1. Introduction

Abstract

Aggregates are defined here as particles of rock which, when brought together in a bound or unbound condition, form part or the whole of an engineering or building structure. Natural sand, gravel and crushed rock aggregates are fundamental to the man-made environment and represent a large proportion of the materials used in the construction industry. Re-use of aggregates has become a more common practice and the substitution of natural aggregates by artificial aggregates made from waste products of other industries is a small part of the industry. Production of aggregates for civil engineering and building construction is one of the world’s major industries. Quarrying is the largest industry in terms of tonnage of output (but not value) in the United Kingdom and even in 1985, production was two and a half times that of coal. With the closure of so many deep coal mines in 1999 this figure was nearly seven times larger. Consumption of aggregates has more than doubled over forty years from 100 million tonnes in 1959 to between 200 and 300 million tonnes per annum throughout the last decade (see Fig. 1.1). Sand and gravel production in 1959 was 67% of the total with crushed rock providing the balance of 33%. By 1998 this situation had changed significantly with crushed rock production increasing substantially to 132 million tonnes (60%) and sand and gravel only to 86 million tonnes (40%). In 1989, growth in demand was strong and a compound growth rate of 3% was forecast leading to