School of Civil and Environmental Engineering

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Browsing School of Civil and Environmental Engineering by Department "Civil Engineering"

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    Assessment of two cone penetration test based methods for evaluating the liquefaction potential of tailings dams.
    (2013-06-12) Torres Cruz, Luis Alberto
    The stability of tailings dams is of great importance to the mining industry. It is well known that soil liquefaction is one of the mechanisms that can compromise the stability of such structures. Given the difficulty of extracting undisturbed samples of any cohesionless material, the use of in situ tests to assess liquefaction potential has been intensely researched. The purpose of this work was to assess the applicability to tailings dams of two CPT-based liquefaction assessment methodologies, namely, the Robertsonbased and the Olson and Stark methodologies. Ten case histories were evaluated. When considering triggering of liquefaction, the Robertson-based and Olson and Stark methodologies correctly predicted the behaviour of four out of five and seven out of ten case histories, respectively. When considering the onset of flow failure, the Olson and Stark methodology correctly predicted the behaviour in four of seven case histories for which a post-triggering analysis was made. The results are useful in understanding the shortcomings of implementing these methodologies on TSFs and the limits of their predictive power.
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    Deterioration Presentation
    (2012-01-30) Ballim, Y
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    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.
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    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.
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    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.
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    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.
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    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).
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    Opening Address to the 2nd International Conference on Concrete Repair, Rehabilitation and Retrofitting. Cape Town 24 November 2008.
    (2004-11-24) Ballim, Yunus
    Most people, whether consciously or unconsciously, are attracted to what I shall call, the “great human narrative” of transformation through journey. We find the narrative attractive because it appears prominently - as a leitmotif - in much of the way in which we construct our religious and cultural understandings of ourselves. The journey narrative speaks strongly to our sense of identity - both as belonging to a group (tribe, nation, human, etc) but also as individual (adult, academic, gardener, etc). We recognise these identities as having been formed through difficult intellectual, spiritual and often, physical journey. Importantly, we think of the personal as well as the shared journey as a process towards a better understanding of complexity – towards a more enlightened view of the world and our place in it.
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    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.