Lerch, Jean Oliver (2016-03)
ENGLISH ABSTRACT: Unreinforced concrete has the inherent shortcomings of low tensile strength and low strain capacity at fracture (ACI Committee 544, 2002). In order to overcome these shortcomings, fibres can be added to the fresh concrete with the aim to introduce ductility to the brittle concrete matrix. Synthetic fibre reinforced concrete (FRC) gained popularity over the past years (Bolat et al., 2014), finding its primary application in ground supported slabs. The purpose of this research is to improve the general understanding of macro synthetic FRC on the single-fibre and the macro-mechanical level. Special attention is given to fibres with various geometric properties such as fibre length, profile and fibre shape. Single-fibre pull-out (SFPO) experiments have been conducted on macro synthetic fibres with various embedment lengths. Fibres were premixed prior to embedment into the fresh concrete paste matrix to investigate in-service conditions. The effect of premixing was especially noted for flat fibres, indicating an increase in interfacial bond exceeding 100 % in contrast to virgin unmixed fibres, depending on the embedment length. Embossed fibre profiling proved to be the most efficient fibre geometry, providing the highest interfacial bond with the surrounding paste matrix. It is generally accepted that a high interfacial bond is a good indication for the overall performance required in typical macro synthetic FRC applications. Additionally, time dependent pull-out (TDPO) experiments have been conducted on single embedded fibres. It was found that premixing has a significant influence on the TDPO performance, withstanding sustained loads considerably longer than unmixed fibres. Embossed fibre geometries revealed substantial resistance against sustained loads, undergoing very little displacement, being representative for small time dependent crack openings in contrast to non-embossed fibre geometries. Non-embossed fibre geometries typically exhibited considerable pull-out displacement, demonstrative for large crack openings. Small time dependent crack opening is a property desired when structural soundness is required. Macro-mechanical tests were performed in order to establish parameters required in the structural design aspect of synthetic FRC, as these type of tests represent the in-service conditions of macro synthetic FRC. It was found that the embossed fibre profile indicated the highest performance followed by that of the flat fibre type. Robust macro-mechanical performance is required for the development of economic macro synthetic FRC elements and a reduced eco-footprint. In addition, macro-mechanical experiments have been conducted on macro synthetic FRC subjected to prolonged mixing times. It has been established that prolonged mixing typically decreases the post-cracking performance of macro synthetic FRC. Therefore, mixing time has a significant influence on the structural performance of macro synthetic FRC. It has been recognised that the best overall structural performance is achieved by embossed fibre geometries. In addition, the mixing stage was found to have a significant influence on the fibre performance in the hardened state, especially for flat fibres. Depending on the type of macro synthetic FRC application, longer fibre lengths are required for higher levels of deformation, while shorter fibre lengths revealed adequate performance for lower levels of deformation. Furthermore, TDPO experiments revealed concerning behaviour of nonembossed polypropylene macro synthetic fibres.
AFRIKAANSE OPSOMMING: Ongewapende beton het die inherente tekortkominge van lae treksterkte en lae vervormingsvermoë met breking (ACI Committee 544, 2002). Om hierdie tekortkominge te oorbrug, kan vesels by die vars beton gevoeg word met die doel om die bros betonmengsel meer rekbaar te maak. Die gewildheid van sintetiese vesel-versterkte beton (VVB) het oor die afgelope jare toegeneem (Bolat et al., 2014), met die vernaamste toepassing in grondondersteunde blaaie. Die doel van hierdie navorsing was om algemene begrip van makrosintetiese VVB op die enkelvesel- en die makromeganiese vlak te verbeter. Spesiale aandag is geskenk aan vesels met verskillende geometriese eienskappe, soos vesellengte, profiel en veselvorm. Enkelvesel-uittrek-eksperimente is uitgevoer op makrosintetiese vesels met verskillende vasleggingslengtes. Vesels is gemeng voor vaslegging in die vars betonbrymatriks om indiens-toestande te ondersoek. Die uitwerking van voorafvermenging is veral gemerk by plat vesels, wat ŉ toename in tweevlak-binding van meer as 100 % getoon het in vergelyking met suiwer onvermengde vesels, na gelang van die vasleggingslengte. Gebosseleerde veselprofilering het geblyk die doeltreffendste veselgeometrie te wees, en het die hoogste tussenvlak-binding met die omliggende brymatriks getoon. Daar word algemeen aanvaar dat ŉ hoë tussenvlak-binding ŉ goeie aanduiding is van die algehele verrigting wat vereis word in tipiese makrosintetiese VVB-toepassings. Hierbenewens is tydafhanklike uittrek-eksperimente op enkelvasgelegde vesels uitgevoer. Daar is bevind dat voorafvermenging ŉ aanmerklike invloed op die tydafhanklike uittrekverrigting het, en dat volgehoue ladings aansienlik langer as onvermengde vesels weerstaan is. Gebosseleerdevesel-geometrieë het aanmerklike weerstand teen volgehoue ladings getoon, en het min verplasing ondergaan, wat erteenwoordigend is van klein tydafhanklike kraakopeninge in teenstelling met niegebosseleerdevesel-geometrieë. egebosseleerdeveselgeometrieë het tipies aanmerklike uittrek-verplasing getoon, met groot kraakopeninge. ŉ Klein tydafhanklike kraakopening is ŉ wenslike eienskap wanneer strukturele treksterkte vereis word. Makromeganiese toetse is uitgevoer om parameters te bepaal wat vereis word vir die strukturele ontwerpaspek van sintetiese VVB, aangesien hierdie soort toetse die indienstoestande van makrosintetiese VVB verteenwoordig. Daar is gevind dat die gebosseleerdevesel-profiel die hoogste verrigting toon, gevolg deur dié van die platvesel-tipe. Robuuste makromeganiese verrigting is nodig vir die ontwikkeling van ekonomiese makrosintetiese VVB-elemente en ŉ verminderde eko-voetspoor. Makromeganiese eksperimente is ook uitgevoer op makrosintetiese VVB wat aan verlengde mengtye blootgestel is. Daar is bevind dat verlengde vermenging tipies die nákrakingsverrigting van makrosintetiese VVB verlaag. Die mengtyd het dus ŉ aanmerklike invloed op die strukturele verrigting van makrosintetiese VVB. Daar is gevind dat die beste algehele strukturele verrigting deur gebosseleerdeveselgeometrieë verkry is. Hierbenewens is gevind dat die mengfase ŉ aanmerklike invloed op die veselverrrigting in die verharde toestand het, veral vir plat vesels. Na gelang van die soort makrosintetiese VVB-toepassing, is langer vesellengtes nodig vir hoër vlakke vervorming, terwyl korter vesellengtes genoegsame verrigting vir laer vlakke vervorming getoon het. Voorts het tydafhanklike uittrek-eksperimente kommerwekkende gedrag van niegebosseleerde polipropileen- makrosintetiese vesels getoon.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98649