Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Compaction is one of the key processes in the construction of road pavement layers. Not only
is it significant in ensuring the structural integrity of the material in the road layers, but it also
has an influence on the engineering properties and performance of the soil material. A poorly
compacted material is characterised by low density, high porosity and below standard shear
strength. This, as a result causes rutting, moisture susceptibility, potholing, corrugations and
passability problems on the road. Therefore, it is vitally important that field compaction is
done correctly. For this reason, laboratory compaction methods have been developed to
simulate the field compaction process in the laboratory.
The Mod AASHTO test has long been used as the laboratory compaction method of choice
by virtue of its simplicity and the lack of bulky equipment required. However, previous
studies have established that the Modified AASHTO method does not adequately simulate
field compaction criteria especially for cohesionless materials. Two reasons have been
advanced;
The Mod AASHTO compaction method does not adequately simulate the compaction
done in the field when the granular mix is laid;
The compaction method may cause disintegration of the material.
Alternative tests have been considered and much research has focused upon the use of a
modified demolition hammer (vibratory hammer) for laboratory compaction of granular
materials.
This study undertook to evaluate the influence of test factors pertinent to the vibratory
hammer compaction method. The influence of these test factors on compaction time and
obtainable material density was assessed with the objective of developing a compaction
method for granular materials. Vibratory hammer compaction tests were conducted on G3
hornfels, G4 hornfels and G7 sandstone material types and to a lesser extent, reclaimed
asphalt (RA). Densities obtained were referenced to Mod AASHTO compaction density.
Findings of the study showed that, the mass of the tamping foot has a significant influence on
the obtainable compaction density. Other factors such as, moisture content, frequency and
frame rigidity were also found to affect compaction with the vibratory hammer. In addition, it
is shown that the surcharge load does not significantly influence the obtainable compaction density but does contribute to the confinement of the material and restricts the upward bounce
of the hammer.
On the basis of the results and findings, a compaction method was proposed, incorporating
test parameters and factors that would provide ideal results for a set compaction time.
Repeatability tests showed that, the developed vibratory hammer compaction method was
effective in compacting graded crushed stone material types (i.e. G3 and G4) and probably
RA. The test was not as effective on the G7 material. Further studies on this material (G7) are
required.
In addition to the previous testing regime, a comparative assessment of the developed
vibratory hammer compaction method in relation to the vibratory table method was done. The
results show that the vibratory hammer is capable of producing specimens of densities
comparable to those of the vibratory table.
A sieve analysis undertaken before and after compaction showed that compaction with the
developed vibratory hammer compaction method does not result in any significant material
disintegration.
Based on the results of this study, a specification for the determination of maximum dry
density and optimum moisture content of granular material using the vibratory hammer is
recommended. / AFRIKAANSE OPSOMMING: Kompaksie is een van die belangrikste prosesse in die konstruksie van die padplaveisel. Dit is
nie net waardevol vir die versekering van strukturele integriteit van die materiaal, maar dit
het ook 'n invloed op die ingenieurseienskappe en vermoë van die grond materiaal. 'n Swak
gekompakteerde materiaal word gekenmerk deur 'n laë digtheid, hoë porositeit, on
onvoldoende skuifweerstand. Die kenmerke maak die material vatbaar vir vogen. Lei tot
spoorvorming, slaggate, golwe en deurgangs probleme op die pad. Dit is dus uiters
noodsaaklik dat veld kompaksie korrek gedoen word. Om hierdie rede, is kompaksie metodes
in die laboratorium ontwikkel om sodaend veldkompaksie te simuleer.
Die “Mod AASHTO” laboratorium kompaksie toets is die gekose laboratorium kompaksie
metode op grond van sy eenvoudigheid en gebruik van minimale toerusting. Vorige studies
het egter bevestig dat die “Mod AASHTO”-metode nie veldkompaksie akkuraat kan simuleer
nie, veral vir kohesielose materiaal. As gevolg van twee hoofredes;
Die Mod AASHTO kompaksiemetode is nie ‘n realistiese en vergelykende simmulering
van kompaksie soos dit in die veld gedoen word nie;
Die kompaksie metode mag verbrokkeling van die materiaal veroorsaak.
Alternatiewe toetse was oorweeg en baie navorsing het gefokus op die gebruik van 'n
aangepaste vibrerende hamer.
Hierdie studie het onderneem om verskeie relevante toetsfaktore van die vibrerende hamer en
hul invloed op die kompaksie en verkrygbare digtheid te bestudeer. Die invloed van hierdie
toetsfaktore op kompaksietyd en verkrygbare materiaal digtheid was geassesseer met die doel
om 'n kompaksiemetode vir granulêre materiaal te ontwikkel.
Vibrerende hammer kompaksietoetse was uitgevoer op G3 hornfels, G4 hornfels en G7
sandsteen materiaal en tot 'n mindere mate herwinde asfalt. Digthede verkry was verwys na
die Mod AASHTO kompaksie digtheid. Resultate van die studie het getoon dat die gewig van
die stamp voet ‘n merkwaardige invloed het op die verkrygbare kompaksie digtheid. Ander
faktore soos voginhoud, frekwensie en raam styfheid het ook getoon om kompaksiedigtheid
te beïnvloed met die vibrerende hammer. Benewens was ook getoon dat die toeslaglading
geen beduidende invloed het op die verkrygbare kompaksie digtheid nie, maar wel bydrae tot
die inperking van die materiaal en verhoed die vertikale terugslag van die hammer. Gebaseer op die resultate en bevindinge was ‘n kompaksiemetode voorgestel wat toets
parameters integreer met toetsfaktore en tot volg ideale resultate vir ‘n gegewe kompaksietyd
voorsien. Herhaalde kalibrasie toetse het getoon dat die ontwikkelde kompaksiemetode
effektief is in die kompaktering van gegradeerde gebreekte klip materiaaltipes (G3 en G4) en
moontlik herwanne asfalt. Die toets was nie so doeltreffend op die G7 materiaal nie. Verdere
studies op hierdie materiaal (G7) is dus nodig.
Addisioneel tot die vorige toets, is bevind dat ‘n vergelykende assesering van die ontwikkelde
vibrerende hammer kompaksiemetode in verhouding tot die vibrerende tafel. Die resultate
wys dat die vibrerende hammer die vermoë het om toetsmonsters met digthede vergelykbaar
met die vibrerende tafel te produseer.
Sifanalise voor en na kompaksie het getoon dat verdigting met die ontwikkelde vibrerende
hamer kompaksie metode nie lei tot die disintegrasie van die materiaal nie. Gebasseer op die
resultate van dié studie was ‘n spesifikasie vir die bepaling van maksimum droé digtheid en
optimale voginhoud van granulêre material aangeraai.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80132 |
| Date | 03 1900 |
| Creators | Chilukwa, Nathan Ntanda |
| Contributors | Jenkins, K. J., Rudman, C., 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 |
| Rights | Stellenbosch University |
Page generated in 0.0027 seconds