Contribution à l'étude des bétons plaqués

Résumé

Les constituants du béton plaqué sont le béton, la colle et l'acier. L'étude systématique du matériau composite doit être menée en faisant varier un certain nombre de paramètres, difficiles à isoler, du fait que les forces d'adhésion se développent entre des substances de nature différente.

Nous avons cherché à élaborer des modéles expérimentaux, qui soient reproductibles. La mesure de l'état de surface des subjectiles, en particulier, a été effectuée avec une très grande précision.

Dans ce travail, nous décrivons deux types d'essais qui permettent d'étudier des ruptures par cisaillement en traction et en compression. Les déformations des éprouvettes ont été mesurées à l'aide de capteurs à jauges électriques. Les faciès de rupture ont été observés au microscope électronique à balayage. Nous relatons quelques résultats expérimentaux obtenus dans la dernière partie.

Summary

Our laboratory is engaged in research on adhesion between concrete and steel, especially as regards surfacereinforced concrete. This expression covers a new method of bonding concrete and steel by means of synthetic resin gluing.

Plain concrete has low shear and tensile strength. Reinforcing enables it to acquires strength for such loads and improves its mechanical properties. Bars are embedded in the concrete which, once hardened, will establish satisfactory bonds.

However, adhesion of a layer of concrete poured on to a steel plate is very poor. Bond will be effective only if a thin layer of resin is placed between the two materials. Another method consists of gluing metal sheets on to hardened concrete. In this way it is possible to reinforce structures to bear loads for which they were not initially designed.

The present paper deals with this latter type of gluing, particularly examining the adhesive strength of the resin which prevents sliding between the steel and concrete surfaces.

Adhesiveness depends on:

• -the composition and qualities of the resin used,

• -the surface state of materials to be glued, above all their roughness,

• -the properties of these surfaces.

Adhesion is a complex phenomenon. Indeed, we know little of the crystalline structure of resins and the various authors writing on the subject have not given a comparable definition of roughness. Moreover, the properties of surfaces develop with time. To contribute to this research, we have tried to set up stable experimental models, capable of offering reproducible results under set conditions. In so doing, we hope to have improved knowledge of the principal problems of adhesion.

The article continues with details of experimental devices to study the shear strength of samples. We define two types of test for shear under tension and compression.

In the second and third parts of this paper, we describe the development of all the techniques used during the various tests and controls. This work is the basis for tests being carried out. The techniques have proved that the composites material (steel-resin-concrete) can be studied systematically only if a number of factors are changed:

• -volumic fraction of components;

• -structure and mechanical properties of material and their bonding surfaces,

• -methods for designing and setting up experimental models

• -loading procedure

The scanning electron micrographs show that it is possible to obtain perfect adhesion between bonding surfaces. Measuring the state of bonding surfaces improves accuracy in judging roughness and will help to draw up basic requirements for the preparation of such surfaces on materials to be assembled. By pursuing this work we hope to be able to define the principal characteristics of adhesion.