Browsing by Author "Diekmann, Michael Andreas"

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    Developing a low embodied carbon-content concrete with conventional concrete properties
    (Stellenbosch : Stellenbosch University, 2019-04) Diekmann, Michael Andreas; Boshoff, William Peter; Combrinck, Riaan; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: In an ever-developing world, the use of concrete as a construction material, and cement as a main constituent thereof, is at a historical peak and set to increase even further in future. At the same time, the world is confronted with environmental challenges partly due to greenhouse gas emissions, to which the production of cement is a large contributor. In order to decrease the emissions and ensure greater sustainability of the concrete industry, it is therefore critical to reduce the cement content in conventional concrete. This reduction in cement content can however not sacrifice the quality of the concrete, in terms of certain properties that conventional concrete exhibits. It is therefore the main objective of this study to develop a low cement-content concrete, and as such a low embodied carbon-content concrete, with conventional concrete properties. Three approaches of achieving this can be defined. Firstly, cement in concrete can be replaced by more environmentally friendly supplementary cementitious materials (SCM) or fillers. Furthermore, the water requirement of concrete can be reduced in order to achieve a lower cement content by, secondly, using superplasticisers or, thirdly, optimising particle packing. This study establishes reference mixes using the first approach, before separately using the latter two approaches to lower the water requirement of the former mixes at a constant slump and water/binder ratio. The three approaches are finally combined in order to establish what are termed the “optimised” mixes in terms of cement content, with conventional concrete properties being the aim. The concrete properties that all mixes are evaluated for include rheological properties, setting time, compressive strength, permeability as part of durability and the equivalent carbon dioxide (CO2e) emissions. Furthermore, certain indices showing the efficiency of use of cement and the CO2e emissions due to the mixes in terms of compressive strength are determined. It was found that the replacement of various fractions of cement showed a pronounced reduction of CO2e emissions, while resulting in mixes with conventional properties. The inclusion of superplasticisers improved the rheological properties of these mixes and further reduced the emissions of the mix, by significantly reducing the cement content. However, this decreased the compressive strength of the mixes. The optimisation of particle packing improved all the measured properties. The combination of all three approaches resulted in mixes with improved rheological properties, as well as a 40% to 60% decrease in the emissions due to the concrete. The compressive strength was negatively effected and halved compared to the reference mix. However, certain mixes still showed better efficiency indices than the reference mixes, meaning they used less cement and CO2e emissions to develop strength. With regard to cement content, they could indeed be termed the “optimised” mixes.