Aggregates have long been regarded simply as 'inert fillers' in concrete, there to provide bulk and economy. A 1931 monograph on 'Cements and Aggregates' stated that 'The coarse aggregate in concrete is simply an inert filler used to reduce the cost', and went on to say that the type of coarse aggregate has relatively small effect on the strength of the concrete, provided it is sound (Baker, 1931). This view has unfortunately prevailed even up to the present time among engineers.