TRAFFIC OPENING TIME AND TIME AVAILABLE FOR COMPACTION FOR FRESH ASPHALT LAYER USING SLAB SPECIMENS MODEL

The Time Available for Asphalt Compaction (TAC) and the Traffic Opening Time (TOT) are highly affected by the mix temperature. These two time intervals are considered as major elements in compaction process. TOT is the time from laying asphalt to the point where the paved road is opened for traffic flow. This time is estimated at the surface temperature of value less than 40 oC at which the reduction rate becomes constant. While the time available for compaction (TAC) is the time from laying to that at which the mixture temperature is 85 oC which is called End Compaction Temperature (TE). In local practice, the asphalt paving control mechanisms quoted from the locally used specifications are normally the limits of the delivery and laying temperatures. There are no items to predict these control elements and to be specifically related to the local conditions. This study aims at providing technical specifications for these elements using laboratory and field tests. Study parameters include: layer thickness, mixing temperature, wind velocity, layer confinement and solar radiation. Hot Mix Asphalt (HMA) slab specimens with fixed dimensions are used in all tests as model for asphalt layer and are compacted using manually operated steel roller. HMA is composed of binder layer with max. aggregate size of ¾”. Temperature measurements are taken from slabs at different positions (middle, corner and surface). The laboratory test results showed ranges for the TOT from 100 to 270 minutes and for TAC as 5 to 52 minutes. Heat losses at different cases are estimated. The losses can reach 75% of mixing temperature. As a validation measure, temperature measurements were taken from variety of paving projects at the filed. The field results confirmed to a large extent the Laboratory tests results