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Research Report 603 The relationship between vehicle axle loadings and pavement wear on local roads

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

In New Zealand heavy vehicles are charged for using the road based on the damage caused passing over the road. The current approach to charging has its origins in American research that found doubling an axle load increased the damage as a power function with an exponent of 4, known as the Fourth Power Law. This was developed with limited pavement and vehicle load types not representative of most of the roads in New Zealand. This research provided reliable evidence on the wear characteristics of New Zealand local road pavements from accelerated pavement loading studies at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF). The aim was to determine the relative damage on different pavement types/strengths. The data was extended with rut depth modelling with repeated load triaxial data and validated with field data from the nationwide long-term pavement performance sites.

Research Report 564 Effects of water on chipseal and basecourse on high-volume roads

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audiences: Road traffic engineers & consultants, Roading contractors

The objectives of this study were to investigate the relationship between permeability of chipseals, waterfilm thickness, basecourse moisture sensitivity, heavy traffic volumes, and premature pavement failure following construction through the use of accelerated pavement testing at CAPTIF. The research has produced some surprising results in that the traditional M/4 basecourse was the worst performer in all cases. However, it must be borne in mind that this research can only be considered applicable to first coat seals, with high water film thicknesses at very high traffic volume.

Research Report 498 The design of stabilised pavements in New Zealand

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

Areas of New Zealand are running out of premium aggregates that meet the demanding specifications used in unbound granular road construction. Stabilising aggregate provides a viable alternative to using premium aggregates. The objective of this project was to improve the sustainability of New Zealand roads via a combination of accelerated pavement tests at the Canterbury accelerated pavement testing indoor facility (CAPTIF) in 2007/08 and 2008/09, and a limited field review of the performance of bound stabilised pavements. A number of recommendations have resulted from this research concerning the design, testing and construction of modified and bound pavement layers.

Research Report 463 Development of tensile fatigue criteria for bound materials

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

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

Research Report 335 Performance tests for road aggregates and alternative materials

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

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.

Research Report 321 Epoxy modified open-graded porous asphalt

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

Investigations into the cohesive properties and oxidation resistance of an acid cured, epoxy modified open-graded porous asphalt (OGPA) were undertaken and an associated accelerated loading test carried out at Transit New Zealand’s CAPTIF facility. Results from the Cantabro test (a test of mixture cohesion relating to the resistance of OGPA to surface abrasion losses) indicated that the early life cohesive properties of cured epoxy OGPA should be comparable to that of standard OGPA at 25°C and markedly superior at 10°C. The modulus of the cured epoxy mixture was much higher than that of the standard OGPA but this is probably of little benefit given that failure through rutting and deformation is uncommon for properly designed OGPA. The superior oxidation resistance of the epoxy material was clearly evident in Cantabro tests conducted at both 25°C and 10°C.

Research Report 319 Benchmarking pavement performance between Transit's LTPP and CAPTIF programmes

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

This report details the findings from research conducted on the Long-Term Pavement Performance Programme (LTPP) and on the Transit New Zealand CAPTIF programme for accelerated pavement testing. The research was aimed at delivering a complete new model format to predict rut progression on New Zealand roads. It was based on earlier findings that suggested some limitations with the current approach using the World Bank’s HDM rutting models. A three-stage modelling approach is recommended:

Firstly, a simpler model is proposed to predict the initial rutting or densification. Average progression rates are proposed for the annual increase of rutting during the normal life of the pavement since no satisfactory model could yield any results which were more accurate. Lastly, a probabilistic model is proposed to predict the probability or risk of a pavement undergoing accelerated rut progression caused by weak layers or overloading.

Research Report 307 Fatigue design criteria for low noise surfaces on New Zealand roads

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

Internationally low noise porous asphalts are typically laid on top of structural asphalt layers. In New Zealand structural asphalt is generally prohibitively expensive and porous asphalt is used directly on chipseal-surfaced unbound granular pavements. Two accelerated pavement tests were undertaken at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF) in 2004–2005. The first test was to develop a horizontal tensile strain versus fatigue life curve and establish a relationship between basecourse surface curvature and fatigue life. The second test evaluated the extension of fatigue life by short trafficking before surfacing rather than using enhanced binders in porous asphalt. The outcomes of the project suggest that the Austroads Rehabilitation Design Guide is very conservative in predicting fatigue and that deformation leads to surface failure before fatigue of the pavement occurs. Pavements to be sealed with low noise surfaces could tolerate more deflection if initial trafficking was undertaken.

Research Report 279 Effect on pavement wear of increased mass limits for heavy vehicles – stage 3

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

To improve the efficiency of the road transport industry, 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. New Zealand has a mass-distance road user charging (RUC) regime where the users pay for the road wear they generate, and therefore there is a need to accurately reflect the wear. Stage 3 of this study, carried out in 2002, aimed to accurately predict road wear from various levels of loading, an accelerated loading test was undertaken at the Canterbury Accelerated Pavement Testing Indoor Facility (CAPTIF) to compare the wear generated by different levels of loading.

Research Report 281 Effect on pavement wear of increased mass limits for heavy vehicles – concluding report

Published: | Category: Activity management , CAPTIF , Research programme , Research & reports | Audience: General

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.