Treatment with nano-silica and bacteria to restore the reduced bond strength between concrete and repair mortar caused by aggressive removal techniques

Abstract

Removal of degraded concrete during repair activities might have a detrimental impact on the bond strength between the concrete and the repair mortar. This research aims to improve the bonding strength in case aggressive removal techniques were used, by the singular and combined application of bacterially induced CaCO3 and colloidal nano-silica (CNS) treatments. Water jetting (WJ) and jackhammering (JH) were compared and the treatments were performed on the substrates prepared with the technique causing the lowest bonding. Pull-off test results on crushed stone concrete (CC) substrates showed that JH substrates possessed the lowest bond strength compared to WJ and unprepared substrates. To assure that reported results are reproducible, pull-off tests were also performed on another type of concrete, gravel concrete (GC). The results showed that in both cases JH-substrates achieved a lower bond strength than unprepared- and WJ-substrates. The reduced bond strength by JH was restored by the CNS treatment irrespective of the concrete composition. Regarding the biodeposition treatment, the spraying technique showed to be superior to the pouring technique. Microstructural analysis confirmed the survival of the bacteria and carbonate precipitation. Porosity of the prepared substrate surfaces was studied by capillary absorption, water absorption (including the gravity effect) and vacuum absorption tests. The reduction in the initial water uptake of CNS-treated samples was evidenced by the precipitation of the silica gel at the superficial layer of the substrate. The efficacy of Energy Dispersive X-Ray Analysis (EDX) to recognize the interlayer of layered composites with a monolithic structure was observed.