Mohammad Ali Khasawneh

Wavelet-based characterisation of asphalt pavement surface macro-texture

This paper utilised wavelet analysis to characterise the macro-texture properties of asphalt pavements. The study included Circular Texture Meter (CTMeter) measurements collected from several asphalt pavement sections in the state of Ohio. The asphalt pavements consisted of two mix designs (Superpave and Marshall), three aggregate types (dolomite, limestone, and gravel), and two binder grades (PG 70-22 and PG 64-22). The wavelet approach was used to determine the wavelength ranges and energy content that affect the macro-texture properties of asphalt pavements. In addition, the normalised energy (NE) parameter was utilised to characterise the overall pavement surface macro-texture. The CTMeter data allowed for obtaining six wavelet decomposition levels, namely d1 through d6, with wavelengths up to 56 mm. The analysis revealed that the macro-texture properties of smooth pavement sections are mainly affected by sub-band levels d1 through d4 (i.e. both fine and coarse aggregates), while the macro-texture properties of the rough pavement sections are mainly affected by sub-band levels d3 and d4 (i.e. coarse aggregates). Similar trends in macro-texture properties were observed between NE and the conventional Mean Profile Depth (MPD). However, the variations in the macro-texture properties were better captured using the NE than the MPD. Therefore, it was concluded that the wavelet approach is better suited to characterise the macro-texture properties of asphalt pavements.

Investigation of the factors influencing wavelet-based macrotexture values for HMA pavements

The primary objective of this work is to identify influential factors on asphalt pavement texture properties and to estimate their relative importance. The analysis is descriptive as well as analytical. Non-parametric procedures and multiple regression techniques were used to identify the significant categorical and quantitative predictors, respectively. The analysis showed that all categorical variables (location, design method, aggregate type, and asphalt binder grade) have statistically significant effect on macrotexture values. The regression analysis and model selection using stepwise regression also showed that air void, nominal maximum aggregate size and percent of trucks or truck traffic count are significant predictors on macrotexture values. Conventional and wavelet-based macrotexture values were statistically analysed in this study.

Macrotexture characterisation of laboratory-compacted hot-mix asphalt specimens using a new asphalt polishing machine

Highway agencies continuously strive to maintain adequate surface friction (or skid resistance) at the interface between vehicle tyres and pavement surfaces to enhance the available friction during all phases of a pavement life time. Conventionally this is attained by monitoring and ultimately overlaying the pavement surface deficiencies. However, this practice is an inactive approach in solving the problem. A more proactive approach would be to carry out the necessary hot-mix asphalt testing in a laboratory setting before construction or during its initial mix design stage. Towards this objective the polishing behaviour of laboratory-prepared specimens has been investigated in terms of friction and macrotexture values. The potential relationship between friction and texture measurements has also been considered. The new asphalt polisher showed a good degree of repeatability. The macrotexture was found to be a significant factor in controlling the frictional properties of asphalt surfaces which was shown by the relatively high correlation between the mean texture depth (MTD) and the British pendulum number (BPN) values. Good correlation was also found when correlating ΔBPN and ΔMTD for each job mix formula and each group based on their polishing susceptibility. Test results of this study that are based on bituminous surfaces made from aggregates produced in Ohio could enrich the Ohio Department of Transportation material specification database for future usage.

Characterisation of asphalt pavement surfaces using torque measurements

Continuous increase in traffic volume in the recent years has resulted in greater surface friction loss of asphalt pavements. While the literature presents several ways of aggregate and asphalt mix screening to ensure that surface characteristics are at an acceptable level of friction to control skid-related accidents, the recommended polishing tests using different accelerated polishing devices are time-consuming and to some extent labour-intensive. Therefore, it is imperative that existing polishing devices be improved to shorten the test duration to a level desired by the industry as well as state and federal agencies. This paper aims at addressing this improvement that uses power unit (or motor) to generate energy enough to rotate the polishing disk at constant rotational speed while being pressed against the specimen surface, then read the power needed from the display screen for the following steps. Multiple verification techniques including comparison studies and statistical analyses were used to examine the validity of this improvement. It was found that data collected by the power unit was repeatable and able to precisely detect surface deterioration history for different asphalt mixes with different polish susceptibility in a manner similar to conventional friction and texture-measuring devices. Hence, aggregates and mixes were classified based on their surface frictional properties. Additionally, results from this study correlated well with results from other studies using conventional methods. Most importantly, it was found to be possible to cut down the polishing test time using torque values in lieu of conventional surface quantification methods.

Investigation of factors affecting the behaviour of subgrade soils resilient modulus using robust statistical methods

Abstract When designing pavements, there are three fundamental external design parameters to evaluate (1) the characteristics of the subgrade upon which the pavement is placed, (2) the applied loads and (3) the environment. This study is based on laboratory testing of cohesive subgrade materials to characterise their resilient modulus properties and to identify the main controlling factors of this property. Experimental results showed a slight increase in resilient modulus values with an increase in confining pressure and a noteworthy decrease in resilient modulus accompanied by an increase in deviatoric stress. This finding was verified statistically. Based on the independent samples t-test analysis, it was revealed that soil type and water content caused statistically significant difference in resilient modulus values. According to one-way ANOVA, deviatoric stress turned out to be influential while confining pressure did not. In addition, it was demonstrated using the two-way ANOVA that none of the two-factor combinations was significant in changing resilient modulus values of A-4a and A-6a soils. Finally, three-way ANOVA showed that changing the deviatoric stress, soil type and water content all together had a noticeable effect on resilient modulus behaviour. Furthermore, all predictive models were found statistically significant at the 0.05 significance level with high predictive power. Confining pressure and deviatoric stress are the two predictors whereas bulk stress was not included by the stepwise regression method. The non-linear regression relatively enhanced the predictive power of all the models.

Effect of crumb tire rubber, microcrystalline synthetic wax, and nano silica on asphalt rheology

This study aims at exploring the influence of different modifiers on the physical and rheological properties of asphalt cements. Crumb Tire Rubber (CTR), Microcrystalline Synthetic Wax (MSW), and Nano Silica (NS) modifiers were used to modify asphalt cement of 60/70 penetration grade. Several percentages of CTR (9, 12, and 16%), MSW (2, 3.5, and 5%), and NS (3, 5, and 7%) by weight of the asphalt cement were tested. The penetration, softening point, flash and fire points, viscosity, dynamic shear rheometer (DSR), and bending beam rheometer (BBR) were carried out in this study. Experimental results showed an improvement in the high-temperature performance of asphalt cement by adding CTR and NS modifiers while adversely affecting properties at low temperatures. Also, the results did not show any enhancement in the high or low-temperature performance by adding MSW to the asphalt cement. The optimum contents of CTR and NS modifiers were found to be 12% and 5% by weight of the asphalt cement, respectively.

Analytical tool to shorten polishing time based on mean texture depth (MTD) of flexible pavements

The reproduction of asphalt pavement surface texture deterioration in the laboratory is usually lengthy. The objective of this work is to find an analytical tool to predict the steady-state mean texture depth (MTD) early in the experiment in order to save time. Data were obtained from laboratory testing carried out on eight job mix formulas of bituminous mixtures. Measurements were collected using the volumetric sand patch method for each hour of polishing. The basic parameter used for this study is the MTD, which is a measure of surface macrotexture. Based on nonlinear regression, an equation was developed to calculate the steady-state macrotexture. The main characteristic of the developed equation allows for calculating the steady-state macrotexture and the onset of steady state. This enables the experimenter to determine when steady state is reached at the desired tolerance during the test, thus reducing the testing time. It was concluded that testing time can be reduced significantly (around 50%-time savings), which may be received positively by highway materials’ agencies worldwide.