Previous projects

This project was initiated from the NZTA’s Review 3: Investment Decision of the Gateway Review Report for Waikato Expressway – Huntly Bypass (Francis et al 2015) for Treasury. Recommendation 2 of the review was

“If not already done, NZTA should consider the urgent installation of suitably instrumented test sections at Taupiri and the CAPTIF facility to further improve confidence in the long-term performance of heavy duty Hi-Lab pavements.”

The priority assigned to the task by the report was “Do Now.”

A test pavement at CAPTIF was constructed with four different Hi-Lab pavement sections, supported by a very weak clay subgrade, to study:

• the performance of a full-strength design with two Hi-Lab layers similar in thickness to the Huntly Bypass design (Test Section B)

• the influence of pavement depth on the performance of Hi-Lab by testing thinner sections (Test Sections B, C and D)

• the influence of maximum aggregate size on the performance of Hi-Lab by testing maximum aggregate sizes of 37.5mm and 63mm (Sections A and C).

This report presents the data from the accelerated pavement testing. The results suggest that the Huntly Hi-Lab design, constructed to the same 2xHi-Lab layer thicknesses in Test Section B, was well designed and unlikely to fail in fatigue if constructed properly in the field. It should be noted that all Hi-Lab trial sections at CAPTIF were constructed on a very weak clay subgrade (CBR≈4%), which is well below the design specifications for the Huntly and other Hi-Lab projects. Also, the loads applied during the testing at CAPTIF were 50% greater than design and the standard legal loading.

The thinner test sections suggest that fatigue is a mode of failure that needs to be designed against.

The comparison of maximum size aggregates in Sections A and C suggests that Hi-Lab 65 would be a superior material for fatigue.

Further analysis of the results forms part of an Auckland University PhD thesis by PGL van Blerk on Hi-Lab materials design and construction.

The aim of this research was to develop and calibrate a residual pavement life model capable of improving upon current estimates of remaining life for newly constructed unbound granular pavements.  

The new model was compared against the best existing model, with the new model providing a significantly improved estimate of residual life.

The new model can be used to provide project level assessments of the remaining life of newly constructed unbound granular pavements. However, a period of field validation is recommended, and the further research recommended is likely to significantly enhance the model’s accuracy and applicability to a wider range of scenarios.

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. A relationship was found between pavement life tested at CAPTIF plus the rut depth modelling and the damage law exponent for the 4 and 6 tonne equivalent axle loads. For short-life pavements the damage law exponent increased.

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.

The recommendations resulting from the research are to:

• prime all new pavements before first-coat sealing to reduce the risk of early failure
• condition new seals before they are loaded in wet conditions, ie avoid the practice of sealing just before it rains as this is likely to increase the probability of failure
• avoid geometric designs that generate large water film thicknesses
• not delay in placing second-coat seals on high-volume roads
• use unsaturated hydraulic models for modelling moisture movement in pavements
• review first-coat seal failures for the factors observed in this report
• undertake field trials of lower permeability M/4 alternatives.

Undertaken as part of a larger collaborative research programme conducted under the auspices of the OECD/ ECMT (European Conference of Ministers of Transport) Joint Transport Research Centre, this research focused on the economic evaluation of long-life pavements. The aim of the research was to investigate the potential of epoxy-modified asphalt as a low-maintenance long-life (>30 years) surfacing material. NZTA’s contribution to the research focused on the potential benefits of epoxy-modified open-graded porous asphalt (EMOGPA).

The two finite element models, validated with data from CAPTIF, were used to calculate rutting for a range of pavement depths on a number of subgrade soils. This information was used to develop pavement thickness design charts from the rut depth predictions and these were compared to the chart for granular pavements in the Austroads design guide.

This research showed that modifying the tested aggregates with 1% cement could reduce rutting and improve the rutting life of the pavement by 200–300% compared to the traditional unbound pavement. Foamed bitumen and cement reduced rutting and created a 500% improvement in life compared to the unbound pavement without any loss of stiffness (fatigue) during the project.

The benefits of modified aggregates can be included in the current Austroads design framework with the empirical procedures developed in the report. The procedures can be used to estimate design life from laboratory mix design data on any proposed material.

The purpose of this research was to develop a methodology from laboratory beam fatigue tests to obtain the tensile fatigue design criteria of aggregates bound by stabilising agents for use in pavement design to guard against cracking and/or a return to an unbound condition within the design life.

The testing found that stabilised aggregate beams can be successfully compacted in a the laboratory resulting in similar strengths (maximum tensile stress) to saw cut beams at CAPTIF and Australia’s accelerated loading facility (ALF).

The analysis method developed calculated conservative fatigue lives for the CAPTIF pavements. The surface of the CAPTIF tests did not crack, but the strain and deflection measurements increased to a typical level for a fully unbound pavement.

This research showed that, if pavements are constructed well, then applying low noise surfaces immediately after construction is possible. From analysis of the first test falling weight deflectometer readings, a conservative approach would consider all deflections having curvatures over 0.25mm to be unacceptable and that such results would require additional analysis. Where the criteria was not met – a short period of trafficking of the underlying pavement would generally lead to acceptable surface life.

Research into potential axle mass limit changes showed that for state highway pavements – the increase to a 8.8 tonne single axle dual tyre for high productivity motor vehicles (HPMV) is unlikely to be significantly damaging to pavement structures or chipseal surfacings. The research also showed that the 4th power law for road user charges is conservative for state highways. Conversely, damage law exponents for low-strength low-volume roads could increase. The most appropriate damage law exponent for use in road user charges should be determined as a function of the pavements strength.

This programme includes analysis of the NZ long-term pavement performance (LTPP) programme and the CAPTIF accelerated pavement testing programme to develop a rutting model for New Zealand conditions. Previous work highlighted some data limitations in the LTTP programme.

The purpose of this project was to examine specific fundamental loading parameters (load magnitude and number of repetitions, tyre inflation pressure and basic tyre type) that influence the behaviour of thin-surfaced granular pavements. The pavement response and performance measurements included continuous surface deflection basins, longitudinal and transverse profiles, and vertical strains in the granular layers and subgrade.

The trial involved constructing six test sections of various asphaltic concrete mixes over 200mm of unbound granular basecourse and a silty clay subgrade. The design life of all test sections was 1.0 x 106 ESA, so the depth of the asphaltic concrete varied from 80mm to 125mm, depending on the characteristics of the different mixes.

The objective of this research programme (three pavements) was to compare the pavement deterioration caused by dynamic loads generated under different types of suspensions: steel parabolic leaf spring and shock absorber, multi-leaf steel suspension, and air bag suspension with shock absorber.

The OECD Scientific Expert Group IR/6 has completed a coordinated international research programme investigating the effect of vehicle dynamic loading on pavement deterioration. The experiment consisted of six interlinked research elements undertaken by researchers from more than 10 countries. Element 1 of the DIVINE programme was an accelerated pavement testing project undertaken at CAPTIF to investigate the relationship between the dynamic loading produced by different suspensions and the resultant pavement performance.