Concrete mixer
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A concrete mixer (also commonly called a cement mixer) is a device that homogeneously combines cement, aggregate such as sand or gravel, and water to form concrete. A typical concrete mixer uses a revolving drum to mix the components. For smaller volume works portable concrete mixers are often used so that the concrete can be made at the construction site, giving the workers ample time to use the concrete before it hardens. An alternative to a machine is mixing concrete or cement by hand. This is usually done in a wheelbarrow; however, several companies have recently begun to sell modified tarps for this purpose.
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[edit] Industrial mixers
Today's market increasingly requires consistent homogeneity and short mixing times for the industrial production of ready-mix concrete, and more so for precast/prestressed concrete. This has resulted in new technologies for concrete production. Worldwide, therefore, twin-shaft batch mixers are becoming more important for high-quality concrete production. They introduce very high turbulence into the mix and achieve about 95% homogeneity at only around 30 seconds mixing time per batch.
[edit] Concrete transport truck
Special concrete transport trucks are made to transport ready-mix concrete from a factory/plant to the construction yard. Because of the difficulty in tipping a large drum attached to the back of a concrete truck, the interior of the drum on a concrete truck is fitted with a spiral blade. In one rotational direction, the concrete is pushed deeper into the drum. This is the direction the drum is rotated while the concrete is being transported to the building site. This is known as "charging" the mixer. When the drum rotates in the other direction, the Archimedes screw-type arrangement "discharges", or forces the concrete out of the drum. From there it may go onto chutes to guide the viscous concrete directly to the job site. If the truck cannot get close enough to the site to use the chutes, the concrete may be discharged into a concrete pump connected to a flexible hose, or onto with a conveyor belt which can be extended some distance (typically ten meters). This is useful for when the concrete needs to be distributed to the back of a garden for instance.
"Rear discharge" (or "butt dumper") trucks require both a driver and a "chuteman" to guide the truck and chute back and forth to place concrete in the manner suitable to the contractor. Newer "front discharge" trucks (or "rightway's") have controls inside the cab of the truck to allow the driver to move the chute in all directions.
A six-axle truck has three "lift axles" -- the first two axles behind the cab (the pusher axles) and the rear-most axle (the tag axle) -- which can be lifted out of the way for off-road operation. When loaded, these axles distribute the weight of the truck. This distribution of weight is essential. Otherwise, roads most traveled on, by vehicles of this size begin to break down. As an added benefit, these axles provide the driver better control of the vehicle during transport. The lift axles are equipped with brakes, and a system that lets them actually turn with the truck during turns, allowing maneuvering that would otherwise be nearly impossible.
Stephen Stepanian filed a patent application for the first truck mixer in 1916. [1] Trucks weigh 20–30,000 pounds (9–13.5 tonnes), and can carry roughly 40,000 pounds (18 tonnes) of concrete although many varying sizes of Mixer Truck are currently in use. The most common truck capacity is six cubic metre.
Most concrete mixers in the UK are limited to a speed of 56 miles per hour.
[edit] Television
An episode of Myth Busters checks if dynamite can be used to clean out dried concrete from inside of a mixer truck. It is concluded that it can be of limited use. For the finale, an excessive amount of explosive is used, and is detonated from a very, very long distance away. Only the engine block is recovered.
[edit] References
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