Principles of Pavement Engineering


Principles of Pavement Engineering

When all is said and done, the pavement industry deals in high-volume, low-cost
materials. In the UK alone, there are approximately 14 000 km of trunk road and
motorway with a surface area of some 250 km2, around 10% of which has to be
resurfaced each year. In the USA, this figure can be multiplied by about six. And
these are not figures that can be dramatically reduced while motor vehicle transport
remains such a key factor in the economy. The choice of materials is, therefore,
limited to those that can be easily and cheaply produced in large quantities – which
inevitably means the raw materials of the earth, namely rock, sand and clay. Any additive
used to give extra quality – such as bitumen or cement – has to be used relatively
sparingly; otherwise society just could not afford it – to say nothing of the environmental
cost of such additives. The job of the pavement engineer, therefore, is to maximise the
potential of these cheap, readily-processable materials. The unit cost of the bulk
materials may be relatively low, but the quantities required are very high indeed,
which means that a modest saving per square metre can multiply up to a very substantial
saving overall. To put it another way, if the life of a road pavement can be extended by
10%, this represents a very large contribution to the local economy

***The long history of the paved highway

It is impossible to know where or when the wheel was invented. It is hard to imagine that
Stone Age humans failed to notice that circular objects such as sections of tree trunk
rolled. The great megalithic tombs of the third millennium BC bear witness to ancient
humans’ ability to move massive stones, and most commentators assume that tree
trunks were used as rollers; not quite a wheel but a similar principle! However, it is
known for certain that the domestication of the horse in southern Russia or the
Ukraine in about 4000 BC was followed not long afterwards by the development of
the cart. It is also known that the great cities of Egypt and Iraq had, by the late third
millennium BC, reached a stage where pavements were needed. Stone slabs on a
rubble base made an excellent and long-lasting pavement surface suitable for both
pedestrian usage and also traffic from donkeys, camels, horses, carts and, by the late
second millennium BC, chariots. Numerous examples survive from Roman times of
such slabbed pavements, often showing the wear of tens of thousands of iron-rimmed
wheels. Traffic levels could be such that the pavement had a finite life

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