Assessment of alkali activated mortars based on different precursors with regard to their suitability for concrete repair

The implementation of repair works on concrete structures is on the increase since many existing concrete buildings have been exposed for long periods of time to different climates, as well as to other severe conditions, and have consequently deteriorated. Repair mortars need to fulfil the requirements of the EN 1504 series before being used in practice. Different mixtures, based on three different precursors (fly ash, ground granulated blast furnace slag, and metakaolin) and processed by alkali activated technology, have been assessed with regard to their suitability for the repair of concrete. Whereas the slag-based repair mortar delaminated from the substrate, and was thus unsuitable for its intended use, the other two mortars which were based on the precursors fly ash and metakaolin exhibited good mechanical properties and good adhesion. The bond strength of the metakaolin and fly ash mortars ranged from 1.8 to 2.3 N/mm2, and thus met these criteria for both structural and non-structural repair mortars. The capillary absorption of all three mixtures was too high to fulfil the criteria of EN 1504-3 for structural repair products, but the fly ash and metakaolin mixtures still have the potential to be used for non-structural repair works. The problem of efflorescence in all three mixtures was also assessed.