Wet concrete is poured.
Concrete is a construction material used throughout the world for its strength, durability and low cost. The raw materials to make it are readily available. One of the few disadvantages of concrete is that almost universally, concrete mixing must be done on site or a reasonable distance away in a concrete mixer. Concrete is the material that results when cement, water, and a mixture of sand and gravel react.
A man smoothing a concrete floor.
This universal building material is the result of an exothermic reaction between the molecules of a mixture of cement and water. Cement consists of pulverized alumina, silica, lime, iron oxide, and magnesium oxide that have been heated to a sintering temperature where the surface tension decreases and the particles stick together. The finished fine powder produces a consistent product that is susceptible to reacting with water. The consistency of the mix is directly related to the quality of the finished concrete structure.
Power trowels can be used to impart a smooth surface finish to freshly poured concrete slabs.
As water is added to the mixer, the cement quickly turns into a slurry and eventually a mixture of a putty-like compound and rocks, sand, and gravel. The mix, now called the concrete mix, will quickly cure in an irreversible reaction. The process, once the water is added, is unstoppable until it is completed. Concrete typically becomes impractical to pour three to seven hours after mixing.
Ready-mix concrete companies have huge piles of sand, gravel, and other aggregates stored on site.
For a large construction job, a batch plan can be set up on the job site. Cement and aggregates are delivered to the batching plant. Reagents are transported to the top of the unit, mixed with water, and then transported or pumped to the desired location. A portable concrete mixer consists of a large mixing tank and reed-type hoses mounted on a flatbed trailer. The concrete is pumped to the exact pour point through hose extensions.
Alternatively, the concrete mix will be poured into a concrete truck, which will then transport it. This specialized truck comes with a constantly rotating chamber with a water supply at the top. The concrete mixer trucks are equipped with the possibility of mixing cement, aggregates and water directly in the rotating chamber. These trucks are subject to rolling over when turning on level ground at speeds up to 12 mph, because the load of concrete raises the center of gravity and constantly shifts.
Continuous concrete pouring refers to the practice of pouring, setting, 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 delineation between batches. A wheelbarrow-sized concrete mixer can be rented at construction supply stores for small jobs.