Methods for Evaluating Fly Ash for Use in Highway Concrete (2013) / Chapter Skim
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Pages 23-48
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23 CFA Characterization Study Results obtained from characterization tests of the 30 sources of CFA are summarized in this section. Additional results are provided in Attachment C
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24 ID Class Sum of Oxides (% wt) Moisture (% wt)
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25 ID Mn2O3 (% wt)
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26 with LOI or fineness as shown in Figure 4.4. Similar to density, AEA dosage is also a uniformity measure for CFA sources and, therefore, only a variability metric is specified.
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27 ID Compressive Strength Ratio (% control) Water Required (% control)
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28 The values listed in Table 4.9 were calculated using the raw data in Table 4.8. Because these were calculated, the test results in Table 4.8 were reported to an extra significant figure (i.e., three decimal places rather than the normal two commonly used for this type of test result)
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29 ID Relative Expansion (% control mixture) Reduction in Expansion (% control mixture)
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30 20 30 40 50 60 70 80 40 50 60 70 80 90 100 110 120 130 R ed uc tio n Re la tiv e to P C2 (% ) Expansion Relative to PC-2 (%)
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31 ash. In addition, the CFAs exhibited a good range of physical properties.
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32 Moisture content and LOI tests are currently limited to a sample mass of 1 g. The small sample mass can affect the precision of the determinations particularly for test results of low magnitudes, as is the case when analyzing CFA; this deficiency could be eliminated by simply increasing the sample mass.
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33 C114, which is very time consuming when working with porcelain crucibles that cool much slower than platinum crucibles typically used with cement. Coal fly ash may contain a significant amount of carbon that can destroy platinum crucibles.
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34 ment. However, the KHI values range from approximately 0 (for inert materials)
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35 7-day KHI (%)
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36 and also correlated with each other. Also, a series of mortar and concrete mixtures were prepared to demonstrate the application of the various tests.
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37 iodine number versus LOI on a semi-log plot for the same CFA sources. This figure highlights the ability of the test to detect differences in adsorption for relatively low LOI ashes.
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38 CFA (Figure 4.26)
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39 adsorption properties -- not the physical property of LOI that may or may not correlate to adsorption capacity. Foam Index Test Correlation to Adsorption Tests The foam index test, in its improved form where the total time of the test is consistent, provides a better representation of the adsorption capacity of CFA than LOI.
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40 shown in Figure 4.29) is used with a CFA that has an iodine number of 3, the capacity of that CFA for AEA-5 would be approximately 0.01 mL/g of CFA.
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41 0 1 2 3 4 5 6 7 8 9 FA-A FA-G FA-H FA-J FA-O FA-T FA-ZM FA-ZN A ir Co nt en t (% v o l.) Ash Source Trial & Error Isotherm Prediction Baseline Air Content 6.6% % LOI 0.94 2.32 0.25 1.59 1.43 0.45 10.69 3.41 Figure 4.35.
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42 significantly. As processing is adapted to remove carbon from CFA, it will be increasingly important to measure the efficacy of that process with respect to its impact on AEA adsorption, not LOI.
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43 adsorption isotherm test and the known weight of CFA in the concrete mixtures was used to determine an adjusted AEA dosage. The results, shown in Table 4.24, indicate that the direct adsorption isotherm estimation produced an air content within the desired range in nine of twelve cases (i.e., 75%)
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44 FA-O would be the most effective, followed by FA-M, FA-Q, FA-H, FA-X, FA-ZA, FA-U, and FA-ZC. Concrete Prism Tests With the exception of long-term outdoor exposure sites or known performance history with the same materials combination, the ASTM C1293 concrete prism test is considered to be the most reliable indicator of the effectiveness of a given level of CFA for mitigating deleterious alkali-silica reactivity.
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45 With a replacement level of 30%, FA-M was right at the 0.04% expansion limit suggesting a 35% replacement would be adequate. At 40% replacement of cement, the low sum-ofthe-oxides CFAs (FA-X, FA-ZA, and FA-ZC)
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46 0.00 0.02 0.04 0.06 0.08 0.10 0.12 50 60 70 80 90 100 Pr is m e xp an si on a t 2 4 m on th s (% ) Sum of Oxides (SiO2+Al2O3+Fe2O3)
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47 tests. For Class C CFAs, the levels indicated by the 14-day ASTM C1567 expansions were equal or higher than the levels indicated by the 12-month ASTM C1293 tests.
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48 The methodology and results of these test experiments are provided in Attachment C Comparison of ASR Test Results Table 4.32 lists the CFA replacement levels required for meeting ASR expansion limits for various tests.
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