Highway Engineering

Structural Design of Pavement Thickness 249

Example 8.5

A continuously reinforced concrete pavement is to carry a traffic loading of

200 msa over its design life.

Estimate the required slab using:

(1) CRCP

(2) CRCR.

Give some surfacing options.

Solution

(1) Required reinforced concrete pavement thickness of 230 mm with 30

mm of thin wearing course system (TWCS)

(2) Required reinforced concrete base thickness of 210 mm with the 100 mm

of surfacing comprising either 45 mm hot rolled asphalt (HRA)

surface course overlaying 55 mm of dense bitumen macadam (DBM)

binder course or15 mm of TWCS overlaying 85 mm of DBM binder

course.

traffic on the highway, surfacing materials can significantly lower noise emis-
sions generated by vehicles. Thin wearing course systems can be significantly
quieter than concrete. It should be noted that, in England, rigid concrete con-
struction is not permitted unless it has an asphalt surfacing. ‘Rigid composite’
denotes continuously reinforced concrete roadbase (CRCR) with 100 mm of
asphalt surfacing. A thin wearing course can also be used with a binder course
making up the remaining part of the required 100 mm. If porous asphalt is used
over CRCR, it should be 50 mm thick over 90 mm of binder course, or 50 mm
thick over 60 mm of binder course with the concrete slab thickness increased
by 10 mm.
In both types of continuous slab, the reinforcement should be 60 mm below
the surface in order to limit the opening of cracks. Laps should be 50 times the
bar’s diameter. Longitudinal reinforcement in CRCP either without surfacing or
with a 30 mm thin wearing course system (TWCS) shall be 0.6% of the cross-
sectional area. The required diameter is 16 mm (deformed steel). Transverse
reinforcement shall be 12 mm in diameter, spaced at 600 mm centres. For CRCR
slabs, the longitudinal reinforcement shall comprise 0.4% of the cross-sectional
area, composed of 12 mm diameter deformed bars.
Figure 8.16 details the design thicknesses for both continuously reinforced
concrete pavements and continuously reinforced concrete roadbases.
It should be noted that these figures assume the existence of a 1 m edge strip.
If this is not available, the slab should be increased using Fig. 8.15.