Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: With the depletion of high quality conventional materials for road pavements, the
consideration of cement stabilisation for sub-base and base layer materials often provide a
feasible solution to the road industry. Like all pavement material types, the design inputs
should be determined using reliable test methods, which provide a good indication of the
property of materials. Any evaluation should provide a better understanding of the
engineering and behavioural properties of the materials. This should form the basis for
ascertaining their suitability for use in the pavement structure. However, the road industry is
dependent on strength testing of cement-stabilised materials as a means to ascertain
material suitability for use. Strength alone does not offer reliable insight regarding the
performance and durability of the stabilised layer. This is because a cement-stabilised layer
may be very stiff but not strong enough to withstand the loading and endure adverse
environmental conditions. Similarly, the stabilised layer may be prone to cracking emanating
from shrinkage, which leads to performance and durability related distresses.
A stabilised sub-base and base of the pavement structure experiences tensile stresses and
strains under traffic loading. At laboratory level, the flexural beam test simulates to an
acceptable degree the mode of stress to strain to which the pavement layer experiences.
However, the test lacks a standard test protocol. This leads to inconsistencies while
evaluating the same material type. Due to this fact, the formulation of a standard laboratory
test procedure is necessary.
Shrinkage cracking is one of the major causes of pavement failure. The manifestation of
wide cracks leads to performance related distresses. Cracks provide zones for the infiltration
of water into the underlying layers, an aspect that results in further deterioration of the
pavement structure. However, the evaluation of shrinkage at laboratory level is not usually
undertaken. Disregarding shrinkage evaluation stems from the fact that a number of
guidelines consider it as a natural material characteristic. The road industry frequently
depends on the use of low cement contents among other techniques as a means to mitigate
shrinkage cracking in cement-stabilised layers. The selection of a mitigation measure usually
lacks reliable data concerning the material’s shrinkage potential. Because of this, the
requirement to evaluate shrinkage at laboratory level as part of a material property measure
provides a good indication regarding the quality of material.
Nanotechnology products such as the Nanotterra Soil® a polymer cement additive are
purported to mitigate shrinkage cracking in cement-stabilised layers. However, their
suitability for use remains unspecified and dependent on the stakeholders. With the
development of a shrinkage method, the evaluation of shrinkage reducing products can be
undertaken.
This research proposes a flexural beam test protocol for cement-stabilised materials,
comprising of a span-depth ratio of nine or greater as fitting to provide a reliable measure of
the material’s flexural strength and elastic modulus. The developed shrinkage test method
provides a good repeatability and is user friendly. The test provides a good indication of the
shrinkage criteria of ferricrete and hornfels with and without the polymer. The efficacy of
the polymer is dependent on the cement content in the mix and the type and quality of the
material. The research provides insight pertaining to the characterisation of shrinkage, behavioural properties, and durability of cement-stabilised materials. Analysis of the
shrinkage crack pattern reveals that use of the polymer lessens the development of tensile
stress in a cement-stabilised layer. Equally, the application of the low cement contents for
stabilisation may not result in cracking of the stabilised layer. This research contributes to a
better understanding of cement-stabilised materials. / AFRIKAANSE OPSOMMING: Namate hoë kwaliteit konvensionele materiale uitgeput raak, word sementstabilisasie van
stutlaag en kroonlaag materiale al hoe meer oorweeg en is dit ʼn geskikte oplossing vir die
padbou-nywerheid. Soos vir alle padboumateriale moet die ontwerpeienskappe bepaal word
deur middel van betroubare toetsmetodes wat ʼn goeie aanduiding van die materiaal se
eienskappe sal gee. Enige evaluering moet ʼn beter insae in die materiaal se
ingenieurseienskappe en gedrag oplewer. Dit moet dan die basis vorm om die materiaal se
gebruik in ʼn padstruktuur te evalueer. Die padbou-nywerheidmaak grootliks staat op die
toetsing van skuifsterkte van sementgestabiliseerde materiaal om die geskiktheid daarvan
vir gebruik te bepaal. Sterkte op sigself lewer egter nie ʼn betroubare maatstaf van die
materiaal se gedrag en duursaamheid nie. Dit is aangesien ʼn sementgestabiliseerde laag
baie solied mag wees maar nogtans nie sterk genoeg om belasting te weerstaan en bestand
teen omgewingstoestande te wees nie. Net so mag ʼn gestabiliseerde laag vatbaar vir
kraakvorming as gevolg van krimping wees en dit kan lei tot duursaamheid-verwante en
werkverwante skade.
ʼn Gestabiliseerde stutlaag en kroonlaag in die plaveiselstruktuur is onderhewig aan
trekspannings en vervormings as gevolg van verkeerslaste. Op laboratoriumvlak boots die
balkbuigtoets die spanning en vervorming wat ʼn plaveisellaag ondervind tot ʼn aanvaarbaar
hoë mate na. Die toets beskik nie oor ʼn standaard-toetsprosedure nie. Dit lei tot afwykings
terwyl dieselfde materiaal evalueer word. Om hierdie rede is die ontwikkeling van ʼn
standaard-laboratoriumprosedure nodig.
Krimpkraking is een van die grootste oorsake van plaveiselswigting. Die onwikkeling van wye
krake lei tot werksverwante skade. Krake veroorsaak areas vir die infiltrasie van water in die
onderliggende plaveisellae wat verdere agteruitgang van die plaveiselstruktuur veroorsaak.
Desnieteenstaande word ʼn evaluering van kraking op laboratoriumvlak selde gedoen. Dit
spruit uit die feit dat ʼn aantal ontwerp-riglyne kraking as ʼn natuurlike materiaaleienskap
beskou. Die padbounywerheid moet dikwels staatmaak, op onder andere, ʼn lae
sementinhoud om krimpkraking te minimeer. Hierdie tipe benadering gaan dikwels mank
aan betroubare inligting oor die materiaal se krimpingspotensiaal. Om hierdie rede is die
ondersoek van krimping op laboratoriumvlak nodig as deel van die ondersoek van die
materiaaleienskappe om die kwaliteit van materiale te bepaal.
Minimeringstegnieke verander deurlopend. Die toepassing van nanotegnologieprodukte,
soos Nanotterra Soil®, ‘n polimeersement bymiddel, wat na bewering krimpkraking in
sementgestabiliseerde lae kan minimeer, kom voortdurend op die mark. Nogtans bly hulle
geskiktheid ongespesifiseerd en afhanklik van die leweransiers. Indien ʼn krimptoetsmetode
ontwikkel word, sal die effektiwiteit van krimpverminderingsmiddels getoets kan word.
Hierdie navorsing stel die ontwikkeling van ʼn toetsprosedure vir ʼn balkbuigtoets voor met ʼn
spanlengte tot diepteverhouding van minstens nege as betroubare maatstaf van ʼn materiaal
se buigsterkte en modulus van elastisiteit. Die ontwikkelde krimptoetsmetode lewer ʼn goeie
herhaalbaarheid en is gebruikersvriendelik. Die toets verskaf ʼn goeie aanduiding van
krimpingskriteria van ferrikreet en horingfels met en sonder polimeer. Die effektiwiteit van
die polimeer hang af van die sementinhoud in die mengsel asook die tipe en kwaliteit van
die materiaal. Die navorsing verskaf insig aangaande die karakterisering van krimping,
gedragseienskappe en duursaamheid van sementgestabiliseerde materiale. Die navorsing
help mee om sementgestabiliseerde materiale beter te verstaan.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/96753 |
| Date | 03 1900 |
| Creators | Mbaraga, Alex Ndiku |
| Contributors | Jenkins, Kim J., 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 | 286 pages : illustrations |
| Rights | Stellenbosch University |
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