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Testing of Accelerated Pozzolanic Activity of Fly Ash
Location
Lexington, Kentucky
Start Date
6-5-2026 8:30 AM
End Date
6-5-2026 9:00 AM
Description
The determination of the pozzolanic reaction in fly ash by ASTM strength activity index has been shown to be problematic, frequently producing false positives. The use of Wenner probe resistivity has been demonstrated to be rapid, simple and non-destructive method, producing no false positives. However, using this method and confirming it with other techniques finds that the reaction itself is slow with a dilatancy of 28 days or more before the measurements become discriminatory, a major drawback to this method. This study used high-temperature, high humidity curing of OPC-based mortars with various fly ash sources to determine how pozzolanic activity accelerates compared to ASTM room temperature curing conditions. The key to production of reliable and consistent data was the development of a new protocol which involved cooling the prisms to room temperature while submerged in water. From the data, it is evident that higher temperatures positively impact the mechanical properties of materials and create material that has more desirable properties in a shorter amount of time compared to room temperature conditions. This was especially true for mix designs containing flyash as the higher curing temperature caused the material to meet peak performance in a shorter period.
Document Type
Presentation
Paper
Archival?
Archival
Testing of Accelerated Pozzolanic Activity of Fly Ash
Lexington, Kentucky
The determination of the pozzolanic reaction in fly ash by ASTM strength activity index has been shown to be problematic, frequently producing false positives. The use of Wenner probe resistivity has been demonstrated to be rapid, simple and non-destructive method, producing no false positives. However, using this method and confirming it with other techniques finds that the reaction itself is slow with a dilatancy of 28 days or more before the measurements become discriminatory, a major drawback to this method. This study used high-temperature, high humidity curing of OPC-based mortars with various fly ash sources to determine how pozzolanic activity accelerates compared to ASTM room temperature curing conditions. The key to production of reliable and consistent data was the development of a new protocol which involved cooling the prisms to room temperature while submerged in water. From the data, it is evident that higher temperatures positively impact the mechanical properties of materials and create material that has more desirable properties in a shorter amount of time compared to room temperature conditions. This was especially true for mix designs containing flyash as the higher curing temperature caused the material to meet peak performance in a shorter period.
