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A concrete mixer truck is a specialized truck used to transport ready-mixed concrete. Due to its shape, it is also commonly called a snail truck or an olive truck. These trucks are equipped with cylindrical mixing drums to carry the mixed concrete. During transportation, the mixing drum continuously rotates to ensure that the concrete does not harden. After delivering the concrete, the inside of the mixing drum is usually washed with water to prevent residual concrete from hardening and occupying space, which would gradually reduce the drum's capacity.
INTRODUCTION
A concrete mixer truck consists of an automotive chassis and a specialized concrete mixing transport device. In China, the chassis for produced concrete mixer trucks mostly adopts a second-class universal chassis provided by the vehicle manufacturer. The specialized mechanisms mainly include a power take-off, front and rear brackets for the mixing drum, reducer, hydraulic system, mixing drum, operating mechanism, cleaning system, etc. The working principle is that the power from the car chassis is taken out through the power take-off, which drives the variable pump of the hydraulic system, converting mechanical energy into hydraulic energy to be transmitted to the quantitative motor. The motor then drives the reducer, which in turn drives the mixing device to mix the concrete.
CLASSIFICATION
Concrete mixer trucks can be classified into three types based on the moisture content of the concrete they transport: wet mix, dry mix, and semi-dry mix.
Most domestic concrete mixer trucks use wet mix types, which can transport concrete produced by mixing plants (stations) or aggregates (sand, gravel), cement, and water in the specified proportions. During transportation, the wet mix is continuously stirred to prevent the concrete from initial setting and segregation. However, the time from concrete production to pouring generally should not exceed 1.5 hours to avoid concrete setting. Therefore, for longer-distance transportation, dry mix and semi-dry mix concrete mixer trucks are used to transport the materials. Dry mix concrete mixer trucks directly load dry aggregates and cement into the mixing drum according to the specified proportions, and the dry materials are stirred during transportation. When the vehicle is about to reach the construction site or at the construction site, water is added to complete the mixing of the concrete. Semi-dry mix concrete mixer trucks transport concrete with aggregates and cement mixed in the specified proportions and containing some water, but the water content is insufficient for pouring. Water is added at the construction site or when the vehicle is about to reach the construction site to complete the mixing.
Before starting, carefully inspect all parts of the mechanical system and confirm they are in good condition before starting.
Before starting, place the mixing control lever in the 'neutral' position.
After starting, place the mixing control lever in the 'discharge' position to drain any water in the drum. When loading materials, the mixing control lever should be placed in the 'loading' position.
When loading material, the mixing operation lever should be placed in the 'loading' position.
Before transportation, the unloading hopper must be secured in the 'travel' position to prevent swinging.
When operating the control stick, you should pause briefly at the 'neutral' position before moving to the next position.
Ensure civilized construction, and do not casually dump excess materials into the buckets. After unloading, it is necessary to clean the mixing drum, material trough, rollers, and other parts.
When people enter the cylinder to remove concrete lumps, the vehicle should be turned off, the ignition key removed, and someone should supervise outside the cylinder.
A concrete mixer truck is a special type of vehicle, and not all drivers can operate it properly. Improper operation can lead to accidents such as overturning, rapid wear of hydraulic pumps, motors, and reducers, or even severe consequences. Therefore, the following measures should be taken:
Before starting the concrete mixer truck, place the drum control lever in the 'stop' position.
After starting the engine, rotate the drum at low speed for about 10 minutes until the hydraulic oil temperature rises above 20°C before commencing work.
When parking the concrete mixer truck outdoors, reverse the drum before loading to drain water and debris, ensuring the quality of the concrete.
During transportation of concrete, ensure the chute is securely fastened to prevent loosening, which could cause swinging and injure pedestrians or affect other vehicles.
When transporting mixed concrete, the drum speed should be 2-10 revolutions per minute. On flat roads, maintain a speed of 2-3 revolutions per minute. On roads with a side slope greater than 50 degrees or with significant lateral movement, stop the drum rotation until road conditions improve.
The time for transporting concrete should not exceed the specified time by the mixing plant. During transportation, the drum should not stop rotating for long periods to prevent concrete segregation. The driver should frequently check the condition of the concrete and report any abnormalities to the dispatch office for prompt handling.
When the mixer truck is loaded with concrete, the on-site stoppage time should not exceed 1 hour. If exceeded, immediately request the site supervisor to handle it promptly.
The slump of the concrete transported by the mixer truck should not be less than 8 cm. In high temperatures, the time from concrete entering the drum to being discharged should not exceed 2 hours. In rainy weather with lower temperatures, it should not exceed 2.5 hours.
Before discharging concrete, rotate the drum at 10-12 revolutions per minute for 1 minute before unloading.
After discharging concrete, immediately use the onboard hose to rinse the feed port, discharge chute, and discharge spout, removing any dirt and residual concrete. Then, add 150-200 liters of clean water to the drum and slowly rotate the drum during the return trip to clean the interior walls, avoiding residue sticking to the drum and blades. Drain this water before reloading.
During transportation of concrete, keep the engine speed between 1000-1400 revolutions per minute to ensure maximum torque. The vehicle speed should not exceed 40 km/h to ensure safety.
After completing work, thoroughly clean the inside and exterior of the drum to avoid leaving any remaining concrete.
When the pump is operating, do not run it empty, and do not use it continuously for more than 15 minutes.
Keep the water tank full to prepare for emergencies. After winter shutdown, drain the water from the tank, pump, pipes, and drum, and park in a sunny, non-flooded area to prevent freezing damage.
Install insulation covers in winter and use antifreeze to protect the mixer truck. Change the fuel grade according to weather changes to ensure normal operation of the machinery.
When inspecting or repairing the hydraulic transmission part of the mixer truck, ensure the engine and hydraulic pump are under no pressure.
When adjusting the clearances, strokes, and pressures of concrete mixer trucks, they should be checked and approved by a dedicated safety officer; when replacing parts, it must be signed by the department head or the general manager, otherwise, relevant personnel will be held accountable if problems occur.
