Thesis (MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Strain Hardening Cement Based Composite (SHCC) is a type of High Performance Fibre
Reinforced Cement-based Composite (HPFRCC). SHCC contains randomly distributed short
fibres which improve the ductility of the material and can resist the full tensile load at strains
up to 5 %. When SHCC is subjected to tensile loading, fine multiple cracking occurs that
portrays a pseudo strain hardening effect as a result. The multiple cracking is what sets SHCC
aside from conventional Reinforced Concrete (RC). Conventional RC forms one large crack
that results in durability problems. The multiple cracks of SHCC typically have an average
crack width of less than 80 μm (Adendorff, 2009), resulting in an improved durability
compared to conventional RC.
The aim of this research project is to quantify the cracking behaviour of SHCC which can be
used to quantify the durability of SHCC. The cracking behaviour is described using a
statistical distribution model, which represents the crack widths distribution and a
mathematical expression that describes the crack pattern. The cracking behaviour was
determined by measuring the cracks during quasi-static uni-axial tensile tests. The cracking
data was collected with the aid of a non-contact surface strain measuring system, namely the
ARAMIS system.
An investigation was performed on the crack measuring setup (ARAMIS) to define a crack
definition that was used during the determination of the cracking behaviour of SHCC. Several
different statistical distributions were considered to describe the distribution of the crack
widths of SHCC. A mathematical expression named the Crack Proximity Index (CPI) which
represents the distances of the cracks to each other was used to describe the crack pattern of
SHCC.
The Gamma distribution was found to best represent the crack widths of SHCC. It was
observed that different crack patterns can be found at the same tensile strain and that the CPI
would differ even though the same crack width distribution was found. A statistical
distribution model was therefore found to describe the CPI distribution of SHCC at different
tensile strains and it was established that the Log-normal distribution best describes the CPI
distribution of SHCC. After the cracking behaviour of SHCC was determined for quasi-static tensile loading, an
investigation was performed to compare it to the cracking behaviour under flexural loading.
A difference in the crack widths, number of cracks and crack pattern was found between
bending and tension. Therefore it was concluded that the cracking behaviour for SHCC is
different under flexural loading than in tension. / AFRIKAANSE OPSOMMING: “Strain Hardening Cement-based Composite” (SHCC) is ‘n tipe “High Performance Fibre
Reinforced Cement-based Composite” (HPFRCC). SHCC bevat kort vesels wat ewekansig
verspreid is, wat die duktiliteit van die material verbeter en dit kan die maksimum trekkrag
weerstaan tot en met ‘n vervorming van 5 %. Wanneer SHCC belas word met ‘n trekkrag,
vorm verskeie fyn krake wat ‘n sogenaamde vervormingsverharding voorstel. Die verskeie
krake onderskei SHCC van normale bewapende beton. Normale bewapende beton vorm een
groot kraak met die gevolg dat duursaamheidsprobleme ontstaan. Die gemiddelde
kraakwydte van SHCC is minder as 80 μm (Adendorff, 2009) en het dus ‘n beter
duursaamheid as normale bewapende beton.
Die doel van die navorsingsprojek is om die kraak gedrag van SHCC te kwantifiseer en wat
dan gebruik kan word om die duursaamheid van SHCC te kwantifiseer. Die kraak gedrag is
beskryf deur ‘n statistiese verspreiding model wat die kraak wydtes se verspreiding voorstel
en ‘n wiskundige uitdrukking wat die kraak patroon beskryf. Die kraak gedrag was bepaal
deur die krake te meet tydens die semi-statiese een-asige trek toetse. Die kraak data was met
behulp van ‘n optiese vervormings toestel, naamlik die ARAMIS, versamel.
‘n Ondersoek is gedoen op die kraak meetings opstelling (ARAMIS), om ‘n kraak definisie te
definieer wat gebruik is om die kraak gedrag te bepaal. Daar is gekyk na verskeie statistiese
verdelings om die kraak wydtes van SHCC te beskryf. Die kraak patroon van SHCC is
beskryf met ‘n wiskundige uitdrukking genoem die “Crack Proximity Index” (CPI) wat die
krake se afstande van mekaar voorstel.
Dit is bevind dat die Gamma verdeling die kraak wydtes van SHCC die beste beskryf. Daar is
waargeneem dat verskillende kraak patrone by dieselfde vervorming verkry kan word en dat
die CPI kan verskil al is die kraak wydte verdeling dieselfde. ‘n Statistiese verdelingsmodel
is dus gevind om die CPI verdeling van SHCC te beskryf by verskillende vervormings, en
daar is vasgestel dat die Log-normaal verdeling die CPI verdeling van SHCC die beste
beskryf. Nadat die kraak gedrag van SHCC bepaal is vir semi-statiese trek-belasting, is ‘n ondersoek
gedoen waar die trek-kraak gedrag vergelyk is met buig-kraak gedrag. ‘n Verskil in die kraak wydtes, aantal krake en kraak patroon is gevind tussen buiging en trek. Dus is die
gevolgtrekking gemaak dat die kraak gedrag van SHCC verskillend is in buiging as in trek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20076 |
| Date | 03 1900 |
| Creators | Nieuwoudt, Pieter Daniel |
| 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 | English |
| Type | Thesis |
| Format | 102 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.002 seconds