Bonding in Cementitious Composites: How Important is it?
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BONDING IN CEMENTITIOUS COMPOSITES:
HOW IMPORTANT IS IT?
SIDNEY MINDESS Department of Civil Engineering, University of British Columbia, Mall, Vancouver, British Columbia, V6T IW5, Canada
2324 Main
ABSTRACT A number of different including:
types
of interfacial bonding occur in
concrete,
i)
bonding between various phases (including anhydrous cement) in the hydrated cement paste (hcp) system; ii) bonding between cement and aggregates; iii) bonding between cement or mortar and the fibres in fibre-reinforced concrete; and iv) bonding between concrete and steel reinforcing bars or prestressing cables. The importance of these types of bonds with respect to the mechanical It is concluded that in some systems, behaviour of concrete is discussed. the mechanical properties are governed primarily by the interfacial bond; in other systems, however, this bond has only a secondary effect.
INTRODUCTION Fresh concrete may contain, in addition to portland cement, chemical admixtures, a number of other materials: i) ii) iii) iv)
water
and
fly ash or other pozzolanic materials; aggregates, with a broad size distribution and variable mineralogical composition; steel reinforcing bars or prestressing cables; and discontinuous fibres, of steel, glass, or natural and synthetic organic materials.
Therefore, can exist;
in
hardened
concrete,
a great many different types
of interface
i)
interfaces between the various phases that make up hydrated portland cement (hcp), including that between the hcp and the unhydrated cement; ii) interfaces between the hcp and the unreacted pozzolanic material; iii) interfaces between the hcp and the aggregate; iv) interfaces between the concrete (or hcp) and the steel reinforcement; and v) interfaces between the mortar (or hcp), and the discontinuous fibres that may be present. The influence of these interfaces on concrete properties was noted as long ago as 1905, when Sabin [1] observed that "since cement mortars are usually employed to bind other materials together, it follows that the adhesive strength is of the greatest importance". While there is almost universal agreement with this statement, quantitative information about the contribution of the interfacial bond to the properties of concrete is difficult to find, for the same reason given by Sabin [i]: "On account of the difficulty
Mat. Res. Soc. Symp. Proc. Vol. 114.
1988 Materials Research Society
Downloaded from https://www.cambridge.org/core. Rice University, on 28 Apr 2020 at 13:12:16, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-114-3
of making tests of adhesive strength, however, the data concerning it are very meager." Thus, while the morphologies of the various types of interfaces are reasonably well understood, their contributions to concrete properties are still largely a matter of conjecture. The elastic properties of cementitious composites can be predicted reasonably well from simple composite models, such as those shown in Fig. l(a).
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