Research Outputs (Civil and Environmental Engineering)
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Browsing Research Outputs (Civil and Environmental Engineering) by Author "Graham, P.C."
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Item Early-age heat evolution of clinker cements in relation to microstructure and composition: Implications for temperature development in large concrete elements.(Elsevier, 2004) Ballim, Y.; Graham, P.C.This paper presents an assessment of the range and extent of variation of heat evolution 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. X-ray fluorescence and optical microscope techniques were then used to characterise each clinker and cement in terms of chemical composition and cement compound morphology. Concretes were then prepared with the laboratory-manufactured cements and these were tested in an adiabatic calorimeter in order to determine the rate of heat evolution from each of the clinker samples. The results of these tests were related to the chemical and morphological characteristics of the corresponding cement clinkers. The results indicate a clear differentiation of clinker cements into low, medium and high heat cements. The relationships between this classification of the heat performance of the cements and the chemistry and morphology of the clinker is not clear at this stage. However, using a finite difference heat model, the paper presents an indication of the implications of the measured heat characteristics of the cement for early-age temperature distributions in large concrete elements.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 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 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 The effects of supplementary cementing materials in modifying the heat of hydration of concrete.(Springer, 2009) Ballim, Y.; Graham, P.C.This paper is intended to provide guidance on the form and extent to which supplementary cementing materials, in combination with Portland cement, modifies the rate of heat evolution during the early stages of hydration in concrete. In this investigation, concretes were prepared with fly ash, condensed silica fume and ground granulated blastfurnace slag, blended with Portland cement in proportions ranging from 5% to 80%. These concretes were subjected to heat of hydration tests under adiabatic conditions and the results were used to assess and quantify the effects of the supplementary cementing materials in altering the heat rate profiles of concrete. The paper also proposes a simplified mathematical form of the heat rate curve for blended cement binders in concrete to allow a design stage assessment of the likely early-age time–temperature profiles in large concrete structures. Such an assessment would be essential in the case of concrete structures where the potential for thermally induced cracking is of concern.Item A maturity approach to the rate of heat evolution in concreate(2003-06-03) Ballim, Y.; Graham, P.C.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 concrete.(ICE Publishing, 2003) 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 that requires a solution of the Fourier equation for heat flow. The results of an experimental study aimed at assessing the suitability of both the Arrhenius and Nurse-Saul maturity relationships is also presented. Three adiabatic calorimeter tests were conducted on each of two concrete mixtures but starting at different temperatures. The results confirm the suitability of this approach and indicate that, of the two maturity relationships assessed, the Arrhenius maturity relationship is the more suitable in this application.