United States Department of Transportation
i
Evaluation of Alternative Sources of Supplementary Cementitious Materials (SCMs) for Concrete Materials in Transportation Infrastructure
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2021-09-01
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[PDF-4.19 MB]
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Edition:Final Research Report: Aug. 2020 – Nov. 2021
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Abstract:Fly ash is the most utilized supplementary cementitious material (SCM) in the US. Nonetheless, rapid decline in coal-fired power generation threatens its supply. The objective of this study was to evaluate alternative SCMs for concrete transportation infrastructure in Region 6. SCMs investigated included reclaimed fly ash (RFA), reclaimed ground bottom ash (GBA), metakaolin (MK), and conventional Class F fly ash (FA) as a reference. SCMs were characterized and the fresh and hardened properties of concrete incorporating different dosages (i.e., 10, 20, and 30% cement replacement by mass) of the individual SCMs (i.e., binary systems) and blended SCM systems of RFA-MK and GBA-MK (i.e., ternary systems) were assessed. All the coal ashes met the requirements for pozzolanic component, CaO, SO3, moisture content, LOI, SAI, and water requirement to be classified as Class F pozzolan according to ASTM C618. MK met all the but the water requirement. Concrete using FA generally exhibited better workability than the control mixture (i.e., without SCMs), whereas concrete incorporating RFA, GBA, and MK presented decrements in workability. Mixtures implementing ternary systems also displayed decrements in workability. Air content of fresh concrete mixtures incorporating binary and ternary systems generally decreased. Relative to the control mixture, decrements in 28-day compressive strength (f’c) were reported when incorporating FA and RFA, yet this was generally not the case for the 90-day f’c. In the case of GBA mixtures, significant differences in f’c were not observed after 28 days nor 90 days. MK mixtures as well as RFA-MK and GBA-MK mixtures generally presented increments in 28-day and 90-day f’c. Concrete mixtures implementing coal ashes did not produce significant differences in 28-day surface resistivity (SR) at any cement replacement levels; yet after 90 days of curing, significant improvements in SR were reported. MK, RFA-MK, and GBA-MK mixtures exhibited significant increments in SR at all dosages after 28 and 90 days of curing. Notably, while the control mixture and mixtures incorporating coal ashes did not meet the 28-day SR requirement for class A1 concrete according to LaDOTD, mixtures implementing MK and ternary systems did in almost all cases. All SCMs were effective at reducing drying shrinkage. Binary systems reduced drying shrinkage by 24.2-69.1%, whereas ternary systems reduced drying shrinkage by 55.2-75.3%. With regards ASR, mixtures implementing SCMs presented significantly lower expansion and the increment in SCMs content further reduced the expansion; thus, signaling a positive effect in suppressing ASR related expansion, specially at high dosages.
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