Q & A
Bridges Home > Q & A > Reactive Powder Concrete

Q: How Is ASR Mitigated In Concrete Bridges?

Alkali-silica reactivity (ASR) is a chemical reaction that sometimes occurs when the silica in certain aggregates reacts with alkali hydroxides in cement paste after the concrete has already hardened (cured). This can create cracks in the concrete and can be tremendously damaging to the performance of concrete.

If supplementary cementitious materials (SCMs) such as fly ash, silica fume, slag, or metakaolin are present in the concrete mixture, they fight to help control this potentially damaging mechanism. These materials can be added at batching as separate concrete ingredients or as components of blended cements. Tests should be performed to determine the correct dosage of SCM to control ASR. Tests can also be run on the coarse and fine aggregates prior to their use in the concrete to determine their potential for ASR. Low-alkali portland cement can also be specified for a bridge project in areas where low-alkali cement is known to adequately control the reaction.

References:

Diagnosis and Control of Alkali-Aggregate Reactions in Concrete, by James A. Farny and Beatrix Kerkhoff, Portland Cement Association, PCA Publication No. IS413, 2007.

Guide Specification for Concrete Subject to Alkali-Silica Reactions, by PCA Durability Subcommittee, Portland Cement Association, PCA Publication No. IS415, 2007.

“Guide Specification for Concrete Subject to ASR,” by Beatrix Kerkhoff, HPC Bridge Views, Issue 51, Sept/Oct 2008.

“FHWA Alkali-Silica Reactivity Development and Deployment Program,” by Gina Ahlstrom, HPC Bridge Views, Issue 51, Sept/Oct 2008.

“ASR Prevention in Texas,” by Brian D. Merrill, HPC Bridge Views, Issue 51, Sept/Oct 2008.

“Virginia’s Approach to ASR,” by D. Stephen Lane, HPC Bridge Views, Issue 51, Sept/Oct 2008.

Click here for more Q&As.