8. Aggregates for concrete

Abstract

Concrete may be defined as a mixture of water, cement or binder, and aggregate, where the water and cement or binder form the paste and the aggregate forms the inert filler. In absolute volume terms the aggregate amounts to 60–80% of the volume of concrete and is, therefore, the major constituent. The aggregate type and volume influences the properties of concrete, its mix proportions and its economy.The desirable and undesirable properties of aggregates for concrete have been thoroughly reviewed in a number of texts on concrete technology (Orchard 1976; American Society for Testing and Materials 1978; Murdock, Brook & Dewar 1997; Fookes 1980; Neville 1995). In practice, difficulties are frequently encountered in translating these properties into specification requirements for aggregates, or in assessing aggregate test results to determine compliance or otherwise with already specified parameters. This chapter considers the principal properties of concrete aggregates with the aim of assisting in the selection of appropriate specification requirements.The essential requirement of an aggregate for concrete is that it remains stable within the concrete and in the particular environment throughout the design life of the concrete. The characteristics of the aggregate must not affect adversely the performance or cost of the concrete in either the fresh or hardened state.For both technical and contractual reasons, these requirements have to be defined quantitatively. This involves the selection of relevant tests and assessment procedures and the specification of appropriate acceptance criteria.