A Self-Learning Manual - Institution of Engineers Mauritius

A Self-Learning Manual
Mastering Different Fields of Civil Engineering Works (VC-Q&A Method) Vincent T. H. CHU
Cement-treated bases are easy to construct and provide a stronger and
more erosion-resistant platform for the concrete slab when compared with
granular subbase. They are normally used for medium to high traffic loads.
However, tensile stresses arising from temperature curling would be
significantly increased by the presence of lean concrete subbase as
compared to granular subbase. Moreover, there is an increase in frictional
resistance between concrete slab and subbase.
Granular subbase is susceptible to erosion and it retains moisture for long
periods. They are normally used only for roads with low to medium traffic
loads.
16. Why does “pumping” sometimes occur at joints in concrete
carriageway?
Pumping at joints in concrete carriageway occurs in the presence of the
following factors:
(i) Fine-grained subgrade;
(ii) Seepage of water into subgrade due to improper or inadequate
drainage design;
(iii) The presence of heavy vehicular loads.
It involves the pumping out of water-borne particles of the subgrade owing
to the deflections at the end of concrete slab. The first mechanism of
pumping involves the softening of subgrade by water and the reduction in
bearing capacity. It causes a larger instantaneous deflection at the slab
ends under heavy traffic loads. During deflection, water containing fine soil
particles is pumped out at the joints. Consequently, voids are formed in
subgrade region and the void size grows by repeating the above sequence
[21].
17. What are the potential problems in corners for concrete pavement?
(PS8)
Consider a panel of concrete slab without any load transferring devices at it
edges. When the concrete panel is subjected to traffic loads, the maximum
stress induced in the concrete panel is at its four corners. Other than panel
corners, the next significant stress induced in concrete slab is its four
edges.
To avoid the structural failure of concrete pavement, one can locally
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