Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: This research investigates the flexibility and the performance properties of bitumen stabilised
materials under the influence of mix variables. The laboratory testing consisted of two main phases.
During the first phase (mix design), the strength and the flexibility of the mixes were assessed
through ITS (Indirect Tensile Strength), UCS (Unconfined Compressive Strength), displacement at
break, strain at break and fracture energy. The second phase consisted of a series of triaxial tests
done to assess the performance properties (shear strength: cohesion and angle of internal friction; and
stiffness: resilient modulus) of the mixes.
The mineral aggregates used in this study were milled from different locations of the R35, near
Bethal. This was a blend of granular material (dolerite, from various locations of the existing base
and subbase layer of the R35) and Reclaimed Asphalt (RA) milled from the existing surfacing.
During the mix design phase, two types of bituminous binders were used (bitumen emulsion and
foamed bitumen) at bitumen content ranges of 2%, 2.4% and 2.8% each. Two types of active filler
were used separately and in combination at a proportion of 1% and 2%. Finally, specimens were
tested in wet and dry conditions for each mix combination. During the triaxial testing phase, only the
optimum bitumen content of 2.4% was used, both for bitumen emulsion and foamed bitumen, with
only cement as active filler in a proportion 1% and 2%. The specimens were tested at different
ranges of densities and saturation levels. The flexibility of the mix was assessed through the fracture energy, the strain and the displacement at
break parameters. An analysis of variance (ANOVA) was conducted on the data to assess the
significance of experimental variables on this property. This property was found to be very sensitive
to bitumen and cement content added to the mix. When assessing the combined effect and the
significance of the variables on the flexibility of the mixes, it was found that fracture energy is
mostly influenced by the cement content, followed by the bitumen content, then the type of treatment
and finally the testing condition. However, the level of significance was not in the same order for the
other two parameters (displacement and strain at break). It was also found that the combined effect
of some independent variables (cement content + testing condition, type of treatment + cement
content + bitumen content) had a significant effect on the fracture energy and the strain at break
respectively.
From the ITS and UCS tests, an increase in strength was noticed with the increase of cement content.
On the other hand, the increase in bitumen content led to a decrease in strength of the material. The
statistical analysis on the ITS and UCS values show that the independent variable with the most significant effect on the ITS is the cement content, followed by the testing conditions, then the
bitumen content and finally the type of treatment. The combined effect of cement content + bitumen
content was found to be significant both for ITS and UCS.
In the second phase triaxial tests were performed in order to evaluate the performance properties of
the mixes. It was found that the increase of the active filler content significantly improves the shear
strength of the material. It was also found that at a fixed cement content, specimens tested at low
density and/or high level of saturation show low shear strength. The Mr-θ model was used to model
the resilient modulus of the mixes and the model coefficients used to evaluate the effect of
experimental variables on the resilient modulus. It was found that the resilient modulus of the mixes
increases as the bulk stress increases. This confirms the stress dependent behaviour of bitumen
stabilised materials. The analysis show that increasing the percentage of active fillers content results
in a significant increase in the resilient modulus values. An increase in relative density also resulted
in an increase in the resilient modulus of the mixes, while the opposite effect was observed with the
increased of the saturation level.
Besides the engineering properties and the mechanical test parameters, other parameters such as the
Tensile Strength Ratio (TSR) was calculated in order to evaluate the moisture sensitivity of the
mixes. Weakening due to moisture was found to be more predominant in the mixes with less active
filler. In addition, bitumen emulsion mixes were found to have a better resistance to moisture
weakening effects compared to foamed bitumen. In addition, a comparison between the rapid curing
and the accelerated curing was done. Higher ITS and UCS results were obtained for specimens cured
using long term curing compared to specimens cured using the accelerated curing method. In conclusion, flexibility is an important property of bitumen road construction material (bitumen
stabilised material include) however, it is not an easy property to measure. Although,
displacement/strain at break and fracture energy from ITS and UCS were able to give us some
indications on the main factors governing the flexibility of bitumen stabilised materials (the bitumen
and active filler content), more accurate and adequate tests are required to evaluate the parameter. / AFRIKAANSE OPSOMMING: Die buigsaamheid en gedragseienskappe van bitumen gestabiliseerde materiale was getoets om
sodoende die invloed van verskeie mengselveranderlikes te evalueer. Die ondersoek het uit twee
fases bestaan. Tydens die eerste fase (mengfase) is die sterkte en buigsaamheid deur middel van
indirekte treksterkte toetse (ITS), onbegrensde druksterkte toetse (UCS), verplasing – en vervorming
by breekpunt sowel as breek-energie toetse gedoen en ondersoek. Die tweede fase het bestaan uit ʼn
reeks drie-assige triaksiaal toetse. Triaksiaaltoetse is uitgevoer om die gedragseienskappe soos die
skuifsterkte, kohesie, hoek van interne wrywing, styfheid en weerstand modulus te ondersoek.
Die gemaalde mineraal-aggregaat wat in hierdie ondersoek gebruik is, was verkry op verskeie areas
van die R35, geleë naby Bethal. Die materiaal is ʼn mengsel van granulêre materiaal (van die
bestaande kroonlaag en stutlaag van die pad) en herwonne asfalt (RA). Tydens die mengontwerp fase
is twee tipes bitumen gebruik naamlik bitumenemulsie en skuimbitumen in hoeveelhede van 2%,
2.4% en 2.8%. Twee tipes aktiewe vulstof (hoeveelhede van onderskeidelik 1% en 2%) was saam
met elk van die verskeie bitumen-hoeveelhede gebruik. Proefstukke van elk van hierdie mengsel
kombinasies is onder beide nat en droë kondisies getoets. Tydens die tweede fase, is slegs die
optimum binder inhoud (2.4%) gebruik vir beide emulsie- en skuimbitumen, gekombineer met 1%
en 2% aktiewe vulstof. Proefstukke was getoets by ʼn reeks van verskillende digthede en
versadigingvlakke. Die buigsaamheid was ondersoek deur middel van breek-energie, vervorming en die verplasing by
breekpunt. ʼn Analise van variasie (ANOVA) is uitgevoer op die toetsdata om sodoende die te
evalueer of die veranderlikes beduidend is ten opsigte van buigsaamheid. Daar is gevind dat die
buigsaamheideienskap sensitief is vir beide bitumen en sement inhoud. Met assessering van die
gekombineerde effek en betekenis van die veranderlikes op die buigsaamheid van die mengsels, is
daar gevind dat die hoogste beduidende veranderlike t.o.v breek-energie die sement inhoud is, gevolg
deur die bitumeninhoud, tipe behandeling en laastens die toetskondisie. Die orde van belangrikheid
verskil vir die ander twee parameters (verplasing en vervorming by breekpunt). Daar is ook gevind
dat die gekombineerde effek van sommige veranderlikes (sement inhoud en toets kondisie, tipe
behandeling en sement inhoud tesame met bitumen inhoud) ook beduidend was t.o.v breek-energie
en vervorming by breekpunt.
Vanuit die ITS en UCS toetse was daar ʼn toename in sterkte waargeneem soos die sementinhoud
toeneem. Aan die anderkant, het ʼn toename in bitumeninhoud ‘n afname in sterkte veroorsaak. Die
statistiese analise van ITS en UCS resultate, toon dat die grootste beduidende onafhanklike t.o.v ITS waardes ook die sement inhoud was, gevolg deur toets kondisies die grootste effek, bitumen inhoud
en die tipe behandeling. Die gekombineerde effek van sementinhoud en bitumeninhoud, was
betekenisvol vir beide ITS en UCS.
Drie-assige triaksiaaltoetse was uitgevoer om die gedragseienskappe van die mengsels te evalueer.
Daar is gevind dat die toename in sement inhoud, die skuif sterkte van die materiaal grootliks
verbeter. By ʼn konstante sementinhoud, wys toetsresultate van proefstukke wat getoets is by lae
digthede en hoë vlakke van versadiging, lae skuif sterkte.
Die Mr – θ model was gebruik om die veerkragsmodulus van die mengsels te moduleer en die
modelkoëffisiënte is gebruik om die effek van eksperimentele veranderlikes op die weerstand
modulus te evalueer. Met toename in die omhullende spanning is ‘n toename in die
veerkragsmodulus waargeneem, wat bevestig dat die gedrag van bitumen gestabiliseerde materiale
spannings afhanklik is. ʼn Toename in die sement en relatiewe digtheid het ʼn merkwaardige toename
in die veerkragsmodulus tot gevolg gehad, terwyl die teenoorgestelde waargeneem is met toename in
versadigingsvlakke.
Buiten die ingenieurseienskap en meganiese toetsfaktore, is ander faktore (soos die trekspanning
verhouding) bereken om die vogsensitiwiteit van die mengsels te evalueer. Mengsels met laer sement
inhoud het groter verswakking ervaar met blootstelling aan water. Bitumenemulsie proefstukke toon
beter weerstand teen water as skuimbitumen. Vergelyking tussen versnelde en korttermyn
nabehandelingsprosedure van proefstukke, toon hoër ITS en UCS waardes vir die versnelde
nabehandelingsprosedure prosedure. Buigsaamheid is ‘n belangrike eienskap van bitumen in padkonstruksie materiale (insluitend bitumen
gestabiliseerde materiale), maar word moeilik gemeet. Alhoewel verplasing/vervorming by
breekpunt en breek energie, bepaal vanaf ITS en UCS, ‘n indikasie toon van die hooffaktore (binder
en sement) wat buigsaamheid van bitumen gestabiliseerde materiaal beïnvloed, word meer akkurate
toetse benodig om die eienskap te ondersoek.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/86594 |
| Date | 04 1900 |
| Creators | Nwando, Tiyon Achille |
| Contributors | Jenkins, K. 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 | xv, 197 p. : ill. |
| Rights | Stellenbosch University |
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