ABSTRACT:

The quality of the aggregates used as building materials is noticeably linked to the quality of the source rocks. That is why researchers have invented many methods in order to control rock material quality. This paper aims to present a classification method of four limestone rocks from quarries in the northern part of Tunisia selected of different geological ages (Lower Jurassic, Upper Cretaceous, and Lower Eocene). This classification is based on ultrasonic measurements and physical and chemical characterization. These physical and chemical characteristics were determined from vacuum water porosity, helium porosity and XRay diffraction tests. This showed a noticeable difference in porosity between the studied rocks. Mineralogy analysis confirms that Calcite is the most predominant mineral. To complete this analysis, SEM images were taken (for a magnification of 1000 and 5000). This allowed visualizing the topography and the morphology of the existing pores and cracks in the samples, as well as their density of occurrence. Finally, the image analysis method applied on the facets of the tested samples made it possible to compare the mesoscopic surface state of the different rocks by introducing the concept of surface crack ratio. The methodology developed allowed us to classify the samples into three groups and to conclude that porosity is the most relevant factor in classifying their quality.

1 INTRODUCTION

Since a long time, the Aggregates were commonly used in the production of concrete, coated stone, railway ballast and in general building and construction applications.

Especially, Aggregates form the skeleton of concretes (essential element of construction) and present about 80% of its weight. They govern both their mechanical characteristics and their costs. Mechanically, concrete derives most of its strength from aggregates and especially from coarse aggregates, due to their higher strength compared to than cement paste. (Added, 2005, Meddah et al, 2010, Wu et al, 2001, Achour, 2007, Pautre, 2011).

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