Thesis (MScEng)-- Stellenbosch University, 2013. / ENGLISH ABSTRACT: Macro synthetic fibre reinforced concrete (SynFRC) is a relatively new concrete for the purpose of
being used in structural elements which only require minimum reinforcement and are supported
continuously by sub-layers. One structural element that is of particular interest is slabs-on-grade
which is supported by a subgrade/sub-base and requires minimum reinforcement to control the
shrinkage strains which may result in cracking.
The aim of this project is to investigate the potential use of macro SynFRC in the application of
controlling drying shrinkage cracking (DSC) in concrete slabs-on-grade. The focus is on the use of
concrete slabs-on-grade that is intended for industrial floors.
The SynFRC material parameters of interest were characterised first with the aid of various
experimental tests. These are: flexural tests, compression tests, friction tests between the SynFRC and
wooden surfaces used for full scale testing, and the shrinkage of the concrete.
Next the post-cracking tensile behaviour of the SynFRC was determined by way of an inverse
analysis. These tensile responses were subsequently used to perform a series of different finite
element analyses. These analyses were performed on specific slabs-on-grade to determine the effects
of the added tensile behaviour of the SynFRC on the DSC.
The results obtained concerned: the spacing of cracks, the maximum and average crack width, and the
difference in crack width between the normal concrete (NC) and the SynFRC. These changes take
place in accordance to the concrete age. From the analyses it was determined that the addition of
fibres gives the concrete a ductility that allows the concrete to crack more than NC, yet does not allow
the cracks to propagate. This applies to low fibre contents of less than 0.4% by volume and a slab
thickness of 200mm, as well as to fibre contents that have Re,3 values of 0.51 and higher. Moreover, it
results in improvements seen when adding fibres if the friction is sticky, meaning when the maximum
friction between the slab and the subgrade is reached with a very small amount of movement. With a
stickier friction though smaller crack widths occur within both the NC and the SynFRC. / AFRIKAANSE OPSOMMING: Makro sintetiese vesel versterkte beton (SynFRC) is 'n relatiewe nuwe beton. Dit het ten doel om
gebruik te word in strukturele elemente wat minimale versterking benodig en wat deurlopend deur
sublae ondersteun word. Een spesifieke strukturele element van belang is grondvloere wat deur 'n
sublaag ondersteun word en wat minimale ondersteuning benodig om die krimping vervorming te
beheer wat moontlike krake kan veroorsaak.
Die doel van die projek was om die potensiële gebruik van makro sintetiese vesels te ondersoek
tydens die beheer van die uitdroog krimp kraking van 'n beton grondvloer. Die fokus was op die
gebruik van betonvloere vir fabrieksdoeleindes.
Die eienskappe van SynFRC materiale is vooraf vasgestel vir die doel van verskeie eksperimentele
toetse. Hierdie toetse sluit in buigbaarheidstoetse, druktoetse, krimping van beton en toets van
wrywing tussen die SynFRC en hout oppervlaktes wat gebruik is vir volskaalse toets.
Die trek gedrag van SynFRC na kraking is vasgestel deur inverse analise. Hierdie trek gedrag is dan
gebruik om 'n reeks eindige element analises uit te voer. Hierdie analises is uitgevoer op spesifieke
grondvloere om die effek te bepaal van verhoogde trek gedrag van SynFRC op die uitdroog krimp
kraking.
Volgens die uitslae sodoende verkry was die kraakspasiëring, die maksimum en gemiddelde
kraakwydte en die verskil in die kraakwydte tussen normale beton en die SynFRC as ‘n funksie van
beton oudedom. Vanuit die analises het dit duidelik geblyk dat die byvoeging van vesels die beton se
smeebaarheid verhoog het en dit het tot gevolg gehad dat die beton meer krake vorm, maar dat die
krake nie vergroot nie. Dit is waargeneem by 'n lae vesel inhoud van minder as 0.4% per volume en 'n
betonblad met 'n dikte van 200mm. Dit is ook waargeneem by 'n hoër vesel volume wat Re,3 waardes
van 0.51 en hoër het. Kleiner kraakwydte is waargeneem waar vesel volume verhoog is indien die
wrywing hoër is, bedoelende dat die maksimum wrywing tussen die betonblad en die sublaag bereik
is met baie min beweging. Daar het wel kleiner kraakwydtes in beide die normale beton en die
SynFRC voorgekom waar daar hoër wrywing was.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/85696 |
| Date | 12 1900 |
| Creators | Van der Westhuizen, Daniel Erasmus |
| Contributors | Boshoff, W. P., Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xvi, 141 p. : ill. |
| Rights | Stellenbosch University |
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