Correlation between the roughness of the substrate surface and the debonding risk

This paper presents the influence of substrate surface preparation on the adhesion strength of
repaired beams system. Bond between new and old concrete has been the subject of a number of investigations,
but in most cases, only adhesion strength was addressed. This parameter was used to estimate the durability
and/or the debonding risk for repaired structure and it’s a generally accepted auditing standards. Usually,
surface preparation of the substrate concrete is considered essential to achieve a durable repair because of
its influence on the bond strength. To better understand debonding mechanism, in particular these related to
surface preparation, roughness parameters were calculated to quantify the influence of surface preparation on
the structural behaviour. Using this approach, repair beams prepared by way of four (4) concrete surface
preparations were characterized. Results obtained show that repaired beams presenting a substrate with a rough surface permit to achieve a monolithic behaviour of the repaired system. Opposite structural behaviour, with large debonding, was recorded for those having smooth surface. However, all surface preparations used have promoted the same bond strength regardless the roughness of the substrate. The resulting analysis highlights the relation between roughness parameter αrough and the debonding mechanism of repaired beams. Such results will be useful to better predict the performance of concrete repairs.