Posts by Kanwarjot Singh

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 70^o induces stresses about 50% more than the stress induced by an angle of 90^o. 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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A layer of waterproof (or separation) membrane is normally placed between sub-base and concrete slab for the following reasons:

(i) It prevents the loss of water from cement paste which affects the strength of concrete slab.
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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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For weak and poor quality subgrade, there is a need to increase the thickness of pavement to compensate for it. In order to save cost for sub-base which is relatively expensive, the concept of capping layer is
introduced in which capping materials of cheap but strong nature are used to cap the weak subgrade. In this way, the thickness of expensive subgrade is not required to be increased.

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Basically, sub-base for a concrete carriageway is provided for the following reasons:

(i) It provides a smooth and even surface between the subgrade and concrete slab. This avoids the problem of uneven frictional stresses arising from the uneven interface under thermal and shrinkage movement. It also improves the uniformity of support provided to concrete slab to enhance even distribution of wheel load to the subgrade.
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