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Concrete is a widely used building material due to its strength, durability, and low cost. It is made from cement, water, sand, and gravel. The mix must be made on-site or within a reasonable distance. Concrete sets quickly and becomes unworkable after 3-7 hours. It can be mixed in a batch plant, portable mixer, or cement truck. Continuous pouring is a method of pouring, settling, and smoothing concrete in one continuous action. Small jobs can use a rented wheelbarrow-sized mixer.
Concrete is a building material used worldwide due to its strength, durability and low cost. The raw materials to make it are easily available. One of the few disadvantages of concrete is that almost universally the concrete mix must be made on site or within a reasonable distance in a concrete mixer. Concrete is the resulting material when cement, water and a mixture of sand and gravel are allowed to react.
This universal building material is the result of an exothermic reaction between the molecules of a cement mixture and water. The cement consists of pulverized alumina, silica, lime, iron oxide and magnesium oxide which have been heated to a sintering temperature at which the surface tension decreases and the particles adhere to each other. The fine, finished powder produces a consistent product which can react with water. The consistency of the mix is directly related to the quality of the finished concrete structure.
When water is added to the concrete mixer, the cement quickly becomes a paste and eventually a mixture of a batter-like compound and rocks, sand and gravel. The mixture, now called concrete, will quickly set in an irreversible reaction. The process, once water is added, is unstoppable until completion. Concrete typically becomes unworkable to pour three to seven hours after mixing.
For a large construction job, a batch plant can be assembled on site. Cement and aggregates are delivered to the batch plant. Reagents are piped to the top of the unit, mixed with water, and then piped or pumped to the desired location. A portable concrete mixer consists of a large mixing tank and hose-like hoses mounted on a flatbed trailer. The concrete is pumped to the exact pouring point through hose extensions.
Alternatively, the concrete mix will be poured into a cement truck, which will then transport it. This specialized truck features a constantly rotating chamber with a water feed at the top. The truck mixers are equipped for the possibility of mixing cement, aggregates and water directly in the rotating chamber. These trucks are prone to tumbles when turning on level ground at speeds up to 12 mph because the load of concrete raises the center of gravity and because it is constantly moving.
Continuous pouring concrete refers to the practice of pouring, settling and smoothing concrete in one continuous action. The concrete mix is still mixed in batches. The batches are timed so that the same amount of mixing occurs in each batch and there is no demarcation between the batches. A wheelbarrow-sized concrete mixer can be rented from home improvement stores for small jobs.
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