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
Level Two (Advanced FAQs)
Part I: Road Joints
1. Which joint sealant is better, acrylic, polysulfide, polyurethane or
silicone? (RJ1)
There are four generic types of joint sealant with high performance. Their
properties are highlighted in the following table:
Acrylic Polysulfide Polyurethane Silicone
Accommodate
12%
movement.
Exhibit
shrinkage
upon curing
Solvent-based.
Poor recovery
in high cyclic
movements
Exhibit
excellent
chemical
resistance
Good
performance
in submerged
conditions.
269
Accommodate
50%
movement.
Excellent
bonding, can
be used
without primer
Good UV
resistance
Accommodate
50%
movement.
Excellent low
temperature
movement
capability
Excellent UV
and heat
stability
2. Can joint sealant provide a perfect watertight seal in joints? (RJ1)
The two main principal functions of joint sealant are to minimize the entry of
surface water and prevent the ingress of incompressible material from
entering the joint. Other minor function of joint sealant is to reduce the
possibility of corrosion of dowel bar by the entrance of de-icing chemicals.
Water entry into joints is undesirable because it leads to the softening of
subgrade and pumping of subgrade fines under heavy traffic. However, it is
impractical to maintain a completely watertight pavement structure. In fact,
vacuum tests show that no sealants could provide 100% watertight seal.
The current philosophy to combat water ingress into joints is only to
minimize but not to completely prevent water from entering the pavement
structure. Instead, a permeable subbase is designed to remove water from
the pavement.
3. In expansion joints why are plastic sleeve normally used in dowel
bars instead of debonding agent? (RJ2)
The purpose of plastic sleeve or debonding agent around dowels bars in