Faculty of Engineering and the Built Environment (Research Outputs)

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Start date: 2014Subject: search.filters.subject.SDG-17: Partnerships for the goals

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    Minimising the risk of thermally induced cracking in mass concrete structures through suitable materials selection and processing
    (Springer, 2018) Ballim, Yunus
    The hydration of cement is an exothermic reaction which generates around 300 kJ/kg of cement hydrated. In mass concrete structures such as dams and large foundations, this heat of hydration causes a significant rise in temperature in the internal sections of the concrete. If thermal gradients between the internal sections and the near-surface zone of the concrete element are sufficiently large, the thermal stress can cause cracking of the concrete. This cracking may cause functional or structural problems in the operation of the structure. In order to minimise the potential for such cracking, it is necessary to minimise the rate and amount of heat that is evolved, particularly during the early period of the hydration process. This can be achieved by design engineers and concrete technologists through judicious selection and processing of concrete-making materials. This paper presents the observations and results obtained over a number of years from adiabatic testing of concretes, computational modelling of temperature development in large concrete structures and direct temperature measurements in actual structures, with a view to understanding the effects of concrete-making materials on temperature development in concrete. The paper considers the effects of different types of rock aggregates, different types of Portland cement, fineness of grinding of the cement, the addition of supplementary cementitious materials and variations in the concrete starting temperature on temperature development in a large concrete element over time. The results indicate that using a coarser ground cement, adding significant amounts of supplementary cementitious materials and cooling the concrete mixture before placing has a more significant effect in reducing the risk of cracking than varying the aggregate type of the Portland cement type.
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    Making a Mark: Wits School of Construction Economics and Management and Its Contribution to the Construction and Property Fields
    (University of the Witwatersrand, Johannesburg, 2024) Laryea, Samuel; Smit-Stachowski, Alexandra; Mphuti, Bongi
    This book is a historical account on the Wits School of Construction Economics and Management, its contributions and impact in society, which is very significant and leaves a positive impression of academic and industry development, despite historical hurdles. It looks at the past, present, and future of the School in the broader context of South African history and the overall development of the university. The process of writing this book has been both challenging and exciting with interesting discoveries about the academic disciplines and the growth trajectory of the School. It was challenging uncovering information from various sources within the university and external sources. It has also been an interesting process learning about the rich history and contributions of a key School within the university to the South African and global society. This book chronicles the careers of some graduates of the School who served in the highest leadership and management roles, and made an indelible mark in the construction industry locally and internationally. The School’s graduates have made substantial contributions to the growth and advancement of the South African construction and property sectors and their respective statutory councils including the South African Council for Quantity Surveying Profession (SACQSP), South African Council for Project and Construction Management Professions (SACPCMP) and the South African Council for the Property Valuers Profession (SACPVP). The School’s graduates have also played leading roles in major construction firms that have built some of the iconic buildings in South Africa and other parts of the world. In recent years, many of the School’s graduates are increasingly being recruited by firms in Europe, Middle East, Australia, and the US, indicating the quality of their education and their value to employers and the global construction industry.
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    Time and frequency nexus among public debt, exchange rate, inflation, monetary policy rate and economic growth in Ghana
    (Elsevier, 2025-01) Owusu Junior, Peterson; Odoom, Absalom; Adu-Asare Idun, Anthony; Akorsu, Patrick Kwashie
    The debate about the influence of public debt on an economy has gained long-standing attention among policy-makers, regulators and academic scholars. The excessive expansion of Ghana’s public debt to GDP demands a fresh insight into the macroeconomic variables that are connected to economic growth. This study utilised wavelet techniques to investigate the nexus and effect of public debt, exchange rate, inflation rate, and monetary policy rate on economic growth in Ghana using monthly data from 2000 to 2022. Diks and Panchenko (2006) was used as a battery test for the wavelet results. We found a significant negative correlation between public debt and GDP at both short- and long-term frequencies, though there was no notable connection in the medium term. The causality analysis suggests a possibility of bidirectional causality between GDP and public debt in both the short and medium term. Interestingly, the COVID-19 pandemic had minimal impact on this relationship when comparing the pre-pandemic and during-pandemic periods. The only observed coherence (negative) between monetary policy and GDP occurred between 2000 and 2003, at low and medium frequencies. The WMCC results depicted that no variable was seen to lead or lag during the pandemic period however, GDP (exchange rate) reacted to shocks first (last) in the short run (long run) prior to the pandemic. The result of this research is crucial for policy implementation. The GDP-public debt negative nexus offers strong evidence for the government to make determined efforts to reduce external borrowing. The positive coherence of exchange rates and the public debt offers a strong incentive to the monetary authorities to make determined efforts to stop the rapid rise of exchange rates.
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    In vitro Evaluation of Porous borosilicate, borophosphate and phosphate Bioactive Glasses Scaffolds fabricated using Foaming Agent for Bone Regeneration
    (Nature Research, 2018) Erasmus, E. P.; Sule, R.; Johnson, O. T.; Massera, J.; Sigalas, I.
    In this work, glasses within the borosilicate borophosphate and phosphate family were sintered into 3D porous scaffolds using 60 and 70 vol. % NH4(HCO3) as a foaming agent. All scaffolds produced remained amorphous; apart from one third of the glasses which crystallized. All produced scaffolds had porosity >50% and interconnected pores in the range of 250–570 μm; as evidenced by μCT. The in-vitro dissolution of the scaffolds in SBF and changes in compression were assessed as a function of immersion time. The pH of the solution containing the borosilicate scaffolds increased due to the typical noncongruent dissolution of this glass family. Borophosphate and phosphate scaffolds induced a decrease in pH upon dissolution attributed to the congruent dissolution of those materials and the large release of phosphate within the media. As prepared, scaffolds showed compressive strength of 1.29 ± 0.21, 1.56 ± 0.63, 3.63 ± 0.69 MPa for the borosilicate, borophosphate and phosphate samples sintered with 60 vol. % NH4 (HCO3), respectively. Evidence of hydroxyapatite precipitation on the borosilicate glass scaffolds was shown by SEM/EDS, XRD and ICP-OES analysis. The borophosphate scaffolds remained stable upon dissolution. The phosphate scaffolds were fully crystallized, leading to very large release of phosphate in the media.