GB2086401A

GB2086401A - Asphalt composition

Info

Publication number: GB2086401A
Application number: GB8033705A
Authority: GB
Original assignee: ECC Quarries Ltd
Current assignee: Camas UK Ltd
Priority date: 1980-10-20
Filing date: 1980-10-20
Publication date: 1982-05-12

Abstract

An asphalt composition of good stability and good flexibility for surfacing roads, airfield runways and other paved areas, comprises mineral material, such as coarse and/or fine aggregates and/or a filler, and a binder which comprises an intimate mixture of an asphaltic cement, such as bitumen, a mixture of bitumen and coal tar pitch or a mixture of bitumen and lake asphalt, and from 1% to 20% by weight, based on the weight of asphaltic cement, of chopped glass fibres which are conveniently between 5 mm and 25 mm in length.

Description

SPECIFICATION Asphalt This invention concerns asphalt suitable for surfacing roads, airfield runways and other paved areas.

Asphalt is a general term for certain mixtures of asphaltic cement and mineral matter. The asphalt cement is generally bitumen, a mixture of bitumen and coal tar pitch, or the product resulting from a mixture of lake asphalt and bitumen and has the effect of binding together the mineral matter to form a coherent, semi-solid mass.

The mineral matter generally comprises a coarse aggregate, a fine aggregate and a filler. The coarse aggregate may be crushed rock, gravel or crushed siag of particle sizes in the ranged from 5mm to 50mm. The fine aggregate may be sand or the product of finely crushing any of the materials which are suitable for coarse aggregates or a mixture of any two or more thereof and generally consists of particles of sizes in the range from 75 microns to 5mm. The filler may be Portland cement or ground limestone and substantially all of its particles are smaller than 75 microns.

An important property which asphalt should possess, especially when it is to be used for the wearing course of a road on which severe traffic conditions are expected, is its stability or resistance to deformation under load. The stability of an asphalt composition is measured according to a procedure which is set forth in British Standard Specification No. 594:1973 "Rolled asphalt (hot process) for roads and other paved areas".

A cylindrical specimen of the composition to be tested is formed at a temperature which varies within the range from 12200 to 1520C according to the nature of the asphaltic cement used, by pouring into a mould of internal diameter 101 .6mm sufficient of the fluid composition to form a cylinder which, after compaction, has a height of 63.5mm. The sample is compacted by allowing a weight of 4.535 kg., sliding on a vertical column, to fall 50 times through a height of 457mm on to a steel disc-shaped foot which is in contact with the upper surface of the asphalt sample in the mould. The mould containing the sample is then reversed end-to-end and the weight is allowed to fall 50 more times with the foot in contact with the opposite surface of the sample.The mould containing the compacted sample is then allowed to cool and the cold sample is ejected from the mould. The sample is stored for at least 1 6 hours at ambient temperatures before testing. Immediately before testing the sample is immersed in a water bath at 600C for from 45 to 75 minutes and is then removed from the water and placed on its edge on a semi-cylindrical lower jaw of a testing head which is heated to 600 C. A semi-cylindrical upper jaw, also heated to 600C, is then placed on the upper edge of the sample and the upper and lower jaws are biased together at a rate of 50.8mm/min.

and the applied force is continuously monitored.

The maximum force in newtons is recorded as the stability of the sample.

Another important property of asphalt for surfacing roads and the like is flexibility.

This property is especially valuable when asphalt is used to resurface an existing concrete road, because the slabs of a concrete road frequently become deformed near the joints and the joints themselves become defective with the result that a layer of asphalt laid over such a surface will crack in the vicinity of the joints if the asphalt lacks sufficient flexibility.

Many attempts have been made to provide an asphalt composition which is both flexible and of good stability. It is known, for example, to modify the asphaltic cement by adding thereto a thermoplastic material such as a copolymer of ethylene and vinyl acetate, but such materials are very expensive. The asphaltic cement may also be improved by incorporating sulphur therein, but at temperatures in excess of 1550C a sulphur containing a'sphaltic cement would give off hydrogen sulphide gas which is extremely hazardous and unpleasant.

Accordingly, a first aspect of the invention provides an asphalt composition for surfacing roads, airfield runways and other paved areas comprising mineral material and a binder wherein the binder comprises an intimate mixture of an asphaltic cement and from 1% to 20% by weight, based on the weight of the asphaltic cement, of chopped glass fibres.

The mineral material comprises a coarse aggregate and/or a fine aggregate and/or a filler, all in accordance with British Standard Specification No. 594:1973.

The asphaltic binder may be, for example, bitumen, a mixture of bitumen and coal tar pitch or the product resulting from a mixture of lake asphalt and bitumen.

The weight of chopped glass fibres mixed with the asphaltic cement is preferably in the range of from 2.5% to 10% by weight, based on the weight of the asphaltic cement.

The chopped glass fibres may conveniently be between 5mm and 25mm in length.

A second aspect of the invention provides a process for preparing an asphalt composition wherein glass fibres are chopped and intimately mixed with an asphaltic cement and the intimate mixture is asphaltic cement and chopped glass fibres is then mixed with mineral material.

Conveniently the glass fibres are fed in the form of a rope to chopping means mounted above a mixing vessel in which the chopped glass fibres are intimately mixed with the asphaltic cement.

Advantageously the glass fibres are treated with a surface active agent before being mixed with the asphaltic cement in order to facilitate wetting of the glass fibres by the asphaltic cement.

It has been found to be essential to mix the chopped glass fibres with the asphaltic cement before the asphaltic cement is mixed with the mineral material. Satisfactory results are not obtained if the chopped glass fibres are mixed with asphaltic cement simultaneously with the mineral material.

Claims

1. An asphalt composition for surfacing roads, airfield runways and other paved areas comprising mineral material and a binder, wherein the binder comprises an intimate mixture of an asphaltic cement and from 1% to 20% by weight, based on the weight of the asphaltic cement, of chopped glass fibres.

2. An asphalt composition according to Claim 1, wherein the weight of chopped glass fibres is in the range of from 2.5% to 10% by weight, based on the weight of the asphaltic cement.

3. An asphalt composition according to Claim 1 or 2, wherein the chopped glass fibres are between 5mm and 25mm in length.

4. A process for preparing an asphalt composition wherein glass fibres are chopped and intimately mixed with an asphaltic cement and the intimate mixture of asphaltic cement and chopped glass fibre is then mixed with mineral material.

5. A process according to claim 4, wherein the glass fibres are fed in the form of a rope to chopping means mounted above a mixing vessel in which the chopped glass fibres are intimately mixed with the asphaltic cement.

6. A process according to claim 4 or 5 in which the glass fibres are treated with a surface active agent before being mixed with the asphaltic cement.