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.
Awarded as the best online publication by CIDC
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.
Read More
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.
Read More
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:
Read More
The principal function of prime coat in bituminous pavement is to protect the subgrade from moisture and weathering. Since the presence of moisture affects the strength of subgrade, the prevention of water entry
during construction is essential to avoid the failure of the pavement. In cold countries, by getting rid of moisture from subgrade, the danger of frost heave can be minimized.
Read More
Longitudinal cracks in bituminous pavement are usually caused by fatigue failure under repeated traffic loading. In thin pavements, cracking starts at the bottom of the bituminous layer where the tensile stress is the highest and then it spreads to the surface as one or more longitudinal cracks. In thick pavements, the cracks usually commence from the top because of high localized tensile stresses from tire-pavement interaction. After repeated loading, the longitudinal cracks develop into a pattern similar to the back of an alligator.
Paver, steel-wheeled roller and pneumatic tire roller compact bituminous material by using the following principles:
(i) The static weight of the paving machines exerts loads on the bituminous material and compresses the material directly beneath the machine. The compacting effort increases with the period of contact
and larger machine weight.
Read More