As with concrete repair and protection projects before and after this one, the contractor was allowed to select and price one of two approved repair specifications provided by Arup; one was for a Ronacrete system, the other from another manufacturer used a combination of more materials, resulting in higher contract cost, neither did it offer the assurance and comfort of a 10 year Insurance Backed Guarantee, something many local authorities came to rely upon after suffering early failures of products from other manufacturers.
Three nine storey blocks of flats were refurbished; works included not only concrete repair but also roofing and window replacement. The concrete repair works required the removal of existing coatings to the concrete using low pressure water and grit blasting – low pressure to reduce the noise nuisance to residents and to minimise the amount of concrete removed in the process. RonaBond Fungicidal Treatment was then applied to kill off mould, fungal growth and algae.
The damaged concrete was identified by the surveyors and cut out to expose sound concrete and clean steel. Rust was removed from exposed steel by wire brushing – no need to grit blast to bright steel when using Ronacrete materials which saves further time and money – and then primed with two coats of Ronafix and cement. The Ronafix mix design D repair mortar of cement, sand, Ronafix and water was mixed and applied to replace the removed concrete.
When repairs were complete a roller applied textured slurry was applied to the walls and soffits to mask the repairs and provide a regular surface to receive the RonaBond Crack Bridging Anti-Carbonation Coating WB. The coating system used was a solvent primer (water based primers were not yet available), followed by an intermediate coat of RonaBond Crack Bridging Anti-Carbonation Coating WB and a top coat of RonaBond Crack Bridging Anti-Carbonation Primer WB was used to achieve surface texture and appearance. RonaBond Anti-Carbonation Coating WB was applied to soffits and at dpc level to allow water to pass through as required.
To indicate the size of the project, 14,000 litres of Ronafix, 31,000 litres of RonaBond Crack Bridging Anti-Carbonation Coating WB and RonaBond Anti-Carbonation Coating WB were used, 20,000m2 of vertical surfaces and 10,000m2 of soffits were treated.
Installation was supervised by Arup engineers, and by Bureau Veritas who ensured materials were applied in accordance with the specification and the requirements of the 10 year Insurance Backed Guarantee scheme.
Compressive strength of unmodified concrete and mortars can continue to increase slowly af... ...Read more