Alkali-Silica Reaction Mitigation Strategies for ITD Concrete Mixes

Project Details







Idaho Transportation Department


Admixtures, Alkali silica reactions, Concrete, Mineral aggregates, Pozzolan

Project description

Every year, Idaho Transportation Department (ITD) spends millions of dollars to repair deteriorated concrete structures around Idaho. One of the leading causes for deterioration of concrete is Alkali-Silica Reaction (ASR), a chemical reaction that develops between the reactive silica in the aggregates and the alkalis within the cement paste, causing expansion and cracking to the structure over a number of years. ASR will eventually compromise the durability and structural integrity of structures and pavements. ITD is currently experiencing problems with secondary cementitious materials (SCMs) test results in terms of consistency and quality of materials. SCMs are critical for concrete durability, longevity, cost, workability, strength, and as a mitigation method to reduce ASR reactions that lead to premature concrete failure. Fly ash is typically used as an SCM by Contractors and Concrete Suppliers. Recently, fly ash production has been decreasing on a national scale, while demand has been increasing. This results in shortages, cost increases, and the need for agencies to accept lower quality materials. Fly ash supplies will become increasingly scarce as coal is replaced by cleaner energy sources in the U.S. Therefore, the supply chain for ITD concrete SCMs is in jeopardy. There are various mineral admixtures commercially available in the United States and Idaho. However, the effectiveness of these admixtures in reducing ASR has not been independently verified in Idaho. The two mineral admixtures that ITD would like to investigate are diatomaceous earth (DE) and natural pozzolans (NP). These two products can be produced locally within the state or in adjacent states. Currently, fly ash used for mitigating ASR is being shipped in from the Midwest or Canada. Given the lack of independently verified data and observations to evaluate the performance of these two mineral admixtures in Idaho, ITD would like to better understand the costs and performance benefits of these admixtures that ITD contractors can obtain locally. Another mitigation approach is the use of nano-silica (NS) admixtures when combined with Idaho aggregates. These tend to be liquid admixtures that are added to the concrete when batched. Very little information is available as to the effectiveness of NS on ASR mitigation. NS admixtures are very consistent and can be easily implemented into existing concrete batch plants. Past studies have shown that a majority of the aggregate sources in Idaho will react with alkalis in cement and thus, do not qualify under the AASHTO T 380 test (expansion ≤ 0.04% is passing). Additionally, using a non-reactive aggregate in concrete for all ITD projects is unrealistic. Therefore, to reduce ASR and provide durability to Idaho’s infrastructure, identification of effective ASR mitigation methods is critical. While there are many manufacturers of mineral admixtures who claim that their product is the best solution, independent testing and verification is required to assure durability of concrete structures in Idaho as well as building confidence for ITD contractors to select the right solutions that would work in Idaho. To accomplish this, ITD seeks researchers to conduct the testing, verification, and cost analysis as well providing recommendations and guidance for implementing the research outcomes.