Variability in Pavement Design

This paper presents the results of a review on variability of key pavement design input variables (asphalt modulus and thickness, subgrade modulus) and assesses effects on pavement performance (fatigue and deformation life). Variability is described by statistical terms such as mean and standard deviation and by its probability density distribution. The subject of reliability in pavement design has pushed many highway organisations around the world to review their design methodologies, mainly empirical, to move towards mechanistic-empirical analysis and design which provide the tools for the designer to evaluate the effect of variations in materials on pavement performance. This research has reinforced this need for understanding how the variability of design parameters affects the pavement performance. This study has only considered flexible pavements. The sites considered for the analysis, all in the UK (including Northern Ireland), were mainly motorways or major trunk roads. Pavement survey data analysed were for Lane 1, the most heavily trafficked lane. Sections 1km long were considered wherever possible. Statistical characterisation of the variation of layer thickness, asphalt stiffness and subgrade stiffness is addressed. A sensitivity analysis is then carried out to assess which parameter(s) have the greater influence on the pavement life. The research shows that, combining the effect of all the parameters considered, the maximum range of 15th and 85th percentiles (as percentages of the mean) was found to be 64% to 558% for the fatigue life and 94% to 808% for the deformation life.

Estimation of Joint and Interface Parameters for the Finite Element Analysis of Jointed Concrete Pavement Using Structural Evaluation Results

In the analysis of jointed concrete pavement, it is necessary to appropriately model certain aspects of the pavement for accurate estimation of its structural responses. These include load transfer at joints (doweled and aggregate interlocked) and interface condition between slab and foundation. This paper presents a backcalculation method for estimating the joint parameters, both transverse and longitudinal, and the interface parameter along with the pavement layer moduli by using the results of structural evaluation of an in-service concrete pavement. The details of the structural evaluation using Falling Weight Deflectometer (FWD) and the two-stage backcalculation procedure using a three-dimensional finite element (FE) model for jointed concrete pavement are discussed. Modulus of dowel support and modulus of interlocking joints are the transverse and longitudinal joint parameters respectively and the coefficient of friction between concrete slab and foundation is the interface parameter considered for the analysis. These parameters are the useful inputs in modeling jointed concrete pavement using finite element method.

Effect of Aggregate Gradation on the Stiffness of Asphalt Mixtures

Aggregate gradation plays an important role in the behaviour of asphalt mixtures. Packing of aggregate is a very important factor that will be affected by changing the aggregate gradation. Many researchers have investigated different ways of describing packing both theoretically and practically. Bailey ratios have recently been used to understand the volumetric properties of mixtures. In this paper, the Bailey ratios have been used, and two further ratios have also been introduced to allow the asphalt mixture gradation to be fully understood. Thirteen different aggregate gradations have been chosen within the 14 mm asphalt concrete specification to investigate the effect of particle size distribution on the stiffness of the mixture. It was found that variation in aggregate gradation has a significant effect on asphalt stiffness, even within specification limits, and a reasonable correlation between the set of ratios investigated and the Indirect Tensile Stiffness.

Investigation of Hot In-Place Recycling Effects on Hot Mix Asphalt Pavement

In March 2006, a hot in-place recycling (HIR) technique was employed for the first time on Lahore-Islamabad Motorway (M-2) to rehabilitate sections where the rut depth was about 40 mm. Since HIR technology was new to Pakistan, research was carried out to study the effects of recycled wearing course on overall pavement performance. This was accomplished by comparing structural adequacy of pavement and material characterization before and after recycling. Laboratory investigations included hot mix asphalt (HMA) volumeteric analysis, aggregate gradation analysis, extracted asphalt properties (penetration test and dynamic shear rheometer (DSR)) and resilient modulus. Analysis of recycled HMA wearing course indicated a reduction in modulus for a mix which was stiff and aged prior to recycling. Relative degradation of the aggregates in HMA wearing course, before and after recycling, was observed; however, it remained close to National Highway Authority (NHA) standard specifications. The research enhanced awareness of HIR among local engineers and contractors.

The Stress Relaxation Of Modified Bitumens

The Asphalt pavements in Central and Eastern Europe have to be resistant to high and very low temperatures and climatic changes. Especially emphasize influence of low temperatures seems to be critical parameter. That is why the modified bitumens with low temperature susceptibility and with high resistance to low temperature cracking are searched for. Dynamic Shear Rheometer (DSR) can be used as a quick method that can evaluate the modification system of bituminous binders. The advantage of DSR testing is also related to possibility of comparison of unaged and aged bitumen. The relaxations of shear stress of several asphalt rubber binders (containing 11 %, 13 %, 15 % and 17 % of crumb rubber) and paving bitumen were determined in DSR at the temperature of 0 °C and −10 °C. Relaxation tests were performed in the controlled strain regime. Total shear strain (rotation of upper geometry) was set to 1 % of the sample thickness and stress was applied for 60 s. Relaxation time was set to a period of 15 minutes. The shear stress relaxation behaviour of unaged bitumens and bitumens aged after 75 minutes and 225 minutes in Rolling Thin Film Oven Test (RTFOT) is presented and discussed.

Investigation And Design Of Durable Pavement Structure Rehabililation

Preservation of the appropriate quality of road assets needs timely rehabilitation of high-level design and construction. Since the actual life cycles of Hungarian road rehabilitation projects are often much lower than expected, research activities of the authors were concentrated on the development of an updated design technology of road pavement rehabilitation using scientifically based algorithms. The paper outlines the elements of a pavement rehabilitation design based on Hungarian and foreign literature survey, detailed own laboratory test series and trial section monitoring. The main steps of the design methodology comprise the Client’s data supply and disposition, site condition evaluation by the designer, deflection measurement in carefully selected points, eventual additional laboratory tests, choosing design subsections, correction of the equivalent thickness of the new asphalt layer, calculation of strain in wearing course. Besides, relationships are presented between various condition parameter data like bearing capacity values, unevenness measuring data and rut depth values. The pavement rehabilitation design technique suggested here – if widely in Hungary – can significantly contribute to attaining a much longer life cycle of rehabilitated roads than by now, and it is (would be) extremely efficient due to the very limited funds available for highway purposes.

Laboratory Trials Of Cold Recycled Foamed Bitumen Asphalt: Raf Waddington

The Defence Infrastructure Organisation requested a pavement evaluation on RAF Waddington and the results indicated that runway rehabilitation and reprofiling was needed in order to meet the physical design requirements set out in the Manual of Aerodrome Design & Safeguarding. The presence of tar in a layer of the old pavement promoted the option of cold recycling this material into the new structure. This paper presents the results from a laboratory investigation into the suitability of cold recycled foamed bitumen asphalt to be used in the structural layers of an airfield pavement. Laboratory mixture designs with foamed bitumen, incorporating asphalt planings from RAF Waddington runway, were produced in URS Infrastructure and Environment Ltd. laboratory. Specimens were used to assess mix performance and in order to add confidence to the design. The last objective of the research was to demonstrate that asphalt planings from RAF Waddington could be recycled into foamed asphalt for incorporation in the runway rehabilitation works. The optimum binder content was determined from Indirect Tensile Stiffness Modulus tests and Indirect Tensile Strength tests, concluding that the optimum binder content was 3.3% by mass. As a common practice in the UK, up to 1.5% by mass of cement was added to the mixture to improve early life performance. To assess the foamed bitumen samples’ performance with time, specimens were prepared and cured for 28, 180 and 360 days at different temperatures. Post curing, the specimens were tested for a range of performance criteria including fatigue, stiffness and durability. The study found that asphalt sampled from the runway at RAF Waddington can be recycled into foamed asphalt, meeting the requirements of Defence Infrastructure Organisation Specification 050.

Development Of A Pavement Rutting Model Using Shakedown Theory

The rutting of flexible pavements during their exploitation is considered to be one of the main problems in UK as well as worldwide. It is a serious mode of distress alongside fatigue in bituminous pavements that may lead to premature failure, as indicated by permanent deformation or rut depth along the wheel load path, and results in early and costly rehabilitation. This kind of pavement distress makes a negative impact to the serviceability characteristics of the flexible pavement, to the residual life of pavement structure and also to the safety and ride quality for traffic. Two design methods have been used to control rutting: one to limit the vertical compressive strain on the top of subgrade and the other to limit rutting to a tolerable amount usually around “12 mm”. Although experimental data and practical experience have been introduced into these design methods through empirical parameters, there is not a simple relationship between the elastic strain and the long-term plastic behaviour of pavement materials. This paper describes a method based on the kinematic shakedown theorem for constructing a mathematical model to predict the long-term behaviour of pavement structures under the action of repeated and cyclic loadings imposed by moving traffic. This method seeks the mechanism from within a class of mechanisms that minimises the shakedown limit load for pavement structures consisting of layers of Mohr-Coulomb materials. The model differs from extant models, in that the cyclic nature of the loading on a pavement is recognised from the outset, and the current method which is based upon foundation analysis, is replaced by a procedure employing shakedown theory that features the capabilities and applications of the developed technique for assessing rutting in flexible pavements. The basic concepts are outlined together with the most recent calculations of the critical design shakedown load. The influence of the design parameters such as, the strength, stiffness and depth of the granular base-course material as well as the consequences of traffic loading (number of equivalent standard axel loads – ESAL’s) are discussed.

Warm Mix Asphalt For Australian Airports

Warm Mix Asphalt (WMA) is a viable alternate to Hot Mix Asphalt (HMA) for airport surfacing in Australia. Limited experience with this technology at Australian airports has prevented its acceptance by airport owners and their designers. WMA does have a significant track record in Europe and the USA, where it has been demonstrated to provide significant environmental, safety, quality and construction flexibility benefits. Differences in available binders and the Australian tendency for thinner asphalt layers and less capable materials makes direct extrapolation of experience from Europe and the USA inappropriate. The aim of this paper is to demonstrate the comparative performance of WMA (by foamed bitumen technology) to HMA as an airport surface layer. Comparison between HMA and WMA has been made during a number of projects at Australian airports since 2012. A formal trial was performed at a military airfield as part of a broader project in 2013. A combination of production verification, quality assurance and mix performance tests were used to make comparisons. Subject to ongoing monitoring and performance testing of the military airfield WMA trial section, WMA is now verified as a viable alternate surfacing material for Australian airport runways.

Site Trials of Recycled and Secondary Aggregates in Concrete and Concrete Blocks in Qatar

A major construction programme is underway in Qatar. A shortage of local aggregate is focusing attention on the use of recycled and secondary aggregates. Site trials using locally available materials in structural concrete and concrete blocks were carried out in three small buildings. By far the largest source of recycled and secondary aggregates in Qatar is construction, demolition and excavation waste, which is generally crudely separated into excavation waste (EW) and construction/demolition waste (CDW). The other material investigated was incinerator bottom ash (IBA). The EW was used to replace 50% of the coarse aggregate in structural C40 concrete, with the CDW replacing 50% and IBA 20% of the coarse aggregate in non-load bearing concrete blocks. The control was 100% imported gabbro coarse aggregate. The trials also incorporated replacement of 60% of the local washed sand with imported crushed rock fines; this was investigated because the reserves of suitable concrete sand in Qatar are limited. Results after one year show the materials giving equivalent or better performance than the primary aggregate controls. The Qatar Construction Specification will be updated to permit greater use of recycled and secondary aggregates (RSA) and further trials are planned in a range of applications, including unbound subbase and pavement concrete. Wider use of these materials will reduce reliance on imported aggregates. The site trials won an award for the most innovative project from the Qatar Contractors Forum 2013.