New road-surfacing guidelines should help pavement designers to understand the technical merits of pavement materials and ensure that important decisions are taken by suitably experienced personnel. Tom Casey and Peter Adams report

Transport Infrastructure Ireland (TII) was established through a merger of the National Roads Authority and the Railway Procurement Agency under the Roads Act 2015, with effect from 1 August 2015.

TII’s primary function is to provide an integrated approach to the future development and operation of the national roads network and light rail infrastructure throughout Ireland. TII brought together two organisations to provide high quality transport infrastructure and services, delivering a better quality of life and supporting economic growth.

TII recognises the value of research and the important role it plays to help us achieve our strategic objectives:

  • It provides an effective mechanism for maintaining up-to-date standards and specifications;
  • It enables procedures to be developed for the efficient and cost-effective management of a very valuable national asset; and
  • It ensures that state-of-art materials and methods are identified and used.

Our road research programme includes collaborative research whereby access to a large project or specialist expertise can be gained. This also provides a very effective means of knowledge transfer and the opportunity to tap into high quality research and leading-edge engineering and technology.

TII participates in European working groups and committees such as FEHRL (Federation of European National Highway Research Laboratories), ERTRAC (European Road Transport Research Advisory Council) and CEDR (Conference of European Directors of Roads). In particular, CEDR recognises the importance of research in the development of sustainable transport and has established a Technical Group (TG) to monitor European research activities and to advise the CEDR Board on issues relating to research.

TII is an active member of TG Research and has in many instances been the project leader on individual CEDR research projects. We have also developed our own programme of research projects that are specific to the relevant aims of the organisation.

Primary function of TII

The primary function of TII under the terms of the Roads Act (2015) is to secure the provision of a safe and efficient network of national roads. For this purpose, we have overall responsibility for planning and supervision of construction and maintenance works on these roads.

In accordance with the Roads Act, TII’s remit includes any training, research and testing activities necessary for the execution of its functions. In recognition of this, we have developed technical specifications that ensure a consistency with our objectives. The development of these specifications is an evolutionary process that has two major drivers based on changes in technology and legislation.

The Design Manual for Roads and Bridges (DMRB) was introduced in 1992 in the UK to bring together all standards, advice notes and other documents relating to the design, assessment and operation of trunk roads, from many separate series of documents previously published. These documents, together with later additions, have been gathered together in 15 volumes to help road transport professionals meet the requirements of quality assurance procedures.

There are many similarities between Ireland and the UK in the type of materials, climatic conditions and vehicle types on our road networks. The scale and development experience in the UK is, however, on a much greater level.

Together with a common language, it made good engineering and economic sense to follow their processes and procedures rather than create a separate approach. In 2001, TII (formerly as the National Roads Authority) adopted the DMRB with an additional addendum inserted to cater for local conditions.

Articles 34 to 36 of the Treaty on the Functioning of the European Union outlines the requirements to ensure quantitative restrictions on imports and exports to which Ireland must abide. The manifestation of this for road-specific materials was the publication by the EU of the Construction Products Regulation (CPR), which came into effect in 2013.

The Regulation lays down conditions for placing a product on the market by establishing “harmonised” rules. This is achieved by the use of harmonised standards, which provide the technical basis required to evaluate the consistency and verification of constancy of their performance level. Harmonised European standards on construction products are developed by technical experts from the European Standardisation Organisations (CEN/CENELEC).

The Technical Committees of CEN and CENELEC work on completing the necessary set of harmonised European standards and test method standards, and further improving existing ones. TII personnel are participants on the CEN standards development committees for bituminous materials.

Using the harmonised European standards, national authorities can set performance requirements applicable to local conditions and TII also participate on the National Standards Authority of Ireland technical committees for construction products.

Developing performance criteria for pavement materials

The first step in the process of developing a set of performance criteria for construction products used on the network was a review of the then-current 900 series in the NRA DMRB for pavement materials in 2013. What began as a process to bring the specification in line with CPR quickly developed into a total process change.

It was evident that the format of the UK-derived DMRB was not easily modified to present a clear and consistent link to the European standards. This was in particular the case for a number of construction products such as Low Energy Bound Materials and micro-surfacings. The process that evolved from this review was a significant transformation of both the content and procedural requirements to ensure compatibility with both the requirements of EU Standards and the CPR to include current editions and anticipated future changes.

TII and its technical consultants ARUP looked at the entire spectrum of applicable documents within the DMRB. They were replaced, modified or added to ensure a consistency within the entire process through the design, procurement, construction and operational phases.

The process starts with the design phase which includes appropriate materials selection. The designer must meet the stated criteria of the Construction Products Regulations (CPR), which state the product should be fit for the use for which they are intended and be durable for the expected design life.

NRA HD 300 (DN-PAV-03074) was developed as an additional document to detail this process. In essence the Designer should utilise all of the necessary documentation to complete the requisite stages. These include selection of products, and both NRA HD 23(GE-PAV-01006) and NRA HD 37(DN-PAV-03024) provide the necessary information to aid this selection.

For surface course designs, it is essential that they comply with NRA HD 36 (DN-PAV-03023). If a product is not covered by a harmonised European Standard, the approval process is set out in NRA HD 301 (DN-PAV-03075).

Series 900 (DN-PAV-03058) is now set out in process specific sections including a separate one for works requirements. As an aid to the compilation and procurement phase material properties are also summarised in look up tables.

This is also the case for the construction phase and it was intended that the tables could provide the contractor and employer representative with a format to compile a checklist to demonstrate compliance with the standard contract performance requirements.

Change to previous methodologies

TII understood that this was a significant change to the previous methodologies. A widespread dissemination programme was undertaken, which included:

  • Consultations with industry;
  • Pre-publication of a draft document;
  • Training events held throughout the country and presentation at national conferences including the National Roads Conference, Regional Roads conference and Institute of Asphalt conferences;
  • Presentation to industry members of the Irish Asphalt Producers Association; and
  • Open-invitation technical meetings.

TII also has a contact and query section specifically for our standards contained within our website. TII and ARUP are aware that there still exists some misunderstandings of the process and, by way of example, using high-friction surfacing/microsurfacings the development of the standards and construction phases can be demonstrated.

The system of assessment prior to the publication of the revised specification depended upon a third-party accreditation of the potential laboratory performance and observation by them of a ‘control’ site to enable a ‘process approval’.

There was no site based, quality-control testing or a method to identify how durable the product was. Investigation through our technical contacts indicated that most failures related to adhesion between the chip and the binder and also between the mixture and the underlying substrate.

Workmanship issues were a considerable factor. Similarities in the nature of the product to micro-surfacings gave rise to the use of a Type Approval Installation Trial (TAIT) approach. The use of an adhesion/shear test to evaluate the bond gave a good indication of the process quality and potential for durability and was the chosen methodology for all ultra-thin applications.

The removal of a specific third party elimates a barrier to trade and the specification alignment to TAITs should facilitate a simpler transition to a verification process should a manufacturer opt to utilise the European Technical Assessment route outlined in the CPR. It is interesting to note that Highways England has since followed a similar approach to the site testing for the same reasoning.

A designer is required to evaluate the site performance of these products and select one that is appropriate for the expected operational conditions. Our research, in conjunction with TRL, the world leader in skid-resistance research, was utilised in a redeveloped HD 36 (DN-PAV-03023) to simplify the selection process whilst improving the material evaluation process.

Unique standard in pavement section

This standard is unique in the pavement section, insofar as the dominant influence is the number of commercial vehicles per lane per day, rather than cumulative number of standard axles. Hence the removal of volumes that would be in excess of expected surfacing life in Ireland afforded better clarity and simplification of the document whilst retaining the essential characteristics.

The inclusion of a whole life cost-assessment clearly sets an onus on the designer to establish what the underlying issues are and how best they will be addressed. The decision-making process is consequently fully aligned to all of the other products and processes within the TII pavement documentation.

In time, the consistency of approach should assist in better understanding the technical merits of the choices available to a pavement designer and ensures that the important decisions are taken by well informed and suitably experienced personnel.

TII has stated consistently that the changes were made to ensure compliance with CPR and EU standards; to align the design-construction process for all pavement materials and to provide a consistent approach in evaluating the suitability and performance of existing and future alternative materials. Future developments based on feedback from site experience will be used to redefine our pavement designs in HD 25-26 (DN-PAV-03021).

This will assist us in the developing a skilled and knowledgeable engineering base capable of independently analysing and responding to changes emanating from the European Union. In the light of current Brexit concerns, it is a timely initiative.

Tom Casey, BSc, MBA, FIEI, Chartered Engineer, is an Engineers Ireland Fellow and graduate of Queens University Belfast, is head of pavements, construction materials and innovation at Transport Infrastructure Ireland. He has over 35 years’ experience of pavements including rigid, composite and fully flexible. Casey is a member of a number of national and European roads standards committees including CEN TC 227 working group 1 and NSAI roads standards. He also manages a number of trans-European pavement and asset-management research projects as a member of Confederation of European Roads Directors (CEDR) Project Executive Boards.

Peter Adams BEng (Hons), Chartered Engineer, is an infrastructure director with Arup Ireland and has 28 years’ experience in delivering major infrastructure projects. These include numerous Irish and international highways projects for road-authority clients and contractors, producing detailed pavement designs and construction specifications. O'RiordanCivilroads,structures and construction,Transport Infrastructure Ireland
Transport Infrastructure Ireland (TII) was established through a merger of the National Roads Authority and the Railway Procurement Agency under the Roads Act 2015, with effect from 1 August 2015. TII's primary function is to provide an integrated approach to the future development and operation of the national roads network...