Friday, 20 January 2023
Austroads has published a new Code of Practice for the Management of Alkali Aggregate Reactivity. This document outlines the management strategies, testing and approval process required to regulate alkali aggregate reactivity in concrete structures.
Alkali aggregate reaction (AAR) is a chemical process which may lead to the premature deterioration of concrete structures. It occurs when free or unstable fine-grained silica in the concrete aggregate reacts with the alkali hydroxides (ie, sodium and potassium) in the concrete constituent materials (cement, supplementary cementitious materials, admixtures, mixing water, aggregates) and potentially from the in-service environment of the particular concrete element. This chemical process can cause serious structural damage and costly repairs.
“This reaction is often referred to as concrete cancer, and it cannot be reversed. In certain climates, it could take years before this reaction is noticed in a normal inspection” said Ross Guppy, Austroads Transport Infrastructure Program Manager. “As testing can be a lengthy process to implement in the middle of a construction contract, this Code of Practice enables the recognition of prior testing and AAR management strategies with forethought.”
“Ensuring prior testing and alkali aggregate reaction management strategies are utilised before aggregates are incorporated into the concrete is vital to mitigate the risk of premature deterioration.”
In many instances, the approval of the aggregate (or blend of aggregates) will be subject to the concrete being manufactured with a blended cement containing supplementary cementitious materials in specified proportions.
Download Code of Practice for the Management of Alkali Aggregate Reactivity