Optimization of Concrete Mixtures for Use in Structural Elements.

摘要

Portland cement is an essential ingredient in concrete. The use of cement is to enhance the strength as well as other hardened properties of concrete mixtures. Determining the accurate amount of cement is important because the required strength may not be achieved if not enough cement is used. By contrast, when using too much cement, concrete cracking may occur that leads to reducing durability. Researchers at the University of Arkansas (UA) have shown that many bridge decks achieve their 28 day design strength of 4000 psi by 7 days of age. Bridge decks having high strength may experience cracking, which affects the durability. The Arkansas State Highway and Transportation Department (AHTD) classifies two types of concrete mixtures that can be used in bridges. The first is Class S concrete, and the second is Class S(AE). Class S is used for the structural components and does not contain air entrainment while Class S (AE) is mainly used for bridge decks and contains air entrainment. AHTD requires the same minimum cementitious material content for both classes of concrete. The purpose of this research is to determine if the cementitious material content of Class S mixtures can be reduced while still meeting AHTD specifications. The research program examined cementitious material content, Class C fly ash content, and water to cementitious material ratio (w/cm) . For all mixtures, selected fresh and hardened concrete properties were measured to ensure that they complied with AHTD requirements.