Grouted Macadam: Material Characterisation for Pavement Design

Chapter 2 Review of “Traditional” Road Pavement Types and Design
cracks across the full width of a slab. According to the Highways Agency (1994b),
the width of cracks in concrete pavements may be classified in three categories:
(i) narrow cracks (< 0.5 mm wide – full aggregate interlock and load transfer);
(ii) medium cracks (between 0.5 and 1.5 mm – partial load transfer, permits ingress
of water); (iii) wide cracks (>1.5 mm – no load transfer, permits ingress of water and
fine detritus).
In contrast to flexible pavements, rutting is not applicable to rigid pavements, due to
the rigid behaviour of concrete. Thus, the degradation of rigid pavements is normally
by thermal or traffic induced cracking or settlement of the concrete slabs. This last
case is a result of problems at the level of the subgrade, namely movement
(pumping) of fines, due to the presence of water, and consequent settlement.
A well-designed and properly constructed concrete road has the potential for a very
long structural life with low maintenance costs. Experience shows that such a road
designed for a 40-year life is in fact likely to have a much longer structural life,
although a renewable bituminous overlay may be necessary to maintain adequate
skid resistance (Croney and Croney, 1991). However, rehabilitation of localised
distress of concrete pavements (shallow spalling, loss of joint seal) is usually more
costly and difficult, compared with flexible pavements, since it is necessary, in many
cases, to do a full depth repair. This situation is even more difficult in continuously
reinforced pavements due to the large quantity of heavy steel reinforcement in the
slab.
When a rigid pavement reaches the end of its life, it may be overlaid with new
concrete or bituminous layers, after being cracked and seated, or removed, crushed
and re-used as a base (Darter, 1992). A concrete pavement overlaid with bituminous
layers is referred as a semi-rigid (or composite) pavement.
2.2.3 Semi-rigid Pavements
A semi-rigid pavement is normally composed of a cementitious base and a
bituminous surface (Figure 2.8). Depending upon the material used as a base, the
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