Browsing by Author "Ebenezer Annan"

Now showing 1 - 7 of 7
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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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    Pull-out behavior of natural fiber from earth-based matrix
    (Journal of Composite Materials, 2016) Kabiru Mustapha; Salifu T Azeko; Ebenezer Annan; Martiale G Zebaze Kana; Leo Daniel; Winston O Soboyejo
    This paper presents the results of a combined experimental and analytical study of the pull-out behavior of natural fiber (grass straw) from an earth-based matrix. A single fiber pull-out approach was used to measure interfacial properties that are significant to toughening brittle materials via fiber reinforcement. This was used to study the interfacial shear strengths of straw fiber-reinforced earth-based composites with a matrix that consists of 60 vol. % laterite, 20 vol. % clay and 20 vol. % cement. The composites that were used in the pull-out tests included composites reinforced with 0, 5, 10 and 20 vol. % of straw fibers. The toughening behavior of fiber-reinforced earth-based matrix was analyzed in terms of their interfacial shear strengths and bridging zones, immediately behind the crack tip. This approach is consistent with microscopic observations that reveal intact bridging fibers behind the crack tip, as a result of debonding of the fiber–matrix interface. Analytical models were used to study the debonding of fiber from the matrix materials, as well as the toughening due to crack-tip shielding via bridging. The results show that increasing the fiber embedment length and the fiber volume fraction (in the earth/cement matrix) increases the peak pull-out load. The debonding process was also found to be associated with a constant friction stress. The combined effects of multiple toughening mechanisms (debonding and crack bridging) are elucidated along with the implications of the results for the design of earth-based composites for potential applications in robust building materials for sustainable eco-friendly homes.
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    Recycling of Polyethylene into Strong and Tough Earth-Based Composite Building Materials
    (Journal of Materials in Civil Engineering, 2016) Salifu T. Azeko; Kabiru Mustapha; Ebenezer Annan; Olushola S. Odusanya; Winston O. Soboyejo
    Polyethylene (PE) waste often piles up in the environment for up to 30 to 50 years, without complete degradation. This paper describes how PE waste can be used as a reinforcement in laterite bricks for sustainable building materials. The bricks are produced with different volume percentages (0–30 vol. %) of PE. The flexural/compressive strengths and fracture toughness values of the composite blocks are compared with those of mortar (produced from river sand and cement). The composite containing 20 vol. % of PE is shown to have the best combination of flexural/compressive strength and fracture toughness. The flexural/compressive strengths and fracture toughness values increase with increasing volume percentage of PE up to 20 vol. %, before decreasing to minimum values for composites with 30 vol. % of PE. The trends in the measured strengths and fracture toughness values are explained using composite and crack bridging models.
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    Reinforcement of cement mortar with recycled polyethylene waste for construction applications
    (2021) Moses K Flomo; Salifu T Azeko; Emmanuel K Arthur; Jamal-Deen Kukurah; Kabiru Mustapha; Ebenezer Annan; Benjamin Agyei-Tuffour
    This current research work combines both experimental and theoretical study of the impact of cement mortar reinforced with recycled polyethylene waste for applications in the construction industry. The work explores incorporating low density polyethylene (LDPE) waste into cement mortar to improve its fracture toughness and flexural strength with balanced compressive strength. Different volume fractions (0, 5, 10, 15, 20, 30, and 40%) of the powdered LDPE were mixed with cement and the density, compressive strength, flexural strength, and the fracture toughness were observed under different testing conditions. All specimens were tested after curing of 7, 14, and 28 days. The results show that there was [Formula: see text]6% increase in the fracture toughness at 5 vol. %, [Formula: see text]7% increase at 10 vol. %, and 24% increases at 20 vol. % of LDPE. Also, it was observed that the weight and compressive strength decreased with increasing volume fraction up to 40 vol. % of LDPE waste. The results for the survival/failure probability show that the PE-mortar composites with PE volume percentages up to 20 vol. % had the highest survival probability. The composite with this volume percentage can withstand crack up to 6 mm, with a survival probability of 0.6.
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    Statistical Distributions of the Strength and Fracture Toughness of Recycled Polyethylene-Reinforced Laterite Composites
    (Journal of Materials in Civil Engineering, 2016) Salifu T. Azeko; Kabiru Mustapha; Ebenezer Annan; Olushola S. Odusanya; Alfred B. O. Soboyejo; Winston O. Soboyejo
    This paper presents the results of combined experimental and theoretical studies of the statistical distributions of the strength and fracture toughness of recycled polyethylene-reinforced laterite composites for potential applications in building materials. The composites are produced with different volume percentages (0–30% v/v) and particle sizes (∼300±0.02, ∼600 ± 0.03, ∼900 ± 0.03, ∼1,200±0.02, ∼1,500±0.04, and 1,800±0.03  μm) of powdered polyethylene (PE) in a laterite matrix. The composites with ∼900±0.03  μm and 20-volume percentage of PE are shown to have the best combination of flexural-compressive strengths and fracture toughness. The statistical variations in the flexural-compressive strengths and fracture toughness are well characterized by the Weibull distributions.
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    Statistics of Flow and the Scaling of Ceramic Water Filters
    (Journal of Environmental Engineering, 2014) Ebenezer Annan; Kabiru Mustapha; Olushola S. Odusanya; Karen Malatesta; Winston O. Soboyejo
    According to the World Health Organization (WHO), there was an increase in the number of people that have access to safe drinking water between 2006 and 2010. Such trends can be accounted for partly by the increasing usage of ceramic water filters that can remove microbial pathogens from water. However, the initial flow rates in such filters are often limited to ranges between 1 and 3  L/h. In this paper, six frustum-shaped ceramic water filters of the same clay:sawdust composition were tested. Each ceramic water filter was filled with water and allowed to filter 20 times. Each time, the flow rate and water level were measured for a consecutive 12 h. Permeability values were estimated for each run of the ceramic water filters. Statistical analysis was performed on flow rates (in the first hour), mean flow rates, and estimated permeability values. The flow rate values (in the first hour) for the six ceramic water filters were found to be between 1.4 and 3.0  L/h. An effective permeability was obtained for ceramic water filters with a range of microscale and nanoscale pore sizes. The statistical variations in the flow rates and effective permeabilities were elucidated along with the potency of a multiple ceramic water filter system for scale-up studies in serving communities that need portable water.
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    Strength and fracture toughness of earth-based natural fiber-reinforced composites
    (Journal of Composite Materials, 2015) Kabiru Mustapha; Ebenezer Annan; Salifu T Azeko; Martiale G Zebaze Kana; Winston O Soboyejo
    This paper presents the results of a combined experimental and theoretical study of the strength, fracture toughness, and resistance-curve behavior of natural fiber-reinforced earth-based composite materials. The composites, which consist of mixtures of laterite, clay, and straw, are stabilized with controlled levels of Ordinary Portland cement. The compositional dependence of compressive, flexural/bend strength, and fracture toughness are explored for different proportions of the constituent materials using composites and crack-tip shielding models. The underlying crack-microstructure interactions associated with resistance-curve behavior were also studied using in situ/ex situ optical microscopy. This revealed evidence of crack bridging by the straw fibers. The measured resistance-curve behavior is also shown to be consistent with predictions from small- and large-scale bridging models. The implications of the results are then discussed for potential applications in the design of robust earth-based building materials for sustainable eco-friendly homes.