Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2009. / ENGLISH ABSTRACT: Strain Hardening Cement-based Composite (SHCC) is part of the High Performance Fibre
Reinforced Cement-based Composite (HPFRCC) family and is a relative new concrete
composite. This Fibre Reinforced Cement-based Composite (FRCC) contains randomly
distributed short fibres and when subjected to a uni-axial tensile load multiple cracking
occurs. The multiple cracking generates fine cracks which are normally smaller than 100
μm and achieve a strain capacity of more than 5 %. There are limited publications
regarding the research of sustained tensile tests on SHCC and especially the cracking
behaviour of SHCC under quasi-static uni-axial as well as sustained tensile loads.
The cracking behaviour is described as the average crack width, number of cracks and
descriptive statistical properties which could be used to represent the distribution of the
multiple fine cracks under uni-axial tension. There are two types of tests that were under
consideration to determine the cracking behaviour of SHCC. The first is quasi-static uniaxial
tensile tests and the second is sustained tensile tests. The latter was dependant on the
uni-axial tensile tests in terms of the sustained load applied. The sustained loads ranged
from 40 % to 80 % of the ultimate tensile resistance recorded from the uni-axial tensile
tests that correspond with a strain rate of 0.001 /s. Different strain rates were used for the
uni-axial tensile tests to determine the effect on the cracking behaviour. The cracking
behaviour was determined with the aid of a non-contact optical 3D digital deformation
measuring device called ARAMIS.
The content of this thesis gives a background study of the cracking behaviour and relevant
research performed on SHCC under certain loads as well as some literature about the timedependant
effects of a cement-based composite.
The functioning of the device called ARAMIS is explained as well as the resulting effects
of this device on the preparation of the test specimens. The experimental framework for the
uni-axial and sustained tensile tests is discussed. Thereafter, the experimental results of the tests are depicted and discussed. The results shed
some light on the basic material properties such as the average ultimate stress and average
ultimate strain, Young’s modulus, etc. for the quasi-static tensile tests as well as shrinkage
and creep of SHCC. The cracking behaviour such as the average crack width, number of
cracks, the variance and skewness of the distribution of the crack widths in the test
specimens for the quasi-static uni-axial and sustained tensile tests are depicted and
discussed.
The cracking behaviour when subjected to uni-axial tensile tests with different strain rates
is significantly governed by the formation of new cracks and the average crack width
remains small with increase in strain. There is no significant difference for the cracking
behaviour found when subjected to different strain rates. However, when SHCC is
subjected to a sustained load then the average crack width is dependant on the number of
cracks that form over time as well as the load level. The formation of fewer and wider
cracks was observed for specimens loaded at average 40 % of the ultimate tensile resistance
stress, however at loading percentages of higher than 65 % more cracks developed which
resulted in a smaller average crack width. / AFRIKAANSE OPSOMMING: Vervorming Verharding Sement gebaseerde samestelling “Strain Hardening Cement-based
Composite” (SHCC) is deel van die familie van “High Performance Fibre Reinforced
Cement-based Composite” (HPFRCC) en is ʼn relatiewe nuwe beton samestelling. Hierdie
vesel versterkte sement gebaseerde beton bevat willekeurig verspreide kort vesels en
veelvoudige klein krake vorm onder monotoniese trekkragte. Hierdie veelvoudige klein
krake is minder as 100 μm wyd en lei tot ʼn vervorming van meer as 5 %. Daar is ʼn tekort
aan navorsing oor die kruip van SHCC sowel as die kraak gedrag van hierdie sement
gebaseerde samestelling onderhewig aan trek.
Die kraak gedrag word beskryf as die gemiddelde kraakwydte, aantal krake en ʼn paar
beskrywende statistiese parameters. Hierdie kraak gedrag parameters kan gebruik word om
ʼn verdeling te kan weergee van die veelvoudige klein krake onder ʼn trek belasting. Twee
tipes toetse was uitgevoer om die kraak gedrag te beskryf. Die eerste tipe toets was
monotoniese trek toetse en die tweede tipe was kruip toetse. Die tweede toets was afhanklik
van die monotoniese trek toetse in terme van die belasting wat gebruik was vir die kruip
toetse. Die belasting was gevarieer vanaf 40 % tot 80 % van die breekbelasting wat bepaal
is met die monotoniese trektoetse wat ooreenstem met ʼn vervorming tempo van 0.001 /s.
Verskillende vervorming tempo’s vir die monotoniese trektoetse was uitgevoer om te
bepaal wat die effek is op die kraak gedrag. Die kraak gedrag was bepaal met behulp van ʼn
geen-kontak optiese 3D digitale deformasie meet instrument genoem ARAMIS.
Die inhoud van die tesis bevat ʼn kort opsoming oor ʼn agtergrond studie van die kraak
gedrag en relevante navorsing oor vesel versterkte sement gebaseerde beton, sowel as
literatuur oor die tydafhanklike effekte van ʼn sement gebaseerde samestelling.
Die beheer en gebruik van die meet instrument ARAMIS word verduidelik, sowel as die
effek van hierdie masjien op die voorbereiding vir die eksperimente. Die eksperimentele
uiteensetting vir die monotoniese en kruip toetse word beskryf. Daarvolgens is die resultate van die eksperimentele toetse getoon en verduidelik. Die
resultate verduidelik die basiese materiaal eienskappe, byvoorbeeld die gemiddelde
breekspanning met die ooreenkomstige breekvervorming, Young’s modulus en so voorts
vir die monotoniese trektoetse, sowel as eienskappe met betrekking tot krimp en kruip van
SHCC. Die kraak gedrag naamlik die gemiddelde kraakwydte, aantal krake per meter,
variansie en die skuinsheid van die ontwikkelde krake met die toets proefstukke vir die
monotoniese en kruip trek toetse word weergegee en verduidelik.
Die kraak gedrag van SHCC wanneer getoets word met verskillende monotoniese trektoets
tempo’s word beheer deur die ontwikkeling van nuwe krake en die gemiddelde kraakwydte
is beduidend laag met toenemende vervorming. Daar is geen beduidende verskil in die
kraak gedrag ten opsigte van die verskillende monotoniese trek tempo’s nie. In teendeel,
wanneer SHCC belas word met ʼn konstante las oor tyd word die gemiddelde kraakwydte
beheer deur die ontwikkeling van nuwe krake sowel as die belasting wat aangewend is.
Onder ʼn belasting van so laag as 40 % van die breekbelasting vorm daar minder krake,
maar met ʼn groter gemiddelde kraakwydte. Wanneer belas word met meer as 65 % van die
breekbelasting vorm meer krake wat lei tot ʼn kleiner gemiddelde kraakwydte.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2847 |
| Date | 12 1900 |
| Creators | Adendorff, Christo Johan |
| Contributors | Boshoff, W. P., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch: University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Rights | University of Stellenbosch |
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