Contributions of in-situ ball penetration tests to the determination of bitumen application rates in the South African surface seal design method

Determination of conventional bitumen application rates in the seal design of South Africa using (Technical Recommendations for Highway (TRH3)) requires information related to conditions on the road at the time of sealing and properties of materials to be used for this purpose. Although the design process and input parameters are described in TRH3, the significance and sensitivity of the various input parameters are perhaps not covered sufficiently to guide designers. The purpose of this paper is to provide additional information with regard to the contribution of in-situ ball penetration tests to the determination of conventional bitumen application rates in the South African surface seal design method. Although ball penetration tests have been widely accepted for use in the determination of bitumen application rates for chip seals, the consequences of injudicious utilization of the test results could result in incorrect application rates for the condition at hand. In-situ ball penetration tests were conducted on a road surface stretch of 104km which was divided into 10 uniform sections based on a visual condition survey. A minimum of 10 ball penetration tests per section were conducted to investigate the contributions of the ball penetration tests to conventional bitumen application rates for chip seals. Results obtained by, reading off the net cold binder from an appropriate aggregate average least dimension chart showed that although net cold binder is a function of seal aggregate embedment potential, aggregate average least dimension, total number of equivalent light vehicles per lane per day, and required textural depth, the contribution of embedment potential obtained by in-situ ball penetration tests to bitumen application rate was more significant than other factors. This paper also describes how relevant the in-situ ball penetration tests are to the determination of bitumen application rates for chip seals.