Roller Compacted Concrete (RCC):
Just the Job for High Compaction Technology
Especially in the USA, Roller Compacted Concrete (RCC) is a common alternative to asphalt and used extensively. RCC consists of uncrushed and/or crushed aggregate, hydraulic binders and sometimes concrete additives. It is mixed in a concrete mixing plant on or near the job site. The mix is transported by conventional feed vehicles and transferred to a paver, which places the material in layers up to 25cm thick. Finally, the concrete layer is compacted with rollers.
On account of the low moisture content of the RCC, it must be carefully sprayed with water directly after rolling. At first, the water is to be sprayed in a fine mist in order to prevent wash-out of the concrete surface. Moisture is added over the course of at least 3 days allowing setting of the concrete. The RCC hardens and increases in strength. In many cases, joints are cut to counteract the formation of cracks.
RCC is stiff enough to be compacted with vibratory rollers. However, the number of roller passes must be kept to a minimum in order to achieve the best possible stability, evenness and surface structure. This is guaranteed by the VÖGELE High Compaction Screed in TP2 version. In addition to a tamper, the screed comes with 2 pressure bars operated by pulsed-flow hydraulics. VÖGELE is the only manufacturer worldwide to offer this pulsed-flow hydraulics technology. A pulse generator inside the system generates high-frequency pressure pulses. These ensure that the pressure bars are in permanent contact with the mix, forcing the mix down until it cannot be compacted any more. This unique technology produces the highest compaction values that can be achieved by a road paver. Plus, roller passes are reduced to an absolute minimum. Often, just static roller passes are sufficient.
Practical Tips for Paving
In order to achieve perfect results when placing RCC, a number of factors must be taken into consideration – referring to the properties of the concrete on the one hand, and to settings of the compacting systems inside the screed on the other.
The moisture content of the concrete is crucial for achieving maximum precompaction values. If the material contains too little water, optimal compaction of the concrete is not possible. If it contains too much water, the screed will risk to sink into the mix. Therefore, in order to determine the optimal moisture content, a test field should always be paved on the job site.
Settings of Compacting Systems in the Screed
Tamper stroke: 7mm
Tamper speed: 1,500 – 1,800 rpm
Pressure of pressure bars: 80 – 100 bar
(depending on the concrete properties)