GB2087407A - Bituminous compositions - Google Patents

Abstract

Bituminous-compositions having good energy absorbing properties contain bitumen, hardened extract, finely divided particles of crosslinked non-thermoplastic rubber and a filler, the amount of finely divided particles of crosslinked non-thermoplastic rubber by weight being equal to or greater than the amount of filler by weight, and the bitumen being a rubberised bitumen in which the rubber is a non-thermoplastic copolymer of at least two mono alpha olefins and a cyclic olefin having an endocyclic bridge and at least two olefinic double bonds. The compositions can be formed into sheets or slabs using rubber compounding equipment and are suitable for use as safety surfaces e.g. children's playgrounds.

Description

SPECIFICATION Bituminous composition This invention relates to a composition containing bitumen and rubber having energy absorbing properties and suitable for use, for example, as a safety surface for children's playgrounds.

Various compositions containing bitumen and rubber have been proposed with greater or lesser energy absorbing properties. In particular compositions containing bitumen, a thermoplastic rubber and a non-thermoplastic rubber have been proposed. For example, Published British Patent Application No.

2036760A relates to a bituminous composition having energy absorbing properties which comprises bitumen, hardened extract, a thermoplastic rubber, finely divided particles of a non-thermoplastic rubber and a filler, in which the amount of non-thermoplastic rubber is equal to or greater than the amount of filler by weight.

Although a thermoplastic rubber is a required component of the bituminous composition prepared according to Published British Patent Application No. 2 036 760A, the applicants have surprisingly discovered that bituminous compositions having similar properties can be prepared by using a bitumen rubberised with a non-thermoplastic rubber in place of the bitumen and thermoplastic rubber. The use of a rubberised bitumen also reduces the amount of mixing and/or preblending required during the production of the energy absorbing compositions which can therefore be produced more economically.

According to the present invention, a bituminous composition having energy absorbing properties comprises bitumen, hardened extract, finely divided particles of crosslinked non-thermoplastic rubber and a filler, the amount of finely divided particles of crosslinked non-thermoplastic rubber by weight being equal to or greater than the amount of filler by weight, in which composition the bitumen is a rubberised bitumen, the rubber of the rubberised bitumen being a non-thermoplastic copolymer of at least two mono alpha olefins and a cyclic olefin having an endocyclic bridge and at least two olefinic double bonds.

The energy absorbing compositions of the present invention preferably contain the following proportions by weight: Rubberised bitumen 100 parts Hardened extract 4-40 parts Crosslinked non-thermoplastic rubber particles 50-175 parts Filler 50-175 parts The compositions may also contain a long chain hydrocarbyl amine (e.g. octadecylamine) in an amount of 0.05-5 parts by weight and preferably 0.1-0.5 parts by weight (based on the weight of rubberised bitumen) to assist in the mixing and milling of the composition.

The amount of crosslinked non-thermoplastic rubber given above is the amount of finely divided particulate rubber and exciudes the non-thermoplastic rubber present in the rubberised bitumen.

Rubberised bituments in which the rubber is a non-thermoplastic copolymer of at least two monoalpha olefins and a cyclic oiefin having an endocyclic bridge and at least two double bonds are known, The olefins may be ethylene and propylene and the cyclic olefin may be dicyclopentadiene or ethylidene norbornene, such rubbers are commonly known as EPDM rubbers.

To ensure homogeneity between the rubber and the bitumen, the copolymer may be incorporated into the bitumen by blowing the copolymer with an aromatic flux oil at 1 50 to 300CC in the presence of a gas containing elemental oxygen. The mixture to be blown may include all or a proportion of the bitumen. If there is no bitumen in the mixture to be blown or only a proportion then the blown product is blended with unblown bitumen as required. Suitable rubberised bitumens may be prepared according to the methods disclosed in British Patent Nos. 1304238, 1325847, 1327535 and 1385006.

British Patent No. 1 304238 claims a method of preparing a bituminous composition, suitable for use as a roof surfacing material in which a mixture of: 23-88% wt, based on the total mixture, of a bituminous substance, 225% wt, based on the total mixture, of a copolymer of at least two mono alpha olefins and a cyclic olefin having an endocyclic bridge and at least two olefinic double bonds, 1075% wt, based on the total mixture, of a flux oil for extending the copolymer, 0--4 parts by weight sulphur per 100 parts by weight of the copolymer, and 03% wt, based on the total mixture, of a polyolefin, is blown with a gas which contains elemental oxygen at a temperature of 1 50 to 3000C.

British Patent 1325847 relates to a process for the production of a bituminous composition which comprises blending a bituminous substance, a copolymer of one or more mono alpha olefins and a cyclic olefin having an endocyclic bridge and at least two olefinic double bonds, an aromatic flux oil and possibly sulphur, and then blowing the blend at 1 50-2600C with a gas which contains elemental oxygen to form a concentrate and then dissolving the concentrate in unblown bitumen.

British Patent 1327535 claims a process for the production of a bituminous composition in which a mixture of: 10-85% wt, based on the total mixture, of a bituminous substance, 525% wt, based on the total mixture, of a copolymer derived from ethylene, propylene, and a cyclic olefin having an endocyclic bridge and at least two olefinic double bonds, and 1085% wt, based on the total mixture, of a flux oil for extending the copolymer, is blown at 1 80-2600C with a gas which contains elemental oxygen, the elastomer being in the latex form when added to the bitumen.

Finally, British Patent No. 1385006 describes a process for the production of a bituminous composition in which a mixture of an aromatic flux oil, an elastomeric copolymer of one or more alpha olefins and an unsaturated hydrocarbon with more than one olefinic double bond and an endocyclic bridge comprising one or more methylene groups and optionally up to 10 parts by weight sulphur per 100 parts of the elastomeric copolymer are blown with an oxygen containing gas at a temperature in the range 1 50-2600C to form a concentrate which is then dissolved in unblown bitumen.

The preferred processes for producing a rubberised bitumen for use in compositions according to the present invention are those described in British Patent Nos. 1304239 and 1325847.

Suitable rubberised bitumens include those sold by Deutsche BP AG under the trade name "Olexobit." The finely divided particles of crosslinked non-thermoplastic rubber may, for example, be finer than 20 mesh BSS. The rubber may be vulcanised rubber, for example, a synthetic rubber, e.g. SBR or polybutadiene or natural rubber. The rubber may be oil extended and/or filled and may be a material produced as a by-product in the manufacture of rubber articles, e.g. tyre crumb, which is the buffings produced when smoothing tyre treads.

The finely divided particles of a crosslinked non/thermoplastic rubber are not believed to blend with the rubberised bitumen but to remain as discrete particles which act to stiffen the composition.

Any of the normal fillers for bituminous compositions may be used. They may be fibrous but are preferably powdered. Examples of suitable fillers are; powdered limestone, silica, alumina, Portland cement, barytes, pulverised fuel ash, talc and asbestos fibres. The presence of a small amount of talc has been found beneficial during the mixing and the filler may include 1-20 parts by weight, based on the total mixture of talc added at the mixing stage.

The hardened extract may be produced by blowing a petroleum extract with an oxygen containing gas, preferably air, at 250-3500C either in the absence or presence of a catalyst, e.g. a Friedel Crafts metal halide such as ferric chloride. Petroleum extracts are obtained by the solvent extraction of distillate petroleum fractions boiling in the lubricating oil range, i.e. 350-6000C and contain a major proportion of aromatic hydrocarbons.

The blowing of the extract is believed to causes condensation of the aromatics giving a hardened product with a high proportion of asphaltenes, cyclics, and insolubles and a relatively low proportion of saturates. The hardened extract may have a penetration of from 0.1 to 6 at 250C as determined by ASTM D5/73 test and a softening point (Ring and Ball) of from 60 to 1 700C.

The ratio by weight of non-thermoplastic rubber particles to filler is preferably in the range 1:1 to 3:1. The hardness of the compositions may be controlled by the proportions of hardened extract and filler and the hardness is preferably from 30-60, on the IRHD scale. At lower hardness values, the compositions tend to be soft and tacky while at higher values they tend to be too stiff and to have reduced energy absorbing properties.

The rebound resilience of the compositions of the present invention is preferably not more than 20% at 250C as measured by a falling weight or pendulum (e.g. Lupke Pendulum method). This compares with figures of more than 30% for most rubbers and indicates that the compositions have a high capacity to absorb impact energy.

Another desirable characteristic of the compositions of the present invention is that they should deform readily under load and recover relatively quickly. Typical recoveries of the distance indented may be of the order of 80% or more after 24 hours.

Compression set is the reverse of recovery and is the residual deformation of a test specimen when subjected to compression under defined conditions. Typically, the compression sets for compositions of the present invention are less than 20% when measured 24 hours after being compressed by 25% at 230C for 22 hours.

The compositions of the present invention may be produced by mixing the components together in a high intensity mixer such as, for example, a Banbury mixer for a period in the range of 2 minutes to one hour. The components may be charged into the Banbury mixer at ambient temperature and the temperature may rise due to the frictional forces to a temperature of about 1 600 C. The material from the Banbury mixer may then be shaped by conventional moulding or sheet forming techniques. For example, the compositions may be fabricated into sheets by milling and calendering or by roller die extrusion The composition according to the present invention may contain a number of additives to aid the processing of the material or to improve their properties. For example, the presence of a long chain hydrocarbyl amine, as mentioned above, will prevent the material sticking to the rollers during calendering and, if the material is to be moulded, the presence of a small amount, e.g. 0.1-2% by weight based on weight of rubberised bitumen, of a fatty acid amide such as oleamide or stearamide will aid the release of the formed article from the mould. A paraffin oil such as Enerpar 23 sold by BP Oil or an aromatic oil such as Enerflex 72 sold by BP Oil may be added in an amount up to 5% by weight as a processing aid. The presence of the oil reduces the time required to process the compositions in the mixer.An anti-ozonant such as Santoflex IP sold by Monsanto may be included in an amount 0--1% by weight in order to improve the material's resistance to cracking caused by ozone during weathering.

The compositions of the present invention may be formed into sheets or tiles for use as safety surfaces, e.g. on children's playgrounds, particularly around swings, slides, etc., where children may fall.

They may also be used as energy absorbing bumpers for vehicles, as ships fenders or as motorway barriers.

Typically the material may be moulded into slabs with dimensions of 500 x 500 x 1 6 mm for use as safety paving. Such paving slabs may be fixed to an underlying surface, e.g. asphalt or concrete, with an adhesive. A suitable adhesive may have the following proportions by weight: Bitumen 91 to 95 parts Thermoplastic rubber particles 5 to 9 parts, preferably 7 to 8 parts 1,1,1, trichloroethane 55 to 100 parts Typically a suitable adhesive may be produced by mixing: 57.5% by weight of 100 penetration bitumen, 4.7% by weight of the thermoplastic rubber Solprene 411 P sold by Phillips Petroleum, ("Solprene" is a Registered Trade Mark), and 37.8% by weight of 1,1,1, trichloroethane.

This invention is illustrated by the following examples.

Tyre crumb or buffings were used in all the Examples as the finely divided particles of crosslinked non-thermoplastic rubber.

EXAMPLE 1 The following materials were charged into the mixing chamber of a 1 litre capacity Banbury mixer: 616 g Olexobit 50, a rubberised bitumen supplied by Deutsche BP AG 205 g hardened extract (softening point 1400C) 684 g Snowcal 6ML, limestone filler sold by Cement Marketing Company Limited. (Snowcal is a Registered Trade Mark).

900 g 40 mesh tyre crumb 4.8 g octadecylamine.

The charge was mixed at 20 rpm for 35 minutes and reached a temperature of about 2000C. The material was discharged from the mixer and milled for 5 minutes on a 12 inch (30.5 cm) wide two roll mill to produce a sheet suitable for moulding.

Specimens of the product were moulded at 1 600C for 5 minutes under 20 tonnes in an 8 inch x 8 inch (20.3 x 20.3 cm) press. The moulded specimens were used in tests to measure the physical properties of the material, the results of which are given in Table 1. The physical properties of a composition prepared according to GB 2036760A and two other commercial products are also included in the Table for comparison. Comparative Material 1 is a material comprising granulated rubber bonded with elastomeric polyurethane resin. Comparative Material 2 is a similar material which may be wet laid.

Dumb-bell shaped specimens of the materials were made from 3 mm thick sheet and used to test the strength and elongation according to BS 903 Pt. A2 1 971 type 1. The test specimens were stretched at the rate of 50 cm/min at 230C and the result in Table 1 show that the material according to the present invention is stronger and has a much greater elongation than either the material according to GB 2036760A or Comparative Material 2. Comparative Material 1 was not tested.

A Lüpke Pendulum method was used to measure resilience. A pendulum weight of 250 g was employed suspended from a height of two metres and at an angle of 180 from the vertical. The first rebound height, expressed as a percentage of the original drop height is a measure of the resilience of the material. The rebound resilience of the specimens was measured at temperatures of --120C, 230C and 600C.

The results obtained for the material according to the present invention were very similar, at all temperatures, to those of the material prepared according to GB 2036760A but were much lower than those obtained with the bonded tyre crumb, Comparative Material 1. This indicates that the energy absorbing properties of the present invention are at least as good as those of the materials described in GB 203 6760A and are better than those of Comparative Material 1.

The Tetrapod Walker test is a simulated wear test which corresponds more closely with actual wear than, for example, and abrasion test. A moulded sheet of the material 30 cm wide, 3 mm thick and of known weight is fitted into a cylindrical drum with a diameter of 22 cm. The edges were butted together and heid in place with adhesive tape. A tetrahedral shaped device called the tetrapod weighing 507 g, was placed inside the cylinder and the ends were sealed with 5 mm thick polythene sheet and a metal backing plate. The tetrapod has four arms spaced 12.5 cm equidistant, with 1 5 mm running spikes fitted to each arm. The cylindrical drum is rotated by rollers for 500,000 revolutions at the rate of 38 rpm. The specimen is then removed from the drum and inspected for wear and weighed to calculate the mass or volume loss occuring during the test.

A hexagonal pattern was moulded onto one side of the specimens used for this test. At the end of 500,000 revolutions the pattern was still visible on the specimen of the material according to the present invention whereas the material according to GB 2036760A showed no trace of the original pattern and was substantially more worn. A sample of the bonded tyre crumb material, Comparative Material 1 , was severely worn with large areas from which tyre crumb has been gouged out of the surface by the spikes. There was a substantial volume of tyre crumb prised out of the surface.

Comparative Material 2 was also severely worn.

The peak deceleration force refers to the maximum deceleration force experienced by a mass of 4.1 kg dropped onto a moulded specimen not less than 15 cm x 15 cm and 16 mm thick. The response is measured by a decelerometer, charge amplified and fed to a transient recorder. The peak deceleration force is measured from the graphic trace on the chart paper.

The mass used was a spherical segment of radius 50 mm of a sphere with a radius of 65 mm.

The material according to the present invention performed as well as the other materials tested. TABLE 1 Physical properties of moulded safety surface prepared in example 1 and other commercial products

Moulded Tile Moulded Preepared Tile According to According to Comparative Comparative Property Units GB 2036760A Example 1 Material 1 Material 2 Thickness mm 16 16 16 15 Specific Gravity 1.2 1.28 0.65 Rebound Resilience % (-12 C) 9 8 31 (23 C) 14 15 51 25-30 (60 C) 21 22 55 Hardness.(IRHD Scale) Degrees 40-45 30 35-40 35 at 23 C Tensile Strength MPa 0.4 1.3 0.8 Elongation % 50 330 100 Tetrapod Walker mg/m 30-40 0 1400 800 Wear Test loss per 500.000 revs Peak Deceleration g 300 313 310 280 Force (4kg hemisphere dropped from height of 1 metre) EXAMPLE 2 63 kg Olexobit 50 rubberised bitumen, 21 kg hardened extract (softening point 1 400C), 70 kg Snowcal 7ML limestone filler, 92 kg 40 mesh tyre crumb, 0.612 kg octadecylamine and 1.225 kg oleamide were charged to a Banbury mixer and mixed for 20 minutes.The mixed compound reached a temperature of 1 530C as a result of frictional heating during mixing. It was discharged onto a two metre wide two roll mill and milled to a sheet approximately 9 mm thick. The material was removed from the mill at a stock temperature of 110 C.

1900 g samples of the above product were milled on a cold laboratory 2 roll mill for 5 minutes into tiles measuring 30.5 x 30.5 x 1.6 cm. IRHD hardness measurements were made on two specimens over a range of temperatures. The results were found to be reproducable and are given in Table 2.

TABLE 2 Hardness (IRHD scale) of moulded material

Temperature( C) -10 0 10 23 40 50 IRHD Sample 1 80 73 67 50.5 42 33 (degrees) Sample 2 82 75 69.5 50 38 31 EXAMPLE 3 511 g Olexobit 50 rubberised bitumen, 170 g hardened extract (softening point 1400C), 578 g Snowcal 7ML limestone filler, 747 g 40 mesh tyre crumb, 4 g octadecylamine were mixed in a Banbury mixer for 1 8 minutes and reached a peak temperature of 1 800 C.

The material was moulded to provide specimens for measuring the following physical properties: IRHD hardness 48 (at 230C) Rebound resilience 15% Compression set (measured 24 hours after being compressed by 25% for 22 hours at 230C) 17% EXAMPLE 4 Two compositions were prepared by mixing the following materials in a Banbury mixer to a peak temperature of 1 450C.

96 by weight of total mixture Material Composition 1 Composition 2 Olexobit 50 rubberised bitumen 25.6 34.1 Snowcal 7ML limestone filler 28.5 28.5 Tyre crumb (40 mesh) 37.4 37.4 Hardened extract 8.5 (softening point 1400C) 100 100 Both compositions also contained 196 octadecylamine and 2% oleamide (based on weight of Olexobit 50).

The compositions were moulded into tiles measuring 305 x 305 x 16 mm with a patterned upper surface and a plain lower surface. The materials were moulded with either (a) silicon release paper or (b) aluminium foil between the plates.

The wet skid resistances of the surface of tiles of each composition were measured using a Road Research Laboratory portable skid resistance meter. The results are shown in Table 3.

TABLE 3-Wet Skid Resistance

Material IRHD hardness Surface Mould Release Wet Skid at 23 C (degrees) type Material Resistance Composition 1 50 patterned silicon 41 patterned aluminium 42 foil plain silicon 41 Composition 2 50 patterned silicon 28 patterned aluminium 16 foil plain silicon 18 plain aluminium 12 foil These results demonstrate that Composition 1 has a much higher skid resistance than Composition 2 irrespective of the mould release material employed.Composition 2 differs from Composition 1 in that all the hardened extract has been replaced by Olexobit 50 but the materials have a similar hardness. Therefore the presence of hardened extract is apparently beneficial in producing a material with higher wet skid resistance.

Specimens of Compositions 1 and 2 were also moulded into sheets measuring 80 x 80 x 1 6 mm and cooled to -250C in a thermostatically controlled water/glycol bath. Specimens of both materials survived an impact test of 5 Joules and being flexed through 1 800C around a 3 cm diameter mandrel.

These results indicate that the inclusion of hardened extract does not impair the energy absorption or flexibility of the material at low temperatures.

EXAMPLE 5 1 6 tiles, measuring 300 x 300 x 1 6 mm were prepared from the formulation described in Example 1. These were bonded to an asphalt surface with four bitumastic adhesives which were prepared as follows.

Adhesive 11850 g of a 200 penetration bitumen were heated to 1 000C in an oven, then transferred to a 5 litre flanged flask fitted with a stirrer and reflux condenser. 1214 g 1,1,1, trichloroethane were added and stirred to form a solution at 700 C. 1 50 g Solprene 411 P thermoplastic rubber ax Phillips Petroleum were added to the solution which was refluxed at 830C for one hour to dissolve the rubber. The flask and contents were cooled to 500C.

Adhesive 2 As for Adhesive 1 except that a 100 penetration bitumen was used.

Adhesive 3 As for Adhesive 1 except that a 100 penetration bitumen was used and the level of Solprene 411 P increased to 200 g.

Adhesive 4 692 g Olexobit 100 penetration bitumen were dissolved in 1237 g 1,1,1, trichloroethane by stirring under reflux in a 5 litre round bottomed flange flask fitted with a reflux condenser.

The asphalt surface was pre-treated with a primer before bonding the tiles to the surface. The primer for adhesives 1 to 3 consisted of a blend of 92.5 parts bitumen, 7.5 parts Solprene 411 P and 245 parts 1,1,1, trichloroethane. The primer for adhesive 4 consisted of 87 parts Olexobit 100 dissolved in 311 9 1,1,1, trichloroethane.

Four tiles were bonded to the surface with each adhesive. Six months later the force required to remove the tiles was measured with a spring balance with a lipped plate measuring 1.5 cm x 2.5 cm which was inserted under the edge of the tiles. The average force in pounds required to pull up tiles bonded with each of the four adhesives is recorded in Table 4.

TABLE 4 Force required to remove tiles bonded to asphalt

Average force (lbs) required Adhesive Type to lift tile from asphalt surface 1. contains 7% Solprene in 200 penetration bitumen 11 2. contains 7% Solprene in 100 penetration bitumen 42 3. contains 10% Solprene in 100 penetration bitumen 6 4. Olexobit 100 penetration bitumen 10 The results indicate that Adhesive 2 showed outstanding capacity to bond the tiles to the asphalt surface.

Claims (11)

1. A bituminous composition having energy absorbing properties comprising bitumen, hardened extract, finely divided particles of crosslinked non-thermoplastic rubber and a filler, the amount of finely divided particles of crosslinked non-thermoplastic rubber by weight being equal to or greater than the amount of filler by weight characterised in that the bitumen is a rubberised bitumen, the rubber of the rubberised bitumen being a non-thermoplastic copolymer of at least two mono alpha olephins and a cyclic olefin having an endocyclic bridge and at least two olefinic double bonds.

2. A bituminous composition as claimed in claim 1 in which the preparation of the rubberised bitumen includes the step of blowing the copolymer, an aromatic flux oil and, optionally, bitumen at a temperature of from 150 to 3000C in the presence of a gas containing elemental oxygen.

3. A bituminous composition according to either of claims 1 or 2 in which the rubberised bitumen is prepared by blowing with a gas which contains elemental oxygen, at a temperature of from 1 50 to 3000C a mixture of: 2388% wt, based on the total mixture, of a bituminous substance, 225% wt, based on the total mixture, of a copolymer of at least two mono alpha olefins and a cyclic olefin having an endocyclic bridge and at least two olefinic double bonds, 1075% wt, based on the total mixture, of a flux oil for extending the copolymer, 0-4 parts by weight sulphur per 100 parts by weight of the copolymer, and 0--3% wt, based on the total mixture, of a polyolefin.

4. A bituminous composition according to either of claims 1 or 2 in which the rubberised bitumen is prepared by blending a bituminous substance, a copolymer of at least two mono alpha olefins and a cyclic olefin having an endocyclic bridge and at least two olenific double bonds, an aromatic flux oil and optionally sulphur and then blowing the blend at a temperature from 150 to 260 C with a gas which contains elemental oxygen to form a concentrate and then dissolving the concentrate in unblown bitumen.

5. A bituminous composition according to any of claims 1 to 4 in which the mono alpha olefins of the copolymer are ethylene and propylene and the cyclic olefin is dicyclopentadiene or ethylidene norbornene.

6. A bituminous composition as claimed in any of claims 1 to 5 having the following components in parts by weight: Rubbersied bitumen 100 parts Hardened extract 4-40 parts Crosslinked non-thermoplastic rubber particles 50-1 75 parts Filler 50-175 parts

7. A bituminous composition as claimed in claim 6 which also contains from 0.05 to 5 parts by weight of a long chain hydrocarbyl amine.

8. A bituminous composition as claimed in any of claims 1 to 7 in which the ratio by weight of crosslinked non-thermoplastic rubber to filler is in the range 1:1 to 3:1.

9. A bituminous composition as claimed in any of claims 1 to 8 which has a hardness from 30 to 60 on the IRHD scale and a rebound resilience of less than 20% at 250C.

10. A bituminous composition as claimed in any of claims 1 to 9 which has a compression set as herein before defined of less than 20%.

11. A bituminous composition as claimed in any of claims 1 to 10 in which the crosslinked nonthermoplastic rubber is a tyre crumb.

1 2. A bituminous composition as herein before described with reference to any one of the Examples 1 to 4.