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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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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Factors influencing a building-material company brand
- Authors: Dangers, Allin R.
- Date: 2012-06-04
- Subjects: Brand loyalty , Facebrick industry , Building materials , Corobrik
- Type: Thesis
- Identifier: uj:2365 , http://hdl.handle.net/10210/4820
- Description: M.Tech. , The following study is concerned with the factors influencing brand loyalty in the facebrick industry. It focuses on what has made other brands successful and what Corobrik has to do to develop the same level of brand loyalty. This study is a journey which incorporates a literature review of branding and what branding means to a company, as well as interviews which showcase areas where Corobrik need to improve to reach the same level of brand loyalty that exceptionally successful brands, such as Coca Cola, Mercedes Benz and BMW enjoy.
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Analysis of elongation variance of tendons using stress-strain graphs
- Authors: Dundu, Morgan , Rupieper, Sebastian
- Date: 2014
- Subjects: South African Design Standards , Tendons (Prestressed concrete) , Bonded tendons , Building materials
- Type: Article
- Identifier: uj:5079 , http://hdl.handle.net/10210/13650
- Description: The South African design standards (SANS 2001-CC1 and COLTO) prescribes an elongation variation limit of ±6% and an average variation limit of ±3%. Most often these limits are exceeded in practice. If the elongation variation of a tendon falls outside the prescribed elongation limits it must be assessed by the engineer. This paper analyses data of bonded tendons from post-tensioned structures. The aim of this study is to explain the elongation variance of tendons in post-tensioned structures using selected stress-strain graphs. These structures include a reservoir (Mthatha 1-10) and a viaduct (Gautrain Jean Avenue P80).
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