Use of Marginal and Unconventional-Source Coal Ashes in Concrete (2024) / Chapter Skim
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4 Conclusions and Proposed Draft Language for Specification
Pages 123-129

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From page 123...
... • Both R3 and modified R3 reactivity tests were able to differentiate reactive coal ashes from inert materials at a heat release threshold of approximately 100 J/g SCM. Using other measures, the values are 30 g/100 g SCM for CH consumption, and 5 g/100 g SCM for bound water.
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From page 124...
... • Differences between Class C and Class F coal ashes were significant, for both standard and unconventional coal ashes, and were much larger than any differences between standard and unconventional ashes. • The CaO content of the ashes influenced the time to peak heat flow, 7-day heat release, 91-day bulk resistivity, 7-day compressive strength, 7-day bound water, and 91-day bound water; most properties increased linearly with CaO content.
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From page 125...
... • In general, high adsorption was neither frequent nor problematic in the set of samples tested and the team believes using unconventional ashes does not present more concern regarding high adsorption than using standard ashes.
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From page 126...
... Coal Ash Uniformity Testing Coal ash suppliers provided uniformity datasets for two standard and two unconventional ashes. The required composite sampling frequency -- monthly or per 3,200 tons -- specified in ASTM C311 for ash properties measured in AASHTO M 295 was assessed using the power analysis, t-test, uniformity assessment, and Levene test for all four ashes.
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From page 127...
... • When comparing the uniformity of the moving mean for the composite samples and subse quently using the Levene test to compare variances, the unconventional ashes had comparable or lower variance in fineness and density compared to the standard ashes, but much higher vari ance in moisture content (except in one instance)
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From page 128...
... Additionally, in this study, concrete made with 17% LOI coal ash was able to be successfully air entrained. Therefore, increased levels of LOI may not translate to poor air entrainment in mortar or concrete mixtures and should not be used to exclude coal ashes.
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From page 129...
... Furthermore, the explicit allowance of processed or beneficiated coal ashes would also officially pass coal ashes B, K, N, O, and R All the ashes tested here were classified as reactive and generally performed well in mortar and concrete testing except for some notable exceptions regarding workability and SA performance.
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Key Terms

  • coal ash
  • unconventional ashes
  • heat release
  • unconventional coal
  • draft language

  • bound water
  • proposed draft
  • standard specification
  • bottom ash
  • foam index

  • air entrainment
  • aea dosage
  • ash adsorption
  • standard ashes
  • ashes generated

  • uniformity testing
  • regular sampling
  • dosage requirements
  • calcium hydroxide
  • composite sampling

  • reactive coal
  • identifying coal
  • ash reactivity
  • concrete strengths
  • cfb ash

  • concrete mixture
  • sai values
  • index measurements
  • team proposes
  • adsorption levels


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