Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Patent
1998-03-23
2000-03-28
Wu, David W.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
524 66, 524 68, 524505, 524526, 524 63, 524 64, C08K 501
Patent
active
060433027
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an impact absorbing macadam suitable for roads, railways, synthetic sports pitches, atheletics tracks, children's safety surfaces and other applications.
Macadam, also called flexible pavement, is a combination of aggregate, which may be naturally occurring or may be crushed rock, and a binder which is usually a bitumen. It may be produced by raising the temperature of both components to 150.degree. C.-180.degree. C., and mixing so that the binder coats the surface of the aggregate. Alternatively, an emulsion of bitumen in water may be used instead of a hot binder, in which case the resulting macadam is referred to as a cold macadam or as emulsion macadam. Macadams are of a granular nature and employ predominantly a single or nominal sized aggregate, the size varying according to the requirement. For instance a macadam may be available with nominal aggregate sizes of 3 mm, 6 mm, 10 mm, 14 mm, 20 mm, 28 mm or 40 mm. The nominal sized aggregate may be combined with smaller sizes in varying proportions to provide an open textured, medium textured or dense macadam. The macadam is placed by hand raking or paving machine and is rolled.
The invention provides an impact absorbing macadam comprising from 10 to 75% by weight of particulate rubber having a particle size of up to 40 mm, from 25 to 90% by weight of an aggregate having a particle size of up to 40 mm and from 5 to 9% by weight of a polymer modified bituminous binder.
SUMMARY OF THE INVENTION
DETAILED DESCRIPTION OF THE INVENTION
The invention provides an impact absorbing macadam comprising from 10 to 75% by weight of particulate rubber having a particle size of up to 40 mm, from 25 to 90% by weight of an aggregate having a particle size of up to 40 mm and from 5 to 9% by weight of a polymer modified bituminous binder.
The impact absorbing macadam of the invention may have a void volume of from 5 to 25%, preferably 17%. The voids may be interconnected, that is allowing a natural path of drainage, the preferred range then being from 15 to 25%. The voids may alternatively be unconnected, that is having a continuous particle size distribution approximating to the maximum density curve, the preferred range then being from 5 to 20%. The macadam may be formulated so as to be open textured, medium textured or dense.
The particulate rubber may be virgin rubber or may be recycled rubber, for example that obtained by grinding used vehicle tyres. Preferably the macadam contains from 25 to 45% of the particulate rubber. The preferred particle sizes are up to 15 mm, and most preferably from 4 to 10 mm. Particulate rubber of different particle sizes may be used, but preferably 10 mm size particles are included.
The aggregate may be any aggregate conventionally used in the production of macadams, either naturally occurring or an industrial by-product. Coarse aggregates, which are those having particle sizes above 2.36 mm, may be included. These course aggregates are preferably of a particle size up to 15 mm. Most preferably the coarse aggregates are of sizes similar to those of the rubber particles used, and macadam according to the invention may contain more than one particle size, e.g. 10 mm aggregate and 6 mm aggregate. Fine aggregates, also known as sands, which are those having particle sizes above 75 microns but below 2.36 mm, may be included in amounts up to 35% by weight of a macadam according to the invention. Fillers, which are ultra-fine aggregates having particle sizes below 75 microns, must be included and may constitute up to 10% by weight of a macadam according to the invention.
The polymer modified bituminous binder comprises an elastomeric polymer, a plastomeric polymer or a mixture thereof in admixture with a compatible bitumen. Suitable polymers include unbranched styrene butadiene styrene block copolymer and styrene butadiene rubber. The binder most suitably constitutes from 6.5 to 7.5% by weight of a macadam according to the invention. The polymer preferably constitutes up to 11% by weight,
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Choi Ling-Siu
Wu David W.
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