ABSTRACT
This chapter discusses how pavements are constructed using simple equipment and local materials. Often the pavement and the subgrade are one and the same thing, with only the local vegetation and top-soil removed. Sands and clays sometimes make useful low-cost pavements but have major disadvantages. For example, sands are easily moved aside by wind, water and traffic and clays become soft and sticky when wet. If the pressure that a subgrade surface can withstand is less than that which would occur beneath the wheels of passing traffic, then a pavement of sufficient thickness must be provided to reduce the pressure on the subgrade. The process used to achieve the required shape is called grading, and graders were some of the earliest tools used by road-makers and remain in use today. A low-cost pavement in a region with available gravel might be suitable; however, gravels found in river beds and glacial drifts have been smoothed and rounded over many centuries. Such rounded stones are difficult to compact into a coherent and impermeable layer as they are easily pushed aside. This led to the more common use of broken (or crushed) stones. Most pavements were constructed in fertile areas where otherwise firm soil was quickly rendered impassable by the presence of water and the passage of previous travellers. As their moisture content increases, all soils lose strength and finally turn into fluid mud. Examples are given of pavements built in such circumstances.
