Effect of a high calcite filler addition upon microstructural, mechanical, shrinkage and transport properties of a mortar

Sands produced from limestone rock deposits in Algeria contain high proportions of fine 0/100 μm particles (named filler hereafter), which are available in large quantities. This study aims to identify the maximum filler amount which may be added to cementitious materials without performance loss. Performance is quantified here as related to varied properties, either microstructural (density, porosity, pore size distribution, capillary absorption, Klinkenberg effect), mechanical (Young's modulus, compressive and flexural strengths), or indicative of durability (intrinsic gas permeability, drying shrinkage and mass loss). To that purpose, mortars with various amounts of filler, ranging from 15 to 45% sand mass (i.e. 45 to 135% cement mass), have been formulated, tested and compared to a reference mortar. As recommended by J. Baron [J. Baron, Les additions normalisées pour le Béton, Les bétons - Bases et données pour leur formulation, Association technique - industrie des liants hydrauliques (in French), Eyrolles Ed., Paris, 1996, pp. 47-57], substitution to sand is privileged, whereby cement proportion and workability are kept constant while water need varies with increasing filler amount. Preliminary XRD analysis of filler powder shows no other minerals than calcite CaCO3 and traces of dolomite CaMg(CO3)2. Results point out the existence of an optimal performance value and a high effect of filler addition. In particular, for high filler amounts, total porosity increases while bigger pore populations diminish. This is confirmed by SEM examinations of the microstructure as well as by the increase of Klinkenberg coefficient β determined from gas permeability measurements, and by capillary absorption results. Moreover, intrinsic gas permeability, compressive and flexural strengths remain remarkably high whatever the filler proportion. Drying shrinkage and mass loss are not impacted dramatically either.