Taleb Al-Rousan

New Methodology for Shape Classification of Aggregates

Aggregate shape characteristics play a major role in determining the structural and functional properties of asphalt mixes. A comprehensive, statistically based methodology for the analysis and classification of the shape characteristics of both fine and coarse aggregates is presented. These characteristics are form (three dimensions of coarse aggregates), angularity, and surface texture. The methodology was developed by measuring the distribution of the shape characteristics of aggregates from a wide range of sources and varying sizes. The limits for the classification groups were determined with the use of a cluster analysis. The new methodology offers several advantages over current methods used in practice. It is based on the distribution of shape characteristics in an aggregate sample rather than on average indices of these characteristics. The coarse aggregate form is determined with the use of a three-dimensional analysis of particles, which allows particles to be distinguished between flat, elonga...

Evaluation of Aggregate Characteristics Affecting HMA Concrete Performance

This report documents the outcomes of the ICAR study on the Evaluation of Aggregate Characteristics Affecting HMA Concrete Performance. This study was conducted with support from the Federal Highway Administration (FHWA) program on Simulation, Imaging, and Mechanics of Asphalt Pavements at Texas A&M University. The first outcome includes assessment of HMA sensitivity to aggregate shape characteristics. Aggregate shape is characterized through detailed measurements of angularity, form, and texture using the Aggregate Imaging System (AIMS). The shape characteristics are presented in terms of the distribution of the property in an aggregate sample rather than an average index of this property. The second outcome of this study is the development of a viscoplastic model for permanent deformation. The model accounts for the aggregate structure in the mix, which is related to the shape properties measured using AIMS. The model capabilities are demonstrated through matching the results of testing various mixes from the Accelerated Loading Facility (ALF) of the FHWA using the triaxial creep and strength tests. In addition, the model is used to predict the response of mixes that include aggregates with different shape characteristics in order to develop relationships between the model parameters and aggregate shape characteristics. As part of the model development, an experiment was conducted to capture and characterize damage evolution in HMA due to permanent deformation. HMA specimens were loaded using a triaxial compression setup to four predefined strain levels at three confining pressures. Consequently, image analysis techniques were used to analyze damage distribution. The results of the damage experiment supported the damage evolution function proposed in the viscoplastic model.

Analysis of Aggregate Shape Characteristics and its Relationship to Hot Mix Asphalt Performance

ABSTRACT This paper presents the development of a methodology for the classification of aggregates based on their shape, angularity, and texture characteristics. This methodology utilizes the Aggregate Imaging System (AIMS) to measure aggregate characteristics, and the clustering statistical method to analyze the measurements. The outcome of this analysis method is the percentage of aggregate particles that belong to groups or clusters that have statistically different characteristics. The “Categorical Counts” method is employed in this study for comparing the characteristics of different aggregate samples. This method detects not only the statistical difference between aggregate samples, but it is also capable of identifying differences in each of the clusters. The quality of AIMS measurements is evaluated through the analysis of repeatability and reproducibility. Finally, statistical analysis was conducted to determine whether aggregate properties are significant enough to influence the measured mechanical properties of a wide range hot mix asphalt (HMA) mixtures or not. Although the results showed that aggregate shape characteristics had strong correlations with measured mechanical properties, the data was not comprehensive enough to develop predictive equations of mechanical properties as functions of aggregate and other mixture properties. Discussion is provided on the laboratory experimental factors that influence the correlations between aggregate characteristics and measured mixture mechanical properties.