Using technology so assess road surface quality

Advances in survey technology and the evolving face of road procurement are driving demand for highway condition data. Mark Thomas, infrastructure services manager at Fugro Aperio writes how surveys of new roads can improve long-term quality While a growing suite of non-intrusive testing, measurement and survey technologies are widely used to target highway repairs and to determine asset management strategies, the use of these powerful tools remains patchy in the early stages of the infrastructure life cycl
Asphalt Paving, Compaction & Testing / April 4, 2014
GPR surveys Middle East
GPR surveys, such of this road in the Middle East, are quick and non-intrusive and provide cost-effective and comprehensive information without damage to the asset or disruption to users
Advances in survey technology and the evolving face of road procurement are driving demand for highway condition data. Mark Thomas, infrastructure services manager at 2929 Fugro Aperio writes how surveys of new roads can improve long-term quality

While a growing suite of non-intrusive testing, measurement and survey technologies are widely used to target highway repairs and to determine asset management strategies, the use of these powerful tools remains patchy in the early stages of the infrastructure life cycle. 

Over the last two decades, highway engineers around the world have realised the benefits of sophisticated technology for surveying road surface characteristics such as roughness, rutting, ravelling, skid resistance.

Engineers also recognise these systems are useful for determining subsurface properties such as strength, construction depth, material boundaries and voids. Specialists have developed integrated non-intrusive survey systems incorporating video, laser, ground penetrating radar (GPR) and deflection instruments, most of which can be installed on vehicles to cover entire networks at traffic speed.

Logistically, these technologies are modular and highly mobile. International survey specialists such as Fugro are experienced in deploying them in challenging environments worldwide with a relatively modest set-up cost. Resulting survey data are used typically for evaluating and planning maintenance work or reporting pavement condition data to public agencies for strategic management of highway assets. In recent years, however, a growing number of clients are seeing the benefit of investing in surveys of new pavements and structures as part of the quality control (QC) and quality assurance (QA) process. Some are also using these surveys to index road value and condition for the purpose of any change of ownership and/or lease management contracts.

The principle aim of any new road assessment is to determine whether the design and material specifications have been met. GPR is often a first choice for establishing construction detail and layer depth, with traffic speed GPR surveys typically covering 100-200km/day. Results can help target subsequent coring, used in turn to corroborate the GPR data, and for materials analysis, such as checking asphalt depth and chemical composition, to ensure it is compliant with the design specifications.

‘Whole site’ assessment is particularly important where there is variability in underlying ground conditions – for instance, where a road section that cuts through a rocky formation intersects a length of road built on silty marine soils. It is common for such conditions to result in a change in pavement detail that is not always documented in construction records. Appropriate non-destructive testing will provide a permanent record of such variations and enable a comparison with the design specifications.

As well as providing rapid coverage and avoiding damage to newly laid roads, another major advantage of this approach is enhanced sampling for better informed decision-making. Where construction records may comprise pavement layer thickness records every few metres and core samples may be taken at intervals of tens, or more commonly hundreds of metres, the output of automated condition surveys is far more detailed. GPR surveys of pavement thickness can generate tens of thousands of measurement points/km of road, while surface characterisation by automated scanning vehicles such as Fugro’s ARAN system produce more than a million readings within the same distance. This gives a much more detailed view of construction consistency and quality across the project site, and a greater chance of spotting any latent defects before the road is operational.
In addition, a combination of non-intrusive scanning and physical sampling provides a much more robust, data-rich log of quality which is simply not possible from site supervision alone. While providing a baseline record of construction condition before the road enters service, it will confirm that the pavement complies with design performance criteria to underpin confidence in agreeing to warranty terms with the client.

Completion testing also provides an ‘as-built’ evidence base that can help settle disputes over any problems that may occur during the initial defects liability period. For example, finding and fixing a carriageway defect before a new road opens to traffic could save significant costs, disruption and potentially damaging legal disputes for all parties – client, agent and contractor.

Comprehensive documentation of both the design and construction of new roads is likely to grow as more highway infrastructure is delivered under private financing arrangements. In design, build and operate contracts, the client passes more risk to the contractor or consortium for potential problems, with defect liability periods moving from two years to five or even 10 years.

Under this type of procurement, the client will relax the prescriptiveness of the contract in favour of descriptive criteria for various aspects of performance such as deformation or smoothness - over a stated period. While this leaves the contractor scope to innovate and use alternative materials, the client still has a vested interest in verifying that the asset is built to specification. 

This assurance can be met by a suite of pavement testing and materials analysis to provide QA of the pavement design, including assessment of materials thickness and composition, structural performance, load bearing capacity and composite pavement strength.  As well as confirming that design specifications have been met, the data provide a benchmark of testing against which the contracted parties can measure subsequent performance and resolve liability if problems arise. Assessment of pavement design and material specifications provides the opportunity not just to ensure that the pavement is structurally and materially capable of achieving the specified design life. It can also play a critical role in determining if a pavement is over- or under-engineered in any aspect, so that the proposed solution, and budget, can be revised with confidence to provide optimum performance. 

Access to big datasets and sophisticated computer analysis software has helped specialists at Fugro progress the concept of analytical pavement design. The approach uses performance modelling and other predictive analyses to characterise materials performance over the required design life, factoring in both capital and maintenance elements to forecast whole-of-life costs. It provides, as near as possible, a scientific prediction of pavement performance linked to a specific site, and an indication of the best value for money for the client and any other parties who may be financing the asset.

Consistent use of pavement testing, from design concept to construction, offers not only a robust trail of QC/QA documentation, but also much better cost control without compromising performance. While the returns from this level of pavement intelligence are significant in the delivery of a new highway, the initial investment will continue to reap benefits during the future management or lease of the highway.
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