Concrete structures are often inhomogeneous and contain a variety of materials (such as cement, aggregates, pores, gypsum, rebar and steel fibres) with varying thermal properties. Concrete, in construction, is a structural material consisting of a hard, chemically inert particulate substance, known as aggregate (usually sand and gravel), which is bound by cement and water. Concrete is a composite material, consisting mainly of Portland cement, water and aggregate (gravel, sand or rock). When these materials are mixed together, they form a workable paste that gradually hardens over time.
Concrete is a building material composed of cement, fine aggregates (sand) and coarse aggregates mixed with water that hardens over time. Portland cement is the most common type of cement used for concrete production. Concrete technology deals with the study of the properties of concrete and its practical applications. Concrete is the second most widely used substance in the world after water and is the most widely used building material.
The design of the mix depends on the type of structure to be built, how the concrete is mixed and delivered, and how it is placed to form the structure. The energy requirements for transporting concrete are low because it is produced locally from local resources, usually manufactured less than 100 kilometres from the construction site. Fresh concrete (before it has finished curing) is highly alkaline and must be handled with appropriate protective equipment. Therefore, to increase its overall strength, steel rods, wires, mesh or cables can be embedded in the concrete before it sets.
Concrete strength values are usually specified as the lowest compressive strength of a cylindrical or cubic specimen, determined by standard test procedures. Concrete is used to create hard surfaces that contribute to surface runoff, which can cause heavy soil erosion, water pollution and flooding, but conversely it can be used to divert, dam and control flooding. Concrete that has been hardened over an embedded metal (usually steel) is called reinforced concrete or ferrocement. Concrete is expected to be a key material for weather-resistant structures, as well as a solution to mitigate pollution from other industries, capturing waste such as coal fly ash or bauxite waste and residues.
Replacing part of the clinker with large quantities of slag or fly ash has often been investigated, based on conventional concrete technology. However, considering the purpose of having resource circularity in the life cycle of concrete, the only application of RCA that could be considered as concrete recycling is the substitution of natural aggregates in concrete mixes. The life cycle assessment (LCA) of low carbon concrete was investigated as a function of the substitution ratios of granulated blast furnace slag (GGBS) and fly ash (FA). Different types of binding materials are used in addition to cement, such as lime for lime concrete and bitumen for asphalt concrete used for road construction.
Concrete is characterised by the type of aggregate or cement used, by the specific qualities it manifests, or by the methods used to produce it. Its invention is often attributed to Joseph Monier, a Parisian gardener who manufactured concrete pots and tubs reinforced with iron mesh; he received a patent in 1867.The recycling or reclamation of concrete reduces the exploitation of natural resources and associated transport costs, and reduces waste disposal.