Thesis(PhD (Civil Engineering))-- University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Bitumen based road surfacing seals and asphalt wearing courses have been used by society's Engineers "to counter the damage to the existing unsurfaced roadways by the newly developed automobile with its rubber driving wheels" since the early 1900's. Early experiments were conducted with both tar and bitumen to find a suitable material to alleviate the situation, and ongoing research has been carried out through the past century and into the new millennium, throughout the world, examining improvements, from materials used, to design and construction methods. However, there is still much to be understood, improved and refined, when considering road surfacing seal design.
Pavement designers have the choice of utilizing either an asphalt (graded aggregate remanufactured
with a bitumen binder and applied as a complete product) or a surfacing seal (including variations of bitumen binder sprayed onto the road surface, with the addition of single size
stones, either in one or two layers of binder and aggregate, i.e. single or double seals) as a
pavement wearing course.
Current road surfacing seal design practice depends on empirical analysis and experience, being primarily a volumetric based assessment of bitumen application. This research project assesses
South African seal design philosophy, investigates design areas where review or updating is
required to accommodate changing bitumen sources and types, and traffic loading. Seal
performance criteria are examined, with the development of a matrix of influences on seal
performance. Using this, the need for a seal design method based on mechanistic material
properties is proposed, and the prototype example of such a numerical model using finite element
method is presented.
To contribute further towards a performance related seal design method, the feasibility of modelling
of road surfacing seals using mechanistic principles was examined. The potential of developing
failure and fatigue criteria or relationships to enable assessment of the expected seal performance, with inclusion of different component material characteristics and variations, varying traffic and
environmental conditions, was also examined.
From assessment of literature, and understanding of the components of the seal, pavement, and influencing factors, a choice of numerical model of seal performance was made. The Finite Element
Method (FEM) Analysis was selected for the purpose of modelling seal performance. The model was developed to enable examination of the interaction of individual seal components (i.e. stone and bitumen), at micro-mechanic scale.
The prototype 3-dimensional numerical seal model was undertaken in 2002 and 2003 at Technical
University Delft, using the CAPA research program. On the basis of the linear calculations the
developed numerical prototype model is able to provide insight into seal behaviour and distinction
between mechanical (seal geometry) and chemical (components) seal aspects, and insight into
stress and strain development in the different seal types. Simulations of different seal,
environmental and traffic scenarios are provided to demonstrate the potential of the model
(excluding seal aggregate interlock and embedment effects at prototype stage).
In order to provide data for the verification of the prototype numerical model, and to further
contribute to the development of a performance related seal design method, performance tests were
developed, with a new tool for assessment of comparative seal performance using the Model Mobile
Load Simulator Accelerated Pavement Testing apparatus. The performance of each different seal
binder type - Penetration grade Mumen, SBS, SBR, EVA and Bitumen Rubber - was undertaken. A
methodology for the assessment of in-service seal performance was developed, and the
performance of the respective seals reported. The results of this examination showed that each
binder type has its unique contribution to seal performance.
These new performance tests will be able to assist designers in the added determination of the
fundamental binder properties on seal performance, and the seals' ability to contribute to the overall
performance of the pavement.
An additional comparative performance test method was developed to enable assessment of the
effect of ageing and moisture, to complement the MMLS results.
In summary, the performance testing has assisted in identifying the critical parameters a seal
designer should consider during the design process.
From this research, it is evident that the current seal design method requires further development to
able designers to predict the effect of:
Varying axle loads, tyre pressures and design speed;
Varying characteristics of the different binders, (i.e. temperature - viscosity relationships,
adhesion and visco-elastic behaviour);
on the performance of seals.
The major areas for suggested improvement in current seal design methods towards a performance
based design method are:
inclusion of variable traffic load and environmental characteristics, including temperature and
moisture influences, and
inclusion of mechanistic material characteristics into the design methodology. / AFRIKAANSE OPSOMMING: Bitumengebaseerde padoppervlakseellae en asfaltslytlae is sedert die 1900's deur ingenieurs
gebruik as teenwig teen die skade wat die pas ontwikkelde voertuig met sy rubberwiele aan
bestaande ryvlakke sonder oppervlakbehandeling aangerig het. In vroeëre eksperimente wat
daarop gemik was om 'n geskikte materiaal te vind om die probleem teen te werk, is 'n kombinasie
van teer en bitumen gebruik. Sedertdien word voortgesette navorsing steeds wêreldwyd gedoen om
verbeterings te ondersoek, nie net ten opsigte van materiale nie maar ook ontwerp- en
konstruksiemetodes. Wat die ontwerp van padoppervlakseëling betref is daar egter heelwat wat
reg begryp, verbeter en verfyn moet word.
Plaveiselontwerpers het die keuse om of 'n asfalt te gebruik (gegradeerde aggregaat
voorafvervaardig met 'n bitumen bindmiddel en aangewend as 'n klaarproduk), of 'n oppervlakseël
(een laag of twee lae [m.a.w. enkel- of dubbelseël] bitumen bindmiddel met aggregaat [enkelgrootte
klippies] bygevoeg, gespuit op die padoppervlak).
In die praktyk berus die ontwerp van padoppervlakseëling tans op empiriese analise en ervaring
(wat hoofsaaklik 'n volumetriesgebaseerde assessering van die aanwending van bitumen is).
Hierdie navorsingsprojek doen 'n waardebepaling van die Suid-Afrikaanse filosofie van seëlontwerp,
en ondersoek ontwerpterreine wat hersiening of bywerking benodig om vir veranderende
bitumenbronne en -tipes, asook verkeerslading, voorsiening te maak. Met die ontwikkeling van 'n
matriks van die invloede op seëlprestasie is die kriteria vir seëlprestasie ondersoek. Op grond
daarvan word aangevoer dat daar 'n behoefte is aan 'n seëlontwerpmetode gebaseer op die
meganistiese eienskappe van materiaal, en word 'n voorbeeld van 'n numeriese modelprototipe wat
die eindige-element-metode gebruik, voorgelê.
Ten einde 'n verdere bydrae te lewer tot die ontwikkeling van 'n prestasiegerigte seëlontwerpmetode,
is die uitvoerbaarheid van die modellering van padoppervlakseëllae gebaseer op meganistiese
beginsels, ondersoek. Daar is ook ondersoek ingestel na die potensiaal vir die ontwikkeling van
kriteria vir die vasstel van mislukking en vermoeidheid of verhoudinge wat die assessering van die
verwagte seëlprestasie (ingesluit die verskillende kenmerke en variasies van
seëlkomponentmateriaal en wisselende verkeers- en omgewingsomstandighede) moontlik kan
maak.
Met oorweging van die bestudeerde literatuur en 'n begrip van die komponente van seël, plaveisel en inwerkende faktore, is 'n keuse van 'n numeriese model vir seëlprestasie gemaak. Die eindige-element-metode (Finite Element Method [FEM]) is gekies as die analitiese metode vir die
modellering van seëlprestasie. Die model is ontwikkel om die ondersoek van die interaksie tussen
individuele seëlkomponente (klip en bitumen) op mikromeganiese skaal moontlik te maak.
Die ontwikkeling van die driedimensionele, numeriese, model-seëlprototipe is tussen 2002 en 2003 by die Delft Tegniese Universiteit gedoen, met gebruikmaking van die CAPA-navorsingsprogram.
Wat lineêre berekenings betref, kan die ontwikkelde numeriese modelprototipe 'n insig gee in seëlgedrag en in die onderskeid tussen aspekte van seëlgeometrie (meganies) en seëlkomponente
(chemies), asook in die spanning- en vervormingsontwikkeling van die verskillende tipes seël.
Simulasies van verskillende seël-, omgewings- en verkeerscenario's word voorgestel om die
potensiaal van die modelprototipe te demonstreer.
Met die oog daarop om data vir die verifikasie van die numeriese modelprototipe te voorsien, en om verder tot die ontwikkeling van 'n prestasiegerigte seëlontwerpmetode by te dra, is prestasietoetse, met 'n nuwe instrument vir die assessering van vergelykende seëlprestasie met behulp van die
Model Mobile Load Simulator Accelerated Pavement Testing apparaat, ontwikkel. Die prestasie van
elke verskillende tipe seëlbindmiddel- penetrasiegraad bitumen, SBS, SBR, EVA en bitumenrubber - is getoets. 'n Metodologie vir die assessering van die ingebruiksprestasie van seëllae is ontwikkel,
en daar is verslag gedoen oor die prestasie van die verskillende seëllae. Die resultate van die
ondersoek het getoon dat elke tipe bindmiddel 'n eie unieke bydrae tot die prestasie van die seël
lewer.
Die nuwe prestasietoets sal ontwerpers help met die bepaling van die grondliggende bindmiddeleienskappe
wat by seëlprestasie ter sprake is, asook van die seël se vermoë om tot die algehele
prestasie van die plaveisel by te dra.
'n Bykomende prestasievergelykingstoetsmetode vir die assessering van die effek van veroudering
en vogtigheid is ontwikkel om die MMLS-resultate aan te vul.
Ter opsomming, die prestasietoetsing het bygedra tot die identifisering van die kritiese parameters
wat die seëlontwerper tydens die ontwerpproses in gedagte behoort te hou.
Die navorsing wat gedoen is, dui daarop dat die huidige seëlontwerpmetode verder ontwikkel moet
word om ontwerpers in staat te stel om die effek van die volgende te kan voorspel:
Wisselende aslas, banddruk en ontwerpspoed; Verskillende kenmerke van die verskillende bindmiddels (bv. temperatuur
viskositeitsverhoudinge, vashegting en viskoëlastiese gedrag).
Wat huidige seëlontwerpmetodes betref, is die hoofterreine waarop 'n verbetering voorgestel word, die insluiting van veranderlike verkeerslas- en omgewingskenmerke, ingesluit die invloed van
temperatuur en vogtigheid, en
insluiting van meganistiese kenmerke van materiaal in die ontwerpmetodologie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/856 |
| Date | 12 1900 |
| Creators | Milne, Terence Ian |
| Contributors | Jenkins, K. J., Van de Ven, Martinus F.C., 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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