Browsing by Author "Wole Soboyejo"

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    Clay Mixtures and the Mechanical Properties of Microporous and Nanoporous Ceramic Water Filters
    (Journal of Materials in Civil Engineering, 2016) Ebenezer Annan; Kwabena Kan-Dapaah; Salifu T. Azeko; Kabiru Mustapha; Joseph Asare; M. G. Zebaze Kana; Wole Soboyejo
    This paper presents the results of an experimental study of the effects of clay mixtures on the mechanical properties of mixed clays with controlled levels of plasticity, prior to the firing of porous ceramic water filters for water filtration. Two clays with well-characterized initial compositions (Iro and Ewuya clays) are mixed with varying proportions to control their plasticity. The mechanical properties of the mixed and fired clays are then studied using a combination of experiments and theoretical models. These include the flexural strength, fracture toughness, Young’s modulus, and thermal shock resistance of fired clay mixtures. The results show that clay mixtures with 45–60 vol.% of Iro clay and 40–55 vol.% Ewuya clay can be used to produce clay composite filters with robust mechanical properties. The thermal shock resistance of a mixed clay filter (containing 50% Iro clay and 50% Ewuya clay) is also explained using a combination of elastic and viscoelastic crack-bridging models. The regimes for effective viscoelastic crack bridging are identified by comparing the relaxation times to the thermal shock durations. The implications of the results are then discussed for the mixing of locally available clays into robust micro- and nanoporous materials for applications in clay ceramic water filters.
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    Mechanical performance of fiber-reinforced alkali activated un-calcined earth-based composites
    (2020) Emeso B. Ojo; Kabirat O. Bello; Odette F. Ngasoh; Tido T. Stanislas; Kabiru Mustapha; Holmer Savastano; Wole Soboyejo
    This paper presents the results of a multi-scale study of the mechanical properties of model earth-based composites. The composites are produced by the alkali activation of in-situ clay minerals within an earthbased matrix that is reinforced with two different fibers (sisal and polypropylene). The local mechanical properties of the fibers, binder and matrix materials are characterized at the nano- and micro-scales using nano-indentation and statistical deconvolution techniques. The macro-mechanical properties are also elucidated using a combination of flexural strength testing, and resistance-curve experiments. The underlying strengthening and toughening mechanisms are explored using a combination of in-situ/exsitu observations and micro-mechanical models. The implications of the results are then discussed for the design of strengthened and toughened earth-based composites that are reinforced with natural fibers (such as sisal) and synthetic fibers (such as polypropylene fibers).