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For concrete carriageway, it is normally classified into two types: reinforced and unreinforced concrete pavement. The reinforcement in reinforced carriageway (in the form of mesh) is used for controlling cracking. Then one may query how unreinforced pavement can control cracking without the use of mesh reinforcement. To answer this question, one should pay attention to the features of unreinforced concrete pavement.
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The skid resistance of road surface is of paramount importance in enhancing road safety. The chance of occurrence of skidding is reduced with an increase of skid resistance.
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The slump of concrete carriageway is purposely specified to be a relatively low value, i.e. 30mm. For concrete carriageway, traffic loads directly act on concrete pavement surface and therefore the surface strength is detrimental to its future performance.
SMA contains high binder content and extreme care should be taken during the placing process of SMA. Multi-tyred rollers are not used in paving SMA because of the possible working of binder to the surface of the
SMA leading to flushing and pick-up.
Skid resistance of road pavement plays an importance role when vehicles take a bend or brake. The use of anti-skid dressing increases the friction to reduce the possibility of skidding. Anti-skid dressing refers to the road surface treatment which includes high-friction calcined bauxite as the high Polished Stone Value artificial aggregate, together with a resin (epoxy, polyurethane) instead of bitumen to tie the aggregate to the road surface. It is more expensive but is more durable in difficult sites such as crossing and roundabout. Moreover, it also has side benefits of good acoustic quality.
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Bitumen emulsions consist of particles of bitumen dispersed in water by using emulsifying agent. When the emulsion breaks, it represents a change from a liquid to a coherent film with bitumen particles coagulating
together. The sign of breaking is the change of colour from brown to black as the colour of emulsion and bitumen is brown and black respectively.
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Surface preparation of bituminous pavement is essential in proper application of tack coat. The entire surface has to be cleared of debris, dust and soils. Otherwise, the tack coat would stick to the debris left on the pavement instead of adhering to the pavement. When delivery or placement equipment is driven over tack coat, it tends to stick to the tire’s of the equipment instead of pavement.
Bleeding occurs in bituminous pavement when a film of asphalt binder appears on road surface. Insufficient air void is a cause of bleeding in which there is insufficient room for asphalt to expand in hot weather and it forces its way to expand to pavement surface. Too much asphalt binder in bituminous material is also a common cause of bleeding. Bleeding is an irreversible process (the bleeded asphalt on pavement surface would not withdraw in winter) so that the amount of asphalt binder on pavement surface increases with time.
Emulsified asphalt is a suspension of asphalt in water by using an emulsifying agent which imposes an electric charge on asphalt particles so that they will join and cement together. Cutback asphalt is simply asphalt dissolved in petroleum. The purpose of adding emulsifying agent in water or petroleum is to reduce viscosity of asphalt in low temperatures.
The colour of emulsion for tack coat is brown initially during the time of application. Later, the colour is changed to black when the asphalt starts to stick to the surrounding and it is described as “break”. For emulsified asphalts, when water has all evaporated, the emulsion is said to have “set”. Cutback emulsion is described to have been “cured” when the solvent has evaporated. There are several problems associated with cutback asphalts:
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