Thesis (MScIng)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: This thesis covers the factors affecting compactibility of hot mix asphalt including gradation,
filler/binder ratios, binder types, binder content, polymer modification, temperature, volumetric
properties etc. The study is not limited to compactibility as the property measured, but also on
the influence of these factors on the mix’s capacity to resist permanent deformation or rutting.
An experimental design was used with a variety of the above factors being included.
Laboratory analysis of the mixes as well as accelerated pavement testing of different mix types
using the one-third scale Model Mobile Load Simulator (MMLS3) was carried out. The
analysis assists in identification of the factors that influence both compactibility and rut
resistance, those influencing the one but not the other, and those factors having no significant
influence. The compactibility of the mixes has been analysed in terms of voids in the mix at a
specific binder content and compaction level. Special consideration was given to the
characterisation of the filler and filler/binder system of some mixes.
It was found that gradation of a mix has a significant influence on compaction and the rutting
performance. High filler/binder ratios were found to be the critical factors influencing the
compactibility of the wearing course mixes investigated, but based on the limited tests
performed, the reduction of the filler/binder ratios for improved compactibility did not
significantly increase rutting under accelerated pavement testing.
As expected, the binder type has a significant influence on the rutting resistance as well as
compactibility. In addition, an increase in binder content facilitated compaction, but decreased
rutting resistance.
Polymer modification considerably improved the rutting resistance of a standard mix under the
same loading conditions. Although some modifiers may improve rutting resistance, it requires
higher compaction temperatures.
The addition of the antistripping agent Gripper L decreased the rutting, aggregate stripping and
also the rate of rutting of the Quartzite LAMBS mix that result from the stripping failuremechanism. Low densities can lead to considerable rutting and moisture damage, especially
when a moisture susceptible aggregate is used.
In terms of compactibility as evaluated with the Superpave Gyratory Compactor, it appears that
there exists a temperature window in which compaction can be achieved, but in terms of
rutting; even a small deviation in temperature can influence rutting results significantly. The
control of the temperature during testing is critical if meaningful comparisons between
different mixes with regard to rutting performance are to be made.
Linear elastic and finite element analysis has been performed to ascertain whether different
specimen geometries would influence the stress distribution within the specimen, and
subsequently the rutting results. It was found that the geometry of test specimens has an
influence on the stress distribution within the specimens, which can influence the permanent
deformation results. The briquette specimens tested in the laboratory also yielded higher rutting
results for the same mix tested in the field. It is therefore important to use specimens that are
most representative of field conditions / AFRIKAANSE OPSOMMING: Hierdie tesis ondersoek die faktore wat ’n invloed het op die kompakteerbaarheid van warm
asfalt. Faktore sluit in onder andere gradering, vulstof/bindstof verhouding, tipe bindstof,
bindstof inhoud, polimeer modifisering, temperatuuur, volumetriese eienskappe, ens. Hierdie
studie is nie net beperk tot kompakteerbaarheid as ‘n gemete eienskap nie, maar ook die
invloed van hierdie faktore op die mengsel se vermoë om weerstand te bied teen permanente
deformasie of spoorvorming.
’n Eksperimentele ontwerp wat ’n verskeidenheid van bogenoemde faktore insluit is gebruik.
Laboratorium analise van die mengsels asook versnelde plaveisel toetse van die verskillende
tipe mengsels is gedoen met die een-derde skaal Mobiele Lassimuleerder (MMLS3). Die
analise help met die identifikasie van die faktore wat beide kompakteerbaarheid en
spoorvorming beïnvloed, asook dié wat slegs die een maar nie die ander beïnvloed, en ook die
faktore wat geen beduidende invloed het nie. Die kompakteerbaarheid is geëvalueer in terme
van die hol ruimtes in die mengsel by ’n bepaalde bindstof inhoud en verdigtingsgraad.
Spesiale aandag is geskenk aan die eienskappe van die vulstof en vulstof/bindstof
wisselwerking van die mengsels.
Die gradering van ’n mengsel het ’n beduidende invloed op kompakteerbaarheid sowel as
spoorvorming. Hoë vulstof/bindstof verhoudings is een van die kritiese faktore wat die
kompakteerbaarheid van die betrokke mengsels beïnvloed, maar laer vulstof/bindstof
verhoudings vir beter kompaksie het nie ’n beduidende toename in wielsporing teweeg gebring
nie.
Soos verwag het die tipe bindstof ’n beduidende invloed op kompakteerbaarheid sowel as
spoorvorming. ’n Toename in bindstof bevorder verdigting, maar lei tot groter wielsporing.
Polimeer modifisering verminder die wielsporing van ’n standard mengsel onder dieselfde
beladingstoestand. Alhoewel modifisering wielsporing verminder, vereis dit hoër kompaksie
temperature.Die toevoeging van die teenstropingsmiddel GripperL verminder spoorvorming, aggregaat
stroping asook die tempo van spoorvorming van die Kwartsiet LAMBS mengsel as gevolg van
die stropingsmeganisme. Lae digthede kan lei tot aansienlike vogskade en spoorvorming; veral
as die aggregaat vatbaar is vir die invloed van vog.
Daar blyk ’n temperatuur interval te wees waarin verdigting met die Superpave Gyratory
Compactor bereik kan word; maar selfs ‘n klein temperatuurafwyking kan beduidende invloed
op die resultate van spoorvorming hê. Temperatuurbeheer is baie belangrik indien sinvolle
vergelykings tussen die sporingsgedrag van verskillende mengsels gemaak moet word.
Lineêr elasties en eindige element analise is uitgevoer om te bepaal of verskillende
toetskonfigurasies die spanningsverdeling binne die toetsmonsters en die spoorvorming
affekteer. Dit is bevind dat die geometrie van toetsmonsters het ’n invloed op die
spanningsverdeling in die monsters wat die sporingsresultate kan beïnvloed. Die
briketmonsters in die laboratorium gee ook groter spoordiepte teenoor dieselfde mengsel wat in
die veld getoets is. Daarom is dit belangrik om verteenwoordigende monsters te gebruik.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16311 |
| Date | 04 1900 |
| Creators | Douries, William John |
| Contributors | Jenkins, K. J., University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xxv, 239 leaves : ill. |
| Rights | University of Stellenbosch |
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