History of PAS 108: How WRAP and BSI Created the Tyre Bale Standard

By:     Conor Murphy

Tyre bales were used in civil engineering applications long before PAS 108 existed. Waste tyre processors in the UK and in the United States were producing bales from the 1980s onwards, and engineers working on projects with limited budgets discovered that large blocks of compressed rubber had interesting properties: they were light, free-draining, chemically resistant, and available at low cost as a waste-derived material.

Early uses were informal. An engineer working on a coastal protection project, a road over soft ground, or a slope stabilisation scheme might specify tyre bales on the basis of practical experience or emerging research, but there was no standard specification to design to and no quality framework to hold suppliers to. Two bale producers might supply bales of very different density, dimensions, and tie wire specification, making it impossible for engineers to use consistent material property values in design calculations. The lack of a standard constrained the adoption of tyre bales in mainstream civil engineering, because procurement systems and design standards could not accommodate materials without defined specifications.

The informal use of tyre bales during this period generated real-world evidence of performance that would later inform the development of PAS 108. Site monitoring data, case studies of both successful and unsuccessful installations, and practical understanding of which bale characteristics mattered most for different applications accumulated through the 1990s and early 2000s, providing the empirical foundation that a standards development process would need.

WRAP’s Role in Building the Evidence Base

The Waste and Resources Action Programme (WRAP) was established in 2000 with a remit to promote resource efficiency, waste reduction, and the development of markets for recycled materials. Waste tyres were an early focus area for WRAP, both because the volume of waste tyres was substantial (approximately 40 million tyres per year in the UK at the time) and because the disposal options available were limited: landfill was already being restricted, and the recycling markets for tyre material needed development.

Civil engineering use of tyre bales represented an attractive market development opportunity for WRAP. The potential annual demand from road construction, coastal defence, and slope stabilisation projects was significant, the material performed well in the applications where it had been used informally, and the barrier to wider adoption was clearly the absence of a recognised specification standard rather than any fundamental limitation of the material.

WRAP commissioned a series of research projects through the early 2000s to characterise the engineering properties of tyre bales systematically. These studies tested bale samples in the laboratory and monitored installed structures in the field. The research programme covered the mechanical properties of individual bales under compressive and shear loading, the hydraulic properties of bale fill layers, the long-term settlement behaviour of bale fill embankments under sustained load, and the environmental chemistry of leachate from tyre bale structures in soil and water contact.

This research programme was not about validating an already-developed standard. It was about generating the data that a standard could be written around. WRAP worked with academic researchers, geotechnical engineering consultancies, and industry partners to produce a body of published technical evidence that demonstrated tyre bales were an engineered material with predictable, documentable properties.

The WRAP technical publications from this period, including guidance documents on tyre bale use in civil engineering that remain relevant reference material today, are the foundation on which PAS 108 was subsequently built.

BSI and the PAS Development Process

BSI (British Standards Institution) is the UK’s national standards body and the organisation through which PAS 108 was developed and published. A Publicly Available Specification (PAS) is a type of standards document that BSI publishes through an accelerated development process compared to a full British Standard. PAS documents are developed with industry input but are owned by BSI and can be converted to full British Standards in time if adoption justifies the formal standards process.

The development of PAS 108 brought together the research evidence generated by WRAP’s programme with the technical input of a stakeholder group that included tyre bale producers, civil engineers with experience of tyre bale applications, geotechnical testing laboratories, and environmental specialists. This group worked within BSI’s standards development framework to define the specification requirements that would form the standard.

The process of turning research data into a specification standard requires decisions that involve professional judgement alongside the technical evidence. What dimensions should a standard bale be? What compressive force is needed to achieve the required density? How many wire ties are needed, and how should they be placed? What tolerances are appropriate for each measurement given the variability inherent in baling tyre materials of varying type and size? These questions were resolved through the deliberation of the standards development group, informed by the research evidence and by practical experience from existing bale production operations.

PAS 108 was first published by BSI in 2007. Its publication was a significant moment for the tyre baling industry and for civil engineering, establishing for the first time a recognised specification against which tyre bale producers could certify their output and civil engineers could specify material for structural applications.

What PAS 108 Established and Why It Mattered

PAS 108 did several things simultaneously that changed the status of tyre bales in the UK market.

It defined a product. Before PAS 108, a tyre bale was whatever a particular producer happened to make. After PAS 108, a PAS 108-compliant tyre bale was a defined product with measurable specification requirements. Producers could manufacture to the specification. Procurement processes could require compliance. Engineers could design to published material property values.

It provided a quality framework. PAS 108 includes requirements for the production process and quality management system, not just the finished bale product. This means a PAS 108 producer is not just measuring bales; they are operating a production system designed to consistently produce compliant bales. The quality management requirements are the mechanism through which specification consistency is maintained across a production run.

It opened procurement routes. Public sector civil engineering procurement operates within frameworks that require materials to meet recognised specifications. Before PAS 108, tyre bales were excluded from most formal procurement processes because they had no recognised specification. After PAS 108, compliant tyre bales could be specified in design drawings, included in bills of quantities, and procured through normal supply chain processes.

It created a market signal for investment. The existence of a recognised standard with a growing civil engineering application market gave tyre bale producers a clear commercial reason to invest in production equipment capable of meeting the specification. Operations that invested in proper baling equipment, pre-processing capability, and quality management systems could access a higher-value market than those producing unspecified bales. This market signal drove improvements in production quality across the UK tyre baling sector.

The Standard’s Evolution and Current Status

Since its original publication in 2007, PAS 108 has been reviewed and updated to reflect accumulating field experience and research findings. Updates have refined some specification requirements and added clarity on matters that produced interpretation questions in the original version. The specification development process continues to be informed by new research, field monitoring data, and feedback from the engineering and production communities using the standard.

The PAS 108 framework has also influenced standards development in other jurisdictions. The United States has its own tyre bale specification standard (ASTM D6270) developed through a different process, and other countries have referenced PAS 108 in developing their own national guidance on tyre bale civil engineering use. The UK standard has had genuine international influence in establishing tyre bales as a recognised engineered material.

For tyre recycling operations producing bales for civil engineering supply, PAS 108 in its current BSI-published form is the operative specification. Equipment capable of producing compliant bales, such as Gradeall’s MKII Tyre Baler, and the associated pre-processing line from the tyre recycling equipment range, represents the production investment that makes civil engineering supply possible.

“The development of PAS 108 transformed the commercial opportunity for tyre bale producers in the UK,” says Conor Murphy, Director of Gradeall International. “Before the standard existed, civil engineering was an informal niche market. After it, the market became accessible through normal procurement and design processes. The standard is what opened the door.” Contact Gradeall International to discuss equipment for PAS 108-compliant production.

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