ABSTRACT
Radical Concrete Technology. Edited by R K Dhir and P C Hewlett. Published in 1996 by E & FN Spon, 2-6 Boundary Row, London SE1 8HN, UK. ISBN 0 419 21480 1.
ABSTRACT. The paper presents the results of an experimental study aiming to assess the frost resistance of 45 cement pastes. The influence of four parameters was studied: the water to binder ratio (0.25, 0.35, and 0.45), the dosage of silica fume (0, 10, and 20% in weight), the type of micro-fibers (steel or carbon), and the fiber dosage (0, 2, and 5% in volume). All mixtures were subjected to 300 rapid freezing and thawing cycles in water and to 50 daily freezing and thawing cycles in presence of deicer salts. They were also subjected to a microscopic determination of the characteristics of the air-void system, and to flexural strength measurements. The results obtained clearly indicate that the use of micro-fibers improve very significantly both the frost durability and the deicer salt scaling resistance of cement pastes. Keywords: micro-fibers, durability, freezing and thawing, deicer salt scaling, air entrainment, steel, carbon, flexural strength Dr Richard Pleau is an Assistant Professor in the School of Architecture at Laval University (Quebec, Canada). His research interests include micro-reinforced cementitious composites, fiber-reinforced concrete, high-performance concrete, frost durability, and air entrainment. Maha Azzabi is a graduate student in the Department of Civil Engineering at Laval University (Quebec, Canada). Her Ph.D. thesis have for object the durability of microreinforced cementitious composites. Dr Michel Pigeon is the Director of the Centre Interuniversitaire de Recherche sur le Béton Sherbrooke/Laval and a Principal Investigator of the Concrete Canada Network of Centres of Excellence on High-Performance Concrete. His research interests include durability, additives, roller-compacted concrete, shotcreting, and repairs. Dr Nemkumar Banthia is an Associate Professor in the Department of Civil Engineering at the University of British Columbia (Vancouver, Canada). His research interests include all aspects related to fiber-reinforced concrete. INTRODUCTION Cement paste is a brittle material. However, the use of micro-fibers at a relatively high dosage (2 to 5% by volume) was found to significantly improve the tensile (or flexural)
strength and the toughness of cementitious materials [1-4]. These fibers can be made with mineral (asbestos, wollastonite), vegetal (cellulose, sisal), or synthetic (steel, carbon, glass, etc.) materials. Due to their very small size (typically 20 µm in diameter by a few mm in length), the micro-fibers are very numerous (up to 500 000 fibers per cm3), and the average spacing between them is usually less than 200 µm. Consequently, the microfibers can restrain the formation, the coalescence and the propagation of microcracks which probably account for the better mechanical properties.
