ABSTRACT:

A new method for analysis of size, shape and roughness of aggregates based on a 3-D-laser-digitising technique is presented. Measurements of aggregate particles are carried out by a system consisting of a laser sensor and a co-ordinate-measuring machine; the accuracy of the system is ±50 mm. Scanned data are processed to create a digital image of aggregates to be employed in further analyses. Size, shape and volume analysis of particles has been conducted in two ways. A so-called geometrical analysis is based on simple applications of analytical geometry. Another method consists of the Fourier transform analysis of the topography of the two halves of the sample defined by a plane intersecting its mass center. Three-dimensional spectra are obtained as a function of two frequencies along the co-ordinate axes. The cross-sections of the spectrum are then investigated and the pattern of the power spectra gives the dimensions and shape of the particles. When comparing the results from these two methods, a very good agreement is obtained. From the spectrum, the texture component can be identified, which gives the roughness of the particles' surfaces. The new technique by Fourier transform analysis is promising giving repeatable results and performing a combined shape-size-texture analysis of the aggregate particles.

INTRODUCTION

Aggregates' size, shape and surface texture can be characterized from a strictly geometric point of view. The particles are three-dimensional objects thus; their size should be described by at least three parameters. The volume would be the most natural parameter quantifying the size of a certain particle, but it cannot be directly correlated with the shape. Therefore some authors (Jansson & Muhr, 1995; Wang et al. 1996) suggested to utilize typical lengths obtained by circumscribing the particle or its images on a picture with simple Euclidean shapes.

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