Estimating efficiency of fly ashes: an alternative definition of k values

Abstract

Assessment of fly ash efficiency based on the mechanical performance of fly ash-modified mortars is not straightforward. Hence, a ‘k value’, or an efficiency factor, of various forms have been proposed and employed in the past. In this study, a simplified value analysis is proposed to handle large sets of compressive strength data. A set of six fly ashes from different sources across the USA were collected and analyzed in this study to gauge their efficiency. In a comparison of fly ash with an ideal inert material (rather than with commonly used Portland cement), the values, or reactivity levels of fly ashes, reported here are dependent on the replacement level and independent of curing age. Such an analysis may be beneficial to industrial concrete labs where significant amount of trial batches and mixes are prepared prior to the commercial employment of a new fly ash or pozzolan.

Keywords:

• efficiency
• k value analysis
• fly ash
• high volume fly ash concrete
• compressive strength

Acknowledgment

The authors are thankful to Tennessee Valley Authority for supplying some of the fly ashes. Inputs, from Wei Zhang on mortar testing and Scott Schlorholtz on XRF testing, are greatly appreciated.

Additional information

Funding

Funding. The authors appreciate the sponsorship of the Oak Ridge Associated Universities (ORAU) – Tennessee Valley Authority (TVA) [grant number 7-22976].