hydrate. The chemical process between water and cement creates a gel-like cement paste that allows for the development of crystals when the wet concrete mixture sets up without any tiny air bubbles or entrained air (air entrainment) so the concrete dries and paste hardens for the formation of fresh concrete. The Safe Work Australia website has a thorough guide to keeping safe from chemicals during various concreting tasks.Portland cement is an artificial binder created by roasting certain types of limestone at very high temperatures (1300°C). Portland cement takes its name from its resemblance to natural Portland stone, quarried on the Isle of Portland in Dorset, England. The calcium, silicon and iron present in the rocks are heated under carefully maintained conditions to form clinker. The heat drives off carbon dioxide, leaving quicklime (calcium oxide). Groundwater is added to this mixture and mixing water causes a chemical reaction that forms what's called calcium silicate hydrate or C-S-H gel. This process, known as the 'pozzolanic' reaction takes anywhere from 4 hours to 3 days to occur and produces an elastic paste with excellent adhesive qualities (it sticks very well to sand and mineral aggregate) but has poor early strength. By adding extra ingredients such as pulverized coal, ground blast furnace slag or other additives along with small amounts of Portland cement, C-S-H crystal grows stronger and gains strength and larger together with the development of U-shaped microscopic bridges that link them together and enhance the concrete's strength. These newly formed crystals are called calcium hydroxide, tricalcium silicate or C-S-H gel.
Concrete is not waterproof on its own but can be made more resistant to water penetration by adding a membrane to the surface of it or making more complex forms such as precast hollow blocks which have an inner empty space giving more opportunity for water to escape if it does manage to penetrate through small cracks in the block. Water repellent chemicals are also available that bond an invisible coating on top of existing cement surfaces which fills in any micro cracks and increases the amount of time needed for water droplets to penetrate through the surface.
Concrete is very strong in compression, that is pushing or squeezing forces, but relatively weak under tension or pulling forces. This means that if you weigh down on or hang anything from concrete, it will resist your weight and hold fast. However, if you were to pull on an unsupported span of concrete (such as a crack between two slabs), it would break quite easily.
The strength of concrete can be increased by adding steel mesh reinforcement or fibres such as glass fibre which allows the strong material to withstand tension more effectively than plain concrete would normally allow.The ability of cement and concrete to expand and contract without fracturing makes it an ideal material for flooring.