Properties of fly ash concrete
The inherent variability of chemical composition and physical characteristics of fly ashes derived from different sources affects properties of both fresh and hardened concrete containing such materials. For this reason, the acceptance of the use of fly ash in concrete is conditioned upon an adequate demonstration that concrete of proper quality and durability can be predictably produced when fly ash is substituted for part of a cement. This study addresses some of the problems related to the design and performance of a fly ash concrete intended for a highway pavement applications. The mix deign procedure was developed which assures the constant quality of paste in a fly ash concrete, thus reducing the direct influence of fly ash characteristics on workability and, consequently, on durability of the resulting concrete. Tests were performed to determine the chloride ions permeability, freezing-thawing resistance, strength, elastic properties, air entrainment characteristics, and densities of concretes containing fly ash. In addition, heat evolution and setting times were studied on pastes containing fly ashes. Five different fly ashes (two Class C and three Class F), and two cements were used in this study. The replacement levels used were 15% and 25% by weight. The results of this study reveal that high quality fly ash concrete can be reliably produced using the proposed mix design procedure. Such concrete contains less cementitious material per cubic yard than does the reference concrete made with the same cement, and is therefore more economical. The durability characteristics are the same or better than those observed for a reference concrete.
Diamond, Purdue University.
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