What is a concrete mixer?

Wet concrete being poured.

Concrete is a building material used worldwide 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 at a reasonable distance in a concrete mixer. Concrete is the resulting material 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 cement and water mixture. Cement consists of pulverized alumina, silica, lime, iron oxide and magnesium oxide that have been heated to a sintering temperature at which the surface tension decreases and the particles adhere to each other. The finished fine powder produces a consistent product susceptible to reaction with water. The consistency of the mix is ​​directly related to the quality of the finished concrete structure.

Electric trowels can be used to impart a smooth surface finish to freshly poured concrete slabs.

As water is added to the concrete mixer, the cement quickly becomes a slurry and ultimately a mixture of a putty-like compound and rocks, sand and gravel. The mix, now called a concrete mix, will quickly cure in an irreversible reaction. The process, once water is added, is unstoppable until it is complete. Concrete typically becomes impractical to pour three to seven hours after mixing.

The ready-mixed 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 at the job site. Cement and aggregate are delivered to the batch 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 cane-like hoses mounted on a flatbed trailer. Concrete is pumped to the exact pour point via hose extensions.

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Alternatively, the concrete mix will be poured into a concrete truck, which will then transport it. This specialized truck comes with a constant rotating chamber with water supply at the top. Concrete mixer trucks are equipped with the possibility of mixing cement, aggregate and water directly in the rotating chamber. These trucks are subject to tipping when turning on level ground at speeds of up to 12 mph, because the concrete load raises the center of gravity and is constantly shifting.

Continuous concrete pouring 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 delineation between batches. A wheelbarrow-sized concrete mixer can be rented from construction supply stores for small jobs.

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