Honors Projects for Civil and Environmental Engineering

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    Optimizing Self-Consolidating Concrete with Hawaiian Aggregate
    (University of Hawaii at Manoa, 2014-01-15) Ito, Akira ; Shen, Lin ; Civil and Environmental Engineering
    Self-Consolidating Concrete (SCC) is a high performance concrete that flows like a fluid under its own weight though formwork and requires no external consolidation like conventional concrete. Advantages include a reduction in labor cost for manual consolidation, decrease in noise pollution from mechanical equipment, uniform surface finishes, and much more. There are problems facing the utilization of SCC in Hawaii due to the angularity, porosity and lower packing density of the local basalt aggregate. The optimal aggregate for SCC is well-graded to promote smooth flow and prevent interlocking. The appropriate amount of cement paste with a favorable rheology and aggregate gradation can account for this. By maximizing the packing density of the aggregate using the Toufar Model, less cement paste is used to fill the interparticle voids, and more can be allocated to increase the flowability and reduce interlocking. Minimizing the use of large (3⁄4”) aggregate, while maintaining a high packing density, increases the passing ability of the mix. By calculating the amount of cement paste needed in the mix according to Krieger-Dougherty Equation, the overall concrete rheology can be adjusted to achieve SCC mixes with desired properties. It is essential that the SCC has an appropriate viscosity and yield stress, in order to prevent segregation whilst maintaining sufficient flowability and passing ability. To modify the rheology of the paste, superplasticizer, fly ash and viscosity modifying admixtures are used. The mixes are tested for static and dynamic segregation as well as its ability to pass rebar reinforcement. With sufficient analysis and testing, high performance SCC mixes can be made with local materials.