oa Civil Engineering = Siviele Ingenieurswese - Stiffness of concrete made with granite and andesite aggregates
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.
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