Hussain Al-Khalid

Performance Evaluation of Full-Scale Sections of Asphalt Pavements in the State of Qatar

The population and economy in the State of Qatar have been increasing in the past 5 years. Accordingly, traffic loading has also increased rapidly, which affected the performance of existing roads and highways. This high traffic loading merits consideration of the design and construction of long-lasting pavements that require minimal maintenance. The Transport Research Laboratory (TRL) in collaboration with the Public Works Authority (PWA) of Qatar constructed a field experiment that consisted of six different pavement sections in order to investigate the influence of using different materials and asphalt mixture designs on performance. This paper presents a comprehensive study for the field evaluation of the performance of these trial sections. The evaluation involved the use of the falling weight deflectometer (FWD) and a vehicle equipped with instruments for measuring permanent deformation and cracking. These field measurements were complemented with laboratory measurements on field cores: the dynamic modulus, flow number, and semicircular bending tests. The results revealed that the increase in temperature between winter and summer in Qatar reduced the stiffness of asphalt mixtures by about 80%. The sections in which polymer-modified bitumen was used had the lowest temperature susceptibility. Moreover, the results showed that the bitumen and aggregate type significantly affected the stiffness and the trial sections’ resistance to rutting and fracture.

Implementation of mechanistic-empirical pavement analysis in the State of Qatar

The State of Qatar is experiencing tremendous growth in infrastructure including road network and highways. The current methods used in design of asphalt pavements in the State of Qatar are empirical and might not be suitable for the design of long-lasting pavements. Given the significant increase in traffic, road authorities in the State of Qatar have been considering the use of mechanistic-empirical methods in the design and analysis of asphalt pavements. This study documents the results of a study in which the mechanistic-empirical pavement design guide (M-E PDG) software was used in the design of asphalt pavements with input parameters that were carefully selected to reresent local materials and climatic conditions. The selection of material properties was based primarily on specifications and design guides in the State of Qatar and on published literature about these materials. The mechanistic-empirical method was also used to assess the benefits of adopting the concepts of perpetual pavement design and also to compare the performance of pavement structures in which various bitumen grades, granular bases and chemically stabilised sub-base were used. A life-cycle cost analysis was carried out to determine the design with the highest net present value among the various options investigated. It is expected that the outcomes of this study would promote the use of mechanistic-empirical methods in the State of Qatar and the region. Inevitably, this will require significant efforts to calibrate material and damage prediction models used in the M-E PDG for more accurate representation of material properties and measured pavements performance.

Rheological Evaluation of Short- and Long-Term Performance for Warm Mix Asphalt (WMA) Binders

Warm-mix asphalt (WMA) additives are environmentally friendly and cost-effective products that lower the viscosity of bituminous binders to allow reduction of mixing and compaction temperatures in asphalt mix production. In this study, two WMA additives were used; Sasobit® and Advera®. Both were mixed in the lab with unmodified 60/70 Pen and modified PG 76-22 binders. Strain oscillation and viscosity measurement tests were performed to determine the rheological properties of the binder with and without WMA additives. Different ageing processes were performed in this study; half and full short-term ageing using the Rolling Thin Film Oven (RTFO) procedure, and long-term ageing using the Pressurized Ageing Vessel (PAV) procedure. Test results have shown that the addition of Sasobit® increased the stiffness of both binders and changed PG grade by one unit up (6 °C PG grade). Also, Sasobit® presented better rutting resistance in modified and unmodified binders than Advera®, while both WMA additives decreased the fatigue cracking resistance. Multiple Stress Creep Recovery (MSCR) test was also conducted on both unaged and RTFO aged binders. Modified binder with Sasobit® and Advera® exhibited the same performance of the original binder after complete short-term ageing. However, Sasobit® increased the potential of rutting resistance in the unmodified binder more than Advera® did. The viscosity measurements revealed that adding Sasobit® to modified or unmodified binders lowered the viscosity more than Advera® did. These measures were considered as preliminary data required for further studies on the effect of WMA additives on the resistance of bituminous binders to fatigue cracking.

Linear and nonlinear viscoelastic and viscoplastic analysis of asphalt binders with warm mix asphalt additives

ABSTRACT Warm-Mix Asphalt (WMA) is a widely used product, which proved a contribution to the reduction in asphalt mixing and compaction temperatures. This reduction leads to lower fuel consumption and smoke emission in asphalt plants. Most of the characterisation of binders used in WMA has focused in the past on measuring linear viscoelastic properties and associated Superpave parameters. Several studies have shown that the average stresses and strains of the asphalt mixture remain mostly within the linear viscoelastic response. However, localised strains in the binder phase of the mixture could reach values high enough to induce nonlinear viscoelastic and viscoplastic deformations. Therefore, this study focuses on an experimental and analytical evaluation of linear, nonlinear viscoelastic and viscoplastic responses of selected binders modified for use in WMA. The first part of the paper analyses the linear viscoelastic material properties and their ability to evaluate permanent deformation resistance. Then, the non-recoverable creep compliance parameter obtained from the Multiple Stress Creep Recovery (MSCR) test is analysed to assess the nonlinear response and permanent deformation of asphalt binders. The paper utilises a nonlinear plasto-viscoelastic (NPVE) approach to assess and quantify the nonlinear plasto-viscoelastic response of binders by separating the recoverable and irrecoverable strains measured in the MSCR test. Two WMA additives were included in this study by mixing them with polymer-modified and unmodified asphalt binders. Analysis of results showed that the NPVE approach captured a higher percentage of recovery than the NLVE approach. However, binder’s performance evaluation and ranking did not change by adopting the NPVE approach. The nonlinear viscoelastic parameters provided insight on the behaviour of asphalt binders mixed with WMA additives during loading cycles. Sasobit showed higher influence than Advera on binders in resisting permanent deformation by increasing the recoverable strain during the unloading phase.

A Simple Fracture Model for Hot Mix Asphalt Based on Fundamental Fatigue Parameters

This work reports the development of a simple mechanistic fracture model based on a modified Paris’ law using the J-integral. An internal damage parameter, namely the fracture index (FIc), was calculated from this model and was used as an index for ranking the fracture performance of different hot mix asphalt materials tested in fatigue. The relaxation test coefficient (m) and the dissipated pseudo strain energy for the fine aggregates matrix (FAM) volume were used as fundamental parameters for deriving this model. The study revealed there is compatibility between the FIc and phenomenological approach using the number of load cycles at failure. In this work, limestone and granite aggregates were used with two binder grades: 40/60 and 160/220 to prepare four mixtures with two different gradations: gap-graded hot rolled asphalt and continuously graded dense bitumen macadam. The study showed that limestone mixes perform better in fracture than their granite counterparts.

Adhesion properties of warm-modified bituminous binders (WMBBs) determined using pull-off tests and atomic force microscopy

The aggregate-binder bond is one of the main factors that affect the durability of asphalt mixtures. This can be investigated based on the energy required to fracture the adhesive bond between binder and aggregate. In this study, the effects of Sasobit, Rediset WMX and Rediset LQ on the adhesive bond strength of an aggregate-binder system is investigated using the pull-off test. Test data are compared with the nano-scale adhesion force determined using atomic force microscopy (AFM) using the PeakForce Quantitative Nanomechanical Mapping (PFQNM) method. The impact of warm mix additives, test temperature and binder grade on the practical work of fracture was investigated. It was found that Sasobit, Rediset WMX and Rediset LQ increased the practical work of fracture by 170%, 100% and 143%, respectively, for the aggregate-binder system produced using 40/60 Pen binder, and 70%, 25% and 50%, respectively, for the system produced using 100/150 Pen binder. The contribution of warm mix additives in improving the practical work of fracture has been linked to the adhesion force determined using AFM. AFM offers great advantage in characterising the nano-scale properties which were shown to include co-localisation of nano-topography with adhesion, ease of sample preparation and reduction in experimental time relative to the direct tension pull-off test.

Nano-scale properties of warm-modified bituminous binders determined with atomic force microscopy

The use of additives to prepare warm asphalt has been a topic of intensive study recently; however, their effect on the nano-mechanical properties of binder material has yet to be studied. This study presents an investigation into the impact of warm additives Sasobit (Flakes, Organic) and Rediset WMX (Pastilles, Organic-Chemical) and LQ (Liquid, Chemical) on topography, modulus and adhesion of warm-modified bituminous binders using atomic force microscopy (AFM) with the PeakForce Quantitative Nanomechanical Mapping (PFQNM) mode. In this study, the warm additives were incorporated into two binder grades, namely 40/60 and 100/150 Pen. PFQNM results show that Sasobit significantly increased the modulus of the binders at the nano-scale by approximately seven times and five times for 40/60 and 100/150 Pen, respectively. Surprisingly, Sasobit also improved the adhesion properties of the bitumen, with the adhesion force increasing from 17.7 to 35.26 nN and from 21.56 to 59.01 nN for 40/60 and 100/150 Pen, respectively. Both Rediset WMX and LQ also improved the adhesion characterisations of warm-modified bituminous binders by around 110% and 50%, respectively. However, the elastic modulus only increased using Rediset WMX because Rediset LQ did not alter the binder properties of net bitumen as it has no effect on the morphological structure of bitumen. In summary, this study provides new insight into the behaviour and response of virgin and modified bitumen, with particular reference to adhesion and modulus.