The variability in commercial laboratory aggregate testing for road construction in South Africa

Abstract

Simple data comparisons were undertaken using project data to illustrate the need for duplicate test analyses in road construction material investigations for hard rock aggregate sources. Test data was sourced from projects commissioned by the South African National Roads Agency SOC Limited (SANRAL). All test results except the polished stone value were reported by commercial geotechnical laboratories that are accredited with the South African National Accreditation System (SANAS). Only samples subjected to duplicate test analyses were used, as this method allows direct comparisons. The tests used for comparison included the polished stone value, wet and dry versions of the Aggregate Crushing Value test, wet and dry versions of the 10% Fines Aggregate Crushing Value test, the ethylene glycol-soaked version of the 10% Fines Aggregate Crushing Value test, and the water absorption test of both the fine (–5.00 mm) and coarse (+5.00 mm) material fractions. The results show that duplicate testing is firmly justified, as test results reported were often highly variable, despite all participating laboratories being SANAS-accredited and using standardised methods. Further consideration was then given to the additional cost of duplicate testing at project stage investigations compared to the cost implications of having erroneously reported materials failing in service or having good-quality materials rejected.