consultant, Construction Technology Laboratories, Inc., Skokie, IL
Modified Test Methods for Sampling and Testing Fly Ash or Natural Pozzolans for Use as a Mineral Admixture in Portland-Cement Concrete (ASTM C 311) Pozzolanic (Strength) Activity Index tests with five fly ashes and two portland cements were done to compare results with those of standard tests. When sand contents (at constant water and cement contents) were varied, strengths of 38°C cured mortars decreased (−30 to −50 kPa/g of sand added in mixes containing 1370 to 1570 grams of sand) for different cement/fly ash blends. When water contents (at constant sand contents) were varied, strengths varied (−125 to +190 kPa/mL), strengths tending to increase because of paste volume increases with water content. Flow of mortars in both kinds of tests increase nearly linearly with paste volume fractions; the slopes are related by a factor of 0.60 ± 0.04. Accelerated curing at 38°C for tests at 28 days usually yields higher relative strengths than after curing at 23°C for 91 days. Multiple linear regression equations using both kinds of test data are solved at specified flow and strength values to determine proportions and mortar volume yields. This more general performance test ranks fly ashes (or cementitious mixtures) by mortar volume yield at equal flow and strength, and is suggested as a candidate to replace the present Strength Activity Index test.
Paper ID: CCA10157J