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Wrap Tyres Programme
Composite construction products
from waste tyres
Turning waste tyres into new products for the construction industry.
Project code: TYR0003 ISBN: 1-84405-351-2
Research date: Nov 2006Mar 2007 Date: March 2007
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Front cover photograph: Plasterboard sandwich panel with a rubber core derived from waste tyres.
IMPORTANT NOTE & DISCLAIMER
WRAP and BRE believe the content of this report to be correct as at the date of writing. However, factors such as prices, levels of recycled content and regulatory
requirements are subject to change and users of the report should check with their suppliers to confirm the current situation. In addition, care should be taken in using
any of the cost information provided as it is based upon numerous project-specific assumptions (such as scale, location, tender context, etc.).
The report does not claim to be exhaustive, nor does it claim to cover all relevant products and specifications available on the market. While steps have been taken to
ensure accuracy, WRAP cannot accept responsibility or be held liable to any person for any loss or damage arising out of or in connection with this information being
inaccurate, incomplete or misleading. It is the responsibility of the potential user of a material or product to consult with the supplier or manufacturer and ascertain
whether a particular product will satisfy their specific requirements.
The listing or featuring of a particular product or company does not constitute an endorsement by WRAP and WRAP cannot guarantee the performance of individual
products or materials. For more detail, please refer to WRAPs Terms & Conditions on its web site: www.wrap.org.uk
Published by
Waste & R esources The Old Academy Tel: 01295 819 900 Helpline freephone
Action P rogramme 21 Horse Fair Fax: 01295 819 911 0808 100 2040
Banbury, Oxon E-mail: info@wrap.org.uk
OX16 0AH
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Executive summary
The construction industry consumes approximately 420 million tonnes of products per year, and therefore utilises
large quantities of raw materials. Alternatives to primary materials in construction products are already widely
used; examples include the use of construction and demolition wastes as aggregates, timber wastes in composite
board products and by-products from steel-making in the manufacture of mineral wool. Examples such as these
contribute to continued improvement of the green credentials of the construction industry.
By 2005, there were over 480,000 tonnes of used tyres arisings per year in the UK (Environment Waste Strategy,
2007). Since July 2006, both whole and shredded tyres have been banned from landfill, following implementation
of the UK Landfill Regulations. There is therefore an urgent need to find new applications and markets for tyre
arisings.
In November 2005, BRE was commissioned by WRAP to identify applications for waste tyres in construction
products. The principal objective of the project was to use tyre waste to develop and provide industry with a
number of new sustainable, viable, low-cost composite construction products that are easy to manufacture. The
aim of the project was to contribute to the remit of WRAP to reduce the volume of waste tyres going to landfill,
and to research new market opportunities for waste tyre-derived materials. The project was completed in March
2007.
The objectives of the project were:
to understand and characterise waste-tyre raw materials; to establish the properties, reactivity and functionality of these raw materials for the development of
construction composites;
to develop a matrix-used tyre-performance-demand model for used tyre-based composites; to investigate the modification of a new generation of reprocessed used tyre constituents, if necessary; to develop new processes for manufacturing these composites.
The main tasks undertaken under the project were as follows:
property testing of the tyre-derived raw materials, including recommendations on raw material modifustry consultative group;
ication;
laboratory manufacture of prototype products identified by BRE and an indassessment of the properties of the developed prototypes;development of a matrix of used tyre vs. property demand for the plasterboard/tyre buffings-derived panel;
ings product;
assessment of economic and market factors.
t and
dix A.
aken further at this stage, some of them because they appear to be uneconomical given
urrent cost models.
redential
te Services, CostDOWN Consultancy, Lafarge
Plasterboard, Hyperlast, Apollo Adhesives and Kingpin.
industrial assessment of the plasterboard/buff
During the project, a series of prototypes based on a range of waste tyre-derived raw materials (shreds, dus
buffings) with plasterboard, oriented strand board (OSB) and laminate floor were produced. A plasterboard
sandwich panel with a rubber layer in the middle was successfully developed and a variety of this subsequently
tested by Lafarge Gypsum, who were interested in its acoustic insulation properties. Further work is still needed
to bring this product to market, but results so far are promising. The results of the tests are given in AppenA range of other potential products were prototyped in the laboratory, including underlay for use beneath
laminate floors, and sandwich panel for door or wall partition with OSB. However (with industry agreement),
these have not been t
c
Members of an industry consultative group contributed to the project through the provision of testing facilities,
materials and advice. Key contributors were: Murfitts Industries, Charles Lawrence International Ltd, C
Environmental Ltd, Tyre Recovery Association, Biffa Was
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Contents
1.0 Int roduct ion ............................................................................................................................. 32.0 Descript ion of the proj ec t ........................................................................................................ 6
2.1 Assessing tyre-derived raw materials ......................................................................................6 2.2 Used tyre-performance-demand model ...................................................................................6
2.3 Manufacture and characterisation of prototype products ..........................................................63.0 Resu lt s and di scussion ............................................................................................................. 83.1 Assessing tyre-derived materials.............................................................................................8
3.1.1 Products available from tyre recyclers ........................................................................83.1.2 Physical properties of the tyre shreds .......................................................................10
3.2 Tyre granules bound with resin ............................................................................................103.2.1 Initial trial mixes .....................................................................................................103.2.2 Initial product development.....................................................................................113.2.3 Further prototypes: laminate floor underlay and plasterboard sandwich panels...........143.2.4 Tests on the tyre/resin mixes...................................................................................153.2.5 Used tyre-performance-demand model.....................................................................183.2.6 Summary of the prototype development...................................................................19
3.3 Market survey .....................................................................................................................193.3.1 Market drivers for the use of tyres in composites ......................................................203.3.2 Overview of the market for recycled tyre materials and resins ...................................203.3.3 Market survey of acoustic plasterboard products.......................................................213.3.4 Market survey of acoustic underlay for laminate flooring ...........................................22
4.0 Envi ronm enta l aspects ........................................................................................................... 22 5.0 Conc lusions ............................................................................................................................ 236.0 Nex t steps .............................................................................................................................. 237.0 Commercial isat ion ................................................................................................................. 238.0 Sources of informa tion consulted .......................................................................................... 25
8.1 References..........................................................................................................................258.2 Websites investigated during market survey..........................................................................25
8.2.1 Tyres .....................................................................................................................25
8.2.2 Products with tyre-derived rubber content................................................................258.2.3 Acoustic underlays ..................................................................................................25 8.2.4 Acoustic boards ......................................................................................................25 8.2.5 Dry lining/partition/ceilings/floors.............................................................................258.2.6 Tyre-derived materials: ...........................................................................................26
Appendix A: Used tyre appl icat ion vs propert y requ irem ent s............................................................ 27 Appendix B: Lafa rge Pl ast erboard test r esu lts................................................................................... 29 Appendix C: Resins considered i n t he project .................................................................................... 31
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1.0 Introduction
The construction industry consumes approximately 420 million tonnes of products per year, and therefore utilises
large quantities of raw materials. Alternatives to primary materials in construction products are already widely
used. Examples include the use of construction and demolition wastes as aggregates, timber wastes in composite
board products and by-products from steel-making in the manufacture of mineral wool. Examples such as these
contribute to the continued improvement of the green credentials of the construction industry.
By 2005, there were over 480,000 tonnes of waste tyre arisings in the UK per year. Since July 2006, both wholeand shredded tyres have been banned from landfill, following implementation of the UK Landfill Regulations.
There is therefore an urgent need to find new applications and markets for waste tyre arisings.
The current uses for waste tyres are listed in Figure 1.
Figure 1 Current uses for waste tyres
Uses and disposal routes Comment Tonnes
Export (used casings) The tyre casing comprises the entire main structural body
of a tyre, often called the carcass.
35,039
Retread (UK and export) The preferred method for re-using worn tyres as it
effectively doubles the life of the tyre. Buffings are
generated in the process.
57,427a
Energy recovery Used as a fuel (primarily in cement kilns). 85,750b
Landfill engineering Whole or shredded tyres can be used in landfill
engineering, for example as part of leachate collections
systems.
59,000c
162,500dMaterial recovery (shred/crumb) Recycled material from end-of-life tyres processed into
different grades of shred and crumb.
a BRMA, RMA & industry figures.b Returns from industry cement kilnsc Based on DTI Landfill Operator survey 2005d Returns from industry.
Used Tyres 2005 - End Uses
(486 578 tonnes)
Material recovery
(shred/crumb)
33%
Energy recovery
17%
Export of used
casings
7%
Re-used as part
worn tyres
7%
Retread UK &
export
12%
Other re-use
0%
Landfill loss
12%
Landfill
engineering
12%
Figure 2 Waste tyre end uses in the UK (source: DTI tyre statistics: 2005)
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It can be seen from Figure 2 that approximately half of all waste tyres undergo material or energy recovery.
A Publicly Available Specification, PAS107, has recently been prepared by the British Standards Institution (BSI) in
collaboration with WRAP to provide a specification for producing grades of size-reduced rubber of consistent and
verifiable quality. A summary sheet for the specification (PAS107: 2007, WRAP/BSI) has been produced by
WRAP). The grades and characteristics of material specified, and their PAS codes, are given in Figure 3.
Figure 3 Characteristics of size-reduced tyre materials (source: PAS107: 2007, WRAP/BSI)
Size range (maxim um dimension)
mmMaterial
CategoryMinimum Maximum
Other characteristics
Rough Cuts 300 None Exposed wire and textiles 1)
Clean Cuts 300 None Less than 5% exposed wire and textiles2)
Rough CutShred
50 300 Exposed wire and textiles
Clean Cut Shred 50 300 Less than 5% exposed wire and textiles2)
Rough Cut Chips 10 50 Exposed wire and textiles
Clean Cut Chips 10 50 No exposed wire. Less than 5% exposed
textiles 2)
Granulate 1.0 10 Free from exposed wire and textiles
Powder 0 1.0 Free from exposed wire and textiles
Fine Pow der 0 0.5 Free from exposed wire and textiles
1) All exposed wire and textiles shall be firmly attached to the body of the rubber fragments
2) Upon Visual Inspection
This project researches the potential uses of tyre shred, crumb or buffed materials that are categorised under
material recovery in Figure 2. The materials assessed fall within the categories RS, CC, G and P (Rough cut
shred, Clean cut chips, Granulate and Powder respectively) according to PAS107. However, this project was
undertaken before the issue of PAS107 and hence the terminology used will differ slightly from the PAS107
terminology.
In November 2005, WRAP commissioned the BRE consultancy to identify applications for waste tyres inconstruction products. The principal objective of the project was to use tyre waste to develop and provide
industry with a number of new sustainable, viable, low-cost composite construction products, which are readily
attainable. The aim of the project was to contribute to WRAPs remit of reducing the volume of waste tyres going
to landfill and to research new market opportunities for waste tyre-derived materials The project was completed
in March 2007.
This report describes the methodology used to identify potential products for the construction industry using
waste tyres, from the classification of the various tyre shreds available to the technical development and testing
of prototypes, and assessment of the market potential for the prototypes developed.
During the project, a series of prototypes based on a range of used tyre-derived raw materials (shreds, dust and
buffings) with plasterboard, oriented strand board (OSB) and laminate floor were produced. A plasterboardsandwich panel with a rubber layer in the middle was successfully developed and a variety of this subsequently
tested by Lafarge Gypsum, who were interested in its acoustic insulation properties. Further work is still needed
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to bring this product to market, but results so far are promising. The results of the tests are given in Appendix A.
A range of other potential products were prototyped in the laboratory, including underlay for use beneath
laminate floors, and sandwich panel for door or wall partition with OSB. However (with industry agreement),
these have not been taken further at this stage, in some cases because they appear to be uneconomic given
current cost models.
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2.0 Description of the projectThe aim of the project was to utilise tyre waste to develop and provide industry with a number of sustainable,
viable, low-cost composite construction products. The overall objectives of the project were achieved through a
number of secondary objectives:
understanding and assessing the primary reprocessed raw materials arising from waste tyres when existing
recycling and recovery processes are adopted;
establishing the property profile of the waste tyre raw materials relevant to the development of composites;
examining the reactivity and functionality of the reprocessed waste tyre raw materials;developing new processes (on a pilot or laboratory scale) for the manufacture of composites based on
recycled tyres;
assessing the market potential for the product(s) developed.
2.1 Assessing tyre-derived raw materials
The main tyre-derived raw materials (shreds, granules, buffings) were assessed for specific gravity and particle
size, shape/appearance/composition. It was not considered necessary, as originally set out in the project
proposal, to formally assess the wettability or detailed microstructure of the rubber since observations of the
workability of the wet mixes was adequate to optimise the blend of rubber and resin.
2.2 Used tyre-performance-demand model
A range of tyre-derived raw materials and potential products were initially considered under the project and
evaluated on the basis of the cost of competitor products. Following an evaluation on that basis, the most
successful prototype (technically and commercially) proved to be a panel based on resin-bound rubber buffings
bonded to plasterboard. A matrix was subsequently developed for plasterboard/buffings composite sandwich
panel products to identify the functional requirements required of the product in the envisaged end-use. In
developing this model, the following questions/issues were considered:
What does the envisaged application demand in terms of product function?
Mechanical performance (stiffness, strength, etc)
Other physical performance (fire resistance, noise attenuation, durability, appearance, etc)
Cost (effectively dictated by the costs of competitive products)
What are the key aspects of the composition of the envisaged product that will enable it to be fit-for-purpose?
How much (indicative) energy will be required to break down the source tyres?
What are the current competitive products?
Price. In some cases identification of direct competitors is not straightforward. Indicative prices givetarget range.
Strengths and weaknesses.
The results of the assessment are given in Section 3.2.5 and Appendix A. Here, the performance and cost of the
successful composite is compared in relation to service classes for plasterboard and competitor acoustic boards.
2.3 Manufacture and characterisation of prototype products
A series of prototypes (comprising a rubber layer and one or more stiffer layers) were developed in BREs
laboratories. These comprised: a wall sandwich panel, plasterboard/rubber stud wall panels, and laminate floor
underlay. The materials utilised in the composites with a tyre-derived rubber layer were plasterboard, laminate
flooring or oriented strand board. Mixes (rubber buffings or shreds) bound with resin were also produced and
cast into sheets for assessment.
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The tyre shreds/resin were assessed (in terms of curing time, workability and quality of binding) in relation to
temperature, resin type and percentage resin content. The rubber buffings/resin were assessed for water vapour
permeability, water absorption and moisture swelling.
The prototypes were assessed for the following properties:
Stiffness (all-visual assessment)
Bonding of rubber layer to substrate (all-visual assessment)
Fire resistance (OSB/rubber sandwich panel only)
Stiffness (plasterboard/buffings only)
Impact resistance (plasterboard/buffings only).
Assessment of the thermal conductivity was not considered worthwhile as it was not relevant to the expected end
uses of the composites.
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3.0 Results and discussion3.1 Assessing tyre-derived materials3.1.1 Products available from tyre recyclersThe raw material composition of car tyres is different from lorry tyres. Lorry tyres have a higher proportion of
natural rubber, a lower proportion of fibre and a greater wall thickness. By contrast, car tyres are made of
synthetic rubber, have a higher proportion of steel and fabric and are therefore less profitable to re-process. This
means that markets for processed truck tyres are better developed than those for car tyres.
This project initially examined products derived from truck tyres with a low degree of processing. However, a
decision was made to concentrate mainly on finding new applications for materials derived from processing car
tyres, for which there is an excess of supply over demand.
The recycling process for tyres consists of various stages. Depending on which level of processing is used,
different materials outputs are available. Rubber shreds can be produced in different sizes depending on the
requirements for the end-use applications. Product prices for shredded tyres generally increase dramatically with
the degree of processing (and reduction in particle size). The most common way to recycle tyres is to use a
mechanical shredder. However, other techniques are now available, such as water jetting and cryogenic
processing (liquid nitrogen) (Waste Management News, 3/10/06; Slater 2006). These may produce feedstocks at
an equivalent or lower cost to other recycling methods.
The main processed tyre raw materials currently available can be summarised as follows:
Shreds/crumb
Tyre shreds and crumb are processed materials that are available in various particle sizes. In general, the finer
the material, the higher the end value (as there are more valuable end uses). However, finer materials do require
greater processing, which also incurs additional cost.
Dust
An unavoidable waste (not deliberately produced) from the production of shreds. The amount of dust produced
depends on the nature of the end product (finer shred leads to more dust). It has relatively low value and no
current uses. Following the ban on tyre material to landfill, dust is currently stockpiled.
Buffings
Buffings are an unavoidable fibrous residue derived from the tyre retreading process, in which the existing tread
is removed and replaced with new tread. Buffings have a relatively low value but are of particular interest to
composite manufacturing companies, due to their fibrous shape, potential interlock properties and small particle
size. Available amounts are expected to increase as a result of initiatives to promote the advantages of retreaded
tyres.
Figure 4 details the shreds and powders derived from tyre recycling that were collected and assessed for the
project.
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Figure 4 Description of the tyre shreds collected for the project
Step of recycling
process
Description of product {includes category code as defined in PAS107}
1. Initial
shredding
Coarse shred: 3050mm, contains steel and fibre
(picture shows example of truck tyre). 30 pieces of
coarse shreds were examined (60% contained only
steel, 20% steel and fabric, 20% fabric only){Rough cut shred, RS}
Size (in mm)
Length Width Thickness
Min. 30 11 6
Max. 144 74 17
Mean 76.6 41 11.2 1 cm
2. Removal of
steel
According to one industry source, car tyres contain
approximately 30% steel. The tyres are shredded
to 1525mm size and the steel is removed
magnetically from the shreds. Approximately 8%
of the rubber remains adhered to the steel.3. Shredding of
rubber
Shreds: 2550 mm, contain rubber and fibres
(picture shows example of car tyre) {Clean cut
chips, CC}
4. Removal of
fibres
Granules: 25mm, rubber only (picture shows
example of car tyre) {granulate, G}
1 cm
1 cm
5. Shredding
by-product
Powder:
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3.1.2 Physical properties of the tyre shredsThe density of various types of tyre shreds d ove was characterised. Results are shown in Figure 5.
igure 5 Density measurement of various tyre shreds from truck tyres
uffings
escribed ab
F
Coarse shreds Shreds Granules B
ensity (kg/m3) 1,460* 1,150* 1,060* 1,150*D*data checked and agreed by industry partne densit typi 500kg/m3 depending on particle
.2 Tyre granules bound with resin1
A series of experiments was carried out at BRE in order to find out the reactivity of car tyre granules with binders
curing time
perature on setting time and binding quality
g quality of tyre granules.
he resins used were all isocyanates, specially designed pre-polymers that can also be used for the manufacture
*
The resins are all manufactured from petroleum sources. The environmental impact of these resins (in terms of
he aim was to produce a well-bonded product with the minimum quantity of resin and at a moderatet of water
the
he results of the trial mixes (using the car tyre granulates) are summarised in Figure 6. The following
have any effect on the quality of the curing: curing at 60 C binds the
quality of the product. The curing time can be as short as
C needed was at least 5% for rubber granules to bind effectively (mixes 11 to
penetrate the strand sufficiently
rs. Bulk ies are cally 400
size
33.2. Initial trial mixes
and to optimise the binding systems both for manufacture and performance of the composites produced. The
following mix parameters were used to establish the quality of the mix:
effect of tem
effect of resin content on binding quality of tyre granules
comparison of resin types in terms of their effect on bindin
Tof reactive hot melts. The isocyanate resins solidify to form a bond and cure under the action of atmospheric andsubstrate moisture to form a product which will not re-melt. Three different types were used (all supplied by theproject partners):
Resin A: Different supplier, but with similar properties to B and C
Resin B: Same supplier as Resin C (viscosity of 775mPa.s at 25 C)
Resin C: Same supplier as Resin B (viscosity of 1,800mPa.s at 25 C).
manufacture and product life cycle) has not been assessed. However, health and safety precautions do have tobe followed. Appendix A gives further details.
Ttemperature (60 C or less). As moisture is an essential ingredient in the curing process, a small amounwas added either during mixing or after compaction. The resin was mixed with the rubber in a bowl mixer. Themixed material was tamped by hand into wooden moulds which were sealed in aluminium foil. Pressure wasapplied through a top board and G-cramps. Heat was applied to the sealed packages in an oven to acceleraterate of curing. With one mix (mix 8), an attempt was made to line the mould surfaces with strand (the woodmaterial used in OSB).
Tobservations were made of mixes 114:
It appeared that temperature did notrubber granules as well as at 160 C (mixes 35).
Temperature only affected the curing time, not the
5 minutes with heat applied.
The minimum amount of Resin
14). However, 4.5% of Resin A was sufficient to bind the granules (mix 9).
It was possible to bond the resin/granule mix with strand as the resin did not
(mix 8).
*This is the SI unit for dynamic viscosity. One Pa.s is equivalent to one newton-second per square metre (Ns m2). The unit is
the viscosity of a fluid in which a tangential force of 1 Newton per square metre maintains a difference in velocity of 1
centimetre per second between two parallel planes 1 centimetre apart.
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It is important to note that the amount of resin required varies with the surface area of the rubber, i.e. the
coarser the rubber shred, the less resin is required. Also, fabric fibres present in the rubber shred increase the
resin absorption of the product, therefore requiring greater volumes.
Figure 6 Initial trial mixes (car tyre-derived rubber granulates/resin)
Mix
no.
Curing
timeaTemperature R esin type Resin (%
wt)
Water (%
wt)
Result/
comments
1 Overnight 60 C Resin C 1.6% None Not cured
2 7 hrs 60 C Resin C 1.6% 2cm3 sprayedonto surface
Cureda
Effect of temperature
3 30 min 160 C Resin C 4.5% 4.5% Cured
4 30 min 100 C Resin C 4.5% 4.5% Cured
5 30 min 60 C Resin C 4.5% 4.5% Cured
Reduced resin content
6 5 min 160 C Resin C 2% 2% Cured but
not boundb
7 5 min 160 C Resin C 1% 1% Cured but
not bound
Trial using wood strand and tyre granules (with pressing)
8 5 min 140 C Resin C 4.5% 4.5% Partialadhesion to
strand
Effect of resin (samples were pressed)
9 10 min 160 C Resin A 4.5% 4.5% Cured
10 10 min 160 C Resin B 4.5% 4.5% Not cured
11 5 min 160 C Resin C 3% 3% Cured, not
well bound
12 5 min 160 C Resin C 8% 8% Cured, well
bound
13 10 min 130 C Resin C 6% 6% Cured, well
bound
14 5 min 140 C Resin C 5% 5% Cured, wellbound
a Cured means that the resin had setb Bound means the tyre granulates were bound to each other to form a solid
3.2.2 Initial product developmentResin C had been found to be effective with relatively low proportions of resin. It was therefore used to make the
further mixes to develop composite products. The scope of the project was to consider two application/product
areas:
Laminate floor underlay
Sandwich construction panels, using oriented strand board (OSB) and plasterboard.
Several samples were made using Resin C, and various rubber materials; see Figure 7 for details.
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Figure 7 Description of the initial prototypes developed
Prototype Application Rubber
used
Other
material
used
Comment
Prototype 1: Sandwich
panel for door
or partition
Truck tyre
shred
(50mm
thick)
OSB High density,
difficult to cut panel
due to presence of
steel. Coarse
shreds did not bondtogether well,
therefore the panel
edges had to be
closed with wooden
edge pieces.
Prototype 2: Sandwich
panel for wall
partition
Truck tyre
powder
(12mm
thick)
Plasterboard Good bonding of
tyre with
plasterboard
good potential
Prototype 3: (side, top and bottom view) Laminate floor
underlay
Truck tyre
powder
(6mm
thick)
Laminate
floor board
Good bonding of
tyre with laminate
floor good
potential
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Prototype 4: Sandwich
panel for door
or partition
Truck
tyres.
Shreds
(12mm
thick)
OSB Good bonding of
tyres with the OSB
Prototype 5: No picture available; the sample
was used for fire testing see schematic
below
Sandwich
panel for door
or partition
Truck tyre
granules
25mm.
(100mm
thick)
OSB Good bonding of
tyres with OSB.
Figure 8 Schematic of Prototype 5
The prototypes developed were discussed with the project partners. It was decided that the subsequent activities
should concentrate on the use of car tyre-derived material (for which there is a need to develop new markets),
rather than truck tyre-derived material for which high-value markets, such as safety surfacings, are already well
developed.
The industrial partners also highlighted the point that, to be of interest, new construction products containing
tyre-derived material would have to be able to compete on price with existing products. The product type that
was chosen for further investigation was theplasterboard sandwich panel for wall partitions(prototype 6) as this
was thought to be a higher-value application than sandwich panels. These were selected for the following
reasons:
There is an active market for acoustic partitions, floor underlay and acoustic board products based onplasterboard.
Good acoustic damping properties can be anticipated from products made with recycled rubber due to its
damping properties.
The raw materials price for tyre-derived rubber makes it attractive for consideration as an ingredient in wall
partitions. This was confirmed in the market survey (Section 3.3).
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3.2.3 Further prototypes: laminate floor underlay and plasterboard sandwich panelsPrototypes 2 and 3 were shown to industry partners to gauge the level of interest from a technical viewpoint. In
parallel, an economic assessment of each of these applications was carried out (see Section 3.3). Further mixes
were also developed using waste car tyre-derived rubber.
One of the concerns with the prototype samples shown in Figure 7 was the stiffness of the rubber layer, as this is
important in determining the acoustic insulation properties. In general terms, the stiffer the layer, the less soundattenuating and the more thermally insulating the layer is. For this particular project, sound attenuation was the
main interest and the prototype samples were deemed too stiff for the best attenuation in both applications. The
type of resin used in the mix is the main parameter affecting the stiffness of the prototype. Another resin (a
polyurethane resin known as Resin D) was therefore used to develop further prototype samples (see Figure 9).
The work also focused on small particle-sized materials (such as buffings) which were considered likely to be
suitable for the fabrication of thin components. These materials also have the advantage of low market price
(10 times the diameter of
the largest particle. Hence, a layer thickness of 10mm was the starting position for the prototypes.
The new prototype samples were made using a polyurethane resin (Resin D) which is activated by atmospheric
moisture. It therefore requires no heat or water addition to the mix. It is also judged to be less stiff than the
isocyanate resins. The manufacturers recommended that, for small particle sizes, 1520% (by weight) of resinshould be used. This is a higher resin content than that used for the first phase and as a result, the cost of the
resin makes up the bulk (approx. 8090%) of the raw materials cost of the resin/rubber layer. (See market
survey, Section 3.3. and Appendix A.)
The sample mixing and compaction procedure was the same as that used to manufacture the previous
prototypes. However, the samples were cured at room temperature and without the addition of water. A longer
curing period was also used compared with the previous laboratory prototype samples. The rubber used for these
samples was buffings (derived from tyre retreading). Buffings are relatively low in cost (see Section 3.3), small in
particle size and do not contain any fibre (which absorbs a large amount of resin). In addition, the small particle
size allows fairly thin components to be made. Two types of prototype were produced (Figure 9).
Both prototype samples that were developed from the buffings during the second phase of the project appeared
less stiff when handled than the samples previously developed. They were therefore considered more promising
for technical investigation as potential acoustic insulation products. The materials mixed easily and the products
were easy to mix and compact. The finished products were well bonded together when cured and appeared to
have a good level of stiffness. The fibrous structure of the buffings also provided a good particle interlock, which
is expected to provide better tensile strength. However, an economic assessment of the floor underlay recipe
showed that the use of buffings in this application was uneconomical compared with alternatives already on the
market (see Section 3.3.4). No further tests were therefore carried out on the floor underlay.
In summary, the sandwich wall panel (Prototype 6) was considered successful. A sandwich panel prototype with
17.5% resin content was successfully manufactured. An initial assessment of the cost of raw materials also
indicated that it could be economically viable and compete on price with competitor partition products. However,
the economic assessment of the materials indicated that the resin represents a major component (around 90%)
of the materials cost. It is expected that, with the development of bioresins that are not based on petrochemicals,the price of the resin component will fall to perhaps half that of the current price of petrochemical resins.
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Figure 9 Description of the second phase of prototypes developed using buffings
Picture Application Resin %
(by
weight)
Rubber
used
Other material
used
Comment
Prototype 6: Sandwich
panel for
wall partition
Resin D:
17.5%
Buffings
(10mm
thick)
Plasterboard Good bonding of
tyre with
plasterboard.
Prototype appears
less stiff thanPrototype 2 good
potential
Prototype 7: Bottom and top view Laminate
floor
underlay
Resin D:
17.5%
Buffings Laminate floor Good bonding of
tyre with laminate
floor. Prototype
appears less stiff
than Prototype 3
good potential
Lafarge Plasterboard showed an interest in the plasterboard sandwich panel and the economic assessment of this
product showed that it was potentially economically viable. The plasterboard samples were therefore tested
further under this project. The results of testing conducted by Lafarge Gypsum, on prototypes similar to
Prototype 6, are given in Appendix A.
3.2.4 Tests on the tyre/resin mixesFire tests
Small-scale fire tests were carried out on two prototype samples:
Prototype 2 (tyre layer: 100mm thick)
Prototype 5 (tyre layer: 100mm thick): granulates were high-value tyre products as they contained no fibre or
steel. Tests on this prototype were carried out mainly to gain information about the behaviour of rubber underfire conditions.
The test regime was adopted from the ISO5660 Cone Calorimeter test (WCTE, 2004). A radiation level of
50kW/m2 was chosen. The test exposes one side of the sample to the irradiation (Figure 10) and monitors the
temperature build-up through the depth of the test specimen with exposure time (for samples of 100mm
thickness). In these tests the temperature build-up was monitored in two locations:1 At the interface between unexposed board and core material2 At the centre of the core material.
This test regime is currently under development at BRE and is being used to assess product performance in
preparation for full-scale fire resistance tests to EN1363. The regime does not replace full-scale fire testing but
has been shown to provide a good indication of key performance characteristics of materials and their use in
structural wall units. It also enables comparison of performance levels of different material types and
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combinations. The test set-up has several advantages, including the possibility to closely observe failure
characteristics of the specimen, especially after the test has been completed.
Figure 10 Stages of small scale-fire test to the modified EN1363
The fire tests showed that whilst the outer layer (in the case of OSB) was burned (Figure 11) or degraded (in the
case of plasterboard, Figure 12), the rubber core merely charred very slowly, rather than igniting or melting (asshown on the right hand sides of both Figures 11 and 12). The temperature probe placed just at the interface
between unexposed board and core material showed that after 30 minutes of exposure to the heat source, the
temperature remained at room temperature.
Figure 11 Hole burned through OSB
4 cm
4 cm
Figure 12 Hole burned through the plasterboard, sheathing, and charred rubber core
Many applications or products have more specific test requirements than can be addressed by a simple test such
as the calorimeter test. Nevertheless, the work done so far does give an early indication that combustibility may
not be a major problem with these products containing tyre rubber. It is also recognised, however, that issues
such as the amount and nature of smoke generated are important. Further testing of prototype products would
be necessary to address these issues fully. Such tests would need to be specific to the intended application to
determine the fire resistance period of, for example, a stud partition with rubber-backed sheathing boards.Polyurethanes such as Resin D are combustible and can regenerate isocyanate fumes. However, phosphate-type
flame retardants can be added which can be very effective barriers to the propagation of flame.
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Further tests on the plasterboard wall partition samples (Prototype 6)
Further samples of Prototype 6 were prepared, using a different Resin D. The tyre layer as prepared for Prototype
6 samples was tested for:
water vapour permeability
permeability
water absorption swelling of the tyre layer with water over time.
Prototype 6 was also tested for:
stiffness (3 point bending). The test method utilises a constant span (100cm) between supports and gives the
amount of maximum deflection from the horizontal (at mid span at the time of failure) and the load required
to cause that failure.
density
impact resistance: The impact test allows materials to be categorised into duty categories of light, medium,
heavy or severe. Appendix A gives further details.
Tensile and compressive strength were not assessed as resistance to bending/deflection of the prototype was
considered more relevant to the performance of partition boards. The results of the tests are summarised in
Figures 13 and 14.
Rubber layers (10mm thickness) were manufactured at BRE with three different resins. These were sent to
Lafarge Gypsum for the manufacture of prototype panels and assessment for potential acoustic benefits. The
results from the tests conducted and the methods adopted are described in Appendix A. An overview of the
results is given in Figure 15.
Figure 13 Results of tests performed on the tyre layer of Prototype 6Test Result Comment
Water Vapour Permeability (BS EN
ISO12572:2001)
650 g/m2 /day The tyre layer is permeable, so cannot be used at a
vapour barrier.
Water Absorption 21.43%
Swelling (tested in water at 20 C
measured after 7 days) (BS EN317:1993)
1.08%
Virtually no swelling, although the water absorption
is high (probably due the presence of voids
between tyre buffings).
1 cm
Figure 14 Results of tests performed on Prototype 6
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Test Results and comments
Stiffness (adapted from EN310:2003)
Sample size: 600mm length x 50mm width x
32mm thickness
Average results (for 3 samples) for Prototype 6: Mean
deflection 12mm under a load of 258.62N
The average result (for 3 samples) for a single layer of
plasterboard: Mean deflection 17mm under a load of 68N.
1 cm
1.73mm indent on board for impact of 10Nm
Suitable for Severe duty
Impact (up to 10Nm) based on BS5234-2 1992
Part 2 and BS8200: 1985 [8, 9]
An indent caused by a
10Nm impact Average
diameter of indents =
23.3mm; depth = 1.73mm
Figure 15 Results of tests performed on prototypes manufactured by Lafarge Gypsum
Test Results and comments
Manufacture
Prototypes with three resin types, identical
thickness were developed and tested using a
method based on ISO16940*
type A : 12.5mm standard + type A resin/rubber
10mm
type B : 12.5mm standard + type B rubber/resin
10mm
type C : 12.5mm standard + type C rubber/resin
10mm
plasterboard layer
rubber/resin layer
Acoustic (damping of vibration of the board)
Acoustic performance: dynamic stiffness anddamping (tested by Lafarge Plasterboard)
All the results were encouraging and showed good results in
terms of dampingof the vibration of the board compared to
conventional products. Damping results were 4% for all
three prototypes.
* ISO16940 Glass in building Glazing and airborne sound insulation Measurement of the mechanical impedance of
laminated glass
3.2.5 Used tyre-performance-demand model
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The most successful prototype (technically and commercially) was a panel based on resin-bound rubber buffings
bonded to plasterboard. A matrix was therefore developed for the plasterboard/buffings composite sandwich
panel material. Function-demand inputs to the model (developed by the BRE team) were as shown in Figure 16.
The results of the assessment of the prototype against the matrix are given in Appendix A. Here, the performance
and cost of the composite is compared in relation to service classes for plasterboard and competitor acoustic
boards.
Figure 16 Function-demand inputs
Resin bindero Resin type
o Resin content (%)
o Resin cost
Tyre/resin layero Stiffness
o Durability (moisture resistance)
o Shear resistance
Tyre-derived rubber
o Tyre-derived material (particle
grading and shape)
o Relative density
Tyre/plasterboard composite performance
o Impact resistance
o Bending strength
o Deflection
o Interlayer bond strength
o Stiffness of rubber/resin layer
o Stiffness of plasterboard layer
o
thickness of rubber/resin layero Thickness of plasterboard layer
Possibil ities for modification of key properties of the overall composite
o Resin type
o Resin content (%)
o Tyre-derived material (particle grading and shape) as received
o Possibility to modify the tyre-derived material
o thickness of rubber/resin layer
o Thickness of plasterboard layer
o Number of layers (2 or 3)
o Options for onsite mixing versus delivery to manufacturer as a roll
3.2.6 Summary of the prototype developmentThe plasterboard sandwich panel with a buffing/ resin layer in the centre (10mm thick), using Resin D was
successfully developed and showed:
Good acoustic properties (vibration damping)
Improved stiffness properties compared to a single plasterboard layer
Impact resistance equivalent to that of a panel suitable for severe duty
The rubber layer had a similar density (kg/m2) to that of a sheet of plasterboard (12mm thickness).
The technical properties of the panel were, therefore, so far very promising. A comparison of the prototype
properties with those of other boards (where available), is given in Appendix A.
With the prototypes manufactured at BRE and tested at Lafarge Gypsum, all the results were encouraging and
showed good results in terms of dampingof the vibration of the board compared to conventional products.Results obtained in the project are compared with data for other plasterboard and acoustic board products in
Appendix A.
3.3 Market survey
One issue raised by the project partners was the need to ensure that the products developed during the projectwere economically competitive with comparable products. A detailed market review was therefore conducted on
the two products identified (acoustic wall board and acoustic underlay).
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3.3.1 Market drivers for the use of tyres in compositesThe main general market drivers for processed tyre materials are summarised below (Figure 17). (+) indicates
drivers that are likely to increase the supply of materials and lead to lower raw materials prices; (-) indicates
drivers that are likely to compete with construction applications for low-cost waste tyre material, reducing supply
and increasing cost. Several manufacturers were contacted and an internet search was carried out to find out the
value of materials derived from waste tyres. Results are given in Figure 18.
Figure 17 Effects of the drivers influencing the market for recycled tyresDriver influencing market for processed tyre materials Effect of driver
+Whole and chopped tyres banned from Landfill (July 2006)
-Competition for restricted supplies of raw materials could act against new entrants tomarkets (Materials Recycling World, Issue 17)
-Competition for coarse shredded rubber with other high-value end uses (e.g. equestriansurfaces), and with cement kiln fuels (Materials Recycling World, issue 17)
+Economies of scale as processing capacity increases
+Current markets are seasonal (equestrian surfaces, lawn treatment). There may therefore bescope for less seasonal products such as construction products
+WRAP drive to stimulate remould tyre market is likely to increase the supply of buffings
Figure 18Value of size-reduced materials derived from waste tyres (approx. figures from manufacturers, 2006)
Material Approx
price
per
tonne
Corresponds
to PAS107
category
code
Description Application
a) Coarse shreds
(3050 mm)
5 ex
works
RS Large tyre shreds with steel and
fibre present
Civil engineering
b) Shreds (5 mm
to 25 mm)
60 CC Flat thin particles; textile fibre
present
Equestrian
surfaces/paths
Coarse
(
>5mm)
c) Small
shreds/granuleswith fibre
(10 mm single
size)
100 CC Flat thin particles; textile fibre
present
Equestrian
surfaces/paths
d) Rubber
granules
(25 mm)
100
120
G Virtually single size shred
material. Minimal textile fibres
Playground
surfacings/turf
reinforcement
e) Tyre fibre 5 - (Rayon/nylon with some rubber) None currently
f) Buffings 4050 - Fibre-like rubber particles up to
3mm long, minimal textile fibre
content, some finer material
None currentlyFine
(
Recommended