Tips for Small Asphalt Laying Contractors
Check the base. Is it well compacted and level? Asphalt cannot be successfully compacted on a poorly compacted or soft base. Levels are important so that a consistent crossfall and asphalt thickness can be achieved.
Where hand work is needed the mix may segregate and leave a stony finish. It’s important that the Supervisor of the work monitor the placement and identify these areas quickly so that the area can be re-worked while the mix is still warm and workable by removing excessive aggregate and working in some finer mix.
Let your client know that freshly placed asphalt can be easily damaged by point loads and spot power steering turns – particularly in the hot weather. Asphalt can take up to 12 months to cure properly depending on how it is used.
Asphalt used for carparks and driveways cures more quickly the more it is trafficked.
It’s important that the temperature of the mix is checked on site either as the truck tips or when the mix is flowing through the paver. If hot mix is less than say 140°C out of the truck then it will be difficult to spread and compact and the resulting finish will be poor.
For warm mix the temperature on site should be a minimum of 120°C.
If you are using an infrared temperature device to check the mix temperature on site, make sure that the temperature is measured only on the flowing asphalt – i.e. as it flows out of the truck or in the paver auger.
The temperature reading on static asphalt can be up to 30°C lower than actual. To get an accurate temperature a steel stem thermometer must be used.
Weather conditions must be considered before work commences. A cold base or windy day will quickly take the temperature out of the asphalt to be placed making it difficult to achieve compaction and good surface finish.
For example, a 30mm layer of asphalt placed at an air temperature of 15°C, a wind speed of 5km/h and a ground temperature of 10°C will cool below the required heat to achieve initial density in just 13 minutes and for a 25mm layer in 7 minutes.
Changing the conditions for the same 30mm layer of asphalt placed at an air temperature of 30°C, a wind speed of 5km/h and a ground temperature of 25°C the asphalt will cool below the required heat to achieve initial density in 18 minutes and for a 25mm layer in 13 minutes.
See also:
An example of a poorly prepared base.
Note that the base is uneven, loose and not properly compacted. This can result in variable asphalt thickness, poor compaction, unsatisfactory surface finish and significantly shorter pavement life.