Concrete is formed when portland cement creates a paste with water that bonds with sand and rock to harden. Cement is manufactured using a tightly controlled chemical combination of calcium, silicon, aluminum, iron and other ingredients. Polymeric concretes are frequently used for repair and construction of other applications, such as drains. Concrete is poured directly from the hopper of the ready mix truck, put into place with a buggy, or pumped into place with a concrete boom pump (see Concrete pumping).
Air entrainment is the use of agents that, when added to concrete during mixing, create a lot of air bubbles that are extremely small and are very close, and most of them remain in hardened concrete. Every major city has a floor-scale model of urban development plans that needs to be constantly updated as small white plastic models become megamalls, housing complexes and concrete towers. Concrete floors were found in the royal palace of Tiryns, Greece, which dates from approximately 1400 to 1200 BC. Additives are materials in powder or fluid form that are added to concrete to give it certain characteristics that cannot be obtained with simple concrete mixes.
Recycling or reclaiming concrete reduces the exploitation of natural resources and the associated transportation costs, and reduces landfills. In addition, concrete contains a wide range of chemicals that give it the desired characteristics for specific applications. An early example in the Hoover Dam used a network of pipes between vertical concrete placements to circulate cooling water during the curing process to prevent harmful overheating. Modern concrete wall systems use both external insulation and thermal mass to create an energy-efficient building.
The Life Cycle Assessment (LCA) of low-carbon concrete was investigated according to the replacement ratios of ground granulated blast furnace slag (GGBS) and fly ash (FA). Similar systems are still used; depending on the volume of the pouring, the concrete mix used and the ambient air temperature, the cooling process can take many months after the concrete is laid. Low kiln temperatures in the burning of lime, lack of pozzolan and poor mixing contributed to a decrease in the quality of concrete and mortar. Reinforced concrete can be precast concrete or cast in situ (in situ) and is used in a wide range of applications, such as construction of slabs, walls, beams, columns, foundations and frames.
Rivers were dumped after World War II, when concrete offered an economical and simple way to rebuild cities devastated by bombing.