Adhesion Between Concrete and Treated or Untreated Flat Metal Surfaces
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ADHESION BETWEEN CONCRETE AND TREATED OR UNTREATED FLAT METAL SURFACES
D.G. MONTGOMERY* AND A. SAMARIN** *University of Wollongong, Department of Civil & Mining Wollongong, N.S.W. 2500, Australia **Boral Research, Wentworthville, N.S.W. 2145, Australia
Engineering,
ABSTRACT Modern construction techniques for floor and slab systems often make use of the composite action developed between steel and concrete. Knowledge of the magnitude of adhesive force, other than mechanical bond, is necessary in the design of permanent steel formwork, which ultimately becomes an integral part of the load bearing reinforced concrete structure. To investigate the extent of adhesion at the interface between concrete and flat metal surfaces, different treatments of the metal surfaces were considered. Results are presented for six types of treated and untreated metal plates when tested in a pull-off mode with conventional concrete. The mode and the type of failures were investigated, and those parameters, which are considered to be significant in the study of this phenomenon, evaluated.
INTRODUCTION Adhesion is a formation of bond between the surface layers of two dissimilar (solid or liquid) bodies, (or phases) brought into contact. Cohesion is a specific case of adhesion within the same body or between the surface layers of two similar bodies. Adhesion is caused by the various types of molecular interactions (e.g. van der Waals forces, ionic or metallic bonds). A limiting case is the formation of a chemical bond at the interphase (chemisorption). Chemical forces arise when a transfer of electrons takes place between the solid and the adsorbed molecules. In essence a chemical compound is formed, but is confined to a layer only one molecule thick at the surface of the solid. Adhesion is usually expressed as a force or work per unit area of contact. Even when two solid surfaces are brought tightly together adhesion between them is usually weak, due to a very small actual area of contact. Increase of the contact area leads to increase in adhesion. High plastic deformations at the interphase can thus lead to improvement in adhesion. The formation of bond between two solids - cement paste and steel, results from an interaction between a liquid, or rather a suspension, which is setting and hardening, while in contact with a solid. The adhesion between the cement paste and steel must be a function of wettability of steel by cement paste suspension. For systems incorporating cement paste it is generally recognized [1,2] that a unique transition zone exists between the adherent and the adhesive materials. At the interphase between cement paste and various substrate materals this zone is usually of higher porosity than the parent matrix and it is often rich in CH and C-S-H. The presence of large numbers of hydroxyls - OH in cement paste must create conditions favourable for the development of hydrogen bond. The amount of water in cement paste affects its structure and strength and the negativity of atoms of adherent bodies affects the hydroge
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