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
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An 12 o C increase in placing temperature doubles the rate of reaction of
hydration. Hence, concrete placed at a higher temperature experiences a
higher rise in temperature. For instance, concrete placed at 32 o C produces
heat of hydration twice as fast when compared with concrete placing at
20 o C. Hence, high concrete placing temperature has significant effect to
the problem of early thermal movement.
21. What are the differences in method to seal moving cracks and
non-moving cracks in concrete?
In devising a suitable method to seal up cracks detected on concrete
surface, it is of paramount importance to determine if further movement
would be expected for the cracks. If the crack is not expected to move
further, it is sufficient to brush cement grout into it. For wider cracks, other
materials like latex-cement mixture may be considered for sealing the
crack.
When further movement is expected for the crack, seals wider than the
cracks are recommended to be applied over the crack in order to reduce
the strain around it to an acceptable level. Moreover, it is desirable to apply
the treatment when the cracks are widest so that the sealing material is not
subject to further extension. Care should be taken to prevent bonding of
sealing material with the bottom of the crack to ensure that only direct
tension forces are experienced in the sealing material.
22. What is the difference in functions between internal waterstop and
external waterstop? (J4)
External waterstops are applied externally on the structures and they
proved to be effective when installed on the face with a net clamping
pressure. For instance, external waterstops can be placed on the outer
face of a basement to guard against water entry into the basement.
Internal waterstops are applied internally within the thickness of concrete
and it is usually adopted when water pressure can act in both ways. They
proved to be effective measures to guard against water flow in both
directions but its success lies on the proper installation of waterstops inside
the concrete structure. For instance, the installation of waterstops inside
concrete slab encounters the problem of improper compaction of concrete
around the waterstops.
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