Abstract

The objective of this laboratory research was to investigate the effects of a higher water-cementitious materials ratio on selected properties of concrete mixtures comprising natural pozzolans. The scope of work included testing of six concrete mixtures, including one for each of three natural pozzolans at two water-cementitious materials ratios of 0.44 and 0.48 and one concrete mixture without pozzolan at a water-cementitious materials ratio of 0.44, which was treated as a baseline in this research. The stiffness and strength of each concrete mixture were measured at 1, 3, and 7 days using concrete specimens that were cast immediately after mixing. Additionally, to investigate the effects of delayed casting time, slump was measured at 0, 15, 30, 45, and 60 minutes after mixing, and cylinders were cast at 15, 30, 45, and 60 minutes for stiffness and strength testing at 7 days. Two mixtures comprising natural pozzolan experienced greater slump loss, on average, than the baseline mixture, while all of the other mixtures experienced less slump loss, on average, than the baseline mixture. Overall, the slump losses of mixtures comprising natural pozzolans were 121% and 71% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively. Modulus of elasticity values ranged from 1692 ksi to 1794 ksi for mixtures comprising natural pozzolan compared to a value of 1791 ksi for the baseline mixture at 7 days. Compressive strength values ranged from 4087 psi to 4152 psi for mixtures comprising natural pozzolan compared to a value of 4795 psi for the baseline mixture at 7 days. The modulus of elasticity values of mixtures comprising pozzolans were 97% and 94% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, at 7 days. Similarly, the compressive strength values of mixtures comprising pozzolans were 86% and 71% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, at 7 days. Comparisons of the 7-day stiffness and strength results associated with casting delay time for mixtures comprising natural pozzolan with those of the baseline mixture indicate that all mixtures comprising natural pozzolan exhibited lower modulus of elasticity and compressive strength than the baseline mixture. Overall, the modulus of elasticity values of mixtures comprising natural pozzolans were 94% and 84% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, for a casting delay time of an hour. Similarly, the compressive strength values of mixtures comprising natural pozzolans were 85% and 64% of that of the baseline mixture for water-cementitious materials ratios of 0.44 and 0.48, respectively, for a casting delay time of an hour.

Degree

College and Department

Ira A. Fulton College of Engineering; Civil and Environmental Engineering

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