GB2617835A

GB2617835A - Stone mastic asphalt comprising recycled fibre

Info

Publication number: GB2617835A
Application number: GB2205699.8A
Authority: GB
Inventors: Poyer Robert
Original assignee: Nappicycle Ltd
Current assignee: Nappicycle Ltd
Priority date: 2022-04-19
Filing date: 2022-04-19
Publication date: 2023-10-25
Also published as: GB202205699D0

Abstract

A stone mastic asphalt wherein recycled absorbent hygiene product fibres are used as the fibre in the stone mastic asphalt. Methods of producing a stone mastic asphalt comprising recycled absorbent hygiene product fibres are also disclosed. The fibres may comprise polyethylene, polypropylene, cellulose, and/or elastomeric polymers. Preferably the fibres are present at 0.01% to 2 % by mass of the mixture, most preferably at between 0.1% and 0.5% by mass of the mixture. Coarse aggregate is present in the mixture at 50-80% by mass and fine aggregate is present at 15-45% by mass of the total mixture. Filler is present at 4-12% by mass of the mixture and the binder is 5-7% by mass. In an embodiment, the aggregate, filler and fibre components are mixed in a first step and then the binder is added, and the mix heated to between 100-200°C. Alternatively, all components may be mixed simultaneously.

Description

Stone mastic asphalt comprising recycled fibre

Field of the Invention

The present invention concerns an asphalt. More particularly, but not exclusively, this invention concerns a method and mix for a stone mastic asphalt.

Background of the Invention

Modern transport infrastructure such as roads and footways require a surface for wheeled vehicles to roll on. Stone mastic asphalt (SMA), also called stone-matrix asphalt, provides a deformation-resistant, durable surfacing material. SMA is commonly used as a durable asphalt surface for residential streets, highways (for example motorways, trunk roads and small roads), airfields and shared use paths. SMA comprises a coarse aggregate that interlocks to form a stone skeleton that resists permanent deformation. The stone skeleton is combined with a putty-like mastic of bitumen and filler to which fibres are added to provide adequate stability of bitumen and to prevent drainage of binder during transport and placement.

SMA is typically composed, by mass, of 50-80% coarse aggregate, 15-45% fine aggregate. 4-12% filler, 5.0-7.5% binder, and 0.1-0.5% per cent fibre.

Typically, the coarse and fine aggregates are rock/sand, the filler is limestone powder and the binder is bitumen. Typically, the fibre content of an SMA is cellulose fibre. Given the relative densities of fibre in comparison to bitumen, aggregate and filler materials, the fibre is a higher percentage of the mix by volume than a percentage by mass. Other fibres types, such as glass fibre and stone wool have been used, although cellulose fibre is generally preferred as it is less expensive.

SMAs are considerably more environmentally friendly than concrete, which is an alternative road surface material. However, it is still an objective to provide an SMA which is more environmentally friendly than previously known SMAs.

SMAs can vary in a number of material properties, depending on the composition of the SMA or the method by which it is prepared. The properties of SMA materials can influence its performance during placement and in-situ durability. Workability during laying directly impacts on the materials compacted air void content and durability. The materials stiffness influences rutting performance, i.e. the pavements ability to carry traffic without deforming in warm weather. SMA's fatigue properties determine how much the material will bend and flex without cracking The present invention seeks to mitigate the above-mentioned problems.

Alternatively or additionally, the present invention seeks to provide an improved 5 SMA.

Summary of the Invention

The present invention provides, according to a first aspect, a stone mastic asphalt, comprising: aggregate; filler; binder; and fibre; wherein the fibre is a recycled absorbent hygiene product fibre.

The SMA uses recycled absorbent hygiene product fibre as the fibre content of the SMA. One advantage of this is that a virgin material fibre is not used in the SMA. The recycled fibre content fibre is recycled from a source which would otherwise be sent to landfill, and therefore incorporating this into SMA is a more environmentally friendly way to produce SMA. The use of the recycled absorbent hygiene product fibre eliminates the need for virgin cellulose fibres to be used in SMA production, which results in a more environmentally friendly SMA. Moreover, cellulose fibre is typically transported for long distances to be used as a raw ingredient in SMA, which has a further negative environmental impact. Given the abundance of absorbent hygiene products throughout the world, it is possible to recycle these products into fibre and transport them much shorter distances for use in SMA. Moreover, SMA which uses recycled absorbent hygiene product fibre have been found to comply with the required testing standards for use as an SMA in road construction.

The workability of the SMA during laying may be improved by the use of recycling absorbent hygiene product fibre in the SMA in comparison to solely cellulose fibre.

The recycled absorbent hygiene product may be a disposable nappy or adult incontinence product such as an incontinence pad.

The recycled absorbent hygiene product fibre may comprise polypropylene.

The recycled absorbent hygiene product fibre may comprise polyethylene. The recycled absorbent hygiene product fibre may comprise cellulose fibre. The cellulose fibre may comprise natural cellulose fibre and/or synthetic cellulose fibre. The recycled absorbent hygiene product fibre may comprise elastomeric polymers.

The recycled absorbent hygiene product fibre may be in the form of pellets, for example pellets between 6mm and lOmm in diameter. The recycled absorbent hygiene product fibre pellets may be added in their pelletized form into the mixture. The recycled absorbent hygiene product fibre may be between 0.01% and 2% by mass of the SMA mixture, for example between 0.1% and 0.5% of the mixture, for example 0.3% of the mixture.

The aggregate component of the SNIA may be coarse aggregate and fine aggregate. Coarse aggregate may be material (such as stone/sand) having a sieve size greater than 2.36mm, and fine aggregate may be material having a sieve size lower than 2.36mm. The coarse aggregate may be 50-80% by mass of the mixture and fine aggregate may be 15-45% by mass of the mixture. The SNIA may comprise 4-12% by mass of the mixture of filler and 5-7.5% by mass of the mixture of binder.

According to a second aspect of the invention there is also provided a method of manufacturing stone mastic asphalt, the method comprising the steps of mixing and heating stone mastic asphalt component materials. The stone mastic asphalt component materials may comprise aggregate, filler, binder and fibre, wherein the fibre comprises a recycled absorbent hygiene product fibre. The heating step may comprise heating the component materials to between 100 and 200 degrees Celsius. The heating step may comprise heating the component materials to between 120 and 150 degrees Celsius. The heating step may comprise heating the component materials to between 130 and 140 degrees Celsius. The heating step may comprise heating the component materials to between 120 and 180 degrees Celsius. The heating step may comprise heating the component materials to between 160 and 200 degrees Celsius The heating step may comprise heating the component materials to between 150 and 200 degrees Celsius. The heating step may comprise heating the component materials to between 170 and 190 degrees Celsius. The heating step may comprise heating the component materials to approximately 180 degrees Celsius.

In another embodiment, the aggregate, filler and recycled absorbent hygiene product fibre are combined in an initial mixing step, and the binder is added in a secondary mixing step. Thus, in this embodiment the mixing step is carried out in two stages -a "dry" mixing stage with aggregate, filler and recycled absorbent hygiene product fibre, and a subsequent "wet" mixing stage wherein bitumen is also mixed into the mixture. Within the mixture, the coarse aggregate may be 50-80% by mass of -4 -the mixture, fine aggregate may be 15-45% by mass of the mixture, filler may be 412% by mass of the mixture, recycled absorbent hygiene product fibre may be 0.10.5% by mass of the mixture and binder may be 5-7.5% by mass of the mixture. Binder may be 5-8% of the mixture by mass SMA made with recycled absorbent hygiene product fibre, in comparison to virgin cellulose fibre, may have any or all of improved hardness, durability, workability at different temperatures, resistance to cracking, resistance to melting, shear resistance, abrasion resistance, cracking resistance, skid resistance and/or noise generation It will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

Description of the Drawings

Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: Figure 1 shows a flow diagram of a method according to a first embodiment of the invention; Figure 2 shows a flow diagram of a method according to a second embodiment of the invention.

Detailed Description

The present invention provides a stone mastic asphalt (SMA) which comprises recycled absorbent hygiene product fibre, where traditionally virgin cellulose fibre is used Recycled absorbent hygiene product fibre is a fibre obtained from recycling used absorbent hygiene products. When bulk absorbent hygiene products are recycled using the process described in UK patent application number 1904418.9, the typical resultant recycled product, in the form of a composite fibre, is given in the table below: -5 -Components Approximate % by weight Cellulose fibre 45% Polypropylene fibre 90,4, Low density polyethylene Elastomeric polymers Inert fines (Grit and Glass) Metals 6% trace % Moisture The values given in the above table are typical and may vary. The cellulose fibre may be between 35-55% of the component fraction, or between 40-50% of the component fraction. The polypropylene fibre may be between 20-40% of the component fraction, or between 25-35% of the component fraction. The low density polyethylene may be between 5-13% of the component fraction, or between 7-11% of the component fraction. The inert fines may be between 4-8% of the component fraction or may be between 5-7% of the component fraction. The moisture content may be between 2-8s/0, or 4-6% of the component fraction.

The composite fibre is a dry, grey fibrous solid formed into friable pellets with a diameter of between 6mm and lOmm. The inventors have realised that this fibre, in the form of these pellets, is suitable for use in the production of SMA, as the pellets unexpectedly break down owing to the abrasive action of the aggregates in the mix being mixed with the pellets, having become distributed very evenly as pellets and then as fibres, throughout the mix. Finding use for composite fibre made from recycled absorbent hygiene products in the construction industry is especially beneficial as the construction industry typically is not prejudiced against use of such a recycled material owing to its origin as used absorbent hygiene products.

Figure 1 shows a method 100 of manufacturing a stone mastic asphalt. The method 100 comprises the step of recycling 110 an absorbent hygiene product 90 to obtain recycled absorbent hygiene product fibre 120. Alternatively, the recycled absorbent hygiene product may be obtained from a third party, for example a recycling company. The method 100 further comprises the step of mixing 130 and heating 140 stone mastic asphalt component materials together to form an SMA mix 160. The stone mastic asphalt component materials comprise aggregate 150, filler 151, binder 152 and the recycled absorbent hygiene product fibre. Figure 2 shows a similar method 200 of manufacturing a stone mastic asphalt wherein the mixing step 130 is instead done in two stages: aggregate 150, filler 151 and recycled absorbent hygiene product fibre 120 are mixed in a first mixing step 231 and the binder 152 is added in a second subsequent mixing step 232. For both of the methods 100, 200, the step of heating 140, 240 is carried out at a temperature of between 100 and 200 degrees Celsius, for example at between 120 and 200 degrees Celsius, for example between 160 and 200 degrees Celsius, for example at 180 degrees Celsius. At the end of the mixing 130, 231, 232 and/or heating steps 140, 240 the SMA comprises approximately 50-80% coarse aggregate by mass of the mixture, 15-45% fine aggregate by mass of mixture, 4-12% filler by mass of the mixture, 0.1-0.5% recycled absorbent hygiene product fibre by mass of the mixture and 5-7.5% binder by mass of the mixture. This SMA is then suitable for being applied and compacted as a road surface.

In another aspect, there is a stone mastic asphalt made according to either of the methods 100, 200 described above. The stone mastic asphalt comprises approximately 50-80% aggregate by mass of the mixture, 15-45% fine aggregate by mass of mixture, 4-12% filler by mass of the mixture, 0.1-0.5% recycled absorbent hygiene product fibre by mass of the mixture and 5-7.5?iiii binder by mass of the mixture. The recycled absorbent hygiene product fibre comprises plastics (such as polypropylene and polyethylene and elastomers) and natural and synthetic cellulose.

Various trials have taken place in which SMA according to the invention have been made and tested. These trials include the following examples.

Example 1

SMA14 binder 40/60 PSV60 (polished stone value) was created using 0.3% (wt?.) recycled absorbent hygiene product fibre in place of standard cellulose fibre, which would have been present in the same 0.3 wt% in a conventional mix. The SMA was produced in a 1.0 tonne batch. The aggregates and fibres were dry mixed for 25 seconds, then the bitumen added, followed by wet mixing for 20 seconds. The SMA was mixed at a temperature (measured at the discharge of the mixer) of 150-180 degrees Celsius. -7 -

The material was transported in trucks for a period between 1-3hrs including waiting times, then laid by a Vogele 1803-3i asphalt paver in a layer 30-60mm thick and compacted by an 8 tonne tandem vibratory roller compactor.

Cores of the compacted material were extracted and tested for Bulk Density (BS EN 12697-6; 2020 Proc B) and Maximum Density (BS EN 12697-5; 2018 Proc A). This showed the material was well compacted and had in-situ air voids contents (BS EN 12697-8: 2018) of 2.6%. This is in comparison to a generic requirement that is 5% Max Air Voids for this type of material. Compositional analysis of the material by (BS EN 12697-1; 2020 / Annex B Proc 1) & (BS EN 12697-2: 2015 + Al 2019) shows it met the requirements for a SMA 14 bind in BS EN 13108-5; 2016 for bitumen content and particle size distribution.

Example 2

Laboratory work under taken on plant produced lOmm SMA (SMA 10 surf 100/150 (60 PSV (polished stone value))) containing 0.3% (wt%) recycled absorbent hygiene product fibre and in comparison to a conventional SMA mix made using standard cellulose fibre, also at 0.3 wt%.

The SMA was sampled and found to be within the specified limits for lOmm SMA from BS EN 13108-5:2016. The binder drainage of SMA made with recycled absorbent hygiene product fibre was found to be identical to the same material made with standard cellulose fibre. Testing the materials to BS EN 12697-18:2017 -Clause 5 Beaker Method, gave results of 0.1% material drained at 180 degrees Celsius for both fibre types.

Binder recovery by BS EN 12697-3; 2013+A1 2018 followed by Penetration and Softening Point (BS EN 1426; 2015 & BS EN 1427; 2015 respectively) showed that recovered binder from SMA containing recycled absorbent hygiene product fibre had very similar properties to binder recovered from SMA containing standard cellulose fibre. The Penetration results of 81 & 82 [0,1mm] and Softening Point values of 48.1 & 48.5 degrees Celsius for the SMAs containing recycled absorbent hygiene product fibre and standard cellulose fibre respectively. All results were within the precision values of their respective test methods. -8 -

Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein.

Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

Claims

Claims 1 A stone mastic asphalt, comprising: aggregate; filler; binder and fibre; wherein the fibre is recycled absorbent hygiene product fibre.
2. A stone mastic asphalt according to claim I, wherein the recycled absorbent hygiene product fibre comprises polypropylene.
3. A stone mastic asphalt according to claim 1 or claim 2, wherein the recycled absorbent hygiene product fibre comprises polyethylene.
4. A stone mastic asphalt according to any preceding claim, wherein the recycled absorbent hygiene product fibre comprises cellulose fibre.
5. A stone mastic asphalt according to claim 4, wherein the cellulose fibre comprises natural and synthetic cellulose fibre.
6. A stone mastic asphalt according to any preceding claim, wherein the recycled absorbent hygiene product fibre comprises elastomeric polymers.
7. A stone mastic asphalt according to any preceding claim, wherein the recycled absorbent hygiene product fibre is between 0.01% and 2% by mass of the mixture.
8. A stone mastic asphalt according to any preceding claim, wherein the recycled absorbent hygiene product fibre is between 0.1% and 0.5% by mass of the mixture.
9. A stone mastic asphalt according to any preceding claim, wherein the aggregate is coarse aggregate and fine aggregate.
-10 - 10. A stone mastic asphalt according to any preceding claim, wherein the coarse aggregate is 50-80% by mass of the mixture and fine aggregate is 15-45% by mass of the mixture.
11. A stone mastic asphalt according to any preceding claim, wherein the filler is 4- 12% by mass of the mixture and the binder is 5-7.5% by mass of the mixture.
12. A method of manufacturing stone mastic asphalt, the method comprising the steps of mixing and heating stone mastic asphalt component materials, the component materials comprising aggregate, filler, binder and fibre, wherein the fibre comprises the recycled absorbent hygiene product fibre.
13. The method according to claim 12, wherein during the heating step the component materials are heated to between 100-200 degrees Celsius
14. The method according to claim 12 or claim 13, wherein the aggregate, filler and recycled absorbent hygiene product fibre are combined in an initial mixing step, and the binder is added in a secondary mixing step.
15. The method according to any of claims 12 to 14, wherein the aggregate is 50-80% by mass of the mixture, fine aggregate is 15-45% by mass of the mixture, filler is 412% by mass of the mixture, recycled absorbent hygiene product fibre is 0.1-0.5% by mass of the mixture and binder is 5-7.5% by mass of the mixture.