Cold joints are a necessary evil in road construction. They cannot be avoided but they can be planned. Following the correct procedures to work next to them will ensure that the risk of failure of the cold joint is decreased.
Transport Malta’s Standards and Specifications outline the requirements for road construction. Quality Assurance and Quality Control procedures will ensure that if the specifications are met the roads will last longer.
Switch OFF vibration in good time before reversing.
Pre-roll without vibration if there is a low pre-compaction by the paver.
Select vibrator frequency on asphalt mix type and laying thickness in line with recommendations from the roller manufacturer. Compact surface layers with high frequency rates. Thick layers from 8cm onwards shall be vibrated with low frequency rates.
DO NOT use excessive speed as you might create the washboarding effect.
Use static compaction when moving downhill. Use vibration only when moving uphill.
When the asphalt temperatures reach 100 degrees celsius switch off vibration to avoid the risk of crushing the aggregates, and will eventually lead to cracks. For the same reason, compact thin asphalt layers only with low vibration effects and few passes or better still entirely without vibration.
With dense mixtures, too much compaction at high temperatures may lead to bitumen being pushed to the surface layer. Consequently, the skid resistance of the road surface will be lowered.
1. Start compaction as early as possible.
2. Drive with the driven drum towards the paver to avoid the formation of ripples and cracks. Combination rollers should be used with the rubber tyres towards the paver.
3. To avoid mix material sticking, drums and tyres must be lightly sprayed with water. They should be moist but not wet.
4. DO NOT use vibration when the machine is at a standstill. This will avoid the formation of waves.
5. Drive smoothly and do not change direction in jerky movements. The use of an automatic speed control system can improve the rolling quality.
6. Switch the vibration on only when the machine is moving. Switch the vibration off in good time before reversing.
7. If the road is cambered start compaction from the lower edge and overlap each pass towards the higher edge.
8. Steer and offset the machine only on compacted material to avoid shoving of asphalt.
9. Never stop the roller on hot mix material since the machine will probably cause deformation of the layer.
10. ALWAYS park the machine at an oblique angle to the direction of the work so that any marks can be smoothed out later.
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Quality Assurance plays a very important role in construction works. It has to be carried out and the process must be well documented. The QA process is documented in an INSPECTION TEST REQUEST BOOK commonly known as an ITRB. [click to continue…]