10. Aggregates in unbound pavement construction
Published:January 01, 2001
In highway and airfield pavements, aggregates are used in various types of unbound or bound materials (standard nomenclature for pavements as used in the United Kingdom is illustrated in Fig. 10.1). This chapter is concerned with both primary (naturally occurring) and secondary (artificial or recycled) aggregates which are not bound by cementitious or bituminous binders. Unbound layers are used in the UK mainly for sub-bases or capping, but elsewhere may be used for bases or, in the case of low volume roads, the whole structure. Cement bound aggregates are discussed in Chapter 8 and bitumen and tar bound aggregates are discussed in Chapter 11. Figure 10.2 shows bitumen macadam being laid over unbound sub-base.
Unbound layers in pavement construction may fulfil some or all of the following functions:
a working platform for construction;
a structural layer (load spreading and resistance to rutting);
a replacement for frost-susceptible subgrade (if necessary);
a drainage layer.
The main use in the UK is as sub-base for which (a) is probably the most important function. Guidance is given in Powell et al. (1984).
The ability to spread load (high stiffness) and to resist rutting (low permanent deformation) is usually associated with closely graded materials whereas open gradings are thought necessary for good drainage. The apparent conflict between these requirements has received considerable attention over recent years (Roy 1981; Jones & Jones 1989). These and other aspects of 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).