Theses and Dissertations

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Browsing Theses and Dissertations by Author "Effiong, Eyo Eyo"

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    Development of models for producing high performance recycled aggregate concrete using extreme vertices design
    (Federal University of Technology, Owerri, 2023-04) Effiong, Eyo Eyo
    This research utilizes statistical methods to develop models (prediction equations) for various properties of high-performance recycled aggregate concrete. These models are further applied to obtain optimum combinations of the components of high-performance recycled aggregate concrete which include water, cement, silica fume, High range water reducing admixture (HRWRA), natural coarse aggregate, recycled coarse aggregate, and fine aggregate. The properties of the HPC studied are the slump, 1-day compressive strength, and 28-day compressive strength. Mixture experiment approach was employed in this research. A selected reference mixture gave the guide for the selection of upper and lower bounds of the mixture components in terms of volume fractions. A total of 46 experimental runs were planned for the mixture experiment design. Minitab statistical software was employed in the design and analysis of the experiment. The experiment design was based on the extreme vertices design for mixture experiment. The mixture experiment was modeled on the Scheffe’s quadratic polynomial. The numerical optimization procedure based on desirability function methodology was used to obtain the optimum components combinations to simultaneously meet all desired response properties. A confirmation experimental test was carried out using predicted mixture component settings from Minitab’s response optimizer, to verify the predictions from the fitted models. A second approach for testing the model was to randomly remove 3 design points from the 46 design points initially used to fit models. New models were fitted using the 43 remaining design points and the models were used to predict the three design points that were randomly removed. The two approaches showed that the developed models had high accuracy because they gave predictions which were close to experimental results, and would have been perfectly accurate in an isolated system, i.e. barring all possible sources of error. Results obtained showed that the range of slump is 80 -170(mm), the range of 1-day compressive strength is 14.6 – 26.4(MPa) and that of 28-day compressive strength is 36.2 – 57.4(MPa), and that it would be possible to obtain 28-day compressive strength of upto 45MPa with upto 43% replacement of natural coarse aggregate by recycled coarse aggregate, and a 28-day compressive strength of upto 55MPa is feasible with only 13.3% replacement. The use of recycled aggregates has therefore been recommended for partial replacement in high performance concrete mixes with expected properties similar to results obtained herein.