Hussain A. Khalid

A comparison between beam and semi-circular bending fracture tests for asphalt

ABSTRACT Mode I and mixed-mode I-II fracture properties of two bituminous mixtures, a Stone Mastic Asphalt and a Dense Bitumen Macadam, have been determined by means of three-point bending tests on notched specimens. Two specimen geometries, namely single-edge notched beam and semi-circular bending, have been used in the study. Comparisons have been made based on two fracture parameters, the stress intensity factor and the fracture energy. Experimental results have shown that for mode I there is good agreement between the stress intensity factors obtained from the two specimen geometries. Moreover, both geometries have been found suitable to study mixed-mode fracture of bituminous materials.

Moisture damage potential of cold asphalt

This paper presents a study of the effects of moisture ingress on the mechanical properties of a cold-laid grave emulsion asphalt mixture. A vacuum moisture saturation technique has been developed to induce different moisture levels in laboratory-prepared specimens, which simulate site conditions deduced from a field trial. For comparison purposes, a hot mix with the same aggregates and base binder was also used in the study. The stiffness of both materials was monitored under different curing conditions for an extended duration. Semi-circular specimens loaded in a three-point bending test were used to determine fracture properties: fracture toughness and fracture energy. Results showed that, although the hot mixture had good fracture properties, the cold mixtures results were only marginally lower. The vacuum saturation treatment led to enhanced yield performance at low temperatures of both mixtures in the fracture test. The high level of moisture treatment given to the cold mixture made it behave like the hot asphalt mixture at low temperatures.

A lysimeter experimental study and numerical characterisation of the leaching of incinerator bottom ash waste

Incinerator bottom ash (IBA) is a residual produced from incinerating municipal solid waste. In the past, IBA presented a big waste disposal problem; however, various recycling approaches have been adopted in recent years to mitigate this problem, as well as to provide a useful alternative to using primary aggregate resources. The use of IBA as an alternative to conventional aggregates in different civil engineering construction applications helps to conserve premium grade aggregate supplies; however, when IBA is in contact with water in the field, as a consequence of precipitation events or changes in water table, elements, such as salts and heavy metals, may be released to the soil and ground water. In this work, IBA waste was mixed with limestone aggregate to produce a blend with acceptable mechanical properties and minimum environmental risks for use as road foundation. The study focused on evaluating potential environmental impacts of some constituents, including sulphate, chloride, sodium, copper, zinc and lead in IBA blends using a lysimeter as a large scale leaching tool. Moreover, a specific scenario simulating field conditions was adopted in the lysimeter to assess the potential impact of changing conditions, such as IBA content in the blend, liquid to solid ratio (L/S) and pH value, on long-term release of heavy metals and salts. Then, numerical modelling was used to predict the release of the aforementioned constituents from IBA based on initial measurement of intrinsic material properties and the kinetic desorption process concept. Experimental results showed that zinc and lead were released in very low concentrations but sodium and sulphate were in high concentrations. The control limestone only blend also demonstrated low release concentrations of constituents in comparison to IBA blends, where constituent concentrations increased with increase in IBA content. Experimental results were compared with numerical results obtained using a non-equilibrium desorption model. Good agreement was found between the two sets of data.

Fracture Characteristics of Asphalt Mixtures Containing Incinerator Bottom Ash Aggregate

The documented results form part of a larger research program to study the mechanical and environmental properties of asphaltic mixtures containing incinerator bottom ash aggregate (IBAA). The fracture characteristics of four mixtures containing 0%, 30%, 60%, and 80% IBAA by weight were investigated under monotonic and cyclic semi-circular bending conditions. The linear elastic fracture mechanics (LEFM) approach was used to evaluate crack resistance of the tested mixtures with the aim of investigating the effect of IBAA content on these properties. LEFM led to the determination of the stress intensity factor, the J-integral, fracture energy, and Paris law parameters. Crack propagation was monitored with a digital camera, and a program developed in-house was adopted in interpreting crack growth. In addition, a new approach was presented to obtain asphalt fatigue damage parameters from fracture tests. Results showed a benefit to be gained in adding IBAA up to a certain amount, beyond which cracking properties become close to those of the control mix.

Deformation Properties of Untreated and Enzyme-Treated Bottom Ash Waste for Use in Foundations

The use of waste and recycled materials in different construction applications is a widespread approach. In this work, incinerator bottom ash (IBA) waste was mixed with limestone at different levels, namely, 0%, 30%, 50%, and 80%, to produce blends for use as pavement foundation layers. The study focused on evaluating the resistance to permanent deformation of IBA–limestone blends, which is vital to prevent or minimize pavement rutting. An experimental program was undertaken to investigate the influence of plant-based enzyme treatment on the behavior of these blends. Cyclic and static triaxial compression tests were adopted to determine the materials’ mechanical characteristics. Emphasis was on examining the effect of various parameters, such as IBA content, enzyme content, moisture content, curing time, stress level, and number of load applications, on the behavior of the investigated blends. The accumulated permanent strain and strain rate were used to describe the blends’ shakedown stress limits. Results showed that IBA blends gave a favorable performance as foundation layers in comparison with the control limestone blend. Enzyme addition improved the permanent deformation resistance for the control limestone blend; however, it did not have any noticeable effect on the IBA blends. According to the shakedown concept analysis, all blends, at a cyclic stress level of more than 21% of the static failure stress, underwent excessive plastic strain.

Assessment of Fracture Properties of Emulsified Asphalt Mixtures

ABSTRACT This paper presents an investigation into factors affecting the fracture properties of a cold-laid material used as base or binder course on medium to lightly trafficked roads. The Semi-Circular Bending beam test has been used to study the effect of temperature and rate of loading on the fracture properties, expressed as fracture toughness and fracture energy, of the cold-laid material in mode I. A Hot Mix Equivalent mixture was used in the study comprising the same aggregates and base binder. An immersion regime adopting vacuum moisture saturation was undertaken to assess the effect of ingested moisture on the measured fracture properties. At −10 and −20°C, the fracture toughness of the cold material was almost independent of temperature. At—20°C, the fracture energy of the cold and hot materials were almost equal irrespective of loading rate. The cold mixture attained reasonably high retained fracture toughness upon vacuum moisture saturation.

Predicting fatigue performance of hot mix asphalt using artificial neural networks

Developing predictive models for fatigue performance is a complex process and can depend on variables including material properties, test conditions and sample geometry. Several models have been developed in this regard; some of these are regression models and are related to mechanistic properties in addition to volumetric properties. In this work, a computational model, based on artificial neural networks (ANNs), is used to predict the fatigue performance of hot mix asphalt (HMA) tested in a dynamic shear rheometer (DSR) technique. Fatigue performance was evaluated according to three approaches: traditional, energy ratio and dissipated pseudo-strain energy. For predicting fatigue performance, two types of ANN models were developed: those dependent on test modes, that is, based on controlled test modes, and those independent of test modes, that is, irrespective of controlled test modes, using fundamental parameters, for example, stiffness modulus, phase angle and volumetric properties. In this work, limestone (L) and granite (G) 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 (HRA) and continuously graded dense bitumen macadam (DBM). The results revealed an excellent correlation between the predicted and experimental data. It was found that the prediction accuracy of the strain test mode was better than that of the stress test mode.

PERFORMANCE BASED CHARACTERISATION OF CRUMB RUBBER ASPHALT MODIFIED USING THE WET PROCESS

ABSTRACT Current EU Directives have justified a fresh look at the use of crumb rubber from used tyres in asphalt for paving applications. A study was undertaken to investigate the influence of crumb rubber modification on binder and mixture performance-based properties. Crumb rubber from two origins, truck- and car-tyre was interacted with two penetration grade bitumens from different crude origins at various concentrations. Performance-related, rheological properties of the neat and rubber modified binders were evaluated at high and low temperatures. Based on their rheological performance, selected binders were incorporated in a Stone Mastic Asphalt mixture whose mechanical properties were evaluated. Emphasis was placed on the resistance of mixtures to permanent deformation, measured in the Wheel Tracking Test, and to fatigue cracking, measured in four-point bending fatigue. An attempt has been made to link performance-based binder and mix properties which are considered to correspond to one another.

Correlating the Rheological Properties of Binders with the Mechaical Properties of their Surface Dressing Systems

This paper presents rheological data in terms of fundamental material properties of three cutback binders, one conventional and two modified with different polymer types. The binders were tested at one frequency over a range of temperatures and conditioning periods. They were then used to produce surface dressing samples which were tested in the Mini Fretting Test under the same conditioning period and temperature conditions as the rheology testing. This test simulates the action of traffic on the dressing. The paper then provides correlations between the fundamental binder properties and the Mini Fretting Test results of the dressings containing the three binders. The correlations highlight the usefulness of the Mini Fretting Test in discriminating between different binder types and in predicting the performance of surface dressings, with particular reference to the early stages when the dressing is most vulnerable.

Backcalculation Models to Evaluate Light Falling Weight Deflectometer Moduli of Road Foundation Layer Made with Bottom Ash Waste

Incinerator bottom ash (IBA) is a residue from burning household waste that once was put into landfills. Nearly two-thirds of this ash is reused, primarily in road construction. In this study, IBA was mixed with limestone to produce a blend with acceptable properties for use as a road foundation layer. In situ simulative testing with a light falling weight deflectometer (LFWD) and subsequent interpretation of the surface deflection data have enabled evaluation of the mechanical properties of the foundation and subgrade layers. An experimental and modeling study of the elastic dynamic response of a foundation layer of IBA waste and limestone that was subjected to LFWD impact loading is presented. Several parameters—such as IBA content, water content, and curing time—were studied. Regression, mathematical, and three-dimensional finite element models were developed to backcalculate the LFWD moduli of the foundation layers. The modeling approach accounted for the static and impact nature of the LFWD load. Results showed that IBA blends underwent less deflection, as a foundation layer, than the control limestone blend. Backcalculated modulus results based on the dynamic effect of the LFWD load produced different values from those calculated by Boussinesqs equation, which is adopted by the LFWD manufacturer.