Methods for Evaluating Fly Ash for Use in Highway Concrete (2013) / Chapter Skim
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8Overview The research to evaluate new and existing test procedures involved five separate tasks that were performed as separate studies. These tasks are briefly described in this section; details are provided in the following sections of this chapter.
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9 section. Additionally, a number of new tests were developed or evaluated; the process used to refine these tests and their method of application is also summarized.
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10 grab sample was obtained for the characterization study. The remainder was placed in a watertight plastic drum, labeled, and placed in storage.
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11 days) to provide an indication of precision.
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12 Characterization of Strength Activity Two different approaches were investigated to examine tests for measuring the effect of CFA on the strength of a cementitious mixture. One approach considered modifications to the current SAI and another examined an approach based on the Keil hydraulic index (KHI)
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13 AEA solution strength and addition rate, the agitation time, and the overall test time)
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14 the test is dynamic and is not based on achieving equilibrium (Külaots et al., 2003) ; other researchers indicate adsorption equilibrium between surfactants such as AEAs and CFA may take hours (Yu et al., 2000)
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15 tests reported were performed using the proposed procedure and each test was completed within 12 to 18 min. In addition, the results of the foam index test were correlated with the results of the CFA iodine number and also the direct adsorption isotherm test.
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16 The CFA iodine number test is determined from a fourpoint isotherm. That is, four pre-specified masses of treated CFA are equilibrated with an iodine-water solution and the reduction in iodine liquid-phase concentration is represented as capacity using the Freundlich isotherm equation.
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17 used to determine the amount of adsorbate removed for any adsorbate solution concentration. The test method presented here is based on ASTM D3860-98(2008)
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18 Adsorption Isotherms The solid phase capacity as well as the initial concentration of the adsorbate governs the amount adsorbed on the solid phase and hence, by difference, the amount of adsorbate remaining in the aqueous phase. The results of the isotherms describe this two-phase equilibrium relationship and can be used to determine the partitioning of the adsorbate between the solid and aqueous phases.
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19 Isotherm Points. For each isotherm point, 40 g of CFA is added to the system.
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20 28 days, and then processed for hardened air determination using a modified version of ASTM C457/C457M-11, Standard Test Method for Microscopical Determination of Parameters of the Air-Void System in Hardened Concrete. The measurements were performed using a flatbed scanner (Sutter, 2007)
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21 automated method. These 11 slabs were then inked with black marker to render the solid constituents black.
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22 cast with studs for length change measurements, and a fourth prism was cast for potential petrographic analysis. After casting, the molds were covered with wet burlap and plastic to reduce surface drying.
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