Alkali-Silica Reaction: Cause, Effects, Mitigation, and Repair

Alkali-Silica Reaction (ASR) can cause significant damage to concrete structures including bridges, roadways, airport runways, and nuclear power plants. When reactive aggregates are included in a mix, the presence of moisture initiates a reaction between the alkaline cement paste and reactive amorphous silica. The result is a gel that continues to dilate, which may cause cracks in the concrete mass.

A research program was undertaken at the University of Toronto with the sponsorship of the Canadian Nuclear Safety Commission (CNSC) to investigate the effects of ASR on large-scale and small-scale concrete specimens. Several specimens were constructed using reactive (ASR) concrete and non-reactive (regular) concrete, and their short-term and long-term structural and mechanical behavior were compared. To accelerate the deterioration of concrete, wall specimens were stored in an environmental chamber, specially constructed with the capacity to store large specimens in controlled high-temperature and high-humidity conditions.

In this presentation, we will discuss the results of the research program, will offer best practices to minimize the risk of ASR in concrete during placement, and will propose several strategies for repair of structures that have been degraded due to ASR.

Learning Objectives:

1. Understand the cause of ASR
2. Understand the effects of ASR on concrete properties and durability
3. Learn best practices for minimizing risk of ASR
4. Become familiar with strategies for remediating structures affected by ASR