The Shell Bitumen Handbook was originally published in 1990, rapidly becoming a key reference document for all in the asphalt industry. It gave engineers an understanding of the bitumen and bituminous materials used in highway pavement construction. It also provided a key reference book for students. The comprehensive index in this new edition demonstrates the major technical changes that have since occurred in the industry in the UK and in the USA with the strategic Highway Research Programme (SHRP); the increasing use of polymer modified and emulsion binders; the complete eclipse of Hot Rolled Asphalt by design mix macadam and Thin surfacing; and use of the Nottingham Asphalt Tester (NAT) for mix property determination. Other test methods have also been updated and terminology changed to match current Europeanisation of British Standards, including the latest aggregate standards.

There has been a significant increase in the use of polymer-modified binders, so it is not surprising that the new volume lists a total of 43 as 'Some addititves used to modify bitumen' and the effect of these on bitumen is well covered. However, the table of benefits claimed uses references from the 1980's; additional work has been done and some performance improvements have been measured on macadam as against 'asphalt' mixtures, and these could have been referred to.

In addition there is now a much longer track record of the use of polymers, which should enable durability to be better defined. The properties of so-called 'Multigrade' binder together with other Shell modified binders are considered; these have worked well in HRA over 15 years. Whether they are as effective with the leaner mixes in macadams remains unexplained.

The section on pigmented binders has been expanded to cope with increased demand by the public for these materials for aesthetic and safety use, and new 'fuel resisting' binders are included. This chapter reminds us that it is a book written by Shell, not simply sponsored by it.

Surprisingly, the section on the cost performance of modified binders remains identical to its predecessor 13 years ago. The recycling of old asphalt (RAP) has now become commonplace. Whilst the descriptive text in this volume about recycling is almost identical to 1990, the more detailed information, on tests for and effects of bitumen ageing and hardening, adhesion, and the influence of bitumen and aggregate properties on the performance of asphalt, is all vital background knowledge for engineers.

The new section of foamed bitumen is particularly welcome. Nonetheless, the statement that 'it cannot be objectively regarded as being equivalent to traditional hot mixed asphalts' is unduly pessimistic. The principal barrier to the introduction of foam bitumen mixtures has been the significant capital investment in hot-mix capability by major suppliers rather than any technical issues.

Most of the asphalt used in maintenance today is HAPAS approved proprietary Thin Surfacing. The essential details and properties for Thin Surfacing have been described directly and by reference. Fatigue resistance, including resistance to reflective cracking, are essential properties and the handbook describes how the properties of the bitumen, probably polymer modified, can affect this performance characteristic beneficially. Surprisingly, it does not even mention the beneficial use of thick polymer modified, glass fibre or geotextile reinforced bond costs as Stress Absorbing Interlayers (SAMI)

The surface dressing section has been expanded and includes a welcome analysis of the relative benefits of cut-back and emulsion binders. The handbook is particularly effective in describing test methods for the properties of bitumen and bituminous mixtures. It also provides easy to read introductions to the manufacture and laying of asphalt pavements and their design, and provides all necessary references for further reading.

The original volume was essential for the bookshelf of all highway engineers. This updated volume is similarly valuable and a worthy successor. It takes its place with pride amongst a very small canon of texts for highway and asphalt professionals and students of the subject.

Transportation Professional, July/August 2003