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Research Report 461 Characterisation and use of stabilised basecourse materials in transportation projects in New Zealand

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

The stabilisation of near-surface granular pavement materials is accepted practice in transportation maintenance and capital development projects in Australasia. Stabilisation in this context involves the mechanical introduction of reactive agents, including cement and foamed bitumen, into existing or manufactured granular materials, with or without existing seal inclusion.

Research Report 305 Adaptation of the AUSTROADS pavement design guide for New Zealand conditions

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

New Zealand granular pavement design is currently based on the assumption that all deformation of the pavement shape under traffic loading occurs in the subgrade. To reflect this theoretical behaviour the AUSTROADS document Pavement design – a guide to structural design of road pavements (AUSTROADS 1992) is based on limiting the vertical strain on the subgrade. AUSTROADS (1992) was adopted as a design methodology by New Zealand in 1996. In 2004 a newer version of the AUSTROADS guide was issued (AUSTROADS, 2004a) and this document is now the current pavement design guide in New Zealand. Just as with the 1992 document AUSTROADS (2004a) continues with the design methodology of minimising the subgrade strain according to the design traffic. This study, initiated in 2004, examines the design methodologies presented in AUSTROADS and evaluates them against available New Zealand research. Various subgrade strain criteria are examined for New Zealand conditions.

Research Report 427 Pavement thickness design charts derived from a rut depth finite element model

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

Repeated load triaxial (RLT) tests were conducted on the granular and subgrade materials used at CAPTIF (NZ Transport Agency's test track). Permanent strain relationships found from RLT testing were later used in finite element models to predict rutting behaviour and magnitude for the pavements tested at the CAPTIF test track. Predicted rutting behaviour and magnitude were close to actual rut depth measurements made during full-scale pavement tests to validate the methods used. This method of assessing rutting in granular materials was used to predict the life or number of axle passes to achieve a rut depth defining the end of life for a range of pavement thicknesses, and the subgrade types to produce new pavement thickness design charts. The results of these rut depth predictions showed the Austroads guide required thicker pavements for low traffic volumes, while the rut depth predictions showed significantly thicker pavements were required for high traffic volumes.

Research report 429 Development of a basecourse/sub-base design criterion

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

The Austroads pavement design guide is currently used in New Zealand for pavement design. It includes a design criterion for the subgrade limiting the subgrade strain value. In the last few years a significant number of early granular pavement failures on high-volume roads have occurred. Investigations into these failed pavements found that most of the surface rutting was from deformation of the granular layers with little or no visible contribution from the subgrade. Therefore, the Austroads design criterion for the subgrade is adequate in terms of providing enough pavement depth to protect the underlying subgrade soil but does not prevent failure in the granular layers. In a parallel research project on rut depth prediction for granular pavements (Arnold and Werkmeister 2010) a range of pavement lives was determined using models derived from repeated load triaxial (RLT) tests.

Research Report 547 Fatigue design criteria for road bridges in New Zealand

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

Road bridges are subjected to millions of cycles of heavy vehicle loading over their design lives, and the introduction of higher vehicle mass limits on New Zealand roads will significantly increase the rates of fatigue damage in bridge superstructures. The NZ Transport Agency's Bridge manual has relied on British and Australian standards for fatigue design criteria, and the aim of this project was to provide the basis for amended fatigue loadings based on New Zealand heavy vehicle characteristics, with allowances for forecast long-term growth in volumes and vehicle masses.

Research Report 499 Modelling of extreme traffic loading effects

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

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.

Research Report 558 Epoxy modified bitumen chip seals

Published: | Category: Activity management , Research programme , Research & reports | Audience: Roading contractors

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.

Research Report 325 The effect of grading on the performance of basecourse aggregate

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

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.

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.

Research Report 384 Tyre/road contact stresses measured and modelled in three coordinate directions

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

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.