Portland cement concrete is considered to be "rigid pavement". Usually the pavement is between 150 - 300 mm thick depending on the volume and weight of the trucks expected to be using it. The advantage of concrete pavement is that it is not subject to "rutting" which is a common problem with asphaltic pavements at higher temperatures. Because of this, concrete highways are common in parts of the USA which are subject to extremely high temperatures. In many cases it becomes a question of cost and an estimate of durability as concrete is generally more durable than asphalt, particularly for roads carrying a lot of heavy truck traffic. The new 407 highway in Toronto was paved with concrete. Most airports use concrete in building their runways as asphalt pavement would not be strong enough. Asphalt pavement is also not appropriate in any location where fuel might get spilled because the fuel dissolves the asphalt.
Except for long-span bridges and moving bridges such as swing bridges and bascule bridges where reduced weight is important, almost all bridge decks are concrete. Those bridge decks that are not made of concrete would be steel that would sometimes be covered with asphalt pavement. Concrete bridge decks are also often covered by asphalt pavement. Continuous Concrete Pavement As the concrete dries, shrinkage occurs which can result in cracking. Concrete is also subject to changes in volume due to temperature changes. In order to control cracking due to volume change, joints are placed at regular intervals along the roadway by cutting the concrete to a certain depth using an abrasive circular saw. Then if contraction occurs the crack will be along the joint. Unfortunately these joints can be felt and even heard as the vehicle passes over them. Continuously Reinforced Concrete Pavement This type of concrete pavement doesn't require joints. A layer of steel bars is placed half way in the slab of concrete. Now when the cracks appear because of shrinkage and volume changes, the longitudinal steel absorbs the tension and the cracks are held tightly closed. No water can get through. This method allows the use of very large continuous slabs of concrete although room for expansion and contraction of the concrete must be left at both ends of the pavement. Environmental Considerations
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