Analytical and laser scanning techniques to determine shape properties of aggregates used in pavements

[摘要] Pavement layers are constructed using a combination of materials, of which rock aggregates constitute a larger proportion. Current understanding is that the performance of pavements is dependent on the aggregate shape properties which include form, angularity and surface texture.However, direct and accurate measurements of aggregate shape properties remain a challenge.The current standard test methods used to evaluate aggregate shape properties cannot measure these properties accurately. Among the reasons contributing to the difficulties in the determination of aggregate shape properties is irregular shapes of aggregate particles. Therefore, current research efforts focus on developing accurate, reliable and innovative techniques for evaluation of aggregate shape properties.The work presented in this dissertation contributes to the current innovative research at the Council for Scientific and Industrial Research (CSIR) in South Africa, to automate themeasurement of aggregate shape properties. The CSIR's present research is aimed at improving pavement performance through better materials characterisation, using laser scanning and advanced modelling techniques. The objective of this study was to investigate improved techniques for the determination of aggregate shape properties using analytical and laser scanning techniques. A three-dimensional (3-D) laser scanning device was used for scanning six types of aggregatesamples commonly used for construction of pavements in South Africa. The laser scan datawere processed to reconstruct 3-D models of the aggregate particles. The models were furtheranalysed to determine the shape properties of the aggregates. Two analysis approaches wereused in this study. The first approach used the aggregate's physical properties (surface area,volume and orthogonal dimensions) measured by using laser scanning technique to computethree different indices to describe the form of aggregates. The computed indices were thesphericity computed by using surface area and volume of an aggregate particle, the sphericitycomputed by using orthogonal dimensions of an aggregate particle, and the flat and elongatedratio computed by using longest and smallest dimensions of an aggregate particle. The secondapproach employed a spherical harmonic analysis technique to analyse the aggregate laser scandata to determine aggregate form, angularity and surface texture indices. A MATLABTM codewas developed for analysis of laser scan data, using the spherical harmonic analysis technique.The analyses contained in this dissertation indicate that the laser-based aggregate shape indiceswere able to describe the shape properties of the aggregates studied. Furthermore, goodcorrelations were observed between the spherical harmonic form indices and the form indicesdetermined by using the aggregate's physical properties. This shows that aggregate laserscanning is a versatile technique for the determination of various indices to describe aggregateshape properties.Further validation of the laser-based technique was achieved by correlating the laser-basedaggregate form indices with the results from two current standard tests; the flakiness index andthe flat and elongated particles ratio tests. The laser-based form indices correlated linearly withboth, the flakiness index and the flat and elongated particles ratio test results. The observedcorrelations provide an indication of the validity of laser-based aggregate shape indices. It isconcluded that the laser based scanning technique could be employed for direct and accuratedetermination of aggregate shape properties.

[发布机构] University of Pretoria