Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1993-07-26
1995-07-25
Szekely, Peter A.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
521 41, 521 455, 524 71, C08L 9500
Patent
active
054362857
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
This invention relates to a composition and method of manufacturing asphalt having improved performance characteristics. In particular, this invention relates to a paving composition comprising recycled crumb rubber in a polymer modified asphalt and a method of making same.
BACKGROUND OF THE INVENTION
Asphalt is the principal material used for constructing roads. A standard mix of asphalt generally comprises approximately 94% grade aggregate and 6% asphalt cement. The standard mix is prone to rutting and cracking. While the standard mix is initially low in cost, it has a high maintenance cost and it contains no recycled materials.
Many attempts have been made to improve the wear characteristics of the roads. Materials such as polyethylene, glass, sand and drywall have been added to the asphalt to improve its characteristics. The use of these materials and their ineffectiveness is widely known and documented.
Previous attempts have failed to differentiate between the problems associated with rutting, ductility, tensile strength, elasticity and adhesion, referred to as the polymer related properties and the problems associated with post compaction rutting and durability, referred to as aggregate related.
Styrene Butadiene Rubber latex (SBR) has been added to asphalt for road construction. A polymer modified mix generally comprises approximately 94% graded aggregate, 5.76% asphalt cement and 0.24% polymer, either SBR or an equivalent polymer such as the polymers available under the trademarks KRATON SBS, STYRELF SBS, GOODRICH and BASF SBR and DUPONT EVA.
The addition of SBR to the asphalt results in improved crack resistance and heat rutting resistance over the standard mix of asphalt. However, the addition of SBR does not have a significant effect on the polymer modified asphalt's ability to resist post compaction rutting. Further, although the polymer modified asphalt is low in maintenance, it is expensive to manufacture and does not contain any recycled materials.
Attempts have been made to add rubber to the standard asphalt mix. A rubber modified mix generally comprises approximately 90% grade aggregate, 7% asphalt cement and 3% rubber.
The rubber modified asphalt contains recycled material and has good post compaction characteristics. However in practise, the rubber modified asphalt fails frequently, has a high rate of maintenance since it exhibits poor aggregate adhesion, poor heat rutting and poor crack resistance characteristics.
The addition of rubber to asphalt hash not been satisfactory since there are three major disadvantages in using rubber in asphalt. First, fine rubber melts during processing diminishing its desired aggregate enhancing properties. Second, porous rubber absorbs the asphalt cement thus reducing the asphalt's ability to bond the aggregate. Third, if the grade of rubber is too large processing of the asphalt can become difficult.
Traditionally, asphalt is manufactured by heating and mixing the components together to form a slurry which can be deposited onto a road surface for compaction. However, the mere addition of rubber in a polymer modified asphalt (as illustrated in EP-A-0 049 485 and FR-A-2 580 658) using the traditional method does not produce suitable results.
SUMMARY OF INVENTION
The disadvantages of the prior art may be overcome by adding graded crumb-rubber to a polymer modified asphalt. In particular, the disadvantages of the prior art may be overcome by using a paving composition comprising graded aggregate, asphalt cement, polymer and graded recycled crumb rubber.
It is also desirable to manufacture a polymer modified asphalt including a graded recycled crumb rubber by preparing an aggregation of asphalt and polymer and heating the aggregation, adding and mixing a graded recycled crumb rubber into the aggregation prior to depositing the paving composition onto a road surface for compaction as pavement.
According to one aspect of the invention, there is provided a composition comprising between 89-93% graded aggregate, 5.76% asphalt cement,
REFERENCES:
patent: 3338849 (1967-08-01), Johnson
patent: 4381357 (1983-04-01), von der Wettern et al.
patent: 4427376 (1984-01-01), Etnyre et al.
patent: 4588634 (1986-05-01), Pagen et al.
Causyn David
Thys Krystina
Fors Arne I.
Horne D. Doak
Imai Jeffrey T.
Szekely Peter A.
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