The benefits to New Zealand of the research programme conducted at CAPTIF since 1987 can be split into tangible and intangible benefits.
The tangible benefits
- Epoxy modified open graded porous asphalt (EMOGPA) has been demonstrated as a viable product at CAPTIF and provides an easy to understand tangible benefit. The testing showed that it was viable to produce and lay, and it performed very well under accelerated loading. Laboratory testing suggests that we will end up with a surfacing product that will increase the life of OGPA surfacing from an average of 7 years to 40 plus years for additional cost of about 30%.. The initial field trial is now 10 years old and the research has the preferred surfacing for Motorway projects with an estimated 5/6 reduction in life-cycle costs for the surfacing. On the existing surfaces using OGPA this could equate to a saving of approximately $20 Million dollar per year. Or perhaps just as importantly – the ability to use more low – noise surfacing without creating a significant demand on maintenance budgets.
- Research into subgrade strain criteria that paved the way for the adoption of the Austroads 1992 Pavement design guide. The Austroads guide has led to more economic designs than the previous pavement design guide. Further research assisted in determining the boundaries of where the Austroads guide is applicable to unbound granular pavements.
- The DIVINE research for the OECD proved that the 4th power law could not used in vehicle dynamics research, spatial repeatability does occur and road friendly suspensions must be in good operational condition to provide any benefit.
- Mass Limits research demonstrated that traditional models for increasing vehicle axle loads on State Highways (that carry most freight traffic) were likely over estimating the impacts. But on weaker local roads they may underestimate the impacts. This lead to improvements in the ability model the impacts of High Productivity Motor Vehicles (HPMVs) on both local and State Highway road networks making the decisions on which routes to allow HPMVs on more robust.
- Another key finding has been in the use of the repeat load triaxial test to examine the unbound materials that make up the bulk of New Zealand’s pavements. The test was validated and calibrated at CAPTIF and finally allows engineers to compare the performance of one basecourse with another in the laboratory. A massive leap forward from our current empirical recipe based specifications. The research findings are incorporated in the NZTA’s design guidance and allow consideration of marginal and recycled aggregates. Recycled crushed glass was included in the NZTA’s basecourse specification based purely on the repeat load triaxial test method that had been validated at CAPTIF.
- Research into chipseal performance under wet loading resulted in some simple early failure risk reduction strategies and improved sealing technique. It also questioned whether a long held local New Zealand view on the permeability basecourse materials could’t be harmonised with the Austroads approach, making design and materials collaboration between the jurisdictions simpler.
- The benefits of stabilising pavements have been captured. These benefits were not captured by the existing Austroads Pavement design guide. This work provides a good understanding of the intermediate steps between relatively weak but cheap unbound pavements that were not working on major projects and strong but expensive structural asphaltic concrete pavements. These techniques are now routinely used by the NZTA on all major projects and the research findings are incorporated in the NZTA’s design guidance greatly reducing the risk of early failure at moderate initial cost and providing desirable life cycle costs.
The intangible benefits
- The CAPTIF research programme has resulted in closer cooperation between researchers in the fields of pavements, transport, vehicle manufacturing, and between researchers and practitioners. Currently Fulton Hogan and Downers have senior technical staff that are actively involved in CAPTIF related research.
- International bodies, such as the OECD and the Transportation Research Board (USA), have invited New Zealand researchers to serve on specialist expert committees and peer review international papers, which is directly attributable to their research involving CAPTIF.
- Improvements in technology and knowledge gained from research at CAPTIF have been transferred directly to university civil engineering students (through lectures and post graduate involvement) and practitioners (through formal presentations at seminars, conferences and meetings, and through informal discussions), thereby significantly increasing the dissemination and implementation of research.
- Tracking of student involvement started in 2000, since then one 4th year student (University of Durham), two Masters students (University of Canterbury and Universität Stuttgart) and five PhD students have completed their doctorates using data from the test track (two from the University of Canterbury, two from The University of Auckland and one from the University of Nottingham. One post-doctoral fellow from the University of Dresden has also studied at CAPTIF, funded by the German Government. This benefited both Germany and New Zealand with significant advances in modelling and testing made. Two more PhD studies are underway with The University of Auckland.
- Students and Researchers who have worked with CAPTIF and gone onto technical roles in industry have maintained links with the facility.
- 25 Research Reports have been written using CAPTIF data and some 85 papers to journals and conferences since 2000.
Conclusions
The American Association of State Highway and Transportation Officials commissioned the NCHRP 433 (2012) report “Significant findings from Full-Scale Accelerated Pavement Testing” that reviewed the benefits of accelerated pavement testing (APT) internationally.
The synthesis was based on two major sources of information. A questionnaire was distributed to 43 known US and international operators and owners of APT devices, the 50 US state departments of transportation representatives, and a group of specialists active in the field of pavement engineering. The second source of information is the conference and journal papers published from 2000 to 2011 and CAPTIF’s research is noted amongst that body of work.
APT was noted to form a vital link between the laboratory evaluation of materials used in pavement layers and the field behavior of these materials when combined into pavement structures. For many years APT provided pavement engineers with knowledge that improved their understanding of pavement materials and structures, as well as their behavior under typical traffic and environmental loading. It formed the basis for developing various theories about pavement behavior and supports most of the current pavement design methods.
The importance of APT was perceived as high, with a major role to be played in pavement structure and basic materials research. The future of APT is primarily perceived as growing and being a normal part of pavement research operations, benefiting improved structural and material design methods, performance modeling, and evaluation of novel materials and structures.
Evaluation of the economic benefits of APT has come to the forefront during the past decade with more programs reporting attempts at performing benefit–cost ratio (BCR)-type evaluations of their research programs. Estimates of BCRs from respondents ranged broadly between 1.4 and 11.6, although some respondents to the questionnaire indicated that their perception of the BCR for their programs is greater than 30. Research at CAPTIF has had similar estimates of BCRs but the importance of the intangible benefits should also not be underestimated.
