Browsing by Author "Bester, Hermanus Lambertus"

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    Generic model for predicting the performance of macro-synthetic fibre reinforced concrete for industrial flooring applications
    (Stellenbosch : Stellenbosch University, 2017-03) Bester, Hermanus Lambertus; Boshoff, William Peter; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The versatility and ready availability of concrete has ensured that this material will continue to be one of great and increasing importance for all types of construction (Domone, 2010). Due to its low tensile strength in comparison with its compressive strength, unreinforced concrete suffers from brittle failure in uni-axial or flexural tension. This drawback can be compensated for by the addition of fibres to the concrete in its fresh state to provide ductility to the brittle concrete matrix. The primary objective of this study is to create generic models which can be implemented to predict the post-cracking performance of Macro-Synthetic Fibre Reinforced Concrete (MSFRC), specifically for industrial flooring applications. To develop the generic models, an extensive background study on FRC is conducted to identify possible factors influencing the performance of MSFRC. Concrete compressive strength, coarse aggregate size, coarse aggregate volume, fibre dosage, and mixing time of MSFRC in its fresh state are identified as the possible influencing factors. Research hypotheses are stated and investigated to determine which of the factors identified have a significant influence on the post-cracking performance of MSFRC, specifically for an experimental macro-synthetic fibre supplied by CHRYSO. Generic linear models are derived to predict the residual flexural tensile strength of MSFRC at specific crack mouth opening displacements (CMOD) and are based on the macro-mechanical tests performed according to EN 14651 (European Norms, 2007). It is concluded that fibre dosage is the only identified factor indicating a significant influence on the residual flexural strength of MSFRC. It is also concluded that the limit of proportionality (LOP), which corresponds to the maximum stress between a CMOD of 0 − 0.05 mm, is only influenced by the compressive strength. Single-fibre pull-out tests (SFPOT) are performed to investigate the effect of compressive strength on the single-fibre performance of the CHRYSO macro-synthetic experimental fibre in its virgin and premixed fibre state. An increase in the performance is evident for the premixed fibres and can be attributed to the mixing process, causing a roughening of the fibre surface and ultimately increasing the fibre-matrix bond characteristics. It is established that compressive strength does not affect the single-fibre performance of the fibre in its virgin state. However, an increase in the performance of the premixed fibres is evident for a decrease in compressive strength, with the explanation of this phenomenon being unclear. Simple- and multiple regression analyses are performed to statistically identify the factors that have a significant effect on the performance of MSFRC and to derive linear models predicting the performance parameters. The regression analyses are based on the obtained macro-mechanical results. As from the visual inspection of the macro-mechanical results, the regression analyses concluded that fibre dosage is the only factor that has a significant effect on the residual flexural tensile strength of MSFRC, and compressive strength as the only factor that influences the LOP. Therefore, the models predicting the performance parameters associated with the residual flexural strength of MSFRC are based on the influence of fibre dosage, and the model predicting the LOP is based on the effect of compressive strength. The models can further be refined with additional experimental data, incorporating a Model Factor (MF) that takes account of additional variation experienced in the construction industry and determining partial material factors (m) to derive suitable design values.