A method of measuring the surface texture of aggregate

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Abstract
Summary A method has been developed for measuring quantitatively the surface texture of particles of concrete aggregate. Various possibilities were considered; the method adopted involves embedding a particle of aggregate in a synthetic resin and obtaining thin sections of the aggregate surrounded by the resin. The interface between stone and resin is magnified 125 times on a projection microscope and traced. The length of the profile obtained is measured by means of a map-measuring wheel and compared with the length of an unevenness line drawn as a series of chords. The difference between the two lengths is taken as a measure of the roughness. The reproducibility of the results is good but the variation between different parts of a stone is large. Thus it is necessary to obtain a considerable number of results in order to give a reliable average. This is largely because of the smallness of the sample length: one tenth of an inch. The method has been used to compare the roughness of a series of twelve different aggregates. It has long been recognized that the surface texture of a particle of aggregate might be an important property in determining the adhesion of binders to its surface. The degree of adhesion might, in turn, be expected to influence the properties of the mix. Difficulty has been encountered in assessing the surface texture quantitatively, and although several methods have been developed to some degree, none has so far been generally accepted or widely used. The method described in this article was developed at the Road Research Laboratory as part of an investigation into the effect of the physical characteristics of aggregates on the properties of concrete made with them.

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