Over recent years, discussions on the maintenance and repair of concrete structures in Australasia and elsewhere have increasingly featured the condition ‘ASR’ (Alkali Silicate Reactivity), sometimes known as ‘AAR’ (Alkali Aggregate Reactivity).
As is well known, ASR/AAR is an expansive reaction within the concrete; and its severity can be driven by localised factors such as environment or the content of the aggregates used within the concrete.
The impact of ASR has increased in recent decades, partly as a result of changes in concrete construction methods arising from the increased demands of the economy.
How is the extent of ASR assessed in the field?
Critically, ASR is commonly identified in the field by the extent and appearance of its cracking.
(See, for example, the US FDA Field Identification Handbook)
You may be aware of the discussions about ASR’s effect of increasing concrete density; and the fact that this may theoretically, under certain circumstances, actually boost the concrete’s durability.
More urgently, there is evidence emerging that this same effect of increasing density may actually mask the cracking occurring in the matrix of the concrete. This means that deterioration may exist and advance considerably before being evident to the naked eye.
As discussed elsewhere, once the process of deterioration has taken hold, it is self-accelerating.
It is critical that concrete ASR is identified and remediated at the earliest possible point.
MARKHAM recommends the application of penetrating catalytic silicates for the arrest and prevention of ASR development.
Better still – consider applying this treatment when the concrete is new, for maximised service life and protection!
