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Cronbach’s alpha reliability coefficient in engineering assessments – a preliminary study on possibilities and precautions

- Ekolu, Stephen O.

Bottom ash and fly ash wastes as alkalinising reagents for neutralising acid mine drainage

- Ekolu, Stephen O., Diop, Souleymane, Azene, Firehiwot

  • Authors: Ekolu, Stephen O. , Diop, Souleymane , Azene, Firehiwot
  • Date: 2012
  • Subjects: Acid mine drainage , Bottom ash , Fly ash , Coal ash
  • Type: Book chapter
  • Identifier: http://ujcontent.uj.ac.za8080/10210/370290 , uj:5024 , http://hdl.handle.net/10210/13461
  • Description: Preliminary investigation was conducted to evaluate the utilization of bottom ash and fly ash by-products on a study limited to their role as alkalizing reagents, with the ultimate objective of examining their potential use for insitu treatment of acid mine drainage (AMD) in South African mines. Bottom ash (BA) and fly ash (FA) obtained from a coal-powered electricity generation station were used in varied combined proportions of 100/0, 90/10, 70/30 BA:FA reagent mixtures and used to conduct neutralization tests done at mix proportions varied from 20:1 to 1:1 AMD to reagent mixtures. Three types of acid mine drainage water from an underground gold mine (AMD-Wz), gold tailings dam (AMD-Lc) and a coal mine (AMD-MpK) were used in the investigation. Water quality tests were carried out before and after the neutralisation treatment. It was found that both bottom ash and fly ash are effective alkalinising reagents for neutralising AMD. The materials were found to be most effective when mixed at a ratio no greater than 5:1 of mine water to reagent. Use of the coal ash wastes effectively removed up to 99% of iron from the AMD. The sulphate concentration was also reduced by the treatment but it remained fairly elevated. Manganese concentration reduced as the pH of the treated water increased, reaching a negliglible concentration of < 1.0 mg/l at pH ≥ 11. Further investigations are underway to examine leaching and weathering characteristics of the reagents.
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Effects of using glasswaste cullets as aggregates in concrete

- Dibodu, Lerato S., Ekolu, Stephen O.

On modern technology diffusion and ancient science in Africa

- Ekolu, Stephen O.

  • Authors: Ekolu, Stephen O.
  • Date: 2017
  • Subjects: Indigenization , Diffusion theory , Universalism
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/248105 , uj:25784 , Citation: Ekolu, S.O. 2017. On modern technology diffusion and ancient science in Africa.
  • Description: Abstract: This paper discusses the disparities leading to technology transfer in developing countries and attempts to explain this process using the diffusion theory. Scientific studies have shown that cognitive abilities have no role in the present under-development of SubSaharan Africa (SSA). These issues are discussed in consideration of the universalist nature of the Science, Engineering and Technology disciplines. It is shown from literature that ancient Africa was not devoid of great science. The necessity to majorly grow modern endogenic science in SSA is emphasized as a basis for an optimistic outlook towards posterity.
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Properties of pervious concrete for hydrologic applications

- Ekolu, Stephen O., Diop, Souleymane, Azene, Firehiwot

  • Authors: Ekolu, Stephen O. , Diop, Souleymane , Azene, Firehiwot
  • Date: 2016
  • Subjects: Pervious concrete , Compressive strength , Porosity
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/214004 , uj:21224 , Citation: Ekolu, S.O., Diop, S & Azene, F. 2016. Properties of pervious concrete for hydrologic applications.
  • Description: Abstract: This paper presents an experimental investigation that was conducted to examine those properties of interest with regard to the passage of water through pervious concrete. A total of 30 mixtures of pervious concrete were prepared at water-cementitious ratios (w/cm) varied from 0.25 to 0.40. Three aggregate types and sizes were used consisting of 13.2, 9.5 and 6.7 mm granite stone; 6.7 mm shale and 9.5 mm dolomite. Pozzolans were incorporated into mixtures in proportions of 20, 30 and 50% fly ash (FA) or 30% and 50% ground granulated blast furnace slag (GGBS). Compressive strength development in the mixtures was monitored at 7, 14, and 60 days. It was found that strength gain after 14 days generally occurred only in mixtures containing pozzolans. A unique behavior in property relations of pervious concrete was found with compressive strength increasing and porosity decreasing with increase in w/cm, contrary to established knowledge of conventional concrete properties. It was found that mixtures made with 6.7 or 9.5 mm granite stone gave porosity and permeability characteristics that were most suitable for hydrologic applications. Similarly, incorporation of 20% FA, 30% or 50% GGBS in the mixtures gave the most appropriate mechanical and transport properties.
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Proposed method of evaluating the eligibility criteria for supplementary assessments

- Ekolu, Stephen O.

Effect of superplasticizers on concrete durability indexes

- Ekolu, Stephen O.

  • Authors: Ekolu, Stephen O.
  • Date: 2014
  • Subjects: Superplasticizers , Concrete durability
  • Type: Book chapter
  • Identifier: uj:5046 , http://hdl.handle.net/10210/13584
  • Description: Use of durability index (DI) is one of the several approaches that have been used or advanced through various test methods for the purpose of evaluating the durability of concrete mixtures. In South Africa, use of DI's has developed through testing and research over the past years. A consortium of three tests of oxygen permeability index (OPI), water sorptivity and chloride conductivity are employed. This paper presents an investigation conducted to determine the effect that superplasticizers may have on durability indexes of concrete. Concrete mixtures of strengths ranging from 30 to 50 MPa were cast using two types of commercially available superplasticizers, herein referred to as GL and RSP. The admixtures were of different chemical bases with RSP being a sulphonated naphthalene superplasticizer while GL was a polycarboxylate ether superplasticizer. The tests conducted were compressive strength, oxygen permeability and water sorptivity. It was found that use of GL increased the compressive strength of concrete by about 10 MPa over the strengths of mixes made using RSP. Correspondingly, GL had an adverse effect on durability performance, as it decreased the OPI and increased the sorptivity indexes. The results implied the possible coarsening of the pore structure of the hardened concrete which could have resulted from the use of GL. Results also showed that the influence of chemical admixtures on hardened concrete properties and durability characteristics of high strength concretes may be less significant for high strength concretes.
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On modern technology diffusion and ancient science in Africa

- Ekolu, Stephen O.

Long-term mitigating effect of lithium nitrate on delayed ettringite formation and ASR in concrete – microscopic analysis

- Ekolu, Stephen O., Rakgosi, Gift, Hooton, Doug R.

On capacity and quality issues in engineering studies across Sub-Saharan Africa : a review

- Ekolu, Stephen O.

Permeable reactive barriers for acid mine drainage treatment : a review

- Shabalala, Ayanda N., Ekolu, Stephen O., Diop, Souleymane

  • Authors: Shabalala, Ayanda N. , Ekolu, Stephen O. , Diop, Souleymane
  • Date: 2014
  • Subjects: Acid mine drainage - Environmental aspects - South Africa , Acid mine drainage - Purification , Permeable reactive barriers , Water - Purification
  • Type: Article
  • Identifier: uj:5072 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13643
  • Description: Contaminated water flowing from abandoned mines is one of the most significant contributors to water pollution. Acid mine drainage (AMD) can have severe impacts on aquatic resources, can stunt terrestrial plant growth and harm wetlands, contaminate groundwater, raise water treatment costs, and damage concrete and metal structures. Permeable reactive barriers (PRBs) are one of the passive treatment technologies widely accepted for sustainable in situ remediation of contaminated groundwater and may be used in the management of localised seepage plumes from mine residues that contaminate shallow groundwater. These barriers provide chemical interactions with AMD as the polluted water flows through it. The ability of PRBs to remediate contaminants is dependent on the type of reactive material used. Some of the reactive media remove contaminants through physical contact while others work by altering the biogeochemical processes in the treatment zone, thus providing conditions conducive for contaminant immobilization or (bio) degradation. A variety of materials has been employed to remove contaminants including heavy metals, chlorinated solvents, aromatic hydrocarbons, and pesticides. This paper gives an overview of the PRB technology, which includes the advantages and limitations of the PRB, the types of reactive materials used, laboratory treatability tests used to evaluate suitable reactive materials and to aid in the designing and the implementation of the PRB and the installations schemes used in PRB field application.
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Sulphate corrosion behaviour of high volume slag concrete

- Ekolu, Stephen O., Ngwenya, Adam

  • Authors: Ekolu, Stephen O. , Ngwenya, Adam
  • Date: 2014
  • Subjects: Concrete - Mixing - Congresses , Concrete - Corrosion , Alumina cement
  • Type: Article
  • Identifier: uj:5063 , ISBN 9781614994657 , ISSN 9781614994664 , http://hdl.handle.net/10210/13626
  • Description: Concrete mixes of water-cementitious ratio (w/c’s) = 0.45, 0.5, 0.65 were used to prepare 100 mm cubes and 75 x 75 x 285 mm prisms. Moderately high alumina slag was incorporated in proportions of 50 or 70% and the specimens immersed in sodium sulphate or magnesium sulphate solutions of 50 g/L as SO4. Emphasis in the study was to assess sulphate resistance using concrete samples and other non-conventional methods. Expansion measurements, mass loss and corrosion attack or physical deterioration of concrete were monitored for 69 weeks. It was found that the results of expansion, mass gain and corrosion were consistent for Na2SO4 solution, showing improved sulphate resistance with increase in ground granulated blast-furnace slag (GGBS) incorporation. The expansion observations under MgSO4, while showing increased resistance with use of GGBS, gave conflicting results between expansion on one hand and, mass gain and corrosion on the other with the most severe corrosion occurring in concrete containing the high 70% GGBS. The corrosion test method appears to give a more realistic indicator of physical damage under MgSO4 attack compared to expansion measurement.
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Relationship between research, innovation and development – a review

- Ekolu, Stephen O.

Permeation properties of recycled concretes containing various types of recovered aggregates

- Ekolu, Stephen O.

  • Authors: Ekolu, Stephen O.
  • Date: 2018
  • Subjects: Recycled concrete , Brick , Rubble
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/279850 , uj:30061 , Citation: Ekolu, S.O. 2018. Permeation properties of recycled concretes containing various types of recovered aggregates.
  • Description: Abstract: This paper reports an experimental study conducted to asses durability characteristics of concretes made using different types of recycled aggregates. Different types of recycled coarse aggregates comprising natural dolomite (DOL), crushed concrete (RCA), recycled rubble (RUBL) and brick (BRIC) were studied using concrete mixtures of water-cement ratios (w/c) = 0.60 and 0.45 containing 100% of the recycled stone. The same type of crushed natural sand was used in all the mixtures. In addition to compressive strength and workability, water sorptivity and oxygen permeability (K) properties of the concretes were measured. It is found that the recycled aggregates showed higher porosity than the control crusher dolomite aggregate. Oxygen permeability results of the recycled aggregate concretes were of the same order of magnitude, giving about K = 2.0 x 10-10 m/s. Recycled brick aggregates produced concretes of consistently higher permeability and water sorptivity than the others. The oxygen permeability values for the various recycled aggregate concretes increased in the order kDOL < KRCA < KRUBL < KBRIC. Permeability of brick aggregate concrete was four times higher than that of control dolomite concrete. The relatively adverse influence of recycled brick on concrete properties is attributed to its highly porous characteristics.
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Influences of external chlorides and synthetic zeolite on delayed ettringite formation

- Ekolu, Stephen O.

Sulphate resistance of concrete made with moderately high alumina slag

- Ekolu, Stephen O., Ngwenya, Adam

  • Authors: Ekolu, Stephen O. , Ngwenya, Adam
  • Date: 2014
  • Subjects: Blast furnaces , Slag cement - South Africa , Mortar - Congresses
  • Type: Article
  • Identifier: uj:5062 , ISBN 978-1-61499-466-4 , ISSN 9781614994657 , http://hdl.handle.net/10210/13625
  • Description: This paper reports findings of ongoing investigation into the effect of high alumina ground granulated blast furnace slag (GGBS) on sulphate resistance of concrete. Slags used in most countries contain low alumina contents and provide high resistance to sulphate attack among other durability improvements. It is however known that slags of high alumina contents do not necessarily improve sulphate resistance but may otherwise adversely influence concrete performance. South African slags have moderately high alumina contents but hardly any studies have been conducted to determine its influence on sulphate resistance of concretes. In this investigation, commercially available slag widely used in South Africa was used. Mortar prisms 25 x 25 x 285 mm of 0.5 water-binder ratio incorporating 30%, 50%, 70% GGBS were prepared and immersed in sodium sulphate solutions of different concentrations of 28 g/L and 50 g/L as SO4. Expansion and mass change of the cementitious systems were monitored. Variables examined were compressive strengths prior to immersion in Na2SO4 solution, slag replacement levels, concentrations of sulphate solutions. It was found that the moderately high alumina slag improved resistance to sulphate attack in correspondence with increase in the replacement levels of the extender. Mixtures that were not cured to develop 20 MPa initial strength prior to exposure in Na2SO4 solution, showed elevated early age expansion while their cured counterparts did not expand. The long-term expansions of mixtures that had not been cured were much higher than expansions of the respective cured mixes. Interestingly, the use of GGBS in proportions exceeding 50% mitigated the adverse effects of early age expansions giving no long-term expansions in any of the mixtures containing the extender.
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Correlation between formative and summative assessment results in engineering studies

- Ekolu, Stephen O.

Potentiodynamic polarization study of the corrosion characteristics of acid mine drainage

- Ekolu, Stephen O., Diop, Souleymane, Azene, Firehiwot

  • Authors: Ekolu, Stephen O. , Diop, Souleymane , Azene, Firehiwot
  • Date: 2014
  • Subjects: Acid mine drainage - South Africa , Concrete - Corrosion
  • Type: Article
  • Identifier: uj:5064 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13627
  • Description: Potentiodynamic tests were carried out to evaluate the attacking characteristics of acid mine drainage (AMD) from South African mines. Tests were done using seven solutions of:- AMD water taken from the field and consisting of two AMD sources from the gold mines and two sources from the coal mines; sulphuric acid, distilled water, synthetic AMD prepared in the laboratory. Tests were done at normal room temperature of 23oC using mild steel and stainless steel samples. Tafel plots were generated and corrosion current (Icorr), corrosion potential (Ecorr), corrosion rates determined in each case. The corrosion rate of AMD from the coal mines was found to be similar to the corrosion of AMD from the gold tailings dam mine, both of which were significantly higher than the corrosion of AMD from the underground gold mine. It is, however, anticipated that the corrosion bevaviour could be different under static conditions and further investigations in this regard are being conducted.
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Thermal behaviour of high volume fly ash concrete and its temperature simulation

- Gaunt, Peter G., Versfeld, Mathew K.R., Ferreira, André, Ekolu, Stephen O.

  • Authors: Gaunt, Peter G. , Versfeld, Mathew K.R. , Ferreira, André , Ekolu, Stephen O.
  • Date: 2017
  • Subjects: High volume fly ash concrete , Compressive strength , Durability
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/248106 , uj:25783 , Citation: Gaunt, P.G. 2017. Thermal behaviour of high volume fly ash concrete and its temperature simulation.
  • Description: Abstract: In this paper, it is shown that Class F fly ash (FA) can be effectively used in high volumes as a supplementary cementitious material (SCM). High volume use of FA is of interest in promoting the development and application of green materials. In South Africa, there is little or no literature on high volume incorporation of locally available FA in concrete. In this investigation, six different concrete mixes of water/cementitious ratios (w/cm’s) = 0.3 and 0.45, were used. The mixtures consisted of 0, 30, 50 and 70% FA. Tests carried out were workability, bleeding, compressive strength and heat of hydration. Large 300 mm cubes were 2 used to study hydration heat development in fresh concrete. As expected, concrete strength decreased as FA content increased owing to the slower rate of strength development in FA mixtures. It was found that heat of hydration generated in HVFA mixes gave lower peak temperatures compared to mixes without FA, producing reductions of 27% to 43.5% in peak temperatures for mixtures containing 50% and 70% FA respectively. Temperature simulation using ConcreteWorks gave predictions correctly depicting the measured temperature profiles but with slight under-estimation of peak temperatures.
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Gravity-fed column configuration for acid mine drainage experiment

- Solomon, Fitsum H., Ekolu, Stephen O., Musonda, Innocent

  • Authors: Solomon, Fitsum H. , Ekolu, Stephen O. , Musonda, Innocent
  • Date: 2019
  • Subjects: Gravity column , Acid Mine Drainage (AMD) , Pervious concrete
  • Language: English
  • Type: Article
  • Identifier: http://hdl.handle.net/10210/404495 , uj:33924 , Citation: Solomon, F.H., Ekolu, S.O. & Musonda, I. 2019. Gravity-fed column configuration for acid mine drainage experiment.
  • Description: Abstract: The aim of this study was to develop a gravity feed column set-up and to set the flow parameters based on experimentally measured flow rates and pressure drops. Prior to the present study the authors used a column set-up in which acid mine drainage was pumped through pervious concrete filled columns. However, power outages due to load shedding often disrupted the experiments. As such, the gravity feed set-up was designed to overcome the need to rely on electrical power supply. The study describes the design set-up of four gravity columns. The design requirements comprised determination of appropriate column sizes, pressure heads and hydraulic gradients required to produce a low flow rate of about 1 mL/min at outlets of the columns filled with pervious concrete media. Of special interest is the hydraulic gradient being responsible for continuous flow in each column. Following completion of the design set-up, continuous flow rates of 0.60 to 0.80 mL/min were attained with a Reynolds number of about 4.0 in the columns filled with pervious concrete. Further research is in progress involving employment of the gravity-feed system for acid mine drainage treatment investigations.
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