Views: 0 Author: Site Editor Publish Time: 2023-06-06 Origin: Site
Special concrete trucks (in-transit mixer trucks) are used to mix concrete and transport it to the construction site.They can be loaded with dry material and water and mixed during transport.They can also be loaded from a "central blend" plant; in this process, the material is already mixed before being loaded.Concrete mixer trucks keep the material in a liquid state by stirring or turning the drum until delivery.These trucks have an internal turbine that pushes the mixed concrete inside the drum against gravity.The drum of the concrete mixer truck is equipped with helical blades inside.In one direction of rotation, the concrete is pushed deeper into the drum. This is the direction the drum rotates when transporting the concrete to the construction site.This is called "charging" the mixer.
Archimedes' screw-like device "discharges," or pushes the concrete out of the drum, when the drum rotates in the other direction. From there it can enter the chute, directing the cohesive concrete directly to the job site.If the truck cannot get close enough to the site to use the chute, the concrete can be discharged into a concrete pump connected to a flexible hose, or onto a conveyor belt that can extend for some distance, usually ten meters or more.Pumps provide the means to move material to precise locations,Multi-story buildings and other distance-restricted locations.Buckets suspended from cranes are also used to place the concrete.Drums are traditionally made of steel, but on some newer trucks, fiberglass has been used as a weight saving measure.A "back dump" truck requires a driver and a "chuteman" to guide the truck and chute back and forth, placing the concrete in a way that suits the contractor. Newer "front dump" trucks have controls in the truck cab that allow the driver to move the chute in all directions.The first front discharge mixer, patented in 1974, was designed and built by Royal W. Sims of Holladay, Utah, USA.
Concrete mixers are equipped with two or more shafts.Four-axle, five-axle and six-axle trucks are the most common, the number depends on the load and local regulations on the allowable load on the road.Axles are essential to evenly distribute loads, allow travel on roads with limited weight, and reduce wear and tear on normal roads.Two- or three-axle trucks are not available for payload in many jurisdictions during the winter months when road weight restrictions are reduced.Other regions may require expensive operating permits.Additional axles other than those used for steering ("steering") or driveline ("drive") may be mounted between the steering and drive, or after the drive.Mixers also typically have multiple steering axes, which often results in a very large turning radius.For ease of maneuvering, additional axles can be "lift axles",which allow them to be raised off the ground so they don't scrub (drag to one side on the ground) during tight turns, or increase the turning radius of the vehicle.The shaft mounted behind the driver is known as a "follower shaft" or "power assist shaft" and is usually equipped with the opposite direction of the steering shaft to reduce scrubbing and to automatically lift when the truck is in reverse.
Tractor-trailer combination mixers, in which the mixer is mounted on a trailer rather than a truck chassis, are used in some jurisdictions, such as Quebec, where even six-axle trucks struggle to carry a useful load.Concrete mixers usually don't leave their factories very far because the concrete starts to set as soon as it's loaded onto the trucks.Many contractors require concrete to be in place within 90 minutes of loading.If the truck breaks down or for other reasons, the concrete in the truck hardens and workers may need to use a jackhammer to get into the bucket.Stephen Stepanian patented the first truck mixer in 1916.Trucks weigh 20,000 to 30,000 pounds (9,070 to 13,600 kilograms) and can carry approximately 40,000 pounds (18,100 kilograms) of concrete, although mixer trucks are in use today in a variety of sizes.The most common truck capacity is 10 cubic yards (7.6 cubic meters).Most concrete mixers in the UK have a speed limit of 56mph (90km/h).