Isolation joints are introduced where the pavement contains manholes and other structures. The joints allow independent movement of the pavement and roadside structures without any connection which otherwise could result in damage.
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Isolation joints are introduced where the pavement contains manholes and other structures. The joints allow independent movement of the pavement and roadside structures without any connection which otherwise could result in damage.
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There is an optimum time to saw contraction joints in new concrete pavement. Sawing cannot be carried out too early because the saw blade would break out particles from pavement and this results in the formation of jagged and rough edges. Such raveling is undesirable as it would impair the appearance and the ability to seal the joint properly.
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The stress induced in acute angle corners of concrete pavement is far much higher than that in right-angle corners of the pavement. For instance, concrete pavement corner of acute angle of 70o induces stresses about 50% more than the stress induced by an angle of 90o. As a result, corners of concrete pavement should not be designed with acute angles to avoid corner cracking. If it is necessary to adopt acute angles for concrete pavement, special reinforcement has to be provided to strengthen these corners.
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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.
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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.
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Subbase serves the following functions in a concrete pavement:
(i) Aid in spreading load of road traffic.
(ii) Prevent pumping of fines from subgrade.
(iii)Protect the subgrade from frost.
(iv) Improve drainage of the pavement structure so that the pavement structure is mostly dry with minimum moisture.
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There are two schools of thought regarding the suitability of bonding between lean concrete base and concrete slab. The first one considers it undesirable to bond them together to minimize reflection cracking in the slab. In essence, bonding would cause cracks in lean concrete base to reflect through the concrete slab which may lead to premature cracking. Hence, bond breaking is achieved by applying wax curing compounds on lean concrete bases.
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When the California Bearing Ratio of subgrade is checked to be below a certain percentage (e.g. 5%), a capping layer is normally provided to reduce the effect of weak subgrade on the structural performance of the road.
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The surfaces of sub-base material for concrete carriageway should be constructed in a regular manner because of the following reasons:
(i) One of the main functions of sub-base in concrete pavement is to provide a smooth and even interface between concrete slab and subgrade so that a uniform support is established. A regular surface of
sub-base assists in reducing the frictional and interlocking forces between concrete slab and sub-base and allowing easier temperature and shrinkage movement.
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