PAS 108 vs ASTM D6270: Comparing UK and US Tyre Bale Standards

By:     Conor Murphy

Tyre bales used in civil engineering applications are governed by different specifications in the UK and the United States. PAS 108, published by BSI and developed with WRAP’s research support, is the UK standard. ASTM D6270, published by ASTM International, is the US standard. Both documents aim to define what a tyre bale must be to qualify for structural civil engineering use, but they take different approaches, reflect different research traditions, and have different implications for tyre bale producers and procurement teams operating in each market.

For UK tyre recycling operations that export equipment or bales internationally, or for engineers working on projects where specification requirements from both standards might be relevant, understanding the similarities and differences between PAS 108 and ASTM D6270 is useful. For US operations using Gradeall equipment, or for engineers in markets that reference either standard, the comparison clarifies which specification requirements apply and where the standards diverge.

Background and Development: Different Paths to the Same Goal

The two standards have distinctly different development histories, which helps explain some of their differences in approach and emphasis.

PAS 108 was developed through a deliberate, research-driven process coordinated by WRAP in the early 2000s, working within BSI’s standards development framework. The process started with comprehensive laboratory and field research on tyre bale properties, generated a substantial body of published technical data, and then used that data to define specification requirements. The standard reflects a top-down approach: research first, specification derived from research findings.

ASTM D6270 was developed through ASTM International’s consensus standards process, which involves committees of industry stakeholders, researchers, and engineers working together to develop and maintain standards. The ASTM process reflects the US approach to standards development, which emphasises industry consensus and tends to be more practice-led than the research-led approach of BSI/WRAP. ASTM D6270 draws on US field experience with tyre bales, primarily from transportation and geotechnical applications.

Both standards are technically credible and reflect genuine engineering knowledge about tyre bale performance. The differences between them are matters of specification detail and measurement approach rather than fundamental disagreement about what properties tyre bales need to have.

Key Specification Comparison

The two standards specify different absolute values for some parameters, reflecting different baseline bale sizes common in each market. UK standard bales produced to PAS 108 dimensions are not identical to US standard bales produced to ASTM D6270 dimensions, and the specific mass and density requirements differ accordingly.

Dimensional and Mass Requirements: Where the Numbers Differ

The dimensional targets in PAS 108 reflect the chamber dimensions of tyre balers commonly used in the UK market, and the mass requirements reflect the tyre types (predominantly car and truck tyres) that dominate the UK waste tyre stream.

ASTM D6270 was developed in a US context where the waste tyre stream composition, common baler sizes, and civil engineering application scales differ somewhat from the UK. The US standard specifies bale dimensions that reflect the balers commonly used in the American tyre recycling industry, which may differ from UK equipment dimensions.

For operators producing bales for both markets, the dimensional difference is a practical consideration. A baler designed to produce PAS 108-compliant bale dimensions will not automatically produce ASTM D6270-compliant bale dimensions if the two specifications differ. Gradeall’s MKII Tyre Baler is configured for PAS 108 production. For operations targeting the US market, the ASTM D6270 requirements need to be confirmed against the equipment specification.

The mass requirements in both standards serve the same purpose: ensuring the bale contains sufficient rubber content to achieve the minimum density required for structural applications. The absolute values differ because the bale dimensions differ, but the underlying principle is identical.

Wire Tie Specification: Similar Requirements, Different Detail

Both PAS 108 and ASTM D6270 specify minimum numbers of wire ties and address tie placement. Both recognise that tie wire specification (number, placement, gauge) is critical to maintaining bale geometry after ejection from the baler. Both standards reflect the understanding that under-tied bales expand after production, changing dimensions and density in ways that compromise structural performance.

The specific requirements on tie count and placement differ in detail between the two standards, reflecting the different bale sizes and production contexts in each market. The MKII Tyre Baler’s automatic six-wire tying system meets PAS 108 tie requirements. For ASTM D6270 compliance, the tie count and placement requirements should be verified against the specific edition of the ASTM standard.

Application Scope: Where Each Standard Focuses

PAS 108 focuses specifically on the tyre bale product specification. It defines what a bale must be, not in detail how it should be used. Application guidance for PAS 108 tyre bales in civil engineering is provided separately through WRAP technical publications, academic research, and professional design guidance, rather than being incorporated into the standard itself.

ASTM D6270 takes a somewhat broader approach, incorporating more application context within the standard document itself. This reflects ASTM’s convention of including practice guidance within standards documents, and the US tradition of providing design guidance alongside material specifications in the same document.

For engineers designing with tyre bales in the UK, PAS 108 provides the material specification and WRAP publications provide the application guidance. For US engineers, ASTM D6270 provides both material specification and some application context. The combined body of knowledge available to engineers designing tyre bale structures in the UK is at least as comprehensive as that available in the US, just distributed across separate documents.

Producing Bales to Both Standards: Practical Considerations

For a tyre recycling operation considering whether to produce bales that could meet both PAS 108 and ASTM D6270, the practical question is whether a single production configuration can meet both specifications.

The short answer is: it depends on whether the dimensional requirements of the two standards overlap. If the bale dimensions specified in PAS 108 fall within the acceptable ranges of ASTM D6270, a baler configured for PAS 108 production may produce bales that also meet ASTM requirements. If the dimensional requirements don’t overlap, producing for both markets would require either different baler configurations or accepting that bales for each market are produced separately.

For the mass and density requirements, the same logic applies. If the PAS 108 mass specification for a given bale size produces a density that also meets ASTM D6270 requirements for the equivalent US bale size, dual compliance may be achievable. If not, production protocols may need to be differentiated.

For Gradeall equipment exported to the United States, the US-market tyre processing and baling context is addressed by Gradeall’s sales and technical team. Contact Gradeall International for guidance on equipment configuration for US market applications. The tyre recycling equipment range includes equipment suitable for the full range of tyre processing and baling requirements in both markets. American English note: in the US market, the material is “tire bales” not “tyre bales”, and US-targeted content from Gradeall follows American spelling conventions.

The Broader International Picture

Beyond PAS 108 and ASTM D6270, several other countries have developed or referenced national guidance on tyre bale civil engineering use. Australia, Canada, and various European countries have drawn on the UK and US research and standards development in creating their own guidance documents, sometimes referencing PAS 108 directly and sometimes adapting it for national context.

This international adoption of tyre bale civil engineering practice, and the cross-referencing of PAS 108 in multiple countries’ guidance documents, reflects the quality of the UK research base and the practical utility of the specification framework WRAP and BSI developed. It also creates commercial opportunities for UK tyre bale producers with PAS 108 production capability who are supplying international markets.

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