In many countries locally available granular materials are an important source for the base course and subbase in the construction of flexible pavements. On low-volume roads, these include fine-grained materials such as well-graded silty and clayey sands (sand-clay), coarse and medium-grained materials such as natural gravels, and materials produced by ripping and rolling rock. Many materials have been used that do not meet conventional selection criteria but still give satisfactory performance. Their choice is based on locally developed selection criteria, nonstandard testing, and attention to construction technique. Selection criteria are presented here for lateritic base course gravels (covering a wide range of climates), crushed lateritic caprock, limestone, and sand-clay. The criteria have been adapted from research in several countries and refined through experience and field research in Western Australia. Some techniques are suggested for low-volume roads to cope with large truck combinations on the basis of the experience of Western Australia, where some road trains have more than 20 axles. Nonstandard test methods include the Western Australia confined compression test accelerated triaxial test and chemical composition tests. Suggestions are made concerning the bitumen surfacing of some materials to improve seal adhesion. Adequate strength by itself is insufficient for the successful use of locally available materials, and attention to construction technique and workability is needed. Guidelines are given on issues such as winning (mining), curing, mixing, oversize and compaction, dry-back, and surface preparation before sealing.
Samenvatting