Resources

The road transport industry in New Zealand has been lobbying for increases in the allowable mass limits for heavy vehicles on the basis that this would give increased efficiency and benefits to the economy. Some of the proposals for increased mass limits involve increased axle load limits which would clearly lead to additional pavement wear. Road controlling authorities, while sharing the industry’s aims for increased efficiencies in the road transport system, are concerned that any additional pavement wear generated by higher axle loads will be paid for, so that the standard of the roading network can be maintained. At present (2005) Road User Charges (RUCs) are based on the fourth power law, which was developed from the AASHO road test in the United States in the 1950s. The pavements and vehicles used for that test differ considerably from those in use in New Zealand today.

The primary objective of the project was the development of criteria to define the end-of–life condition of pavements. These criteria could then be used in pavement performance modelling to obtain a more robust measure of remaining life. Another objective was the generation of a new model for maintenance costs. This could then be combined with the existing models for roughness and rutting to define a distress level at which rehabilitation should occur. None of the maintenance cost models developed were particularly successful in producing a reliable prediction of maintenance costs based on the pavement characteristics available from RAMM. Therefore, a logit model was developed to predict rehabilitation decisions. The major factors in the rehabilitation model were maintenance costs, traffic levels and roughness. The rehabilitation decision model derived for this study predicted rehabilitation decisions well. Approximately 72% of pavements that had been rehabilitated were predicted as requiring rehabilitation.

The historical development of the traditional Marshall and the modern gyratory-based, performance-related asphalt mix design procedures is described. New Zealand is progressively adopting performance-related specifications and implementing performance contracts for road maintenance and construction. Thus, in 2002, asphalt mixes sourced from a range of asphalt manufacturers located around New Zealand were subjected to a comprehensive laboratory testing regime, to determine their volumetric- and performance-related properties, such as modulus. Two sets of asphalt specimens were created, using either Marshall or gyratory compaction procedures, based on existing mix designs. They were then tested by AUSTROADS APRG18 procedures and equipment to provide performance-related data.

This report describes research in 2004 and 2005 aimed at improving the means by which the durability of bitumens manufactured or imported to New Zealand for use in chipseals is assessed and monitored. Bitumen durability refers to the long-term resistance to oxidative hardening of the material in the field. Although, in-service, all bitumens harden with time through reaction with oxygen in the air, excessive rates of hardening (poor durability) can lead to premature binder embrittlement and surfacing failure resulting in cracking and chip loss. Some means of assessing durability by accelerating the process in the laboratory is necessary. However, no internationally accepted ‘standard’ exists for bitumen durability, as for some other bitumen tests (eg penetration). Keywords: bitumen, chipseal, durability, oxidation, pavements, roads, testing

Flexural beam breakage and fatigue tests were conducted in 2008–11 to determine their relationships with pavement fatigue life and tensile strain for a range of New Zealand materials for use in pavement design of stabilised aggregates. The results showed that the tensile fatigue relationships from several fatigue tests under repetitive loading could be approximated by single flexural beam breakage tests. These relationships resulted in significantly longer pavement lives than the Austroads pavement design criteria but still predicted shorter fatigue lives than what actually occurred at the Canterbury accelerated pavement testing indoor facility (CAPTIF) test track, indicating some conservatism in the approach. Further research is required to validate the tensile fatigue design procedure against actual field data. Keywords: aggregates, basecourse, CAPTIF, fatigue, beam fatigue testing, modulus, pavement design, strain, tensile strain criteria, tensile strength

Pavement performance modelling for New Zealand roading networks, currently relies on an adjusted structural number (SNP) which is a single parameter intended to describe the performance of a multi-layered pavement structure in terms of its rate of deterioration with respect to all structural distress modes, as well as non-structural modes. This parameter had its origin in the AASHO road test in the late 1950s, before the advent of analytical methods. Hence refinement to keep abreast of current practice in pavement engineering is overdue. This research describes the basis for a new set of structural indices and how these can be used to obtain improved prediction of pavement performance: both at network level and for project level rehabilitation of individual roads. The results are (i) effective use of all the data contained in RAMM, (ii) more reliable assignment of network forward work programmes, (iii) reduced cost through targeting only those sections...

Aggregates used as base materials in thin-surfaced granular pavements common to New Zealand contribute at least half the wheeltrack rutting and roughness seen at the surface. Currently, no reliable cost-effective measure of an aggregate’s resistance to rutting in specifications exists. Several test methods using the repeated load triaxial (RLT) apparatus were investigated for use in specifications for basecourse aggregates. Rut depth prediction methods and pavement finite modelling were applied to the RLT results to determine traffic loading limits for the aggregates tested. It was found that the average slope from the six-stage RLT test was the best predictor of traffic loading limit and this test was recommended for use in basecourse specifications.

This research project had the objective of identifying areas where changes could be made in the use of thin layers of asphalt so that improvements in performance could be obtained. The project was not designed to investigate quality issues, but was to concentrate on materials and selection. The project was initiated because the NZ Transport Agency had found that costs of resurfacing using asphalt had escalated and the lives being achieved appeared to be short. This research in this report, which was undertaken between 2007 and 2012, investigated the following areas:

To improve the efficiency of the road transport industry in New Zealand, a range of mass limit increases for heavy vehicles has been proposed. Some of the options for mass increases include increasing the axle load limit, which would inevitably lead to increased road wear. As New Zealand has a mass-distance road user charging regime where the users pay for the road wear they generate, this increased wear is in itself not a problem provided that the charges accurately reflect the wear. At present, road user charges are based on the fourth power law, which was developed from the AASHO road test carried out in the United States in the 1950s. The pavements and vehicles used for that test differ considerably from those in use in New Zealand today.

This report details the progress made in tests in Oklahoma, USA ,and Christchurch, New Zealand, during the period August 2004 to June 2005, exploring digital imaging technology to measure chipseal surface texture. It details the research methodology to develop a technology to replace the sand circle test as a means to measure chipseal surface texture more accurately and safely. The project used digital imagery and exploited ‘information theory’ to develop a quantitative relationship between texture measured by the sand circle test and the fast Fourier transform of a digital image of the surface taken at the same spot as the test. The preliminary correlation achieved and reported in the interim report has been confirmed by a larger group of data collected after the interim report was written. A reliable statistical correlation using linear regression analysis with a coefficient of determination of 80% between digital image processing output and sand circle...