Bror
BRARD,STESTINTO THE 2Ist CENTURY:
SODIUMSULFATESOUNDNESS
TESTINGOF
DIMENSIONSTONE
David West
Hyder Consulting,Sydney
ABSTRACT: The testing of dimension stonefbr durability by cyclic immersion in a sodium sulfate
solution and drying to allow its crystallisationin pores goes back nearly 200 years.This paper
describesthe publishedhistory of salt crystallisationtests for porous building stone in Europe,
particularlyin the United Kingdom, and in Australia.
Standardmethodsfbr sodium sulfate soundnesstestshave been publishedin Australia and Europe
over the past few years.The key parametersin thesetwo methodsfor testing of dimensionstone are
compared.Available data comparingvariationsin procedure,using a rangeof Australian sandstones,
are presentedand discussed.Thesedata are correlatedwith other physical propertieswhich serve as
predictorsof durability, as well as observationsof stoneperformancein serviceover the pastcentury.
The usefulnessof the sodium sulfatesoundnesstest as a durability predictorfbr Sydneysandstoneis
discussed,and conclusionsaboutthe accuracyand applicability of the procedureare presented.
1. HISTORYOF PROCEDURE
EUROPEAND USA
developedby the UK Building ResearchStation
(DSIR, 1928 in Knofel, Hoffmann and
The father of sodium sulfatesoundnesstesting is
S n e t h l a g e ,1 9 8 7 ; S c h a f t e r , 1 9 3 2 i n W a l l a c e ,
recognised as Brard (de Thury et al., 1828
l 9 7 l ) , b a s e do n t h e m e t h o d o f O r t o n ( 1 9 1 9 ) .
Luquer,1895in Wallace,1971),who describeda
Results from these methods were found to be
method for evaluatingthe susceptibilityof stone reproducible provided that the conditions were
to damage by freezing and thawing using carefully controlled.
Glauber's salt (sodium sulfate).Developments
Further work in the 1950s and 1960s by
during the 19th Century were described by
Honeyborne (Honeyborne and Harris, 1958;
Luquer(1895).At this stage,the testwas usedas Honeyborne, 1964) at the Building Research
an acceleratedfreezingtest.
Station establishedthe method in the UK. This
Many variations to the method were used, history can then be traced through to Price
including salts such as magnesium,calcium and (1978) and his descriptionof the use of the test
potassiumsulfates.potassiumnitrate and sodium fbr evaluatingdurability of stone.
chloride. However, generalopinion was evidentMeanwhile work in Germany had led to the
ly that the sodium sulfate soundnesstest did not
adoptionof a test method using a saturatedsolugive a reliable estimateof damagefrom freeze- tion of sodium sulfate.but diff'erentdurationsfor
quotedin Wallace,1971).
thaw (Schaffer,1932,
each stageof the cycle. This was publishedas
Researchinto stonedurability during the 1920s D I N 5 2 1 1 1 i n 1 9 1 6 ( K n o f e l . H o f f m a n n a n d
and 1930s began to identify the role played by
S n e t h l a g el 9, 8 7 ) .
solublesalts.The sodium sulf'atesoundnesstest
Further work was carried out at the Building
was re-established
as a meansof assessingthe R e s e a r c h E s t a b l i s h m e n t a n d p u b l i s h e d b y
resistanceof stone to crystallisationof soluble Honeyborne(1982) on French limestones;by
salts.It was acknowledgedthat there was a need Leary (1983) on British limestones;by Leary
(1986)on British sandstones,
to carefully control the conditions of the test, in
and by Hart (1988)
order to ensurethe formation of only one type of
on British magnesianlimestones.This research
sodium sulfatecrystal (Kesslerand Sligh, 1928 was used as the basis for durability classificaquotedin Wallace,1971).
tions for limestonesand sandstones.The test
Sodium sulfate soundnesstests,using either a
procedure adopted for sandstonesutilised a
s o l u t i o n c o n t a i n i n g 1 4 c / cb y w e i g h t o f t h e saturated solution of sodium sulfate (Leary,
hydrated salt or a saturated solution, were
1986).
138
During th
on Dimensi
of a salt cr1
sulfatesou
past the sr
comm.).
Binda anc
into the effr
the resultst
nesstest us
longer dry
humidity in,
Ross and
Butlin (19
applicablet
and slatedu
soundnesst
In 1990
criticised I
sulfate sou
on the nur
and Masse
set for turl
sodium su
industry.
Meanwh
as a Europ
committee
draft of EN
Determinat
was ballote
beenpublis
The key
Appendix r
Australian
2. HISTC
AUST
The early
testing of
described
quoted in
mechanisr
salts,but dr
sodium sul
performan
evidently r
the British
( 1 9 6 s ,1 9 6
used the I
testing,an
for porous
Brard' s Test into the 2 I st Century: SodiumSulfuteSoundnessTestingoJDimensionStone(West)
)F
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Iest
During the mid-1980s,ASTM CommitteeCl8
on Dimension Stoneconsideredthe development
of a salt crystallisationtest basedon the sodium
sulfate soundnesstest, but this did not proceed
past the subcommittee level (Winkler, pers.
comm.).
Binda and Baronio (1987) reportedon research
into the effect of drying times and humidity on
the results of a saturatedsodium sulfate soundnesstest using brick specimens.This found that
longer drying times and decreasedrelative
humidity increasedthe rate of deterioration.
Ross and Butlin (1989) and Ross, Hart and
B u t l i n ( 1 9 9l ) d e s c r i b e d a n u m b e r o f t e s t s
of sandstone,limestone
applicableto assessment
and slatedurability, including the sodium sulfate
test.
soundness
In 1990, Sedman and Stanley (1990a, b)
criticised the reproducibility of the sodium
sulfate soundnesstest, with particular emphasis
on the number of specimensrequired. Ross
and Massey(1990)responded,but the stagewas
set for further criticism of the validity of the
sodium sulfate soundnesstest by the stone
industry.
Meanwhile, the procedurehad been proposed
as a European standardand was subject to the
committee development processes.The final
draft of EN12370 Natural stone test methodsDeterminationof resistanceto salt crystallisation
was ballotedat the end of 1998.This has since
beenpublishedas a Europeanstandard.
The key parametersin 8N12370 are given in
Appendix A, where they are comparedwith the
AustralianASNZS4456.l0 MethodA.
:,
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2. HISTORYOF PROCEDURE
AUSTRALIA
The early history of sodium sulfate durability
testing of Australian dimension stones was
d e s c r i b e db y W a l l a c e ( 1 9 7 1 ) . F i n c h ( 1 9 5 5 ,
q u o t e d i n W a l l a c e , 1 9 7 1 ) i n v e s t i g a t e dt h e
mechanismsof stone decay causedby soluble
salts,but doesnot appearto have undertakenany
sodium sulfatetestingto correlatewith the stone
performance in structures. Various authors
evidently reported using the tests developedby
the British ResearchStation in the 1920s.Minty
( 1 9 6 5 ,1 9 6 6a n d 1 9 7 0 ;q u o t e di n W a l l a c e ,1 9 7 1 )
used the ASTM C88 procedurefor aggregate
testing,and concludedthis was too aggressive
for porousstone.
Wallace himself carried out a program of
sodium sulfate testing on NSW dimension
stones.He describesa procedure remarkably
similar to that contained in EN 12310, and
apparentlybasedon the British BRS methods.
He used 14olo sodium sulfate solution for
sandstones.as well as saturatedsodium sulfate
marblesand granites.
solutionfor sandstones,
The resultsof this testing were comparedwith
performanceof the various materialsin use, and
a degreeof correlationwas obtained.Wallace
suggestedthat the sodium sulfate test was a
useful indicator of durability, although care had
to be taken to ensure that the results were
reproducible (and therefore comparable).He
identified two different patternsof behaviourfor
in the sodium sulfatetest.
sandstones
tendedto
Fine-grainedargillaceoussandstones
suffer minor loss of surfacegrains, followed by
suddenloss of a 3-5 mm thicknessof an entire
face. This would manifest itself as a surface
crack in one cycle, and during hydration in a
subsequentcycle, the surfacelayer would detach
with
(seeFigure l(1)). Quartz-richsandstones,
less clay present,tended to suffer successive
removal of surface grains, with rounding of
arrisesleading to significantloss of mass (see
Figure 1(2)).
The tests on marbles and granitescarried out
by Wallace using the saturatedsodium sulfate
solution indicatedthat the graniteswere typically
not affected to any seriousdegree.Some minor
loss of mica, or pitting of weatheredfeldspar
crystalsoccurred,but no other deteriorationwas
noted.
Crystalline marbles suffered mass losses in
the range l-27c, although some specimens,
particularly those of the more coarse-grained
varieties,disintegrated.The non-crystallineor
very finely crystallinemarbleswere not affected
in any significant manner. Marbles or dense
limestones containing veins were typically
affectedby erosionor splitting along the veins.
W a l l a c e ( 1 9 7 1 ) c o n c l u d e dt h a t w h i l s t t h e
sodium sulfate tests duplicated the pattern of
deterioration found in service, there was no
correlation between performancein the sodium
sulfate test and other physical properties.He
recommendedthat the sodium sulfate test be
incorporated into the overall durability
of dimensionstone,but that results
assessment
from the test shouldnot be usedin isolation.
r39
Sydney-The
(I)
B ra
SandstoneCity
80
F I N E G R A I N E DA R G I L L A C E O U SANOSTONES
S
I .o
fit
I
I
It
I
.c
CD
t!
540
EARLY CYCLES
gf orriscr
5 l i g h tr o u n d i n o
MID_TEST
A b s o r p t i o no f s o l t s o l u t i o n
'd'.
to dcpth
Strerrqs
o p p l i c do t r c a i o no f d o t t o d
linc by cxponrion
o
o
LATTER CYCLES
C r y s t o l l i s o t i o no I s o l t o n d
r u b s c q u c n th y d r o t i o nl o r c e s
fho skin lrom thc corc - o
l y p o o l r c a u l o rc x f o l i o t i o n
M ID - T E S T
LATTER CYCLES
Typicol roundcd thopo
ql coopl.tign of test
Fig. 1. Nature of deterioration of Australian argillaceous and quartz sandstonesduring the sodium sulfate
soundnesstest (following Wallace, 1971).
Spry (1983) carried out testing of thirty
commercially available Australian dimension
sandstones.
Included in the testscarried out were
sodium sulfate soundnesswith a 14% solution:
water absorption and porosity measurements;
compressivestrengthand petrographicanalyses.
He also inspecteda wide range of buildings
constructedfrom most of these sandstones.and
provided a subjective correlation between their
serviceperformanceand the results of the tests.
Spry then attempted to correlate durability, as
measuredby the sodium sulfate test, with other
physicalproperties.
As part of this process, Spry adopted a
durability classificationsystemas follows:
A class(most durable)
B class
C class
D class(leastdurable)
0-5Vomassloss
5-l0%o
l0-20Vo
2V100Eo
He stated that D class sandstonescould be
considered unsuitable for use in exposed
positions (plinths, cornices, sills, mouldings,
etc.), in prestigemodem buildings, and in highly
polluted urban or coastal environments. Spry
also plotted sodium sulfatetest resultson a graph
of water absorptionagainstcompressivestrength
(seeFigure 2).
Following publication of this work, Standards
Australia commenced work on a suite of test
methodsfor dimensionstone.The sodium sulfate
test was one of theseprocedures.Ongoing testing
and discussionled to concernsthat the oven
drying temperatureof l0"C might have caused
more rapid deterioration of the argillaceous
sandstones
than was due to the salt crystallisation
alone. Review of the sodium sulfate hydration
chemistry, and of other test methods (in
particular ASTM dimension stone tests)
suggestedthe use of an oven drying temperature
of 6oC.
A comparativeprogram of testing using l4Vo
sodium sulfate solution and an oven temperature
of 65"C was undertakenby West (unpublished,
1987). This used previously untestedspecimens
of someof the sandstones
testedby Spry in 1983.
Theseresults,along with those obtainedby Spry
t40
I
t*
1-
_l_-
I
TL
-
L o s s o l r u r l q c cm
r ooltccr ri oi ol l
.
Tts r o
o
lt
(?) QUARTZ SANDSTONES
EARLY CYCLES
Minorlosr of rurfoci oroins
r-
oE i-3oo T''---
T
0
I
( 1 9 8 3 )a r e
how these :
compressr
(le83).
As are
Australia
reduction ir
stone dur
publishedb
A class(t
B class
C class
D c l a s s(
The dimr
published I
sodium sul
of test met
pavers wh
Methods oJ
pavers in
AS/I{2S44
to salt atta
compared \
3. COMF
AS/N
Whilst the
and AS/N
related, thr
that results
not compa
Brard' s Test into the 2 LstCentur v-:Sodium Sulfate SoundnessTesting of Dimension
Stone (West)
BO
t!
o.
E
boo
tl
t
Ja
ID
tlf
-40
gt
o
,6
Fig. 2. Sodium sulfare
soundnessof Australian
sandstoneswith respect
to water absorption and
compresslve strength;
testedat 105'C. Following Spry, 1983.
.Dn
(t
a
E
o
0
o
8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4
apparentporo3ity {% by vol.}
(1983) are given in Appendix B. Figure 3 shows
how theseresults fit on the water absorptionvs
compresslve strength plot prepared by Spry
(1983).
As a result of this work, the Standards
Australia committee adopted the proposed
reduction in oven-drying temperature.A revised
stone durability classification system was
publishedby Spry (1989):
A class(most durable)
B class
C class
D class(leastdurable)
VlVo massloss
l-5To
5-10Vo
l0-l00Ea
28
30
Size of specimen:EN12370 requires 40 mm
cubes;A5[.{254456. l0 uses50 mm cubes.
n u m b e r o f s p e c i m e n s :E N 1 2 3 7 0 r e q u i r e s a
m i n i m u m o f 6 s p e c i m e n s ;A S / N 2 S 4 4 5 6 . 1 0
specifiesonly 3.
Sodium sulfatesolution: EN12370 requiresfresh
solutionat every cycle; .45/l.{254456.l0 requires
that the solution be unchanged,and only topped
up as necessary.
Dr)zing temperature: EN 12370 specifies
105+5'C;ASA{2S4456.10stiputares
65+3"C.
The dimension stone standardshave not been
published by StandardsAustralia. However, the
sodium sulfate test was incorporatedinto a suite
of test methodsfor masonry units and segmental
pavers which was published as AS/N2S4456
Methods of testfor masonry units and segmental
pavers in 1997. The relevant parameters of
ASNZS4456 Method l0: Determiningresistance
to salt attack, Method A for dimensionstone are
comparedwith ENl2370 in Appendix A.
3. COMPARISON
OF EN1237O
AND
ASiNZS4456
Whilst the test proceduresdescribedin EN12370
and AS/NZS4456.10 Method A are closely
related, there are eight differences which mean
that results obtained using the two methods are
not comparable.Thesedifferencesare:
Room temperature: EN 12310 specifies
20+0.5'C;ASNZS4456.l0 requiresl9+3"C.
Storing of specimens:During interruption of
cycling EN12370 requires thar specimensbe
storedin the oven at 105+5oC;4,5A{254456.10
stipulatesthat specimensbe storedin desiccator.
Treatmentafter l5 cycles:EN12370 requiresa
24 how soak in water followed by washing and
drying at 105+5'C; ASNZS4456.t0 specifies
weighing after l5 cycles as well as collection,
drying and weighing of residuesin a container.
Measurementof mass:ENl2370 measuresmass
loss after washing; ASNZS4456.l0 measures
the greater of mass loss after 15 cycles or the
massof the residue.
141
Sydney-The
SandstoneCit,t,
5.2 Measurement of Mass Loss
The data from different methods of measuring
the mass loss show that when this is determined
at 15 cycles it is less than that obtained by
weighing the dried residuefor specimens,in all
casesup to a loss of around 107o.Above this
amount,the differencebecomesmarginal.Below
approximately 1Vo mass loss measured by
weighing the residue,the mass loss cannot be
measuredat l5 cycles becausethe specimens
retain saltsand are heavierthan at the beginning
of the testingcycle.
When the specimensare subjectedto surface
washing,there is minimal changefor specimens
4. RESULTS- AUSTRALIAN
with a 1'lo mass loss measuredby weighing the
SANDSTONES
residue,but a significantincreasein measured
As describedabove,Spry (1983)reportedon the mass loss for most other specimens.There is no
testing of thirty different samplesof Australian closecorrelationbetweenthe massloss measured
sandstonesusing 14olosodium sulfate solution after surface washing and that determined by
with a drying temperatureof 105+5'C. West weighing the residue.
An extended wash leads to even greater
(unpublished,1987) repeatedthe testing for a
selectionof unusedsamplesof those materials, discrepanciesbetweenthe measuredmass loss
and that measuredby weighing the residue.This
using l4Vo sodium sulfate solution with a drying
temperatureof 65+3"C, in the same laboratory is particularly obvious for specimenswith a loss
between 5-207o. where the mass loss measured
and using essentiallythe same equipment. The
afler extended washing is greater than that
resultsfrom thesetwo test programsare given in
measuredby weighing the residue.
Appendix B.
These data provided the basis for recomAdditional data from thesetestsrelating to the
measurementof massloss are given in Appendix mending that the residue collected after testing
C. Thesedata comparethe massloss determined be dried and weighed, as this is the mass which
has actually beenlost from the specimensduring
in four ways:
. Measuredafter 15 cycles;
testing.
. After surfacewashingat 15 cycles;
. Weighing of dried residue after 15 cycles; 5.3 Correlation of Durability with Strength
and Porosity
and
. After extendedsoakins.in water.
Examinationof Figures 2 and 3 showsthat there
is generally a correlation between high
D
I
S
C
U
S
S
I
O
N
5.
durability, representedby low mass loss in the
salt crystallisationtest, and high compressive
Temperature
5.1 Drying
strength and low apparentporosity. There is
The results from the two sets of tests show that overlapbetweeneachof Spry's durability classes
mass lossesat a drying temperatureof 65oC are for both setsof testing,particularlyclassesB and
substantiallyless than those at 105'C. The rank- C. However, samplesclassifiedin classesA and
ing of the two setsis also similar, althoughthere D are clearly separableby compressivestrength
are somediscrepancies.Of particular interestare and apparentporosity, as well as by the salt
the substantialdiscrepanciesin behaviourof the crystallisationresults.
Bondi sandstone(#26) and one of the Helidon
samples (#5). Further testing would have been 5.4 Performance in Service
necessary to identify the source of these Spry (1983) attempted to correlate the perfbrdiscrepancies.There is clear differentiation mance of the sandstoneshe tested with the
resultsof the salt crystallisationtest. This was
between various sandstonesat both drying
difficult due to the time elapsed between
temperatures.
With the exception of the number of specimens
tested,the significanceof each difference is not
clearly understood.Some differences(such as
the drying temperature,and the procedure for
measuringmassloss)have a substantialeffect on
the results.Others,such as the specimenstoring
during cycling interruptions,may have much less
inf-luence.
The best methodof investigatingtheseissues
would be to undertakea program of comparative
testing, preferably by more than one laboratory
but using specimenspreparedfrom the same
samples.
142
Bra
building c
samples,a
and situati
Neverthele
the interpr
sodium sul
ln order
issue,cons
different
performan
'
required.
constructe
(suchas a s
salt damp)
the sodium
from the s
stonesfor t
6. VALIT
SULF
6.1Histo
Questions
sulfatesou
stonedura
procedure
covereditr
process,ar
test is rele
endured ir
original. T
inherent r
method.
The resu
validity of
variabilitl
required.
variability
also requ
display sig
ACTOSS Sfi
function ,
'
processes
to correlr
understan
specimen
they were
Inter-lat
'round-rot
informati
sulfate te
laboratori
Brard' s Test into the 2I st Centurv-;sodium SulfateSoundnessTesting,o.fDimensionSrone(West)
.J.i\UIlng
. .r . s n n i n e d
: - , , : n e db y
:.... in all
:: .- , , r e t h i s
. - - " , , . .B e l o w
- : . . .- l r e d b ]
. . , . r i - t f l ob
te
:-, -:3almens
- , - . .r n n i ns
.i:.. .,surface
- reclmens
, : :hin-e the
;
:lle&SUf9d
- . I:rr.re is no
.- :reasured
'- '
: r - r l n e db y
:
- : . greoter
.-:.:llllSS 1OSS
: -- . .- : u e T
. his
:-.,.thaloss
., :]leasured
: ' : - : : l . t nt h a t
:- recom::r tesilng
....:.. ri.'hich
'
--r. drrrino
> : r en g t h
- :hat there
: - 3 1 1h i g h
. ,.: in the
,::pressive
' There is
- t:\ classes
. , - . e sB a n d
,..3.A and
.
- .rrenoth
- . rhe salt
--nerfnr-
.rith the
This was
rc't\\'€9Il
building construction and quarrying of his
samples,as well as the range of environments
and situationsin which the stoneswere used.
Nevertheless,his observationstendedto support
the interpretation that a lower mass loss in the
sodium sulfatetest indicatedhigher durability.
In order to gain a better appreciationof this
issue,constructionof test walls containingthe
different stones and monitoring of their
performance over at least a decade would be
required. These test walls would need to be
constructed in situations subiect to salt attack
(such as a seawall, or in an areasubjectto rising
salt damp). Specimensfor testing according to
the sodium sulfatetest would needto be prepared
from the same blocks of stone used to prepare
stonesfor the testwalls.
6. VALIDITY OF THE SODIUM
TEST
SULFATESOUNDNESS
6.1Historyof Concems
Questions about the validity of the sodium
sulfatesoundnesstest as a predictorof dimension
stone durability have been raised throughoutthe
procedure's existence. These questions have
most stagesof the
coveredits appropriateness,
process,and the type of material for which the
test is relevant. Nevertheless,the procedurehas
endured in a format remarkably similar to the
original. This alone suggeststhat there is some
inherent validity and usefulnessfor this test
method.
The resultspresentedin this paper supportthe
validity of the test, but further researchinto the
variability and reproducibility of results is
required. An appreciation of the inherent
variability of dimensionstonesbeing testedts
also required. Sandstone,in particular, can
display significantchangesin physicalproperties
across small distances in the ground, as a
function of the sedimentary and diagenetic
processeswhich formed it. This makesit difficult
to correlate results unless there is a good
understandingof the original position of the test
specimensin the sandstonedeposit from which
they were taken.
Inter-laboratorycomparisontesting (so-called
'round-robin' studies)would also provide useful
information on the reproducibility of sodium
sulfate test results. both within and between
Iaboratories.
6.2 Control of the Drying Stage
Discussionswith the BRE in 1999 (Yates,pers
comm.) indicated that their key concerns with
sulfate test reproducibility revolved around
control of the oven-drying process.These
concernsmirror opinions expressedin Australia
by laboratories with experience in this test
procedure.
The humidity and rate of drying in the oven
can influence the hydration state of the sodium
sulfate crystals formed in the pores of the test
specimens. This will then influence the
magnitudeof forcesimposedwithin the poresby
the sodium sulfate crystals. Slow drying in a
humid oven atmosphere may permit large
hydrated sodium sulfate crystals to form in the
rock pores. A faster drying rate or a drier
environment may limit the growth of hydrated
crystals,with only the smalleranhydrouscrystals
being formed.
Observationsof sandstonespecimensduring
the sodium sulfate test indicate that material is
most commonly lost from the specimensduring
the first few secondsof the immersion cycle.
This is probably due to expansionof the sodium
sulfate crystals during rehydration from the
anhydrousstate.
Given such behaviour,the specimendamage
causedby the sodium sulfatetest can be expected
to be greatest where oven drying is slow and
humidity high. Large hydratedcrystalswill form
twice in each cycle, during drying and during
immersion. A more rapid drying rate in a drier
environmentwill causehydrated sodium sulf'ate
crystals to grow only once in each cycle d u r i n gt h e i n i t i a li m m e r s i o n .
It is therefore suggestedthat the reproducibility of resultsfrom the sodium sulfatetest is
dependentupon the consistencyof oven-drying
conditions.Sincethis is perhapsthe hardestof all
test factors to monitor and understand,let alone
control, it is likely that the reproducibility of the
sodium sulfate test will continue to be relatively
poor.
This does not mean that these results are
invalid, but some caution must be taken not to
interpret the results too rigidly. The arbitrary
classboundariesof Spry (1983, 1989)shouldbe
considered flexible where results from the
sodium sulfate test fall across a single class
boundary. A spread across three or even four
diiferent classesmight indicate a problem with
r43
Sydney-The
SandstoneCitY
The data which formed the basis for
developmentof the Australian Standardmethod
are presented,along with justification for the
adoption of a lower drying temperatureand the
requirement for weighing of the residue.
Further researchis neededto better understand
the sourceof resultsvariability from this test' It is
possible that inter-laboratory tests' along with
comparison between the Europeanand Australian
Standards,could provide valuable information'
reproducibility of the test, as would variationsin
results obtained by different laboratories,
particularly where the specimenswere prepared
from a single samPleblock.
6.3 Number of Specimens
Another source of inconsistencyin the test as
performed in Australia is the small number of
specimens.Experimentaldata in many fields of
materials testing indicate a relatively large
spreadof resultswhere only three specrmensare
tested for a particular property. This is
particularly the case where the material is
natural rather than manufactured. The use of
five, seven or ten specimens is common for
the determination of other physical properties'
Given that the major cost in carrying out
the sodium sulfate test is the time taken daily
to rotate the specimensthrough each cycle,
there is a strong argument for increasing the
number of specimenstested to reduce results
8. ACKNOWLEDGMENTS
I could not have written this paper without the
inspiration and guidance of Dr Alan Spry, to
whom I am indebted. Much of the history of
sodium sulfate testing was documentedby Ian
Wallace in his PhD thesis(1971), and by Carr,
Strickland,McDonald and Bortz (1996).Most of
the testing reported here was originally
undertaken in the laboratories of Australian
Mineral DevelopmentLaboratories,now Amdel
Limited. Copies of test reports containing much
of the data were provided by Gosford Quarries
variability.
AND
7. CONCLUSIONS
RECOMMENDATIONS
Pty Limited.
Thanks are also due to Gib Mclntee, Chairman
ASTM Committee C18 at the time, for the
of
This paper describes the history of sodium
to prepare the background informatron
invitation
sulfate testing of dimension stone,and suggests
in this paper for presentation at the
contained
that the test providesvaluable information about
joint
C18 and CEN TC246 Sympostum
ASTM
in
the likely durability of sandstonesused
and Weathering Standardsfor
Durability
buildings, particularly where subject to salt on
in Canara,Italy in May 1999'
Stone
Dimension
attack.
f
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