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Why are stone mastic asphalt used in heavily trafficked roads?

Stone mastic asphalt (SMA) developed in Germany in late sixties. It is characterized by having a high proportion of coarse aggregates that interlock to form a strong aggregate skeleton. Typical SMA composition
consists of 70-80% coarse aggregates, 10% filler and 6% binder.

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What are the differences between anionic emulsions and cationic emulsions?

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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Why is it necessary to ensure cleanliness of bituminous pavement before applying tack coat?

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.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

What is the significance of bleeding in bituminous 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.

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This question is taken from book named – A Self Learning Manual – Mastering Different Fields of Civil Engineering Works (VC-Q-A-Method) by Vincent T. H. CHU.

Should emulsified asphalts or cutback asphalts be selected as tack coat in bituminous roadworks?

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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