English: Mudrocks occur in many parts of southern Africa and large quantities
are used in road construction. This study involved research on the "state
of the art" of the road construction aspects of mudrocks in southern Africa,
as well as the general engineering-geological properties of such rocks and
the assessment of the most appropriate tests for classifying mudrocks for
road construction purposes.
The "state of the art" investigation, done by means of interviews with
users of the material, revealed much confusion about the terminology related
to these rocks. It was therefore decided to use the term "mudrock" as the
all-embracing term with "shale" and "mudstone" indicating fissile and
massive varieties respectively. The survey also found mudrock to be an important
construction material, especially in the Cape Province and Natal,
where it is used up to subbase level. Large differences of opinion exist
regarding the general road-building qualities of mudrocks. No particular
problem pertaining to construction with mudrock was identified, but the
break-down phenomenon on exposure gave rise to most of the concern expressed.
It was felt that other tests, additional to the standard ones used in road
construction, are necessary to characterize mudrocks.
A wide variety of property investigations and tests was performed on
14 mudrocks, sampled as soon as possible after excavation, from different
geological formations throughout South Africa. Although the samples were
selected to cover a wide range of engineering geological properties, since
they were limited in number it cannot be claimed that they are necessarily
representative of the whole range of southern African mudrocks.
Standard road construction tests showed some samples to be of subbase
standard. Plasticity indices were usually low. The addition of four
per cent lime generally caused a marked increase in the CBR strength. An
"accelerated weathering" test, in which CBR compactions were followed by
wet-dry cycles, indicated the different rates of break-down of the samples.
Extensive free swell tests on cubes, pretreated differently before immersion
in water, showed that the majority of samples expand less than one percent
during immersion after oven-drying.
tended to break down expanded more.
Air-drying increased the expansiveness
of the rocks to levels similar to those obtained after oven-drying. The
mudrocks were found to absorb water at different rates. In an experiment during which test cubes were subjected to temperature and humidity changes,
it was found that the mudrocks were more sensitive to humidity changes,
both as far as volume changes and moisture adsorption were concerned.
However, even large variations in temperature and humidity were not able
to produce a visual break-down such as was observed for some samples when
they were immersed in water.
The results from classification tests were investigated and correlated
to select tests which showed the best possibilities for mudrock classification.
It is considered that a road construction material needs to be resistant
to crushing, abrasion, and decomposition. The 10 per cent FACT,
carried out on dried and soaked samples, is preferred for testing the
resistance to crushing. A wet ball mill test was developed for testing
resistance to abrasion. This test was more successful in separating samples
of different qualities than the Los Angeles abrasion test and the results
correlated well with those obtained from an ultrasonic disaggregation test.
The sand equivalent test is recommended to determine the presence of deleterious
material in the crushed mudrock. The break-down of mudrocks at various
rates on exposure is not fully evaluated by the above tests, nor by
the standard road construction tests. Two varieties of the break-down
phenomenon were observed although there appears to be a gradation between
the two processes, i.e. the break-down of the rock into hard fragments
(disintegration) and the break-down into silt or clay-sized particles
(slaking). It is considered that slaking can be measured by means of the
slake durability test, but disintegration should be evaluated qualitatively
by performing a five-cycle wet-dry test, using water. Tests, such as the
Washington degradation, ethylene glycol soaking, methylene blue adsorption,
sodium sulphate soundness, rate of slaking and conductivity, were found to
be unsuitable for general classification purposes.
Afrikaans: Modderrots word in verskeie dele van suidelike Afrika aangetref en
groat hoeveelhede daarvan word in padbou gebruik. In hierdie studie is
die huidige gebruike, sowel as die algemene ingenieurs-geologiese eienskappe
van sodanige rots en die beoordeling van die mees geskikte toetse met
betrekking tot die klassifikasie van modderrots vir padbou-doeleindes in
suidelike Afrika, ondersoek.
Die ondersoek na die huidige gebruike wat verband hou met modderrots,
gedoen deur onderhoude met gebruikers van die materiaal te voer, het getoon
dat daar heelwat verwarring bestaan oar die terminologie wat betrekking het
op hierdie rotse. Daar is dus besluit om die term "modderrots" as die
allesomvattende term te gebruik met "skalie" en "moddersteen" onderskeidelik
as fissiele en massiewe tipes. Die opname het oak getoon dat modderrots
n belangrike konstruksie-materiaal is, veral in die Kaapprovinsie en Natal
waar dit tot in die stutlaag gebruik word. Daar bestaan groat meningsverskille
oar die algemene padboueienskappe van modderrots. Geen besondere
probleem behorende tot the gebruik van modderrots in padbou is waargeneem
nie maar die verskynsel van opbreek na blootstelling wek die meeste kommer.
Daar is gevoel dat, benewens die standaardpadboutoetse, nag bykomende toetse
nodig is vir die karakterisering van modderrotse.
n Groot verskeidenheid ondersoeke na en toetse van die eienskappe is
uitgevoer op 14 modderrotse, waarvan monsters so gou moontlik na uitgrawing
uit verskillende geologiese formasies dwarsoor Suid-Afrika verkry is.
Alhoewel die monsters gekies is om n wye reeks ingenieurs-geologiese eienskappe
te dek, is hulle vanwee die beperkte getal nie noodwendig verteenwoordigend
van die hele reeks suider Afrikaanse modderrotse nie.
Standaard padboutoetse het getoon dat sommige van die monsters van
stutlaaggehalte was. Plastisiteitsindekse was oar die algemeen laag terwyl
die byvoeging van vier persent kalk gewoonlik n aansienlike KDV sterktetoename
tot gevolg gehad het. n Versnelde verweringstoets waartydens
KDV-verdigting gevolg is deur nat-droogsiklusse het die verskillende tempo's
van opbreking van die monsters getoon. Uitgebreide vrysweltoetse, uitgevoer
op kubusse wat verskillend behandel is voor indompeling in die water,
het getoon dat meeste van die monsters minder as een persent swel tydens
indompeling na oonddroging. Sommige verweerde rotse en diegene wat geneig was om op te breek het egter meer geswel. Lugdroging het die uitswelvermoe
van die rotse verhoog tot op dieselfde vlak as die wat na oonddroging
verkry is. Daar is gevind dat modderrotse water teen verskillende
tempo's absorbeer. In 'n eksperiment waartydens toetskubusse aan temperatuur-
en humiditeitsveranderinge blootgestel is, is daar gevind dat
modderrots meer gevoelig is vir humiditeitsveranderinge. Dit geld
vir beide volume-veranderinge en vogadsorpsie. Nietemin, kon selfs groot
wisselings in temperatuur en humiditeit nie sigbare opbreking te weeg bring
nie, soos wat wel waargeneem is by sommige van die monsters by indompeling
in water.
Die resultate verkry uit klassifikasietoetse is ondersoek en gekorreleer
om die mees geskikte toetse vir modderrots-klassifikasie te kies. Daar
word geag dat 'n padboumateriaal bestand moet wees teen vergruising, afskuring
en ontbinding. Die 10 persent FAVT, uitgevoer op gedroogde en
geweekte monsters, word vir die toets van bestandheid teen vergruising
verkies. 'n Nat balmeultoets is vir die toets van bestandheid teen afskuring
ontwikkel. Hierdie toets was meer suksesvol in die skeiding van
monsters van verskillende kwaliteite as die Los Angeles-afskuurtoets, en
die resultate het goed gekorreleer met die wat verkry is uit 'n ultrasoniese
disaggregasietoets. Die sand-ekwivalenttoets word aanbeveel om die teenwoordigheid
van skadelike materiaal in die vergruisde modderrots te bepaal.
Die opbreking van modderrots teen verskillende tempo's as gevolg
van blootstelling word nie deur bostaande toetse of deur die standaardpadboutoetse
geevalueer nie. Twee variasies van die opbreekverskynsel is
waargeneem alhoewel dit blyk dat daar nie 'n definitiewe skeiding tussen
die twee prosesse is nie; d.i. opbreking van die rots tot harde stukkies
(disintegrasie) en opbreking na slik- of kleigrootte partikels (blus).
Daar word geag dat blus deur middel van die blusduursaamheidstoets bepaal
kan word, maar disintegrasie moet kwalitatief evalueer word deur 'n vyfsiklus
nat-droogtoets met water uit te voer. Toetse soos Washingtondegradasie,
weking in etileenglikol, metileenblou-adsorpsie, natriumsulfaatgaafheid,
tempo van blus en geleidingsvermoe is as ongeskik vir algemene
klassifikasie doeleindes bevind.
