Concretes containing two types of aggregate, crushed granite and crushed andesite from the Witwatersrand area, were studied in order to quantify the influence of aggregate stiffness and volume concentration on elastic properties. Representative paste and mortar mixes were extracted from the basic concrete mixes, and elastic properties of these materials, as well as of rock core specimens from the two aggregate types, were determined. The study involved correlations of concrete properties with predictions using various two-phase models based on micro-rheological principles. It was found that granite concretes conformed best with a model assuming no bond between paste and aggregate (the Series Model), while andesite concretes were best modelled by the Hobbs Model, which assumes full bonding between the phases. Regarding practical design, the tests have partially validated the recently introduced empirical expression in BS 8110, with Ko values of 19 GPa and 27 GPa being recommended for the particular granite and andesite aggregates respectively.
Investigation of a number of premature basecourse failures on roads throughout Southern Africa has shown that In nearly every case the plasticity index (PI) and the fines of the basecaurse material passing the 0,425 mm sieve (P425) exceeded the specification limits. In some cases the problems were built in, but in others the material degraded under traffic and in the presence of excess moisture to material that was incapable of functioning as a basecourse.
The hydraulic behaviour of compound channels is made complex by the interactions between main channel and floodplain flows. Oversimplified analysis can result in large errors in estimates of carrying capacities or flood levels. In this paper existing discharge computation methods were reviewed and new techniques were presented that were consistently more reliable than those in current use.