The alkali-silica reaction (ASR), often nicknamed “concrete cancer,” is a destructive chemical reaction that can occur in concrete between the highly-alkaline pore solution in typical cement paste and reactive forms of silica that are sometimes in the aggregates used in the concrete. Water – including atmospheric moisture at a relative humidity about 80-85% – is essential to the reaction.
The process begins when the high pH (alkaline) pore solution in hydrating cement attacks the reactive silica, dissolving it. It then reacts with the alkalis to form a viscous, water-attracting alkali-silica gel. The gel absorbs moisture from the surrounding environment and swells significantly, generating pressure within the concrete and causing expansion.
The swelling starts internally, causing microcracking of the aggregate and paste. Over the years this leads to visible cracking patterns on the surface, spalling, gel exudation (white deposits), pop-outs, and other damage to the concrete. In severe cases, the expansion disrupts structural integrity, reduces strength and stiffness, and accelerates other kinds of deterioration.
Why ASR Is Important
First identified in the 1940s, ASR is one of the most significant durability threats to concrete structures worldwide, second only to steel reinforcement corrosion as a deterioration mechanism. ASR is insidious because it is slow and progressive, often not becoming apparent until 5 to 30+ years after construction. Once initiated it is essentially irreversible and can lead to premature loss of serviceability, expensive repairs, or even demolition of structures.
The economic and safety implications are substantial: repairing or replacing ASR-damaged infrastructure costs billions globally each year. ASR also compromises structural performance by causing cracking that allows ingress of water, chlorides, and other aggressive agents, shortening service life.
Aeternum Minimizes the ASR Problem
ASR is usually managed with careful material selection and mix design, including using non-reactive or low-reactivity ingredients, limiting the total alkali content in the concrete, applying admixtures, or incorporating supplementary cementitious materials such as fly ash or slag that either bind alkalis or reduce the pore solution alkalinity. Using Aeternum inherently avoids ASR problems:
These are the results of testing concrete made with Aeternum versus concrete made with OPC, at the same strength. The test was performed per ASTM C1260. OPC-based concrete exceeded the expansion limit of 0.1% within 7 days. Expansion with Aeternum-based concrete remained significantly lower than the limit throughout the entire measurement period of two years.
