Civil Engineering

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Now showing 1 - 5 of 11
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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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    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.
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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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    Deterioration Presentation
    (2012-01-30) Ballim, Y