Comparative laboratory performance of hot rolled sheet (HRS) and asphalt treated base (ATB)

Abstract

In the current round of highway pavement betterment project in Indonesia, especially in West Jawa, Asphalt Treated Base (ATB) with 55% of coarse aggregate is used as a regulating course and is overlaid with a Hot Rolled Sheet mix containing 30% of coarse aggregate. ATB, a gap graded mixture is very close in composition to the BS 594-1985 specification for 50% coarse aggregate and the HRS is very close to BS 594-1985 specification for type F wearing course no. 9 (30/14). Information from the betterment projects indicates that the bitumen content of the HRS used is about 15% higher than that of the ATB mix. The purpose of the investigation described in this thesis was to compare these mixes on the basis of laboratory performance tests. Tests used were Marshall test, indirect tension test, wheel tracking test and skid resistance test. For the particular conditions under which this investigation was carried out, it may be concluded that on the basis of strength parameters the performance of ATB is comparable with that of HRS. In terms of resistance to rutting at elevated temperature (60 degree C), ATB has a clear superiority over HRS. ATB has an optimum binder content of 5.5% while that of HRS is 8.2%. The lower optimum binder content of the ATB combined with a high voids content (>8%) may present durability problems if this material is used as a wearing course. Laboratory measurements of skid resistance indicate equal performance in terms of BPN and within the specified value for critical sites while the texture depth of the ATB is approximately twice that of the HRS. Field mixes, as measured in the laboratory, is in excess of the maximum value recommended for wearing course mixes in Indonesian conditions. A study should be made of current methods of aggregate production in order to establish if gradations obtained comply with specification.