A laser-based assessment of road construction aggregate shape and texture properties and their relationship with material shear strength, a pilot study

Abstract

Experimental research was undertaken to exploit the use of an innovative laser scanning tool and to apply the equipment to the study of (G1) road construction aggregate obtained from crushed rock quarry sources. The aim of the research was to better quantify particle shape and surface texture characteristics and an attempt was made to relate these to the shear strength properties of the materials investigated. By obtaining a better understanding of the effects that particle shape and texture have on the shear strength properties of a material, the overall efficiency of construction aggregate may be improved. Physical material properties and possible effects related to the (geological) origin of the materials were also considered. In order to assess the particle data obtained from scan results, models were derived which could sort individual particles in order, based on their shape and/or surface texture. These models were created by experimental modelling of physical particle properties (i.e. dimensions, volume and surface area) obtained from scan results. A total of 1149 particles scan data were collected. After experimentation, at least two working concept models were proposed using the scan data, one of which was ultimately abandoned as the model was affected by the elongation (i.e. shape) of particles. The second model proved to be better than the first and was further refined to develop a reference system for each particle size to enable comparison of particle textures. After developing the comparative models described above, the aggregate texture value (ATV) was conceived and refined. A system was developed whereby an aggregate texture value was derived for the elongated and regular constituents of an aggregate sample, after separating particle data based on the particles shape. The aggregate texture value weighed in the average model value calculated based on the grading analysis of a particular sample as well as the percentage of elongated particles in a specific size constituent of a sample. The newly developed aggregate texture value was then related to limited tri-axial shear test results to establish whether there is a correlation between the parameter and the shear strength properties of the aggregate. Findings indicate that the models developed and the newly derived aggregate texture value hold significant potential in better quantifying the shear behaviour of aggregates. While this research is based on a limited sample size and data, it is considered a pilot project and the preliminary results justify further, extensive data accumulation and model refinement.