Paper presented at the 20th Annual South African Transport Conference 16 - 20 July 2001 "Meeting the transport challenges in Southern Africa", CSIR International Convention Centre, Pretoria, South Africa.
The Average Least Dimension (ALD)of surfacing aggregates is required for the determination of the quantity of a bituminous product to be sprayed in the case of normal road surface treatments. The ALD is also needed for the calculation of the spread rate of surfacing aggregates. Method TMH1-B18(a), which is based on measuring the least dimension of an aggregate is the reference method for the determination of the ALD in South Africa. The accuracy of the measured ALD method depends on the sampling process, the sample size, measuring equipment, the interpretation of the least dimension, and the fraction of the sample not measured. The computational method TMH1-B18T(b), currently in use, is inaccurate and also does not take full account of the nature of the particle size distribution which has an effect on the estimated measured ALD. The computational method developed, as discussed in this paper, was designed to reduce the error between ALD measured and ALD computed by introducing more factors which will have a significant decreasing effect on the estimated measured ALD error.
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