6. Description and classification of aggregates
Published:January 01, 2001
The description and, in particular, the classification of aggregates in a manner appropriate to their use in the construction industry has long posed problems, not only of a scientific nature but also from practical and commercial points of view.
Naturally occurring rock materials can be classified in a variety of ways, the method chosen depending on the nature of the rock and the use for which the classification is required. Age, colour, fossil content, grain size, mineralogy, mode of formation and compressive strength are but some of the many approaches that have been used. The most common method is that developed from the classical geological approach, which is based essentially on the mode of formation. Hence natural rock material is divided into three main classes: igneous, sedimentary and metamorphic. These groups are then subdivided, principally on the basis of their mineralogy and texture.
The numerous subdivisions possible in this fundamental geological system inevitably results in a nomenclature which is too cumbersome for general use in the construction industry. As a consequence, various schemes have been developed to simplify the classification of aggregates, some intended for general use, others to meet specific purposes.
Some level of petrographic examination is necessary for virtually all classification schemes and a detailed petrological description can be helpful in assessing the performance of an aggregate and in detecting potentially deleterious substances.
This chapter reviews current classification schemes for natural aggregates and discusses their development. A recommended approach for classification is presented and procedures for the
Figures & Tables
Aggregates: Sand, gravel and crushed rock aggregates for construction purposes
In 1985, the Geological Society published Aggregates as the first volume in its Engineering Geology Special Publication series. It met with immediate acclaim, being awarded the Brewis Trophy by SAGA in 1986.
“If your work involves the use of aggregates, buy this book and read no further; this volume will be an essential and valuable reference that you will use for many years.” (Canadian Geotechnical Journal 1988)
In 1989, the working party whose work had resulted in the publication of Aggregates was reconvened to revise, update and extend their report. Each chapter was reviewed by independent referees. The second and greatly improved edition, published in 1993 and reprinted in 1998, represented the distillation of a vast body of knowledge and experience held not only by the members of the working party, but also by many international experts, scientists and engineers who contributed as reviewers, referees and corresponding authors.
Owing to continued demand for this unique reference book, a group of aggregate specialists was convened in 1999 in order to review thoroughly and update Aggregates for this third edition.
Outline of contents: Introduction; Occurrences; Field investigations; Extraction; Processing; Classification; Testing; Aggregates for concrete; Aggregates for mortar; Unbound aggregates; Bituminous bound aggregates; Rail ballast; Filter media; Appendix: Aggregate properties; Glossary; Index.
Working Party Members and/or third edition Reviewers: Mr L. Collis (formerly Sandberg); Professor P. G. Fookes (Chairman; consulting engineering geologist), Mr R. A. Fox (formerly RMC Aggregates (UK) Ltd), Professor G. P. Hammersley (formerly Laing Technology Group, now BRE), Mr P. M. Harris (formerly BGS), Dr I. E. Higginbottom (formerly Wimpey Environmental Ltd), Mr J. Lay (RMC Aggregates (UK) Ltd), Dr G. Lees (formerly University of Birmingham), Mr D. I. Roberts (Land and Mineral Resource consultants), Mr A. R. Roeder (formerly British Cement Association), Dr I. Sims (Secretary; formerly Sandberg, now STATS Limited), Dr M. R. Smith (formerly Imperial College, now the Institute of Quarrying), Dr R. G. Thurrell (formerly BGS), Dr G. West (formerly TRL).