2. Academic Wits University Research Outputs (All submissions)
Permanent URI for this communityhttps://hdl.handle.net/10539/36826
Browse
10 results
Search Results
Item Undergraduate engineering training through institutional collaboration in the Southern African region.(Higher Education South Africa (HESA)., 2005) Ilemobade, A.A.; Ballim, Y.The University of the Witwatersrand (Wits) and The University of Namibia (UNAM) signed an Agreement of Co-operation (AOC) in 2000. This agreement, which formalised an existing informal collaboration, was primarily targeted at facilitating the transfer of potential Unam undergraduate engineering students to pursue engineering studies at the WITS Faculty of Engineering as well as improving staff collaboration in research and teaching. Students from UNAM's pre-engineering programme and science departments have been beneficiaries of this agreement. Four years later, an evaluation of the collaboration reveals critical issues vis-à-vis decreasing student enrolments, unimpressive student graduation rates, and financial and operational complexities affecting student mobility - all of which have institutional as well as regional implications. This paper presents highlights and pertinent lessons of the collaboration, and recommendations for similar collaboration in the Southern African region both at an institutional and regional level. As a whole, the paper uses the Wits experience to extrapolate principles and strategic issues facing institutions involved in academic collaboration and cross-border movement of students within the Southern Africa region.Item Effectiveness of the fineness of two South African Portland cements for controlling early-age temperature development in concrete.(The South African Institution Of Civil Engineering., 2011) Graham, P.C.; Ballim, Y.; Kazirukanyo, J.B.Temperature gradients due to heat of hydration of cement can cause cracking and present serious structural and serviceability concerns in concrete structures. Engineers use a wide range of strategies to limit the potential for such cracking, mainly by minimising the maximum temperature in the concrete. This paper considers the possibility of using more coarsely ground cement as one of the strategies for reducing the maximum concrete temperature. Two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were tested in an adiabatic calorimeter to determine the heat evolution characteristics. The measured results were then used in a computational model to calculate the temperature profiles likely to occur in two types of concrete elements. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the use of coarse-ground cement as a means of reducing the maximum temperature in concrete is more effective in the case of concrete elements with high cement content but of moderate dimensions. In sections of larger dimension, coarse-ground cements show lower levels of temperature reduction but also lower thermal gradients.Item Reflections on future needs in concrete durability research and development.(CRC Press, Taylor & Francis Group, 2008) Ballim, Y.; Alexander, M.G.; Beushausen, H.D.; Moyo, P.There is no doubt that, over the past two decades, we have made enormous advances in the understanding and practice of concrete durability. Spurred by the often experienced early deterioration of reinforced concrete structures, with high capital investment for repair and rehabilitation, conceptions of design for durability have gained an increasingly higher level of importance in recent years. Durability design is beginning to be considered of equal importance as design for safety and serviceability. Nevertheless, durability concerns remain and early deterioration still attracts much expenditure. This paper is aimed at identifying important developments made in the field of concrete durability during the past two decades. Based on current design practice and current knowledge, future research and development needs are discussed, focusing on the influences of constituent materials, deterioration prevention methods, service life modelling of reinforced concrete structures, and performance-based test methods.Item Reflections on future needs in concrete durability research and development(2012-02-03) Ballim, Y.; Alexander, M.G.; Beushausen, H.D; Moyo, P.There is no doubt that, over the past two decades, we have made enormous advances in the understanding and practice of concrete durability. Spurred by the often experienced early deterioration of reinforced concrete structures, with high capital investment for repair and rehabilitation, conceptions of design for durability have gained an increasingly higher level of importance in recent years.Item Effectiveness of the fi neness of two South African Portland cements for controllingearly-age temperaturedevelopment in concrete(2011-04-01) Graham, P.C.; Ballim, Y.; Kazirukanyo, J.In developing an assessment of the quantum and rate of heat evolution from hydrating cement, an important controllable variable is the fineness of grinding of the cement. This paper presents the results of a project in which two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were subjected to testing in an adiabatic calorimeter to determine the heat evolution characteristics. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the potential benefits of a so-called low heat cement can be lost if the cement is too finely ground. Based on simulations of temperature development using the different cement types tested, the results indicate that the fineness of grinding of cement is a more important parameter in the case of concrete elements with high cement contents but of moderate dimensions. In sections of larger dimension, coarse ground cements show lower levels of temperature development with lower thermal gradients.Item Early-age Thermal Characteristics of Clinker Cements in Relation to Microstructure and Composition: Implications for Temperature Development in Large Concrete Elements(2004) Ballim, Y.; Graham, P.C.This paper presents an assessment of the heat response of nominally similar cement clinkers from a range of cement production facilities in South Africa. Clinker samples were collected at nine cement plants and cements were prepared by grinding each clinker with a uniform quality of gypsum. XRF and optical microscope techniques were then used to characterise each clinker and cement in terms of chemical composition and cement compound morphology.Item A Maturity Approach to the Rate of Heat Evolution in Concrete(2003-06-03) Ballim, Y.; Graham, P.C.This paper discusses the use of the concept of maturity as a means of combining the effects of time and temperature in describing the rate of heat evolution from hydrating cement in concrete. The proposed maturity approach allows the rate of heat evolution determined from an adiabatic test to be expressed in a form which is independent of the starting temperature of the test. This relationship can then be directly used in a time-temperature prediction model which requires a solution of the Fourier equation for heat flow.Item A maturity approach to the rate of heat evolution in concreate(2003-06-03) Ballim, Y.; Graham, P.C.Item Modelling the cooling of concreate by piped water(2009-03-25) Myers, T.G.; Fowkes, N.D.; Ballim, Y.Piped water is used to remove hydration heat from concrete blocks during construction. In this paper we develop an approximate model for this process. The problem reduces to solving a one-dimensional heat equation in the concrete, coupled with a first order differential equation for the water temperature. Numerical results are presented and the effect of varying model parameters shown. An analytical solution is also provided for a steady-state constant heat generation model. This helps highlight the dependence on certain parameters and can therefore provide an aid in the design of cooling systems.Item Modelling the cooling of concrete by piped water(2009-03-25) Myers, T.G.; Fowkes, N.D.; Ballim, Y.The chemical reaction can lead to temperature rises in excess of 50 K and it can take a number of years before the concrete cools to the ambient temperature. Prior to construction of the Hoover dam engineers at the U.S. Bureau of Reclamation estimated that if the dam were built in a single continuous pour the concrete would require 125 years to cool to the ambient temperature and that the resulting stresses would have caused the dam to crack and fail (U.S. Bureau of Reclamation 2005).