The number of commercial vehicles using Irish roads has increased considerably in recent years, leading to higher demands being placed on pavement materials and increased use of polymer modified bitumens. This has also coincided with significant changes in Governmental policy which has produced large increases in Irish recycling rates. Improved recycling levels are set to provide Ireland with a new challenge: to find potential uses for the large quantities of recycled polymer that are becoming available. Towards this end, the potential of developing a recycled polymer modified binder was investigated. The polymers most commonly recycled in Ireland were identified and sourced from industry. Fundamental bitumen tests were conducted to assess the effect of the recycled polymer and a mixing methodology developed. It was found that the addition of 4% recycled HDPE into a pen grade binder produced the most promising results, and the mixing process was then optimised with respect to mixing parameters and binder additives. A developmental recycled binder was produced and compared in performance tests to binders currently used in road construction practice. Results obtained from wheel track and fatigue tests show that although the binder does not deliver equivalent performance levels to a proprietary polymer modified binder, it does out-perform traditional binders used in stone mastic asphalt. Recommendations are offered on the further development of the recycled polymer modified binder to achieve the standards currently required.

/pdf/development-of-a-recycled-polymer-modified-binder-for-use-in-nkkyjcrxe0.pdf

Development of a recycled polymer modified binder for use in stone mastic asphalt

This fully revised fourth edition covers all aspects of the technology of roads and road transport. It forms a comprehensive but accessible reference for all professionals and students interested in roads, road transport and the wide range of disciplines involved with roads. International in scope, it embraces all aspects of urban and rural road technology, drawing on the author's many decades of consulting and operational experience in the financing, planning, design, construction, operation and management of roads in various countries, and is built on a sound theoretical basis. The book begins with coverage of the important procedures involved in the construction of roads, from road planning policies and design considerations to the selection of materials and the building of roads and bridges. It then offers insights into road operating environments that include driver behaviour, traffic flow, lighting and maintenance, and assesses the cost, economics, transport implications and environmental impact of road use. (a)

Handbook of road technology

Finite element modelling of flexible pavements on soft soil subgrades

Multiscale fracture simulation of three-point bending asphalt mixture beam considering material heterogeneity

This paper presents the physical properties of recycled asphalt pavement RAP and its influence on the mechanical perfor- mance of a binder course asphalt pavement mix. A series of binder course mixes were designed containing varying percentages of RAP. A mix made from only virgin material was selected as the control mix for the investigation. The effect of introducing RAP into the binder course mix was evaluated through a series of laboratory tests including the Marshall test, the indirect tensile stiffness modulus test, the indirect tensile fatigue test and the water sensitivity test. A circular wheel track CWT was developed in order to study the dynamic effects of a rolling wheel traveling over an asphalt pavement. The CWT was commissioned within a temperature controlled room along with a customized data acquisition system. The system involves the testing of rectangular slabs and allows for the investigation of dynamic tensile strain. The laboratory tests have shown that the introduction of RAP to the binder course mix resulted in an improvement in all mechanical properties. In particular, it was found that the mix containing up to 30% RAP, displayed improved fatigue resistance relative to the control mix manufactured from virgin materials.

/pdf/influence-of-recycled-asphalt-pavement-on-fatigue-3lpnsxmuf5.pdf

Influence of Recycled Asphalt Pavement on Fatigue Performance of Asphalt Concrete Base Courses

The potential of variable tire pressure technology to minimize distress on flexible pavements with thin asphalt surfacing layers and peat soil subgrade was evaluated using in-situ stress-strain data. Pavement interfacial strains and corresponding subgrade stresses imposed by a three-axle truck were measured and used to estimate the fatigue life of the surfacing layer. Three levels of truck wheel loads in combination with four tire inflation pressures (350, 490, 630, and 770 kPa) were used to evaluate the potential distress by the single steering wheel and rear dual wheels in tandem. Results suggest that lateral strain due to the single steering wheel is the most critical to fatigue failure, which is influenced by the viscoelastic nature of asphalt, and therefore truck speed and axle configuration are important. Lower tire pressures increased the fatigue life of the surfacing layer with respect to the rear dual wheels and the steering wheel by up to 200 and 300%, respectively. Haulage trucks with systems for managing variable tire pressure such as the central tire inflation systems may therefore enhance the serviceability of pavements overlying peat or other soft soil foundations.

/pdf/minimizing-distress-on-flexible-pavements-using-variable-do2i6309zf.pdf

Minimizing Distress on Flexible Pavements Using Variable Tire Pressure

One of the primary structural distress modes found in bituminous pavement layers is fatigue cracking, resulting from repeated application of traffic-induced stresses. The development of a four-point bending test arrangement to determine the dynamic mechanical properties of rectangular beam specimens (305345350 mm dimensions! of bituminous mixtures is discussed. This novel system allows the crack-damaged surfaces of beam specimens to be inspected and monitored digitally in situ during fatigue tests. The test fixture, which was integrated with a closed-loop servo hydraulic feedback system, incorporates a constant clamping mechanism and uses a combined displacement and loading mode of control. A series of four-point bending fatigue tests were performed on specimens of two standard Irish mixtures: a hot rolled asphalt and dense base course macadam. The digitally imaged information on fatigue cracking was used to measure the extent of damage and to characterize a linear elastic fracture mechanics model.

/pdf/evaluating-four-point-bend-fatigue-of-asphalt-mix-using-4bxjbl5y2x.pdf

Evaluating Four-Point Bend Fatigue of Asphalt Mix Using Image Analysis

In order to better simulate the dynamic effects of a rolling wheel travelling over an asphalt pavement, and to better understand the initiation and growth of cracks in bituminous pavement layers, a wheeltracking fatigue simulation facility was developed. This experimental facility permitted the testing of large slab specimens (305×305×50mm) using dynamic wheel loadings. The slab specimens were supported on a soft elastomeric foundation that simulated overlay behaviour on top of a weak pavement structure. Digital photography and image analysis techniques were utilised to monitor the initiation and propagation of fatigue cracks on the bottom of these slabs. Two standard Irish mixtures, a Dense Base Course Macadam (DBC) and Hot Rolled Asphalt (HRA), were evaluated with the fatigue simulation facility. Crack damage was seen to initiate on the bottom face of the slab specimen in a direction parallel to the direction of wheel travel. These cracks would interconnect to form a full width crack that propa...

/pdf/wheeltracking-fatigue-simulation-of-bituminous-mixtures-ut2shjelh4.pdf

Wheeltracking Fatigue Simulation of Bituminous Mixtures

The in-service behaviour of a standard Irish Dense Base Coarse Macadam mixture (DBC) was evaluated by using the material to overlay a road section, which was based upon a weak pavement structure. The response of the layer under a fully laden dual axle truck was examined using a series of pressure cells and asphalt strain gauges that were embedded in the test section. The section was traversed repeatedly until a network of fatigue cracks was observed on the road surface. The transverse horizontal tensile strain was found to be the most critical parameter with respect to crack initiation. When based on in-situ measured strain data, the analytical model that was developed to predict pavement performance on the basis of fundamental laboratory test data, was found to underestimate the in-service fatigue life of the DBC mixture by a factor of 13.5. The underestimation may be attributed to factors that are not accounted for in the analytical models such as material healing, traffic wander and in-situ en...

/pdf/in-situ-accelerated-testing-of-bituminous-mixtures-3cqnhrvf67.pdf

In-situ accelerated testing of bituminous mixtures

The in-service behaviour of a standard Irish Dense Base Coarse Macadam mixture (DBC) was evaluated by using the material to overlay a road section, which was based upon a weak pavement structure. The response of the layer under a fully laden dual axle truck was examined using a series of pressure cells and asphalt strain gauges that were embedded in the test section. The section was traversed repeatedly until a network of fatigue cracks was observed on the road surface. The transverse horizontal tensile strain was found to be the most critical parameter in initiating pavement damage. INTRODUCTION Full scale test facilities offer particular advantages over simulated laboratory programmes: the effects of size, construction, substructure, boundary and loading conditions correspond more closely to the actual on-site conditions than can be simulated directly with model experiments. However, it is seldom possible to control temperature and moisture when using such facilities and consequently there are always inherent disparities when attempting to relate laboratory and in-situ test data. Recent investigations have focussed on the mechanical performance of standard bituminous mixtures using uniaxial fatigue tests [1-3] and fatigue wheel tracking laboratory tests [4]. The present paper describes a full scale accelerated loading performance test on a 20mm Dense Base Coarse Macadam [6] which overlaid a peat based forest access roads [5]. Such forest roads generally have a weak pavement structure, which consists of a surface dressed granular base and a subbase (±0.5m deep) that overlay deep peat foundations. In general, peat (a soft biogenic deposit) provides a poor foundation for roads as it is frequently weak [7] and compressible, particularly after prolonged dry periods [8]. Various damage assessment procedures are used to evaluate the structural integrity of a pavement, for example the monitoring of crack initiation and propagation and permanent deformation on the pavement surface. In-situ material properties can be evaluated by measuring surface deflections with a Falling Weight Deflectometer (FWD), while internal stresses and strains can be monitored by use of appropriate transducers that are located at critical positions within a pavement structure. Environmental factors such as the moisture level in the subgrade and the pavement temperature can also be monitored. The present research has characterised and quantified the in-situ mechanical performance of a standard Irish Dense Base Course Macadam (DBC) by measuring surface strains, crack growth and subgrade stresses at incremental levels of fatigue cycles under controlled load conditions. LAYOUT AND CONSTRUCTION OF TEST SECTION A suitable section of a forest access road was identified for the experiment. Figure 1 shows a schematic representation of the monitoring section, the dimensions of which are 3.3m (road width) by 35m (length of overlaid area). A central area in the outer wheel path was selected for instrumentation with pavement transducers, the detailed layout of which is shown in Figure 2. FWD points were marked over the test area to measure the global pavement response. Crack monitoring grids were randomly spaced in the outer wheel path over 15m along the section. A total of 19 grids were marked out to monitor cracking. Four permanent deformation cross section measurement positions were identified, two at both ends of the crack monitoring strip. The traffic counter was located at the end of the test section. The counter had to be placed as far away as possible from the crack monitoring and permanent deformation measurement positions since counter cables had to be machined into the overlay which could induce initial defects. 0m 5m 10m 15m 20m 25m 30m 35m Traffic counter Permanent deformation measurement cross section Crack monitoring area FWD deflection point Instrumented area (detail in Fig.2) 1 2 3 4 North Overlay chamfer Figure 1. Layout of experimental road pavement section. Road center 460

/pdf/full-scale-accelerated-testing-of-bituminous-road-pavement-jjlfs0aoim.pdf

Anton M. Hartman

Papers

Minimizing Distress on Flexible Pavements Using Variable Tire Pressure

Evaluating Four-Point Bend Fatigue of Asphalt Mix Using Image Analysis

Wheeltracking Fatigue Simulation of Bituminous Mixtures

In-situ accelerated testing of bituminous mixtures

Full Scale Accelerated Testing of Bituminous Road Pavement Mixtures