Tyre bales have been used in civil engineering and construction for decades, but for much of that time their use was informal. Engineers working with tyre bales had no standardised specification to design to, no consistent product to procure, and no quality baseline to hold suppliers to. Two bales from different producers could vary significantly in density, dimensions, and tie specification, making structural design calculations unreliable and supply chains unpredictable.
PAS 108 was developed to solve this. Published by BSI (British Standards Institution) with input from WRAP (Waste and Resources Action Programme) and the civil engineering sector, PAS 108 is the publicly available specification that defines what a tyre bale must be to qualify for use in civil engineering applications. It covers dimensions, mass, density, tie wire specification, and the processes by which bales are manufactured and quality-assured.
The existence of PAS 108 changed the status of tyre bales from a novel waste-derived material of variable quality into an engineered product with a documented specification. Engineers can now design structures using PAS 108 tyre bales with confidence that the product they specify will be manufactured to consistent dimensions and mass. Recyclers producing PAS 108 bales have a defined target to manufacture to, a quality framework to operate within, and a credible product specification to present to potential buyers.
For any tyre recycling operation producing bales for civil engineering supply, understanding PAS 108 is not optional. It defines the product you are making.
PAS 108 sets requirements across several areas. Each requirement exists for a reason connected to how tyre bales perform in civil engineering applications.
Bale dimensions. PAS 108 specifies target dimensions for the finished bale. The standard’s dimensional requirements ensure bales can be handled with consistent equipment, stacked predictably, and used in structures designed to specified dimensions. Bales that vary significantly in size from the specification create problems in the field: irregular stacking, inconsistent interlock between adjacent bales, and structures that don’t match the design drawings.
Bale mass. A PAS 108 bale has a specified minimum mass. Mass requirements ensure that bales contain sufficient rubber content to perform as the structural material the engineer has specified. A bale that meets dimensional targets but is below mass specification is likely to be under-compressed and will not achieve the density properties used in design calculations.
Bale density. Density (mass divided by volume) is a key engineering property of a tyre bale. It influences the bale’s compressive stiffness, its resistance to deformation under sustained load, and the drainage characteristics of a bale-fill structure. PAS 108 density requirements ensure the bale behaves as predicted in engineering models.
Tie wire specification. Baling wire holds the compressed tyre mass in its baled form. PAS 108 specifies the number of ties, their placement, and the wire specification (gauge, tensile strength). Under-specified ties on a high-compression bale can fail progressively after the bale is ejected, leading to bale expansion that changes its dimensions and density properties.
Tyre type consistency. PAS 108 addresses tyre type consistency within bales. Mixing significantly different tyre types within a single bale creates inconsistency in bale properties because different tyre types compress differently. Operators targeting PAS 108 compliance should sort tyre types before baling rather than loading whatever is available.
Documentation and quality management. PAS 108 includes requirements for production records, quality management, and the documentation that accompanies bale deliveries. Civil engineers specifying PAS 108 bales need to be able to verify that the bales they receive were made to the standard. This requires documentation from the producer.
Producing PAS 108-compliant bales consistently requires the right equipment, operated correctly, with the right tyre pre-processing and quality monitoring in place.
Equipment specification. Not all tyre balers produce PAS 108-compliant bales. The compressive force, baling chamber dimensions, and tie wire system of the baler all affect whether the output meets the standard’s requirements. Gradeall’s MKII Tyre Baler is designed to produce PAS 108-compliant bales from car and truck tyres. The machine’s chamber dimensions, compression force, and six-wire tying system are configured to the specification requirements.
Tyre pre-processing. The quality and consistency of the tyre input affects the quality and consistency of the bale output. For car tyre bales, properly sorted, rim-free tyres bale predictably. For truck tyre bales, sidewall cutting before baling significantly improves density and consistency. Gradeall’s truck tyre sidewall cutter is the standard pre-processing step for truck tyre PAS 108 production; the removed sidewall reduces spring-back resistance and allows the tyre body to compress to the density required by the standard. For the full tyre processing equipment range, see Gradeall’s tyre recycling equipment.
Loading consistency. The number of tyres loaded per bale, and their loading orientation, affects bale mass and density. Operators need to follow a consistent loading protocol rather than loading by visual judgement. Most operations that produce PAS 108 bales develop a tyre count and loading orientation standard for each tyre size they process.
Tie wire quality. The wire used must meet the specification for tensile strength and gauge. Sub-specification wire may not hold the compressed bale mass reliably, particularly in the weeks after production when some spring-back occurs. Use wire specified for the baler and the standard being produced to.
Quality monitoring. PAS 108 production requires ongoing quality monitoring: checking bale dimensions and mass against the specification, recording results, and acting on any drift from the target. A baling operation that produces to specification initially but doesn’t monitor ongoing production will drift out of compliance without knowing it.
PAS 108 compliance is specifically required for tyre bale applications in civil engineering and construction where the bale is a structural or functional element of the design. The main applications include:
Lightweight embankment fill. Tyre bales used to reduce the load on weak or compressible ground beneath embankments must meet PAS 108, because the engineer’s design is based on the density and compressive properties that the standard defines.
Retaining wall backfill. Tyre bales used as free-draining backfill behind retaining walls need consistent dimensions and density to perform reliably in this role over time.
Road construction over soft ground. Access roads and haul roads built over areas with poor bearing capacity use tyre bale foundations to distribute load. PAS 108 bales provide the consistent mechanical properties the design requires.
Slope stabilisation. Tyre bales placed on eroding slopes or used in landslip repair need to be dimensionally consistent to interlock effectively and provide the design load distribution.
Noise and vibration attenuation. Some applications use tyre bale walls as acoustic or vibration barriers, exploiting the rubber’s damping properties. PAS 108 bales provide consistent acoustic performance.
In all of these applications, the engineer has designed to specified material properties. PAS 108 is the framework that connects the designer’s specification to the producer’s output.
Understanding the limits of PAS 108 is as important as understanding what it requires.
PAS 108 covers the manufactured bale product. It does not specify how tyre bales should be used in specific engineering applications. The structural design of any installation using tyre bales remains the engineer’s responsibility and should be based on the geotechnical and structural properties of the bale as documented in the research literature supporting PAS 108’s development.
PAS 108 does not supersede planning consent, environmental permit requirements, or site-specific conditions. A tyre bale fill installation on a regulated site still requires all the relevant consents and permits regardless of whether the bales themselves are PAS 108-compliant.
PAS 108 also does not address the end-of-life management of tyre bale structures. When a temporary tyre bale structure is decommissioned, or when a permanent installation is eventually removed, the tyre bales at that point are waste tyres and must be managed accordingly under waste regulations.
Gradeall has been manufacturing tyre baling equipment for nearly 40 years from its facility in Dungannon, Northern Ireland. The MKII Tyre Baler produces up to 6 PAS 108-compliant bales per hour, with consistent chamber dimensions, programmable compression force, and a six-wire automatic tying system. Equipment is exported to over 100 countries worldwide.
“Producing consistent PAS 108 bales is about getting every stage right, from the tyre input and loading through to the wire specification and ejection,” says Conor Murphy, Director of Gradeall International. “The baler is the critical piece of equipment, but it only performs to specification if the input tyres are properly prepared and the operator is following a consistent loading protocol.”
For operations looking to establish PAS 108 production, the starting point is specifying the right baler, understanding the tyre pre-processing requirements for the tyre types being processed, and setting up a quality monitoring system from the first day of production. Contact Gradeall International to discuss equipment specification and production setup for PAS 108 bale manufacturing.
PAS 108 is not legislation; it is a publicly available specification published by BSI. However, engineers specifying tyre bales in structural applications will typically require PAS 108 compliance as a condition of the specification. Procurement contracts for tyre bales in civil engineering contexts almost always require PAS 108 compliance. In practice, PAS 108 compliance is a commercial necessity for supply to the civil engineering market.
Through production records documenting bale dimensions, mass, tyre input type, and loading quantities for each batch produced, alongside a quality management system that demonstrates ongoing compliance monitoring. Some procurement contracts require third-party verification; others accept producer self-certification with documented records.
Only if it is capable of achieving the required compression force, has the appropriate chamber dimensions, and can apply the required tie wire specification. Not all balers on the market are capable of PAS 108 production. Confirm the specification with the baler manufacturer before purchasing equipment for PAS 108 production.
Yes. PAS 108 covers tyre bales from car and truck tyres. The specification requirements are the same regardless of tyre type, but achieving them from truck tyres requires more attention to pre-processing. Sidewall cutting using Gradeall’s truck tyre sidewall cutter before baling is standard practice for consistent PAS 108 truck tyre bale production.
A non-compliant bale may vary in dimensions, mass, density, and tie specification. These variations affect how the bale performs in civil engineering applications, how consistently it can be handled and installed, and whether the engineer’s design assumptions hold. Non-compliant bales are not suitable for structural civil engineering applications, though they may still be acceptable for energy recovery or other non-structural uses.
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