SAPEM Chapter 2 - Sanral

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South African Pavement Engineering Manual Chapter 2: Pavement Composition and Behaviour 1. INTRODUCTION This chapter lays the foundation for the other chapters of SAPEM, and provides much of the background information required to understand the elements that go into pavement engineering. The chapter starts with the history of roads and continues with the basic principles of roads. The rationale behind the structures used for pavements, and typical pavement structures are presented, including the types and characteristics of materials used in typical pavements. A section on material science is included, to explain the concepts used when analysing pavement structures. The chapter ends with sections on climate, variability and life cycle strategy. Section 1: Introduction Page 1
South African Pavement Engineering Manual Chapter 2: Pavement Composition and Behaviour 2. HISTORY This section looks at the history of roads, from their development, to the history of pavement design. The necessity of roads is also discussed. 2.1 Development of Roads An understanding of how pavement technology evolved requires a look back into the historical developments of roads. In ancient times there was nothing more than a sparse network of tracks for humans to reach feeding and drinking places. These tracks differed only slightly from the tracks made by the movement of foraging animals. The primary difference was that obstacles, e.g., boulders, were removed from the more important routes and thorn bushes were trimmed back by humans. More elaborate lines of communication than these simple tracks did not appear until the number of humans in certain areas reached a stage where their social structures and networks demanded more permanent contact between communities. Roads thus appeared when groups of people started to interact with each other by travelling, doing business, fighting, and socializing. This occurred around 3500 BC. At this time, the invention of the wheel and development of chariots and wagons showed that the existing soil or subgrade on the interlinking routes was inadequate. Layers of better quality material were required to protect the subgrade, giving rise to the pavement structure. The earliest records of paved roads for wheeled traffic date from about 2200 BC in Babylonia (modern Iraq), in Crete from about 1500 BC and in Egypt from about 540 BC. In Europe, the first substantial roads were built by the Romans, with a network of more than 100 000 kilometres of road built between 400 BC and 400 AD. The Roman roads were cambered to shed rainwater and were constructed on a foundation of large stones with a wearing course of smaller stones and gravel, constrained between raised stone kerbs, as illustrated in Figure 1. Figure 2.2. Typical Roman Pavement Figure 1. Typical Roman Pavement (McCauley, 1974) The Romans were the best road builders of the remote ages. Conquests achieved through war games were one of the reasons for this. The Romans needed a good network of roads to control their conquered subject-nations. The army needed to be able to move fast to quell any revolting groups. The Roman roads were cobbled with a base system that was dependent on the subgrade. They developed a three or four layer system, illustrated in Figure 2, consisting of: Top layer Base, sometimes stabilised Subbase Subgrade Section 2: History Page 2
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SAPEM Chapter 2 - Sanral

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