Resources

As the demand for a cost-effective and environmentally friendly pavement stabilisation method increases, so has foamed bitumen stabilisation for unbound granular pavement layers started to gain broad acceptance worldwide.

In New Zealand, premature failure of low volume, low strength state highways and local authority roads has sometimes occurred due to significant changes in heavy commercial vehicle traffic. Current New Zealand pavement deterioration models (eg NZ-dTIMS and HDM) were not designed to simulate these sudden increases in traffic loading and their effects over short distances. The NZ-dTIMS and HDM models along with other pavement distress models were investigated to establish their suitability for modelling extreme variations in traffic loading. The relationships between measurements of structural strength and pavement condition data were investigated for selected pavements. The sensitivities of some pavement deterioration and pavement distress models to extreme traffic loading were also investigated. The key finding was that the extreme traffic loading must be sustained for a lengthy duration to show up in RAMM pavement condition and reactive maintenance cost data.

The research investigated aspects of the use of epoxy modified bitumen for construction of chip seals. Changes in the shear modulus, needle penetration and cohesive energy of the epoxy bitumen were used to monitor changes in the material as it cured at 35℃ and 45℃ and after accelerated ageing at 85℃ for 177 days. Wheel-tracking tests were used to determine the ability of the material to resist chip embedment and flushing. The adhesion to aggregate and resistance to water-induced stripping was also measured.

A laboratory study was undertaken to determine the effect of grading/particle size distribution on permanent deformation in multi-stage repeated load triaxial (RLT) tests. Results showed the coarse gradings with a Talbot’s exponent n-value of 0.8 had the least amount of permanent deformation for high-moisture contents near saturation. Finer gradings with an n-value of 0.3 had the least deformation in all of the tests in dry conditions at less than 70% of optimum moisture content. Similar performance in terms of permanent deformation was obtained if variations of the n-value were less than 13%. Based on limiting the variations in n-value to ± 13% new grading envelopes for use in the new Transit New Zealand specification for RLT testing were proposed.

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.

To enable the improvement of the modelling of pavement response and performance, the measurement of full-scale tyre surface contact stress distributions in all three of the coordinate directions was undertaken. An apparatus comprising strain-gauged pins housed in a strong steel box, mounted flush with the pavement surface was built. The pins were designed to sense the contact forces imposed on them by the tyres.

This project was designed to investigate the importance of drainage maintenance for pavement performance and to recommend a maintenance strategy. With restrained funding for pavement renewals drainage maintenance is a cost-effective method to ensure optimum pavement performance.

Performance specified maintenance contracts (PSMC) have been operational in New Zealand for more than six years. These contracts are driven by key performance measures (KPMs) that are used to define the expectations of the road agencies and monitor the progress and performance of the contractor. As the effectiveness and efficiency of the KPMs is vital for achieving the desired results, it is essential to examine the effectiveness of the current KPMs in controlling and directing the maintenance contracts. The report examines the interpretations of the collected data using average and mode. The poor representation of the total network condition by the traditionally used average is illustrated by numerous examples. Alternative representation of the network condition is proposed and illustrated by using the mode of the data set.

The falling weight deflectometer (FWD) which measures pavement deflections was assessed for its ability to predict the life of a newly constructed or rehabilitated pavement. FWD measurements used in the study were from NZ Transport Agency’s test track CAPTIF, roads that have failed and from two Performance Specified Maintenance Contracts where the actual life from rutting and roughness measurements could be determined. Three different methods to calculate life from FWD measurements were trialled. The first, a simple Austroads method that uses the central deflection only and was found to either grossly over predict life by a factor of 1000 times more than the actual life or grossly under predict the life. The second two methods trialled were based on Austroads Mechanistic Pavement Design where the life is determined from the vertical compressive strain at the top of the subgrade.

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.