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.
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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.
This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.
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