In Germany thousands of mixer trucks are in operation every day, for supplying fresh concrete from the factory directly to the installation site. More and more frequently, the types concerned are high-strength concretes with highly effective concrete admixtures or steel-fiber reinforced concretes, which increasingly lead to caking inside the drum, thus requiring cleaning after transportation. In addition, especially during the warm period of the year, during transportation standard types also form deposits in the mixer drums, on exterior walls and, in particular, the rear sides of the spiral blades; they quickly harden and accumulate with each application.
The deposits carried along can account for up to 0.7 m³ of the loading capacity of a mixer truck. In this way, tons of surplus material that is no longer needed travel across our roads not only blocking loading capacity of the trucks, but also leading to high energy consumption.
Concrete residues not removable sustainably so far
Although the problem is well known, it can only be solved if alternative solutions are found in addition to the prevailing practice. Until now, the hardened concrete residues inside the drum are usually removed in a time-consuming way at larger intervals. The most common solution is to climb into the drum to clean it by means of a pneumatic hammer manually. This physically demanding work – almost like a miner‘s job – inside the narrow concrete drum is quite dangerous, which can lead to serious occupational accidents despite specific accident prevention regulations. Furthermore, it is not possible to avoid damages on the drum and the screw conveyor caused by lumps of concrete falling down and a daily cleaning process carried out in this way is even impossible.
Another method is working with ultra-high pressure cleaning, cutting the hardened concrete in a water jet procedure out of the drum. Generally, this cleaning method has to be carried out by an external service provider, as only trained personnel is in the position to operate the special device and to clean the drum. However, large lumps of concrete may fall down during cleaning which may damage the drum and the auger. What is more, the noise level during cleaning is almost comparable to that of an airplane taking off.
All in all, the methods described are not sustainable and, moreover, block the vehicle for up to a complete working day. In addition, the effect only lasts for a short time, then the caking is growing again and the payload is declining.
New approach of Walter Gerätebau
So as to make use of the savings potential, an approach has to be found which is sustainable and can be operated by the truck driver. The approach of Walter Gerätebau GmbH meets these requirements and is a method that prevents the occurrence of the problematic caking all together. Walter has already developed feasible solutions for cleaning the interior of the concrete mixers, the funnel of the mixer and the truck; they are based on the principle of early high-pressure cleaning, using water pressure effectively for the removal of material residues in a still wet state.
The truck mixer drums are cleaned on a daily basis or before every idle time before delivery; for this purpose, the driver activates the cleaning station after emptying of residues at the recycling container. Then an adjustable cleaning lance with cleaning nozzle head is automatically moved into the drum. Once the nozzle head is safely sitting inside the drum, high-pressure cleaning starts at 220 bar. The drum rotation provides for rinsing everywhere inside – even parts which are difficult to access – on the rear sides of the spiral blade. The resulting wastewater is perfectly filtered and can be reused for the next drum cleaning process. The lance moves out of the drum after the cleaning process and is available for the next truck mixer.
In this way, up to ten cleaning processes are possible within an hour in a fully automatic manner. The short cleaning time during which the truck mixer is not available, is more than compensated by the permanently increased transport capacity and a longer service life of the drum.
More investment security and occupational safety
The funnel has to be movable to allow the cleaning lance to move inside the mixer truck. There are more and more ready-mix trucks equipped with a swiv-eling funnels offered on the market. For this purpose, Walter Gerätebau GmbH has developed a useful retrofit kit, equipping the truck funnel with a swivel mechanism. Consequently, the solution of Walter allows easy cleaning of the truck drum on a regular basis: an optimum loading capacity is maintained, wear and tear of the drum is reduced and the truck can be operated more efficiently.
Due to the fact that the system has been developed in practice and has been in operation for some time, it could be estimated on the basis of those figures whether the solution is really cost-efficient. It can be assumed that an investment in such a drum cleaning system pays off within 18 to 24 months, depending on the structure of the company as well as the number and equipment of the trucks (funnels). This even does not consider the fact that using the same delivery quantity of concrete up to two vehicles of the fleet are operating superfluously and/or a higher delivery quantity can be achieved by the same number of vehicles.
An increase in occupational safety for the staff members, having to clean inside the drums manually, is an important aspect likewise and can have a positive effect on the contributions to the accident insurance. As the BG RCI (German Accident Prevention & Insurance Association for the Raw Materials and Chemicals Industry) already funds the drum cleaning process as a service, the potential operator should check whether the installation of such a system is eligible, either.