PAS 108 vs Non-Compliant Tyre Bales: Why Specification Matters

By:     Kieran Donnelly

Two bales sit side by side on a civil engineering site. Both are compressed rubber, bound with wire, roughly the same shape. One will perform exactly as the structural design requires. The other may settle, shift, or fail procurement entirely — and from the outside, you cannot tell which is which.

That gap between compliant and non-compliant tyre bales is what this guide addresses. PAS 108 vs non-compliant tyre bales is not a technical debate for standards committees; it’s a commercial and structural reality that affects every producer supplying the civil engineering market, every contractor specifying bale materials, and every engineer signing off on a design. Get it wrong, and the consequences range from a rejected delivery to a remediation bill.

This guide sets out exactly what PAS 108 requires, where non-compliant bales fall short, and what that means for performance, procurement, and liability.

Two Bales That Look the Same But Aren’t

From a distance, a PAS 108-compliant tyre bale and a non-compliant bale look identical. Both are compressed masses of rubber tyres, roughly rectangular, bound with wire. The visual similarity leads some buyers and producers to treat them as equivalent. They are not.

The difference is not arbitrary bureaucracy. PAS 108 defines the material properties that civil engineers use when they design structures with tyre bales. Bale density, compressive stiffness, dimensions, and tie wire specification are all values that appear in design calculations. When the installed bale matches those values, the structure performs as designed. When it doesn’t, the structure may underperform, fail to comply with the design specification, or, in the worst case,e create a safety or serviceability problem that is expensive to remediate.

This guide sets out exactly what separates compliant from non-compliant bales, why each requirement in the standard exists, and what the practical consequences of non-compliance are for producers, contractors, and end users. It also addresses the commercial reality: in the civil engineering market, PAS 108 compliance is not optional. It is the admission criterion.

The Specific Requirements PAS 108 Sets

Understanding the comparison requires knowing what PAS 108 actually specifies. The standard sets requirements across several measurable parameters.

Bale dimensions. PAS 108 specifies target dimensions for the finished bale within defined tolerances. The dimensional requirement exists because engineers designing tyre bale structures assume consistent bale sizes. A structure designed on the basis of standard bale dimensions will not perform as designed if the actual bales vary significantly from those dimensions. Undersized bales create voids between bale courses that reduce the structure’s load-carrying capacity and introduce differential settlement. Oversized bales create installation problems and may not fit within the designed structure geometry.

Bale mass. The standard specifies a minimum mass for PAS 108 bales. Mass is a proxy for the quantity of tyre material within the bale. An under-mass bale has less rubber content than the specification requires, which in most cases means it has also been under-compressed. Under-mass bales are lighter in density, softer in compressive stiffness, and less stable as structural elements than specification bales.

Bale density. Density (mass divided by volume) is the engineering property that links mass and dimensions into a single value used in design calculations. A bale can technically meet a mass requirement and a dimensional requirement separately while still failing a density requirement if the relationship between the two is wrong. PAS 108’s density requirement ensures internal consistency: a bale that meets density is a bale where mass and volume are in the right proportion.

Tie wire specification. The number, placement, and specification of the baling wires are defined in PAS 108. Under-specified ties (too few wires, wire gauge too light, or wires in the wrong positions) allow the compressed tyre mass to expand after baling, changing the bale’s dimensions and density. A bale that is correctly compressed at ejection but that expands over the following days or weeks because the ties are inadequate is a non-compliant bale, regardless of whether its initial measurements appeared correct.

Tyre type. PAS 108 addresses the consistency of tyre types within bales. Different tyre types (car, van, truck, OTR) have significantly different sidewall construction, rubber content, and compressibility. A bale containing a random mix of tyre types has unpredictable material properties compared to a bale of consistent tyre type. PAS 108 production requires tyre sorting before baling as a baseline operational practice.

What Non-Compliant Bales Actually Look Like in Practice

Non-compliant bales are not a single category. They exist on a spectrum of deviation from the standard, and the consequences of non-compliance scale with the extent of the deviation.

Under-compressed bales are the most common non-compliance type. They occur when the baler does not reach the specified compressive force, when the chamber is loaded with too few tyres, or when the hydraulic system of an ageing or poorly maintained baler has lost pressure. Under-compressed bales appear complete but are lower in density and softer than specified. Under load, they deform more than designed and may settle differentially within a structure.

Inconsistently sized bales result from varying tyre loading quantities or from a baler with worn chamber components that no longer produce consistent geometry. Inconsistent dimensions create installation problems in the field: bale courses that don’t sit level, gaps between adjacent bales that reduce the structure’s load distribution, and overall structure geometry that doesn’t match the design drawings.

Under-tied bales emerge from balers with wire feed faults, inadequate wire specification, or operators bypassing tie cycles to increase throughput. A bale with fewer ties than specified, or with ties placed in the wrong positions, will expand progressively after ejection. The expansion is typically most pronounced in the first few days after production, meaning a bale that passed a visual inspection at the production facility may be non-compliant by the time it arrives on site.

Mixed-tyre bales result from poor intake sorting or deliberate mixing of tyre types to manage throughput. The unpredictable material properties of a mixed-tyre bale make it unsuitable for structural applications where the design uses specific material property values.

The Consequences of Using Non-Compliant Bales

The consequences of installing non-compliant bales in a civil engineering application depend on the extent of the non-compliance and the nature of the application.

For road and embankment foundations, under-dense bales settle more than designed, causing differential settlement in the road surface above. The differential settlement creates a road that is difficult to maintain to the required ride quality and may accelerate pavement deterioration over a wider area than the settlement zone itself. In a worst-case scenario on a steep approach, differential settlement can create a safety hazard.

For retaining wall drainage backfill, the primary consequences of non-compliant bales relate to dimensional inconsistency rather than density. Irregular bale dimensions create preferential flow paths through the drainage zone and may leave areas of the wall inadequately drained. Over time, this can increase pore water pressure in isolated zones behind the wall, potentially affecting wall performance.

For slope stabilisation, under-mass or under-dense bales are less stable as individual units and provide a lower total gravitational resistance to slope movement. In a slope that is already marginal in stability, installing bales below the design density could reduce the factor of safety below the required minimum.

For the producer, supplying non-compliant bales to a civil engineering project creates contractual exposure. If the bales are tested on site and found non-compliant, the contractor can reject the delivery and claim for costs associated with the rejected material and any delays. If non-compliant bales are installed and their non-compliance contributes to a structural problem, the producer may share liability for the remediation costs.

Why the Equipment You Use Determines Compliance

PAS 108 compliance is not achievable through better intentions or more careful visual inspection. It requires the right equipment, configured and maintained correctly.

A baler that cannot achieve the specified compressive force cannot produce compliant bales, regardless of how carefully it is operated. A baler with a worn hydraulic pump that drops below the specified pressure mid-cycle will produce under-compressed bales. A wire feed system with a fault that intermittently skips a tie position will produce under-tied bales that look correct visually.

Gradeall’s MKII Tyre Baler is designed to produce PAS 108-compliant bales. The chamber dimensions, compressive force specification, automatic six-wire tying system, and programmable control system are configured to the standard’s requirements. Regular maintenance, including hydraulic pressure testing against the specification and wire feed system inspection at scheduled intervals, is what keeps the machine producing to specification over time.

Pre-processing also determines compliance. For truck tyre bales, sidewall cutting using the truck tyre sidewall cutter before baling is the difference between reliably achieving the density specification and struggling to reach it consistently. The removed sidewall eliminates the spring-back force that prevents the tyre body from compressing to the required density. For car tyres, consistent tyre sorting and loading to the established per-bale loading quantity is the pre-processing discipline that determines compliance. See the full tyre recycling equipment range for every stage of compliant production.

The Commercial Reality: Non-Compliant Bales Cannot Access the Civil Engineering Market

For tyre recycling operations, the civil engineering supply chain is one of the most valuable outlets for bale production. PAS 108 bales supplied to road construction, slope stabilisation, retaining wall, and flood defence projects command consistent demand and provide a documented, high-value end use for processed tyre material.

Non-compliant bales are excluded from this market by procurement requirements, not by preference. Civil engineering contracts that specify PAS 108 bales require the producer to demonstrate compliance through production documentation. A producer who cannot provide this documentation cannot supply the civil engineering market, regardless of the apparent quality of their product.

The investment in PAS 108-capable production equipment, the pre-processing line, the quality management system, and the documentation process is the commercial investment that opens the civil engineering market. Producers who make this investment have access to a higher-value, more stable outlet than those who produce non-compliant bales for energy recovery or general industrial use.

“We see the difference clearly in the market,” says Conor Murphy, Director of Gradeall International. “Operations that have invested in proper equipment and pre-processing consistently find the civil engineering market, where the bale has a documented, high-value end use. Operations running older or under-specified equipment are restricted to lower-value outlets that are also less stable. The equipment investment is also a commercial investment.”

Contact Gradeall International to discuss the equipment specification required for PAS 108-compliant bale production.

Frequently Asked Questions

Specification questions come up at every stage of tyre bale procurement, from initial equipment investment through to on-site delivery verification. Here are the questions Gradeall hears most often from producers, contractors, and engineers working with PAS 108 bales.

← Back to news