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Cold-formed circular hollow sections under axial compression

  • Authors: Dundu, Morgan , Chabalala, Vongani
  • Date: 2014
  • Subjects: Columns, Concrete , Concrete slabs , Reinforced concrete construction , Concrete beams , South African Design Standards
  • Type: Article
  • Identifier: uj:5068 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13639
  • Description: Two series of experiments were carried out to investigate the behaviour of pinned-ended circular hollow section (CHS) columns, subjected to axial compressive load. A total of 30 columns were tested in this investigation; 20 columns in Series 1 and 10 columns in Series 2. The outside diameter-to-thickness ratio (d/t) and the slenderness ratio (KL/r) ranged from 29.7 to 46.4 and 20.8 to 82.2 for Series 1, respectively, and from 55.0 to 62.9 and 10.7 to 34.9 for Series 2, respectively. In general, Series 1 columns failed by overall flexural buckling and, whilst Series 2 columns failed by local ring-type buckling. The test strengths of the columns were compared with the strengths predicted by the South African design standard (SANS10162-1) and the European design standard (EN 1993-1-1).
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Compression tests of Mi Panels

  • Authors: Bukasa, G. M. , Dundu, M.
  • Date: 2014
  • Subjects: Reinforced concrete construction , Concrete beams , Flexure , Concrete - Deterioration
  • Type: Article
  • Identifier: uj:5073 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13644
  • Description: A number of compression tests of Mi Panels are presented. The use of lightweight Mi Panels as building system allows the reduction of construction time and waste in the building environment. The compression tests are performed to simulate the behaviour of the wall, when subjected to vertical loads from the roof. Two LVDTs were placed at mid-height of the panels during the compression tests, to record the lateral displacement. Mi Panels failed by fracturing into two parts at mid-height. No cracks in the panel were observed before overall flexural buckling failure. The tests showed that the panels are capable of carrying the required loads, and can be used in place of brick walls.
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Compressive strength and durability of fly ash stabilized dolomitic waste as a lightweight construction material

  • Authors: Aneke, Ikechukwu F. , Okonta, Felix N.
  • Date: 2014
  • Subjects: Fly ash , Subsidences (Earth movements) - South Africa , Dolomitic waste
  • Type: Article
  • Identifier: uj:5075 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13646
  • Description: Due to the seriousness of environmental pollution and the production of huge energy consuming building and construction materials, the development of new eco-friendly and energy saving building materials to overcome these issues has been gaining increasing attention. South Africa has largest number of dolomite deposits in Southern Africa, if not in the entire Africa. Nonetheless most of the dolomite in South Africa has some impurities of which they are neglected in dumping site (millions of tons). This paper looked at finding alternative use for this dolomitic waste (DW) by stabilizing this waste with another waste called fly ash (FA), introduction of gypsum as an activator will trigger a pozzolanic reaction in presences of water. As a result of this, the product of this reaction will be a useful material in construction and as well solve the difficulties i.e. environmental, social and cost often associated with storing and handling of this waste. This work went as far as providing an alternative for low-cost construction materials that can help deal with South African housing problems. The waste material was analyzed from geomaterial and geochemistry view point, the chemical reaction between these materials: dolomitic waste and fly ash were illustrated. The XRF, SEM and EDS of the reacted product were looked at, the strength gained by the reaction after sample preparation for 28 days were also shown. However various geotechnical laboratory experiments were conducted ranging from proctor compaction test, compressive strength test and a mathematical model was generated to predict the compressive strength and these results were compared to compressive strength values obtained from the laboratory.
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Concrete filled double skin circular tubes : a review

  • Authors: Essopjee, Yoosuf , Dundu, Morgan
  • Date: 2014
  • Subjects: Prestressed concrete construction , Columns, Concrete , Plates, Iron and steel
  • Type: Article
  • Identifier: uj:5083 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13654
  • Description: A review of the research conducted on the compressive strength of concrete filled double skin circular tubes (CFDSCT) columns is conducted. Variables of the CFDSCT considered in this review include the concrete strength, steel strength, inner and outer tube diameter, steel thickness and length of the stub columns. Test results show that the composite columns had compressive strengths of up to 41% higher than the sum of the individual strengths of the section. All the outer tubes of these composite columns by failed local buckling. A review of the design equations proposed are presented and discussed. The paper also identifies gaps for further research for these types of columns.
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Effect of wetting and air curing durations on strength of stabilized sands

  • Authors: Moatlhodi, Lerato J. , Okonta, Felix N.
  • Date: 2014
  • Subjects: Sandcrete blocks , Low-cost houses - South Africa , Building materials , High strength concrete , Portland cement , Fly ash
  • Type: Article
  • Identifier: uj:5076 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13647
  • Description: Low cost houses in most developing countries are constructed from sandcrete blocks manufactured from sand-cement mortar. In South Africa, failure of many of these blocks has been experienced leading to collapse of the structures. Lack of sufficient compressive strength in the manufactured blocks was attributed as the main cause of the failures. The unconfined compressive strength (UCS) of sandcrete blocks can however be improved by curing the blocks under different conditions. Therefore the objective of this study was to evaluate the effect of different wetting and air drying durations would have on the strength and the stiffness of the cubes produced. Weakly cemented sand cubes, with different cement contents and cement-fly ash binder ratios compacted at the optimum moisture content, were prepared. The 28 days UCS was determined, modulus of elasticity and moisture contents of sample specimen was also determined. The results showed that curing cubes under water for 7 days and then air curing for 21 days yield maximum UCS and modulus of elasticity for sands cemented by plain Portland cement, and that 3 days under water curing produced maximum results for sands stabilized by cement-fly ash binder. It was however found that under water for 28 days results in minimum strength. Therefore the longer the cubes are cured under water minimum strengths were achieved.
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Effects of multi-walled carbon nanotubes on strength and interfacial transition zone of concrete

  • Authors: Van Tonder, P. , Mafokoane, T.T.
  • Date: 2014
  • Subjects: Carbon nanotubes , Concrete - Mixing , Materials - Testing
  • Type: Article
  • Identifier: uj:5057 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13619
  • Description: Multi-walled carbon nanotubes (MWCNTs) were used to try and eliminate the aggregate interfacial transition zone. Different concrete mixes were used in fixed proportions along with varying concentrations of CNTs. The CNTs were applied in different concentrations, namely, 0.05 wt%, 0.1 wt% and 0.2 wt%, per dry weight. CNTs were dispersed using sonication. Concrete specimens were tested for compressive, flexural and split-tensile strengths. For each test, thirteen mix designs were investigated which included untreated aggregates and CNTs, and treated aggregates and CNTs. The results were compared with the results of the control concrete. The results showed that the use of CNTs improves the compressive, flexural and split-tensile strengths. It was concluded that CNTs minimize the ITZ.
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Flexural failure modes of steel plate-strengthened reinforced concrete elements

Flexural tests of Mi Panels

  • Authors: Bukasa, G. M. , Dundu, M.
  • Date: 2014
  • Subjects: Concrete beams , Flexure , Fiber cement , Fiber-reinforced concrete
  • Type: Article
  • Identifier: uj:5074 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13645
  • Description: Two series of flexural tests on 2700x600x75 mm Mi Panels are presented. The inner core of these lightweight panels is made from mixing polystyrene beads called Neopor, high strength cement, and water. A chemical is used as binding agent to bond the inner core to the external fibre cement sheets of 4.5 mm thickness. The experimental programme consists of two series of tests with different loading conditions; the first series has line loads at one-third point from each end support and the second series has line loads, at quarter and three quarter span of the panels. All flexural tests are performed to simulate the behaviour of the wall, when subjected to wind loads. Although the panels failed by fracturing, the tests showed that the panels are capable of carrying the required loads.
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Influence of a new viscosity modifying admixture on the performance of different superplasticizers

  • 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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Limits of elongation variation of tenadons in post-tensioning

  • Authors: Dundu, Morgan , Rupieper, Sebastian
  • Date: 2014
  • Subjects: Tendons (Prestressed concrete) , Prestressed concrete construction , South African Design Standards
  • Type: Article
  • Identifier: uj:5069 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13640
  • Description: This paper analyses tensioning data obtained from a variety of projects that have been completed in South Africa in recent years in order to determine the causes of variation in elongation and suggest practical elongation limits. Current limits, prescribed by the South African standards (SANS 2001-CC1 and COLTO), of elongation variation limit of ±6% and an average elongation variation limit of ±3% are causing huge problems to the post-tensioning industry. The scatter of tendon elongation results is often greater than the range prescribed by these standards. This usually requires the contractor to re-tension the tendons at huge financial costs. In most cases the results obtained after re-tensioning are the same.
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Mechanical properties of green concrete with Palm Nut Shell as low cost aggregate

  • Authors: Agbenyeku, Emem-Obong Emmanuel , Okonta, Felix Ndubisi
  • Date: 2014
  • Subjects: Sustainable construction , Prestressed concrete construction , Concrete - Testing , Building materials , Palm Nut Shell
  • Type: Article
  • Identifier: uj:5077 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13648
  • Description: The cost saving benefits of aggregate replacement in concrete works are well documented. The utilization of Supplementary Aggregate Materials (SAMs) in concrete engineering without compromising standards in concrete works remain very attractive to both infrastructure developers and design engineers. However, there is continual search for low cost beneficial substitute materials. The mechanical properties of green concrete produced from Palm Nut Shell (PNS) as coarse aggregate was investigated. The abundance of PNS (light weight waste product of palm oil production) in West Africa created the impetus for the study. Series of laboratory tests such as; Slump, Compaction factor, Density, Schmidt hammer and Compressive strength tests were conducted on specimens of 10, 20, 30, 40 and 50% replacements of dry weight of PNS as coarse aggregate and specimens of natural aggregate as control sample. The specimens were cured at relative humidity (RH) of 95-100% and temperature (T) of 22-25oC in a chamber for periods of 7, 14, 21 and 28 days. The results showed the PNS samples to have relatively medium to high workability ranging from 24-47 mm for slump height and values of 0.85 to 0.90 for compaction factors. A general strength development was observed across the different samples with the PNS sample reaching strength of 48.7 N/mm2 at 28 days curing. The 50% replacement specimens which mobilized UCS of 28.7 N/mm2 met the requirement for lightweight concrete however, 30% is the optimum for a partial aggregate replacement in green concrete as UCS of 39.2 N/mm2 was mobilized in 28 days. Thus PNS is a suitable concrete constituent and can be a major cost reduction factor especially in low cost rural projects with streamlined loading requirements.
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Methods for flexural strengthening of reinforced concrete elements using steel plates

  • Authors: Olajumoke, Akinropo Musiliu , Dundu, Morgan
  • Date: 2014
  • Subjects: Concrete beams , Plates, Iron and steel , Reinforced concrete , Flexure
  • Type: Article
  • Identifier: http://ujcontent.uj.ac.za8080/10210/380017 , uj:5078 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13649
  • Description: When reinforced concrete elements are incapable of safely sustaining the anticipated load, flexural strengthening may be necessary. Two major construction methods have been reported in literature for strengthening reinforced concrete (RC) elements in bending. These methods include Externally Bonded Reinforcement (EBR) and Near Surface Mounting (NSM). The aim of this paper is review these methods, including the extensive surface preparation that must be performed on bonded elements. Previous investigations have shown that these techniques are effective in salvaging old and distressed reinforced concrete structures. This paper identifies the problems associated with the utilisation of steel plates as strengthening material for RC elements in EBR and NSM techniques.
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Permeable reactive barriers for acid mine drainage treatment : a review

  • 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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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.
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Potentiodynamic polarization study of the corrosion characteristics of acid mine drainage

  • 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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Preliminary study of strength of coal composites

  • Authors: Moatlhodi, Lerato J. , Okonta, Felix N.
  • Date: 2014
  • Subjects: Columns, Concrete , Composite materials , Pillar failure
  • Type: Article
  • Identifier: uj:5081 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13652
  • Description: Large scale floor convergence and sudden failure of pillars in room-and pillar underground mining have been reported in various countries over many years. Failure of these mines has been attributed, amongst other causes, to the stiffness criterion used by the mining operators and most importantly mine design practices, that tend to reduce the width-to-height ratio i.e. slender pillars in pursuit of greater coal recovery yields, in order to maximize coal recovery in the seam. It is recorded that the room-and-pillar method can leave behind about 40% of the total coal available for mining. The current study seeks to determine the appropriate width-height ratio for coal composite and stabilized coal pillars. Pure coal was mixed with granular soil and stabilized with cement to form cylindrical composite columns which were crushed to determine their unconfined compressive strength at different width-to-height ratios. The strength increased with the increase in W/H of the columns. Increase in coal percentage in a composite reduces the strength. The stabilized coal pillars mobilized less strength than the composite pillars. Based on limited data, relationships amongst column strength W/H and mix ratios were formulated and are proposed for the estimation of strength of mine support structures. More data is however required to formulate a general regression equation.
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Radiological assessment of high density shielding concrete for neutron radiography

  • 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.
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The effects of natural and artificial UV exposure on the physical properties of synthetic turf used for various sports fields

  • Authors: Zuzarte, Adriano Coutinho , Deon, KRUGER
  • Date: 2014
  • Subjects: Ultraviolet radiation , Sports facilities
  • Type: Article
  • Identifier: uj:5061 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13624
  • Description: Since its induction at the Astrodome, in 1965 synthetic turf has been improved and adapted to now be accepted as a playing surface for a variety of sports. These sports include Rugby, Soccer and Field hockey. As synthetic turf is most likely destined for outdoor use it will be subject to Ultra Violet (UV) degradation in the form of Ultra Violet light band A (UVA), Ultra Violet light band B (UVB) or a combination of both. Synthetic turf is a polymer based material, specifically polyethylene for this study. For this reason it is useful to investigate how polyethylene degrades due to UV. Absorbed UV causes a break in the intermolecular bonds of the polyethylene, which leads to cracking, inhibiting the material to perform as initially intended. Colour change is also a consequence of extended exposure to UV. Various UV stabilizers are used, by manufacturers, in order to slow this process down. These however are largely dependent on the type of UV being exposed. Natural UV testing of new materials is time consuming, thus accelerated weathering testers such as the QUV/spray machines are used to simulate artificial UV and accelerate this process. A correlation between natural and artificial UV is sometimes difficult to achieve. For this reason both natural and artificial UV exposures were performed in this study. Through these various exposures to the samples, it was possible to indeed confirm that UV degrades synthetic turf as well as the processes leading to it. It was also confirmed that the samples would meet the sporting standards set out by the Internaltional Rugby Board (IRB), Fédération Internationale de Football Association (FIFA) and International Hockey Federation (FIH), for use as a playing surface. A correlation between natural and artificial UV in terms of colour change was achieved with UVA being found as thepredominant type of natural UV exposure in Johannesburg, during the winter months. Solutions were also provided to mitigate the degrading effects of UV on synthetic turf, these solutions would however need further investigation.
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Thin spray rock liners with different concentrations of nanoclays

  • Authors: Van Tonder, P. , Booysen, C.J , Van Tonder, P
  • Date: 2014
  • Subjects: Nanostructured materials , Polymer-impregnated concrete , Reinforced concrete construction
  • Type: Article
  • Identifier: uj:5080 , ISBN 9781614994657 , ISBN 9781614994664 , http://hdl.handle.net/10210/13651
  • Description: This study investigates the possibility of effectively replacing polymers in thin sprayed liners (TSL’s) with nanoclay particles. In the industry Nano particles are used in many different products to enhance their properties. The strength properties was analysed to see if the addition of nanoclays improve the strengths of the TSL product. Different concentrations of nanoclay were added to a standard TSL mixture in the place of polymer particles. The different composites were tested for Tensile Strength, Compression Strength, Shear Strength and Shear Bond Strength. Though there are other parameters to be tested, the study will only focus on those mentioned above, as they were considered to be the most important. The materials used for testing these characteristics were supplied by Oxyfibre. The mixtures have consisted of four different composites that included the standard mixture, 2% nanoclays, 4% nanoclays and 6% nanoclays.
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