Concrete’s durability properties and deterioration mechanisms of precast concrete facades and balconies

Systematic condition assessments have been performed for concrete facades and balconies for more than 30 years. For this study data from concrete’s durability properties and deterioration mechanisms have been gathered from buildings erected in the 1990s. The scope of this study is to determine if the instructions, which have come into force in 1990s, had any effect on durability of concrete.

All the properties of concrete had improved when compared to the older building stock. Carbonation has slowed for facades and balconies. The share of slow carbonation has increased and the share for fast carbonation decreased. The cover depths have also improved and meet the requirements more often. Cover depths less than 20 mm are rarely found anymore. For these reasons the aimed service life is more likely to be met.

The air-entrainment of the concrete has improved making it more freeze-thaw resistant but completely non-air-entrained concrete can still be found occasionally. Despite that the freeze-thaw deterioration degree has stayed low for both facades and balconies.

Secondary void fillings have decreased. The most commonly found one is ettringite. A connection between ettringite and freeze-thaw damage was found. Freeze-thaw damage is more likely when ettringite is present and the degree of it is more severe than in concrete without pore fillers.

The risk for alkali-silica reaction is higher in newer building stock. Aggregates from class II, i.e., possibly reactive aggregate, were found in 70% of the samples and from class III, i.e., likely reactive aggregate, in 4%. With these results it is obvious that laboratories cannot only look for the gel associated with the reaction. Other signs e.g., fine grained quartz should be looked for.

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