Resources

Melter slag is a major by-product of the steel manufacturing process, and its potential for use as an aggregate in open-graded emulsion mixes (OGEMs), is the topic of this report. Crushed melter slag was first tested in 1991 for use in constructing access roads within a steel mill complex in New Zealand. Its performance was later trialled on a state highway intersection for about 4 years (1994–1997). The report details the results of the monitoring and evaluates its use as aggregate. Keywords: aggregate, bitumen, emulsion, melter slag, New Zealand, OGEM, overlay, pavement, roads, trials

Criteria for selecting riprap to protect bridge abutments against scour were investigated. Experiments were conducted with a spill-through abutment under both clear-water and live bed conditions in a laboratory flume. The riprap size and apron size and extent were varied. The data were compiled graphically, with dimensionless variables representing riprap size and apron extent on the axes. A useful relationship was found, with a clear zone of partial failure. Keywords: bridge scour, riprap, protection, hydraulic modelling, abutment, live bed, mobile bed, riprap apron

A computer simulation study was conducted to investigate the viability of harmonising rut depth measurements from different automated rut depth measurement profilometers. A computer program was written which allowed for a standard reference transverse profile to be analysed by any number of profilometer sensors and spacings. The software generated a variety of rut depth statistics. The software was used to investigate the effect of the number of sensors on the predicted rut depth. It was found that the accuracy of the rut depth was proportional to the number of sensors and that this sampling effect results in an underestimation of 2–4 mm for the profilometers used in NZ. The pseudo-rut model was found to be inappropriate for predicting rut depth. It did not prove possible to test the wire model due to the shape of the reference profiles.

Bridge damage, especially due to pounding and unseating at expansion joints has been observed in almost all major earthquakes. It is the result of large relative displacements of girders, in excess of the designed gap width and seating length. Research shows that relative displacements of neighbouring bridge segments depend on the fundamental frequencies of the adjacent structures, spatially varying ground motions and soil-structure interaction (SSI). To evaluate the significance of the influence of these factors, three identical bridge models with a scale ratio of 1:125 were tested using shake tables. Another study involved one of these models pounding with movable abutments. Lastly, another scaled model of 1:22 was field tested to study the SSI effect in comparison with the fixed-base results. The scaled models were designed in accordance with the principles of similitude.

New Zealand's road network uses pavement types of widely differing properties, ranging from very smooth asphaltic concrete to coarse chipseal surfaces having macrotexture levels not often found elsewhere in the world. A research programme was undertaken between 1988 and 1995 to investigate the effect of surface texture of a road on the rolling resistance of a typical tyre/car combination. Data available in the international literature was reviewed during 1994–95 following analysis of the New Zealand results. A comparison of the coastdown and steady state torque methods established that the latter was more suitable for measuring vehicle drag forces on public roads. Accordingly, it was used to obtain static and dynamic rolling resistance coefficients for 12 different road surfaces having approximately the same roughness, but with macrotexture depths which ranged from 0. 6 mm to 2. 7 mm.

The application of geosynthetics (ie geogrids) for the stabilisation of basecourses prepared with a River Run rounded gravel aggregate was investigated. Reductions in the rate of rut formation by over 50% were observed when geogrids were included either at the basecourse/sub-base interface or at half-height of the basecourse. The rate of rut formation was reduced further if a square type geogrid was used in place of a triaxial type geogrid. It was found that the basecourse rutted rapidly if the surface was not confined, due to the lack of particle interlock and surface confining stress. If the surface was confined with a thin (ie < 40mm) asphalt layer to bind together the particles in the surface, then the aggregate provided significant support and reduced rutting by over 90%, even without the addition of geosynthetic stabilisation.

Precast pre-tensioned concrete bridge construction became common in New Zealand in the 1950s and a large number of pre-tensioned concrete bridges were constructed between 1953 and 1980. These bridges do not meet today’s durability requirements and many are at risk of chloride-induced pre-tensioned reinforcement corrosion. This deterioration can be difficult to detect in visual inspections and has immediate structural implications, so prediction or early detection of at-risk structures is critical for bridges to achieve their required service lives. This report presents an assessment of the New Zealand pre-tensioned concrete bridge stock and identifies bridges at risk of pre-tensioned reinforcement corrosion. Construction eras based on evolving construction practices are identified, and examples of typical beam types used in each era are presented. The exposure classification of each pre-tensioned concrete bridge on the state highway network was remotely estimated using a Google Earth-based tool developed for the purpose.

Geotextiles are permeable textile fabrics used in engineering applications. This report is a review of geotextiles and their uses in pavements of both sealed and unsealed roads. Also reviewed is the use of geotextiles for filtration and sub-surface drainage. Most of the readily available geotextiles are of either woven or non-woven construction using synthetic fibres. The types of synthetic geotextiles and their generalised porperties are described. Specific properties are given for the geotextiles currently available in New Zealand. The test methods used to measure a geotextile's general, mechanical, hydraulic and durability properties are commented on. The four main functions a geotextile can perform are separation, filtration, reinforcement and drainage. The function or funtions a geotextile performs in any specific application depends both on the situation and on the geotextile. Understanding of the function(s) performed in each of the many situations covered is essential for proper geotextile selection and usage.

Aspects of bitumen performance in chipseals related to the development of a New Zealand performance-based specification for chipseal binders were investigated. Compatibility with kerosene: Differences due to the base (unmodified) viscosity were far greater than those produced by small differences in kerosene compatibility showing that this requirement is probably unnecessary in the new specification. Adhesion to aggregate: Acid number and a ‘wetting test’ based on the MSCR test (AASHTO T 350-14) at 25⁰C were suggested for inclusion in the new specification. Such tests provide protection against likely poorly performing bitumens and help ensure batch to batch consistency. The tests would be carried out in conjunction with Vialit plate tests. Chip retention: Bitumen cohesive energy as a control property for chip retention was investigated. The measured cohesive energy is strongly affected by the viscoelastic properties of the binder.

The reproducibility and repeatability of the sand circle test for measuring texture depth in pavement surfaces was compared with a new test using wallpaper size and a flexible perspex plate covered by a rubber pad. The new test was found to be more precise. Keywords: sand circle, texture depth, Transit New Zealand stationary laser profilometer, repeatability, reproducibility, alternative test, wallpaper size