Fifth International Colloquium Industrial Floors’03, (Ed . P. Seidler, Technische Akademie Esslingen), Ostfidern/Stuttgart, Germany (21-23 January 2003), pp613-620. Adhesion of Self Compacting Concrete on Old Concrete Structures L. COURARD, A. DARIMONT, X. WILLEM, C. GEERS and R. DEGEIMBRE University of Liege, Department GéomaC, Research Unit in Building Materials, Belgium J. WIERTZ Ministry of Equipment and Transport, Liege, Belgium SUMMARY The repair of concrete deck slabs or balcony needs a special composition of concrete, and Self-Compacting Concrete (SCC) is advantageously used for such repair operation. The rheology of the material is of prime importance and needs to be adapted to ensure the penetration of SCC beneath the concrete plate structure as well as the adhesion to the old concrete substrate. Several materials have been used and characterised by means of a physical, chemical and mechanical test program. A test procedure is proposed to assess the efficiency and quality of the repair technique and material. Analysis of the interface between concrete substrate and SCC is given on the basis of a pull-off test and microscopical observations. 1 INTRODUCTION Adhesion quality will depend on the properties of the two bodies to be bonded: mechanical interlocking, thermodynamic and electro-physical interactions are the mechanisms at the base of the interface creation and stability [1,2]. Contact creation between concrete substrate and repair materials imposes that the latter be sufficiently low viscous in order to spread on the surface and penetrate into the capillaries of the superficial concrete layer [3]. This is why contact must happen as soon and as quickly as possible, as viscosity increases with time due to the setting process and evaporation of the liquid phase of the repair material. Balconies (Fig. 1) are particular concrete structures subjected to a many potential degradation processes: water is the main vehicle for the intrusion of aggressive substances [4], but it is also at the base of degradation due to freeze-thaw cycles or dissolution of minerals. When the upper surface is protected by a waterproofing layer, it is often necessary to repair the under face, for aesthetic or structural reasons. Dry-mixture shotcrete and patch repairs are two classical methods that can be used for repairing these concrete elements. The first method can give high values of adhesion and limit shrinkage by using adapted W/C ratio and admixtures: the main disadvantage of shotcrete in this case is dust and rebound, which are unacceptable for areas like housing and buildings. 1 concrete slab 2 low-strength concrete for slope 3 waterproofing membrane 4 sand stabilised with cement 5 ceramic tiles laid on mortar Figure 1 : Typical balcony structure Patch repairing is very time- and labour- consuming. A comparison of costs [4] takes into account the time necessary to do the job, the cost of materials and the renting of machinery: installation, scaffolding, surface preparation, volume of repair materials and workers’ salary can be considered as equal (table 1). Self-compacting concrete (SCC) appears to be an interesting option if it is possible to fix and reuse a mould under the structure [5]. 5 1 2 3 4