Cement trucks transport concrete from the batching plant to the construction site. They spin to mix the concrete, and the truck must keep up to prevent the mixture from hardening. The truck rotates in one direction while the concrete is incorporated in the opposite direction. This is known as counter-rotation, and it helps prevent the concrete from settling.
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Mixing Speeds and Horsepower
A clutch inside the truck’s cab regulates the mixing speed of a cement truck. The speed can vary depending on whether the concrete was thoroughly mixed before being loaded into the truck or whether the truck was required to do most of the mixing. The typical mixing speed is 1.57 rad/s (15 rpm), whereas the rate used for transporting pre-mixed concrete ranges from 0.2 rad/s (2 rpm) to 0.6 rad/s (6 rpm). Cement trucks have six-cylinder engines that produce around 300 horsepower, allowing them to spin quickly and haul a heavy load without overworking the engine.
There are various types of cement trucks, each with a different spinning speed. The faster the truck spins, the more cement it can hold. However, the important aspect is how the cement truck works, not how fast it can turn.
Why Cement Mixers Turn Anti-Clockwise
Cement mixers turn counterclockwise to ensure that the wet concrete is well mixed and does not dry out or become sticky. After mixing, the drum is discharged by turning it counterclockwise.
The Purpose of Wheels on Top of a Cement Truck
The wheels on top of a cement truck are auxiliary wheels that help support the truck’s weight and keep it stable on the road. They also distribute the concrete’s weight evenly across the truck’s body. The wheels on top of the cement truck tanks usually rotate during mixing, preventing the tank from tipping over when stopped and mixing the concrete as the truck moves.
How Long Concrete Can Be Kept in a Truck
In cool or wet weather, concrete can take several hours to harden, meaning it can be kept in the truck for up to two hours. However, if the concrete starts to set too quickly, it must be placed immediately. Proper planning is crucial when pouring concrete in cool weather to avoid delays or issues.
Why Cement Trucks Have a Small Chute
Cement trucks have a small chute to pour concrete into forms, such as the foundation of a building. It ensures that the concrete is poured in a controlled and precise manner without spillage. A large chute would make it more challenging for the concrete to flow and more likely to spill. The small chute also helps prevent the concrete from hardening too quickly, as it is kept in a closed system until it is ready to be used.
Disposing of Extra Cement
When a concrete truck finishes a job, it often has extra cement in the tank. The excess cement can be cleaned out at the next job site, disposed of at a local dumping ground, or returned to the mixer plant for future use. Returning the extra cement to the mixer plant is the most common solution, as it reduces waste.
Conclusion
A cement truck is an invaluable tool for expediting the concrete mixing process, surpassing manual labor in terms of speed. It rotates, ensuring even weight distribution of the concrete and preventing rapid hardening due to water evaporation, although the rate at which this occurs is influenced by temperature and humidity. Additionally, the truck features a small chute and a top wheel, enabling the even flow of concrete, minimizing spillage, and supporting the truck’s weight.
