Browsing by Author "Boshoff, William Peter"

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    Evaluation of locally available synthetic macro fibres in a single-fibre pullout test in concrete
    (South African Institution of Civil Engineering, 2018-03) Odendaal, C. M.; Babafemi, A. J.; Combrinck, R.; De Villiers, W. I.; Boshoff, William Peter
    ENGLISH ABSTRACT: There is increasing use of synthetic macro fibres in concrete applications. However, the performance of these fibres varies, based on various factors. This study investigates the fibre/ matrix interface performance of four types of synthetic macro fibres locally available in the South African construction market. The influence of water-cement ratio (w/c), fibre embedment length, fibre properties and fibre snubbing angle on the single-fibre pull-out behaviour is studied in this paper. The influence of some of these properties on the compressive strength is also evaluated. Three mix designs and four fibre types were used for the investigation. All tests were performed in a controlled climate room. Specimens with single fibres were tested in a Universal Testing Machine. Scanning Electron Microscope (SEM) images of pulled out fibres were examined for inferences. The results have shown that w/c has no influence on the pull-out load of synthetic macro fibres. However, the pull-out load increases with increase in fibre embedment length and equivalent fibre diameter. Pull-out load increases for flat fibres bent along their strong axis as the fibre snubbing angle increases. While crimped fibres with improved geometry show optimum pull-out performance when pulled out perpendicularly to the crack plane, flat fibres performed better at the snubbing angles tested. SEM images also show more surface damage on fibres with irregular geometry.
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    Time-dependant behaviour of engineered cement-based composites
    (Stellenbosch : University of Stellenbosch, 2007-03) Boshoff, William Peter; Van Zijl, G. P. A. G.; University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering.
    ECC (Engineered Cement-based Composites) is a type of HPC (High Performance Concrete) that was engineered to overcome the weaknesses of ordinary concrete. It shows high ductility as it can resist the full tensile load at a strain of more than 3 %. This superior response is achieved with multiple cracking under tensile loading which has a pseudo strain hardening phenomenon as result. The purpose of the research project reported in this dissertation is to investigate and characterise the time-dependant behaviour of ECC and create a constitutive model to numerically simulate the static and time-dependant behaviour of ECC. To investigate the time-dependant behaviour experimentally, rate and creep tests were done on the meso- and macro-level while rate tests were done on the structurallevel. The meso-level was represented by the pull-out testing of fibres embedded in the cement-based matrix and direct tensile tests were done for the macro-level. Flexural tests on thin beams were done to simulate the structural-level. Strong time-dependant behaviour was found on all three these levels. On the meso-level, the most prominent finding is that the failure mechanism can change with a change of strain rate, i.e. fibre pull-out at a low pull-out rate, while with a high pullout rate, fibre rupture can occur. Even though the strength of a tensile specimen on the macro-level showed a dependence on the strain rate, the ductility remained constant over four orders of magnitude of the strain rate. On the structural-level, however, a reduction of the flexural ductility was found with an increase of the ...