Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Reinforced concrete is susceptible to cracking. This makes it less durable than
it would be had it been crack-free. Ingress of harmful substances into reinforced
concrete through cracks – which causes corrosion of steel – is not desirable.
This can be mitigated by the use of fibre reinforced-concretes or mortars
showing strain hardening properties accompanied by improved ductility and
multiple cracking under tensile loading. Such materials are called Strainhardening
cementitious composites (SHCC’s).
At Stellenbosch University, work has been done in previous years on SHCC to
determine its behaviour under various loading conditions. Some of the aspects
of the material that have been studied are the behaviour under uni-axial tensile
loading, uni-axial compression and shear. The behaviour of SHCC under biaxial
stresses was investigated to enable the prediction of the material behaviour
under complex stress conditions.
Square plate specimens of nominal dimensions 100 x 100 x 20 mm were cast
and subjected to biaxial compressive loading at stress path angles of 00, 150,
300 and 450; which were equivalent to vertical/horizontal stress ratios of 0/1,
0.27/1, 0.58/1 and 1/1 respectively, at ages 23 to 33 days. Comparisons were
made between specimens tested using steel platens and those tested using
Vesconite sheets. Those tested using Vesconite yielded lower failure stresses.
Vesconite was used to reduce the retraining effect of the frictional force
between the specimens and the steel platens.
Poisson’s ratios were calculated for specimens tested using steel and those
tested using Vesconite. The values for Vesconite were found to be higher than
for steel. Additionally, the values for the uni-axial case were different from those
obtained for other stress ratios. This could have been due to the assumption
made that plane stress was realised and that Elastic moduli in tension and in compression was the same. The possibility of the existence of a triaxial stress
state could render the calculated Poisson’s ratios incorrect.
Shear slip type failure accompanied by wedging was observed. Vertical to near
diagonal cracks were evident on the front faces of the specimens for the stress
path angles of 00 to 450 respectively. The observed crack patterns showed
closely spaced multiple micro-cracking on the narrow edges of specimens
indicating Strain-hardening behaviour. The stress-strain curves also showed a
slight indication of strain-hardening where tensile strains were measured. / AFRIKAANSE OPSOMMING: Gewapende beton is vatbaar vir krake. Dit maak dit minder duursaam as
wanneer dit kraak-vry is. Instroming van skadelike stowwe in gewapende beton
deur middel van krake - wat korrosie van staal veroorsaak - is nie wenslik nie.
Dit kan verbeter word deur die gebruik van veselversterkte beton of mortel wat
vervormingsverharding eienskappe toon, vergesel deur verbeterde rekbaarheid
en veelvuldige krake onder trekspanning. Sulke materiaal word Strainhardening
cementitious composites (SHCC's) genoem.
Die Universiteit Stellenbosch, het in vorige jare werk gedoen om SHCC se
gedrag te bepaal onder verskillende belastingstoestande. Sommige van die
aspekte van die materiaal wat bestudeer is, is gedrag onder uni-aksiale trek,
uni-aksiale druk en skuif. Die gedrag van SHCC onder biaksiale spannings is
ondersoek om voorspelling van materiaalgedrag onder komplekse
spanningstoestande moontlik te maak.
Vierkantige plaat monsters van nominale dimensies 100 x 100 x 20 mm is
gemaak en aan biaksiale drukkragte onderwerp, met spannningspad hoeke van
00, 150, 300 en 450; wat soortgelyk is aan die horisontale spanning verhoudings
van 0/1, 0.27/1, 0.58/1 en 1/1 onderskeidelik, op ouderdomme 23-33 dae.
Vergelykings is getref tussen monsters getoets met staal plate en diegene
getoets word met Vesconite plate. Die proefstukke getoets met Vesconite het
laer falingsspannings opgelewer. Vesconite is gebruik om die uitwerking van die
wrywingskrag tussen die monsters en die staal plate te verminder.
Poisson se verhouding is bereken vir die staal en Vesconite monsters
afsonderlik. Daar is gevind dat die Vesconite waarde hoër was as die vir staal.
Daarbenewens het die waardes vir die uni-aksiale geval, verskil van dié vir
ander spanningsverhoudings. Dit kan wees as gevolg van die aanname van
vlakspanning en dat die Elastiese moduli in druk en in trek dieselfde is. Die moontlikheid van die bestaan van 'n drie-dimensionele spanningstoestand, kan
beteken dat die berekende Poisson’s verhoudings onakkuraat is.
Skuif-glip tipe faling, vergesel deur vaswigting is waargeneem. Vertikale tot
feitlik diagonale krake is duidelik sigbaar op die voorkant van die monsters vir
spanningspadhoeke van 0-450 onderskeidelik. Die waargeneemde kraak
patrone het nou gespasieerde, veelvuldige mikro-krake op die smal randte van
die monsters, wat dui op vervormingsverharding. Die spanningsvervormings
kurwes het ook effense aanduidings getoon van die vervormingsverharding
waar trekvervorming gemeet is.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5242 |
| Date | 12 1900 |
| Creators | Molapo, Katiso Tokoloho |
| Contributors | Van Zijl, G. P. A. G., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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