Analysis of determinants of revolving credit for small and medium construction enterprises : a case of Gauteng province
- Balogun, Olanrewaju Abdul, Ansary, Nazeem, Ekolu, Stephen
- Authors: Balogun, Olanrewaju Abdul , Ansary, Nazeem , Ekolu, Stephen
- Date: 2017
- Subjects: Determinants credit revolving , Construction enterprises small and medium , South Africa
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/260742 , uj:27467 , Citation: Balogun, O.A., Ansary, N. & Ekolu, S. 2017. Analysis of determinants of revolving credit for small and medium construction enterprises : a case of Gauteng province. Creative Construction Conference 2017, CCC 2017, 19-22 June 2017, Primosten, Croatia. doi: 10.1016/j.proeng.2017.07.196
- Description: Abstract: Small and medium construction enterprises (SMEs) are an important vehicle to drive the economic growth globally. However, this enterprise sector has been constrained by different factors that stifle their full participation in the main stream economy specially credit accessibility. There is paucity of research to verify the determinants that predict revolving credit accessibility from financial institutions in South Africa. The data was obtained using questionnaire survey. 179 small and medium contractors responded from conveniently sampled respondents in Gauteng province in South Africa. The data was analysed using Statistical Package for the Social Sciences (SPSS) version 22. The study found that the dependant variable i.e. revolving credit was not predicted by the independent variables suggested i.e. gender, age group, current position, organization ownership, tax number, location and collateral. The finding informs bank managers they should not force clients to submit collateral before awarding credit to the SMEs. The suggested model that was tested attained the Hosmer and Lemeshow Test goodness of fit hence the results were credible. However, a further study is proposed for the entire country as the researchers acknowledge limitation on the chosen location of study.
- Full Text:
- Authors: Balogun, Olanrewaju Abdul , Ansary, Nazeem , Ekolu, Stephen
- Date: 2017
- Subjects: Determinants credit revolving , Construction enterprises small and medium , South Africa
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/260742 , uj:27467 , Citation: Balogun, O.A., Ansary, N. & Ekolu, S. 2017. Analysis of determinants of revolving credit for small and medium construction enterprises : a case of Gauteng province. Creative Construction Conference 2017, CCC 2017, 19-22 June 2017, Primosten, Croatia. doi: 10.1016/j.proeng.2017.07.196
- Description: Abstract: Small and medium construction enterprises (SMEs) are an important vehicle to drive the economic growth globally. However, this enterprise sector has been constrained by different factors that stifle their full participation in the main stream economy specially credit accessibility. There is paucity of research to verify the determinants that predict revolving credit accessibility from financial institutions in South Africa. The data was obtained using questionnaire survey. 179 small and medium contractors responded from conveniently sampled respondents in Gauteng province in South Africa. The data was analysed using Statistical Package for the Social Sciences (SPSS) version 22. The study found that the dependant variable i.e. revolving credit was not predicted by the independent variables suggested i.e. gender, age group, current position, organization ownership, tax number, location and collateral. The finding informs bank managers they should not force clients to submit collateral before awarding credit to the SMEs. The suggested model that was tested attained the Hosmer and Lemeshow Test goodness of fit hence the results were credible. However, a further study is proposed for the entire country as the researchers acknowledge limitation on the chosen location of study.
- Full Text:
Comparison of in-situ and lab-measured void contents for a bituminous pavement of a carriageway
- Kizyalla, Lewis Kabwe, Ekolu, Stephen
- Authors: Kizyalla, Lewis Kabwe , Ekolu, Stephen
- Date: 2014
- Subjects: Pavements, Bituminous - Quality control , Void content
- Type: Book chapter
- Identifier: uj:5044 , http://hdl.handle.net/10210/13564
- Description: In situ air voids are a function of mix design (aggregate type and gradation, and bitumen content), manufacture and the level of compaction achieved during construction and subsequent traffic [1-2]. During the improvement of N12-19 highway construction project between Snake road interchange and Kingsway interchange in Johannesburg, South Africa, the quality control (QC) of a bitumen treated base layer was done according to Committee of Land Transport Officials (COLTO) specifications where compliance is a statistical judgment of three parameters namely, the relative compaction, binder content (lab binder) and voids in the mix (lab air voids). The focus of this paper is to analyse only one of the three parameters namely, voids content obtained from the laboratory and from in-situ field measurements. It was found that for a given random sample, there is a considerable difference between in-situ void and lab void for the same material. Therefore, it becomes interesting to statistically evaluate the random sample results of in-situ air voids in order to decide on its compliance with quality control requirements.
- Full Text:
- Authors: Kizyalla, Lewis Kabwe , Ekolu, Stephen
- Date: 2014
- Subjects: Pavements, Bituminous - Quality control , Void content
- Type: Book chapter
- Identifier: uj:5044 , http://hdl.handle.net/10210/13564
- Description: In situ air voids are a function of mix design (aggregate type and gradation, and bitumen content), manufacture and the level of compaction achieved during construction and subsequent traffic [1-2]. During the improvement of N12-19 highway construction project between Snake road interchange and Kingsway interchange in Johannesburg, South Africa, the quality control (QC) of a bitumen treated base layer was done according to Committee of Land Transport Officials (COLTO) specifications where compliance is a statistical judgment of three parameters namely, the relative compaction, binder content (lab binder) and voids in the mix (lab air voids). The focus of this paper is to analyse only one of the three parameters namely, voids content obtained from the laboratory and from in-situ field measurements. It was found that for a given random sample, there is a considerable difference between in-situ void and lab void for the same material. Therefore, it becomes interesting to statistically evaluate the random sample results of in-situ air voids in order to decide on its compliance with quality control requirements.
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Condition assessment of a Johannesburg skyscraper
- Ekolu, Stephen, Van Ede, Willem F.
- Authors: Ekolu, Stephen , Van Ede, Willem F.
- Date: 2014
- Subjects: Skyscrapers - Evaluation
- Type: Book chapter
- Identifier: uj:5045 , ISSN 9781614994664 , http://hdl.handle.net/10210/13565
- Description: This paper presents a condition assessment conducted on a Johannesburg skyscraper. It had become apparent that concrete spalling occurred in areas of the top 11m of the Southern and Western facades of the reinforced concrete skyscraper constructed in the 1970’s. However, the extent of the problem was unknown. The only information available were two photographs showing spalled concrete and severely corroded reinforcement bars. Some literature search pertaining to the structure was conducted after which, visual inspection and mapping of spalled areas and cracks were conducted. This was followed by a cover meter survey, a half-cell potential survey, and the removal of 20 (twenty) cores for laboratory testing. It was found that the typical problems associated with carbonation and insufficient cover resulted in the corrosion of reinforcement which then led to the spalling observed.
- Full Text:
- Authors: Ekolu, Stephen , Van Ede, Willem F.
- Date: 2014
- Subjects: Skyscrapers - Evaluation
- Type: Book chapter
- Identifier: uj:5045 , ISSN 9781614994664 , http://hdl.handle.net/10210/13565
- Description: This paper presents a condition assessment conducted on a Johannesburg skyscraper. It had become apparent that concrete spalling occurred in areas of the top 11m of the Southern and Western facades of the reinforced concrete skyscraper constructed in the 1970’s. However, the extent of the problem was unknown. The only information available were two photographs showing spalled concrete and severely corroded reinforcement bars. Some literature search pertaining to the structure was conducted after which, visual inspection and mapping of spalled areas and cracks were conducted. This was followed by a cover meter survey, a half-cell potential survey, and the removal of 20 (twenty) cores for laboratory testing. It was found that the typical problems associated with carbonation and insufficient cover resulted in the corrosion of reinforcement which then led to the spalling observed.
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Effect of clay-concrete lining on canal seepage towards the drainage region – an analysis using Finite-Element method
- Solomon, Fitsum, Ekolu, Stephen
- Authors: Solomon, Fitsum , Ekolu, Stephen
- Date: 2014
- Subjects: Canals , Seepage , Drainage , Finite element method , Canals - Linings
- Type: Book chapter
- Identifier: uj:5049 , http://hdl.handle.net/10210/13588
- Description: For proper design of a drainage system that utilizes lined canals, knowledge of the seepage into a soil substrate/drainage region is necessary so that the drainage blanket and /or filter type and thickness, and the size of collector pipes can all be designed. The work presented in this paper is based on the problem of steady-state seepage from a hypothetical irrigation canal into the substrate/drainage region towards asymmetrical trapezoidal concrete-lined canal. The problem is solved using a finite element based software program to determine the flow volume into the drainage region. Typical values of soil permeability coefficients of single and two-layer subsoil from literature are used along with experimental results of a laboratory study done for the design seepage coefficient of clay-cement concrete as lining material. The water flow effect of canal seepage discharge analyzed shows that the effectiveness of canal lining in reducing seepage is less when drainage distance is large. This study may contribute towards a better understanding on design of hydraulic conductivity under hydraulic structures. It will systematically enumerate the many, often straightforward factors that determine coefficient of permeability for compliance purposes. This could also involve a re-estimation of the values of the permeability coefficient and the factors on which the coefficient depends.
- Full Text:
- Authors: Solomon, Fitsum , Ekolu, Stephen
- Date: 2014
- Subjects: Canals , Seepage , Drainage , Finite element method , Canals - Linings
- Type: Book chapter
- Identifier: uj:5049 , http://hdl.handle.net/10210/13588
- Description: For proper design of a drainage system that utilizes lined canals, knowledge of the seepage into a soil substrate/drainage region is necessary so that the drainage blanket and /or filter type and thickness, and the size of collector pipes can all be designed. The work presented in this paper is based on the problem of steady-state seepage from a hypothetical irrigation canal into the substrate/drainage region towards asymmetrical trapezoidal concrete-lined canal. The problem is solved using a finite element based software program to determine the flow volume into the drainage region. Typical values of soil permeability coefficients of single and two-layer subsoil from literature are used along with experimental results of a laboratory study done for the design seepage coefficient of clay-cement concrete as lining material. The water flow effect of canal seepage discharge analyzed shows that the effectiveness of canal lining in reducing seepage is less when drainage distance is large. This study may contribute towards a better understanding on design of hydraulic conductivity under hydraulic structures. It will systematically enumerate the many, often straightforward factors that determine coefficient of permeability for compliance purposes. This could also involve a re-estimation of the values of the permeability coefficient and the factors on which the coefficient depends.
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Effect of surface treatments on abrasion and permeation properties of clay concretes
- Solomon, Fitsum, Ekolu, Stephen
- Authors: Solomon, Fitsum , Ekolu, Stephen
- Date: 2014
- Subjects: Reinforced concrete , Concrete construction , Floors, Concrete - Design and construction
- Type: Article
- Identifier: uj:5066 , ISBN 9781614994657 , ISSN 9781614994664 , http://hdl.handle.net/10210/13637
- Description: The resistance of concrete surfaces to various types of wear can be a defining performance characteristic in certain applications. Some concrete structures are required to be abrasion-resistant; among them are dams, canals, roads, floors, footpaths, parking lots, and paths in parks. The work reported in this paper is based on a laboratory study of the concrete-surface treatments (CSTs) consisting of dry shake and screeding. Four control concrete mixtures were prepared with ordinary Portland cement (OPC), having a cement content (CC) of 350 kg/m3 at water-cementitious ratio (w/cc) = 0.70, 0.75; and 280 kg/m3 CC of w/cc = 0.80, 0.85. Other concrete mixtures were then prepared by substituting OPC in the control mixtures with 10, 20, 30, and 40% local raw clay. Compressive strength, abrasion resistance, and air permeability of the surface-treated concretes were measured at the ages of six months, while drying shrinkage was monitored for up to year. Drying shrinkage of concrete reduced with decrease in w/cc ratio and increased with increase in raw clay content. Among all the mixtures, the control concrete of w/cm ratio = 0.70 and the claycement concrete containing w/cm=0.80 at 70% OPC/30% raw clay showed the least and highest shrinkage increments respectively. Abrasion resistance of concrete, measured by the rotating-cutter method, increased with increasing clay content and decreasing compressive strength. However, abrasion performance results of clay-cement concrete mixtures with CSTs were generally higher. Air permeability of the concretes was measured and its relationship with the depth of abrasion of the concrete was examined
- Full Text:
- Authors: Solomon, Fitsum , Ekolu, Stephen
- Date: 2014
- Subjects: Reinforced concrete , Concrete construction , Floors, Concrete - Design and construction
- Type: Article
- Identifier: uj:5066 , ISBN 9781614994657 , ISSN 9781614994664 , http://hdl.handle.net/10210/13637
- Description: The resistance of concrete surfaces to various types of wear can be a defining performance characteristic in certain applications. Some concrete structures are required to be abrasion-resistant; among them are dams, canals, roads, floors, footpaths, parking lots, and paths in parks. The work reported in this paper is based on a laboratory study of the concrete-surface treatments (CSTs) consisting of dry shake and screeding. Four control concrete mixtures were prepared with ordinary Portland cement (OPC), having a cement content (CC) of 350 kg/m3 at water-cementitious ratio (w/cc) = 0.70, 0.75; and 280 kg/m3 CC of w/cc = 0.80, 0.85. Other concrete mixtures were then prepared by substituting OPC in the control mixtures with 10, 20, 30, and 40% local raw clay. Compressive strength, abrasion resistance, and air permeability of the surface-treated concretes were measured at the ages of six months, while drying shrinkage was monitored for up to year. Drying shrinkage of concrete reduced with decrease in w/cc ratio and increased with increase in raw clay content. Among all the mixtures, the control concrete of w/cm ratio = 0.70 and the claycement concrete containing w/cm=0.80 at 70% OPC/30% raw clay showed the least and highest shrinkage increments respectively. Abrasion resistance of concrete, measured by the rotating-cutter method, increased with increasing clay content and decreasing compressive strength. However, abrasion performance results of clay-cement concrete mixtures with CSTs were generally higher. Air permeability of the concretes was measured and its relationship with the depth of abrasion of the concrete was examined
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Failure of structure in East Africa with focus on the causes of failures in the construction phase
- Alinaitwe, Henry Mwanaki, Ekolu, Stephen
- Authors: Alinaitwe, Henry Mwanaki , Ekolu, Stephen
- Date: 2014
- Subjects: Structural failures - East Africa , Reinforced concrete construction - East Africa , Construction industry - East Africa
- Type: Book chapter
- Identifier: uj:5035 , http://hdl.handle.net/10210/13555
- Description: Despite the relatively well-established concrete practice in the East African region, there are frequent incidents of construction failures, resulting into heavy loss of lives and property. The main objective of this paper was to examine structures that have failed during the construction phase, in East Africa, since the start of the 21st century; identify and discuss the primary causes and sources of failures. A classic failure case of building collapse, herein referred to as BBJ building, has been used to examine the most important issues related to construction failures. Following the analysis of reports of technical investigations undertaken on the collapsed structure, it was found that failures in reinforced concrete (RC) structures during construction, result from five primary causes of: (1) poor materials and workmanship, (2) design and construction errors, (3) absence of professional supervision of site- works, (4) wrong implementation of construction methods, (5) neglect of design approval procedures. Secondary issues that are complicit to construction failures are:- attempts to severely minimize construction cost, neglect of inspection and monitoring by local authorities, influence peddling by proprietors. It is evident that construction failures can be minimized if the right procedures are followed in the design, construction and operation of the structures; a matter that is of interest to stakeholders of the Built Environment.
- Full Text:
- Authors: Alinaitwe, Henry Mwanaki , Ekolu, Stephen
- Date: 2014
- Subjects: Structural failures - East Africa , Reinforced concrete construction - East Africa , Construction industry - East Africa
- Type: Book chapter
- Identifier: uj:5035 , http://hdl.handle.net/10210/13555
- Description: Despite the relatively well-established concrete practice in the East African region, there are frequent incidents of construction failures, resulting into heavy loss of lives and property. The main objective of this paper was to examine structures that have failed during the construction phase, in East Africa, since the start of the 21st century; identify and discuss the primary causes and sources of failures. A classic failure case of building collapse, herein referred to as BBJ building, has been used to examine the most important issues related to construction failures. Following the analysis of reports of technical investigations undertaken on the collapsed structure, it was found that failures in reinforced concrete (RC) structures during construction, result from five primary causes of: (1) poor materials and workmanship, (2) design and construction errors, (3) absence of professional supervision of site- works, (4) wrong implementation of construction methods, (5) neglect of design approval procedures. Secondary issues that are complicit to construction failures are:- attempts to severely minimize construction cost, neglect of inspection and monitoring by local authorities, influence peddling by proprietors. It is evident that construction failures can be minimized if the right procedures are followed in the design, construction and operation of the structures; a matter that is of interest to stakeholders of the Built Environment.
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Field investigation of slab deterioration due to carbonation in a concrete building
- Araya, Eleni B, Ekolu, Stephen
- Authors: Araya, Eleni B , Ekolu, Stephen
- Date: 2019
- Subjects: Carbonation , Cover , Corrosion
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/407006 , uj:34242 , Citation: Araya, E.B., Ekolu, S. 2019 : Field investigation of slab deterioration due to carbonation in a concrete building.
- Description: Abstract : This paper presents an investigation on a deteriorated slab of a two-story building located in Johannesburg, South Africa. The structure has been in use as a residential building for more than 60 years. The top slab of the first floor was delaminated and reinforcement bars were severely corroded. Condition assessment of the building was done using the Schmidt hammer test, cover-meter survey and half-cell potential measurements. In addition to the non-destructive tests done, X-ray diffraction and scanning electron microscopy were also conducted on the deteriorated concrete.
- Full Text:
- Authors: Araya, Eleni B , Ekolu, Stephen
- Date: 2019
- Subjects: Carbonation , Cover , Corrosion
- Language: English
- Type: Conference proceedings
- Identifier: http://hdl.handle.net/10210/407006 , uj:34242 , Citation: Araya, E.B., Ekolu, S. 2019 : Field investigation of slab deterioration due to carbonation in a concrete building.
- Description: Abstract : This paper presents an investigation on a deteriorated slab of a two-story building located in Johannesburg, South Africa. The structure has been in use as a residential building for more than 60 years. The top slab of the first floor was delaminated and reinforcement bars were severely corroded. Condition assessment of the building was done using the Schmidt hammer test, cover-meter survey and half-cell potential measurements. In addition to the non-destructive tests done, X-ray diffraction and scanning electron microscopy were also conducted on the deteriorated concrete.
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Influence of a new viscosity modifying admixture on the performance of different superplasticizers
- Kazurikanyo, Jean-Bosco, Ekolu, Stephen
- Authors: Kazurikanyo, Jean-Bosco , Ekolu, Stephen
- Date: 2014
- Subjects: Cement - Viscosity , Plasticizers - Viscosity , Cement - Additives
- Type: Book chapter
- Identifier: uj:5038 , ISBN 9781614994664 , http://hdl.handle.net/10210/13558
- Description: An investigation was conducted on a new viscosity modifier, herein referred to as VMA, to determine its effects and compatibility with commercially available superplasticizers and local cements. Marsh cone tests were conducted on cement pastes to compare saturation points and the influence of the viscosity modifying admixture. It was found that the VMA gave improved results when used with a polycarboxylate-based superplasticizer and also reduces the required dosage of the superplasticizer needed to achieve specific fluidity. However, it was observed that the VMA showed no influence whatsoever, when used with the phosphonate based-superplasticizer. These findings underscore the importance of establishing compatibilities and interactions when more than one admixture is used in fresh concrete.
- Full Text:
- Authors: Kazurikanyo, Jean-Bosco , Ekolu, Stephen
- Date: 2014
- Subjects: Cement - Viscosity , Plasticizers - Viscosity , Cement - Additives
- Type: Book chapter
- Identifier: uj:5038 , ISBN 9781614994664 , http://hdl.handle.net/10210/13558
- Description: An investigation was conducted on a new viscosity modifier, herein referred to as VMA, to determine its effects and compatibility with commercially available superplasticizers and local cements. Marsh cone tests were conducted on cement pastes to compare saturation points and the influence of the viscosity modifying admixture. It was found that the VMA gave improved results when used with a polycarboxylate-based superplasticizer and also reduces the required dosage of the superplasticizer needed to achieve specific fluidity. However, it was observed that the VMA showed no influence whatsoever, when used with the phosphonate based-superplasticizer. These findings underscore the importance of establishing compatibilities and interactions when more than one admixture is used in fresh concrete.
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Material selection and mix design of radiation shielding concrete
- Ramushu, Mokgobi A., Ekolu, Stephen
- Authors: Ramushu, Mokgobi A. , Ekolu, Stephen
- Date: 2014
- Subjects: Shielding (Radiation) , Concrete , Aggregates (Building materials)
- Type: Book chapter
- Identifier: uj:5036 , http://hdl.handle.net/10210/13556
- Description: Based on the compiled literature and the availability of materials that could be used, concrete was selected as the best shielding material. Further work was carried out to develop a specific mixture that would shield the radioactive energies. The important special concrete ingredients that were considered in the mix design were high density aggregates and boron-containing aggregates. Various high density concrete mixtures of w/c (water/cementitious ratio) = 0.42, 0.45, 0.5 and 0.6, were prepared and adjusted appropriately in order to obtain the desired mix characteristics. The final (high density shielding concrete) mix produced was workable and cohesive with average 28- day compressive cube strength of 30 MPa, w/c = 0.51 and density of 4231 kg/m3. The concrete had high slump with a height and spread of 230 mm and 510 mm respectively. It was composed of CEM 52.5 N, silica fume, water, hematite sand, hematite stones, steel shots, colemanite and chemical admixtures.
- Full Text:
- Authors: Ramushu, Mokgobi A. , Ekolu, Stephen
- Date: 2014
- Subjects: Shielding (Radiation) , Concrete , Aggregates (Building materials)
- Type: Book chapter
- Identifier: uj:5036 , http://hdl.handle.net/10210/13556
- Description: Based on the compiled literature and the availability of materials that could be used, concrete was selected as the best shielding material. Further work was carried out to develop a specific mixture that would shield the radioactive energies. The important special concrete ingredients that were considered in the mix design were high density aggregates and boron-containing aggregates. Various high density concrete mixtures of w/c (water/cementitious ratio) = 0.42, 0.45, 0.5 and 0.6, were prepared and adjusted appropriately in order to obtain the desired mix characteristics. The final (high density shielding concrete) mix produced was workable and cohesive with average 28- day compressive cube strength of 30 MPa, w/c = 0.51 and density of 4231 kg/m3. The concrete had high slump with a height and spread of 230 mm and 510 mm respectively. It was composed of CEM 52.5 N, silica fume, water, hematite sand, hematite stones, steel shots, colemanite and chemical admixtures.
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Potential South African standard sand for cement mortar testing and research
- Authors: Ekolu, Stephen
- Date: 2014
- Subjects: Concrete - Testing , Strength of materials , Sand - Specifications - South Africa , Mortar - Testing
- Type: Book chapter
- Identifier: uj:5037 , ISBN 9781614994664 , http://hdl.handle.net/10210/13557
- Description: Mortars are used extensively in accelerated methods of testing the physical properties of cementitious materials. Mortar strength is invariably used to determine cement strength grade of cements and for general evaluation of material behavior, as typically employed in research and testing. Presently, the South African (SA) cement industry imports standard from Europe for cement testing purposes. This study was conducted to formulate South African standard sand that could be used to conduct mortar strength tests for compliance to specifications and for general research purposes. Two formulations of local South African silica sands, referenced as SA513S and SA413S, were developed to suit standard gradings. The formulated South African standard sands (SASS) where tested in comparison with European standard sand (ENSS) of EN196-1 and American graded standard sand (GSS) of ASTM C- 778. Following the formulation and grading of SASS, mortar mixtures of 1:3:0.5 cement to sand to water were cast in 50 mm cubes and tested for compressive strength for ages up to 90 days. Two types of cements were employed in the tests, the ordinary Portland cement CEM 1 42.5N and pozzolanic cement CEM V 32.5N. Comparison of the 28-day compressive strength results between the four SS types showed an excellent agreement, giving standard deviations of 1.96 and 2.51 for CEM I and CEM V. The flow results for the standard sand types varied, with EN196-1 giving the highest mortar flow followed by GSS sand and SA413S. The GSS and SA513S gave precisely the same flow results.
- Full Text:
- Authors: Ekolu, Stephen
- Date: 2014
- Subjects: Concrete - Testing , Strength of materials , Sand - Specifications - South Africa , Mortar - Testing
- Type: Book chapter
- Identifier: uj:5037 , ISBN 9781614994664 , http://hdl.handle.net/10210/13557
- Description: Mortars are used extensively in accelerated methods of testing the physical properties of cementitious materials. Mortar strength is invariably used to determine cement strength grade of cements and for general evaluation of material behavior, as typically employed in research and testing. Presently, the South African (SA) cement industry imports standard from Europe for cement testing purposes. This study was conducted to formulate South African standard sand that could be used to conduct mortar strength tests for compliance to specifications and for general research purposes. Two formulations of local South African silica sands, referenced as SA513S and SA413S, were developed to suit standard gradings. The formulated South African standard sands (SASS) where tested in comparison with European standard sand (ENSS) of EN196-1 and American graded standard sand (GSS) of ASTM C- 778. Following the formulation and grading of SASS, mortar mixtures of 1:3:0.5 cement to sand to water were cast in 50 mm cubes and tested for compressive strength for ages up to 90 days. Two types of cements were employed in the tests, the ordinary Portland cement CEM 1 42.5N and pozzolanic cement CEM V 32.5N. Comparison of the 28-day compressive strength results between the four SS types showed an excellent agreement, giving standard deviations of 1.96 and 2.51 for CEM I and CEM V. The flow results for the standard sand types varied, with EN196-1 giving the highest mortar flow followed by GSS sand and SA413S. The GSS and SA513S gave precisely the same flow results.
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Radiological assessment of high density shielding concrete for neutron radiography
- Ekolu, Stephen, Ramushu, Mokgobi A.
- Authors: Ekolu, Stephen , Ramushu, Mokgobi A.
- Date: 2014
- Subjects: Concrete , Concrete - Mixing , Concrete blocks
- Type: Article
- Identifier: uj:5070 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13641
- Description: A radiation shield is a physical barrier placed between a source of ionizing radiation and the object to be protected from the radiation. In this research, concrete was selected as the best shielding material. An investigation was carried out to evaluate a specific concrete mixture developed in [1] for shielding of radiation energies. The high density shielding concrete (HDSC) concrete had 28-day compressive cube strength of 30 MPa, w/c (water/cementitious ratio) of 0.51 and density of 4231 kg/m3. It composed of CEM 52.5 N, silica fume, hematite aggregates, steel shots, colemanite and chemical admixtures. This paper presents an evaluation of the shielding properties of the HDSC using foil activation method. It is shown that the HDSC mixture achieved the desired shielding capabilities within the first 250 mm thickness of the concrete block.
- Full Text:
- Authors: Ekolu, Stephen , Ramushu, Mokgobi A.
- Date: 2014
- Subjects: Concrete , Concrete - Mixing , Concrete blocks
- Type: Article
- Identifier: uj:5070 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13641
- Description: A radiation shield is a physical barrier placed between a source of ionizing radiation and the object to be protected from the radiation. In this research, concrete was selected as the best shielding material. An investigation was carried out to evaluate a specific concrete mixture developed in [1] for shielding of radiation energies. The high density shielding concrete (HDSC) concrete had 28-day compressive cube strength of 30 MPa, w/c (water/cementitious ratio) of 0.51 and density of 4231 kg/m3. It composed of CEM 52.5 N, silica fume, hematite aggregates, steel shots, colemanite and chemical admixtures. This paper presents an evaluation of the shielding properties of the HDSC using foil activation method. It is shown that the HDSC mixture achieved the desired shielding capabilities within the first 250 mm thickness of the concrete block.
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Simple criteria for evaluating sulphate attack in concrete
- Authors: Ekolu, Stephen
- Date: 2014
- Subjects: Concrete - Mixing , Blast furnaces , Slag cement , Concrete
- Type: Article
- Identifier: uj:5082 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13653
- Description: This paper attempts to analyse results from the standard test methods employed for sulphate attack and evaluates their correlations, consistency and contrasts, as well as physical observations. Data from expansions and mass change of 25 x25 x 285 mm mortar prisms and 75 x 75 x 285 mm concrete prisms were used. Mortar mixtures consisted of 1: 2.25: 0.5 cement to sand to water while concrete mixtures were of water-cementitious ratio (w/cm) of 0.45, 0.50, 0.65. Mixtures were made using CEM I 42.5N with or without 30, 50, 70% ground granulated blast furnace slag (GGBS) and stored in sodium sulphate solutions of 28 g/L and 50 g/L as SO4. Results show that ASTM C 1012 mortar expansion criteria of 0.10% corresponds to 1.2% mass gain. Similarly, concrete prism expansion criteria of 0.05% is equivalent to 0.75% mass gain. It is proposed that in the absence of expansion monitoring, the use of mass gain criteria of 1.2% mass in mortar prisms or 0.75% in concrete prisms may be sufficient for evaluating sulphate attack.
- Full Text:
- Authors: Ekolu, Stephen
- Date: 2014
- Subjects: Concrete - Mixing , Blast furnaces , Slag cement , Concrete
- Type: Article
- Identifier: uj:5082 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13653
- Description: This paper attempts to analyse results from the standard test methods employed for sulphate attack and evaluates their correlations, consistency and contrasts, as well as physical observations. Data from expansions and mass change of 25 x25 x 285 mm mortar prisms and 75 x 75 x 285 mm concrete prisms were used. Mortar mixtures consisted of 1: 2.25: 0.5 cement to sand to water while concrete mixtures were of water-cementitious ratio (w/cm) of 0.45, 0.50, 0.65. Mixtures were made using CEM I 42.5N with or without 30, 50, 70% ground granulated blast furnace slag (GGBS) and stored in sodium sulphate solutions of 28 g/L and 50 g/L as SO4. Results show that ASTM C 1012 mortar expansion criteria of 0.10% corresponds to 1.2% mass gain. Similarly, concrete prism expansion criteria of 0.05% is equivalent to 0.75% mass gain. It is proposed that in the absence of expansion monitoring, the use of mass gain criteria of 1.2% mass in mortar prisms or 0.75% in concrete prisms may be sufficient for evaluating sulphate attack.
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