Evaluation of aggregate imaging techniques for quantification of morphological characteristics

Aggregate morphological characteristics, including shape, angularity, and surface texture, have a significant impact on the engineering properties of construction materials such as hot-mix asphalt and hydraulic cement concrete. Consequently, the quantification of morphological characteristics of aggregates is essential for quality control of both aggregate production and pavement construction. Imaging techniques provide a cost-effective means for measuring the aggregate morphological characteristics conveniently without tedious work. However, these imaging techniques adopt various mathematical methods with different instrument setups and result in different definitions of morphological descriptors that are usually incomparable with each other. This paper evaluates prevalent imaging techniques used for aggregate morphological characteristics analysis, including equipment cost, repeatability, reliability, accuracy, and measured morphological parameters. Three imaging techniques (second-generation Aggregate Imaging Measurement System, first-generation University of Illinois aggregate image analyzer, and Fourier transform interferometer system), are further evaluated by comparing the analysis results of seven types of aggregates passing a 3/4-in. sieve and retained on a 1/2-in. sieve with manual measurements and visual rankings. Analysis of variance between measurements using different methods is also conducted to evaluate the accuracy of each aggregate imaging system. From the data analysis, recommendations that depend on morphological characteristics of most interest to engineers are made for the selection of appropriate imaging-analysis techniques.