Effect of concrete surface treatment on adhesion in repair systems

Abstract

Existing concrete surfaces need to be roughened to a profile necessary to achieve mechanical interlocking with any repair material. In this study, different surface treatments (e.g. grinding, sandblasting, shotblasting, hand-and mechanical milling) were performed and the quality of the preparation established on the basis of three main parameters: surface geometry, superficial concrete microcracking and adhesion. Surface geometry was characterised on the basis of the measurement of surface profile-profilometry-and the analysis of statistical and amplitude parameters calculated from the waviness (lower frequencies) and the roughness (higher frequencies) profiles of the surface. Investigations were also performed to assess the quality of the superficial zone of concrete and cracks were systematically observed in relation to surface treatment where both scanning electron microscopy and light microscopy were used for analysis. Finally, a repair mortar, with or without bond coat, was applied to the concrete substrates in order to measure adhesion. Relationships clearly show the effect of roughness on adhesion in the case where no bond coat was used and also the influence of the power of the surface treatment on the waviness shape of the profile and the presence of microcracks in the near-surface layer, related to failure type.

Near-to-surface properties affecting bond strength in concrete repair

“…Treatment of concrete substrate is commonly used for cleaning, removing laitance layer and roughening the surface. However, it can induce microcracking if it is not well operated with regard to the quality and the strength of concrete [4][5][6]. Even if roughening is not considered as the most important factor for interface quality [2], it seems however to influence bond strength.…”

On the evaluation of interface quality in concrete repair system by means of impact-echo signal analysis

“…It has been widely demonstrated that it can significantly influence on the microcracking level and surface roughness, substrate saturation level and as a consequence it may affect the bond strength between repair material and concrete substrate [3,[13][14][15][16][17][18]. The effect of surface quality on impact-echo signal was investigated for two groups of concrete substrates ( Table 1).…”

Specification Guidelines for Surface Preparation of Concrete Prior to Repair

“…The saw cut surfaces shall be roughened prior to application of a repair material (Garbacz et al 2005). It is best achieved by sand or grit blasting at the same time as cleaning of exposed reinforcement.…”

“…The decisions about surface preparation and its roughness in particular, cannot be made without knowing the properties and application requirements of the selected repair/overlay material (Garbacz et al 2005).…”