Alternate Mitigation Materials For Alkali-Silica
Reaction (ASR) In Concrete
By Zachoria J. Ballard, William S. Caires, Stanley R. Peters
Contractors are finding it difficult to obtain Class F fly ash for concrete paving projects, but CDOT specifications do not currently
allow Class N fly ash to be substituted for Class F fly ash. The purpose of this study was to determine the effectiveness of Class N fly
ash and other pozzolans for mitigating alkali-silica reaction (ASR) and resisting sulfate attack. First, a literature review was
performed to find research on Class N fly ash. Second, other state departments of transportation (DOTs) were contacted to determine
if Class N fly ash is used and how it is specified. Third, laboratory tests were conducted to determine the effectiveness of Class N fly
ash and other materials in mitigating ASR when compared to Class F fly ash. Using one source of Class F fly ash, one source of Class
N, and one source of reactive aggregate (fine and course), the effectiveness of Class N was determined by testing each combination in
accordance to Colorado Procedures CP-L 4201 and CP-L 4202. Class N fly ash was found to be effective in mitigating ASR. Once
the effectiveness of Class N and other products tested was determined, further testing on Class D mix design was performed for
potential effects on fresh and hardened concrete. Testing included entrained air on plastic concrete, rapid chloride permeability
(ASTM C1202-05), and compressive strength at 7, 28, and 56 days.
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