Aggregate for Bituminous Pavement

• Generally for bituminous or asphalt pavement, the aggregates constitute 88%-96% by weight or more than 75% by volume. The AASHTO standard specifications provide that:
• “The aggregate shall consist of hard, durable practices of fragments of stone or gravel and sand or other fine mineral particles free from vegetable matter and lumps or balls of clay and of such nature it can be compacted readily to form a firm, stable layers. It shall conform to the grading requirements shown in table 3 when tested by AASHTO T-11 and 27”.

Aggregate for Portland Cement Concrete Pavement

• The presence of organic impurities in the intended for concreting road pavement may cause slow or non-hardening of the concrete. Under AASHTO T-21 standard test, the aggregates is treated with a mixture of Sodium Hydrochloride Solution and when the treated aggregate turns dark, organic materials are said to be present in the aggregate.
• The strength of fine aggregate is measured by the compression tests of sand-cement mortar.
• Soundness of fine aggregate is measured by their resistance to deterioration under the action of solutions of Sodium or Magnesium Sulfate. The sodium sulfate test is five cycle. The maxinun loss under AASHTO specifications is 10%.
• For coarse aggregate the requirement consists of crushed stone, gravel, blast furnace slag, or approved inert materials of similar characteristics or combination thereof having hard, strong durable pieces free from adherent coatings.

Mineral Filler

• The strength of the road pavement will be increased if dust additives which denses the graded mixture is added. It is called mineral filler which reduces the void contents in the mixture. This dust additive is not the ordinary dust that is being found in our floor or tables.

Dust additive is classified into:

• Finely powered limestone
• Slag
• Hydrated lime
• Portland Cement
• Trap Rock Dust
• Fly Ash

Bituminous Material & Binder

Bituminous material or asphalt is a various (gelatinous) liquid used as binder for aggregates in road construction. At normal temperature, asphalt is either lightly thicker than water or hard but brittle material that breaks under a hammer blow when cold.

• Bituminous material is in liquid form when mixed or combined with aggregates. This liquid form maybe produced either by heating the hard asphalt, by dissolving in solvent or by emulsifying in water. However, there are bituminous liquid materials available and ready to use.
• The action of the asphalt binder depends on its type and the aggregate it is combined with. The purpose of the asphalt binder is to resist the abrasive force brought about by heavy traffic.
• If the pavement is of the open type, consisting entirely of coarse particles and asphalt, heavy binder is needed requiring more asphalt. On the other hand, if the aggregates on the pavement contains fine particles, cohesion will be developed by the surface tension in the thin asphalt film surrounding these fine articles hence, less viscous asphalt is required.

Bituminous Binder

• Asphalt cement is used as binder for almost high types of bituminous pavement. Asphalt cement is a semi-solid hydrocarbons retained after fuel and lubricating oils are removed from petroleum. The softest grade used for pavement is the 200-300 penetration and the hardest is the 60-70 penetration.
• Penetration refers to the consistencies of asphalt cement as describes under AASHTO T-49. It is the distance that a standard needle penetrates a sample under known conditions of loading time and temperature. Recently, the loading used in grading asphalt cement is viscosity test rather than the penetration test.
• Cutback or Liquid Asphalt
• The liquid asphalt is a petroleum product consisting of asphalt cement with a liquid distillate (diesel, kerosene or gasoline). The less viscous asphalt contains up to 50% diluents and the more viscous contains diluents as little as 15%.
• The use of cutback is being frowned for two reasons:
• It is a usable fuel.
• It is an air pollutant.
• Cutback or liquid asphalt is classified into:
• Slow curing (SC) road soils.
• Medium Curing (MC) cutback asphalt.
• Rapid Curing (RC) cutback asphalt.
• Emulsifield Asphalt is a kind of mixture wherein the minute globules or asphalt disperses in water. Asphalt content ranges from 55%-75% by weight. Emulsion could be applied or mixed at normal temperature, because when the water content evaporates the asphalt remains.