Construction Site Vehicles 7

It's good, when someone asks questions, it's even better, if he/she knows the answer themselves. 'What is to be done with the remaining unused concrete?' was the question. If everything goes well, the 'ready-mix truck' or 'ready-mix transporter' has a recycling system at it's disposal, in the works, where it normally loads the concrete, and, that it's open day and night.

Germany is after all, pretty far advanced as far as environmental protection is concerned, brought about by their civil consciousness. When recycling unused concrete, it is rinsed out using, also recyclable water, thus losing its ability to harden. Afterwards one has a transportable bulk material which can be sent off for disposal.

The layman may be aware, that when mixing concrete, water is a fixed value and cannot simply be added at will. If concrete, e.g., should flow more easily where it is to be used, this has to be done by adding special chemicals, at best, just before the delivery.

Indeed, easily flowing concrete is a disadvantage for the transportation. One only has to imagine, just how strong the forces are when the concrete moves from one side to the other when cornering and one can't cancel out the danger of it spilling out of the drum-opening either. It is difficult enough to handle the forwards movement of the mass when braking for a tail-back or the sideways shift in a curve.

Let's go back to the subject on environmental protection and deal with the link from the engine to the hydraulic drum-drive, which, all too often, is still carried out and controlled mechanically. A modulation of the Diesel engine, e.g., when unloading the drum at the construction site, does not take place.

The Bosch Rexroth system not only regulates the RPM of the drum through a variable axial piston pump (picture 2), but also influences the Diesel engine simultaneously through the CAN-bus. Thus, an excessively high RPM during the trip is prevented and with it, the danger of the vehicle tipping over. Coming back to the subject of environmental protection, which also benefits from such a regulation of the Diesel engine, both through the consumption as well as the noise emission. At Bosch-Rexroth in the meantime, axial piston pumps are being offered, which drive the concrete pumps with approx. 450 bar of high pressure.

To keep the above mentioned remaining or unused concrete to a minimum, smaller mixer vehicles, e.g., would be more favourable. At the moment, the regional Chinese market is considered as being suitable for such vehicles. They manage the previously mentioned high pressure with smaller hydraulic cylinders. In addition, through a faster reacting regulation, the system becomes more manageable. In the meantime, at the other end of the scales, loading capacities of up to 24 cubic metres are possible. 11/14