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
concrete structure. Moreover, the size of cover block should be minimized
so that the chances of water penetration to the periphery would be
reduced.
6. Do engineers need to cater for corrosion protection of lifting
anchors in precast concrete units?
The corrosion of lifting anchors in precast concrete units has to be
prevented because the corroded lifting units cause an increase in steel
volume leading to the spalling of nearby surface concrete. Consequently,
steel reinforcement of the precast concrete units may be exposed and this
in turns results in the corrosion of steel reinforcement and the reduction in
the load carrying capacity of the precast units. To combat the potential
corrosion problem, the lifting anchors could be covered with a layer of
mortar to hide them from the possible external corrosion agents.
Alternatively, galvanized or stainless steel lifting anchors can be
considered in aggressive environment.
7. What are the potential problems of excessive concrete covers?
(CS1)
In reinforced concrete structures cover is normally provided to protect steel
reinforcement from corrosion and to provide fire resistance. However, the
use of cover more than required is undesirable in the following ways [25]:
(i) The size of crack is controlled by the distance of longitudinal bars to the
point of section under consideration. The closer a bar is to this point,
the smaller is the crack width. Therefore, closely spaced bars with
smaller cover will give narrower cracks than widely spaced bars with
larger cover. Consequently, with an increase in concrete cover the
crack width will increase.
(ii) The weight of the concrete structure is increased by an increase in
concrete cover. This effect is a critical factor in the design of floating
ships and platforms where self-weight is an important design criterion.
(iii) For the same depth of concrete section, the increase of concrete cover
results in the reduction of the lever arm of internal resisting force.
8. Is mild steel or high yield steel suitable as lifting hoops in precast
concrete? (PC1)
The strength of high yield steel is undoubtedly higher than mild steel and
hence high yield steel is commonly used as main steel reinforcement in
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