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Cite this articleAl-Jabban W, Laue J, Knutsson S and Al-Ansari NBriefing: Common laboratory procedures to prepare and cure stabilised soil specimens: a shortreview. Geotechnical Research,https://doi.org/10.1680/jgere.19.00035
BriefingPaper 1900035Received 30/08/2019; Accepted 17/12/2019
Published with permission by the ICE under theCC-BY 4.0 license.(http://creativecommons.org/licenses/by/4.0/)
Keywords: codes of practice &standards/geotechnical engineering/strength & testing of materials
Geotechnical Research
Briefing: Common laboratory procedures toprepare and cure stabilised soil specimens:a short review
1 Wathiq Al-Jabban BSc, MSc, PhDDepartment of Civil, Environmental and Natural ResourcesEngineering, Lulea University of Technology, Lulea, Sweden;Department of Civil Engineering, University of Babylon, Hilla, Iraq(Orcid:0000-0003-3474-7340)
2 Jan Laue BSc, MSc, PhD
Department of Civil, Environmental and Natural ResourcesEngineering, Lulea University of Technology, Lulea, Sweden(Orcid:0000-0003-1935-1743)3 Sven Knutsson BSc, MSc, PhD
Department of Civil, Environmental and Natural ResourcesEngineering, Lulea University of Technology, Lulea, Sweden(Orcid:0000-0002-1365-8552)4 Nadhir Al-Ansari BSc, MSc, PhD
Department of Civil, Environmental and Natural ResourcesEngineering, Lulea University of Technology, Lulea, Sweden(corresponding author: [email protected])(Orcid:0000-0002-6790-2653)1 2 3 4
Soil stabilisation is used extensively to improve the physical and mechanical properties of soils to achieve thedesired strength and durability properties. During the design process, laboratory investigation is conducted firstly toobtain an enhancement in soil strength and stiffness, in addition to the type and amount of binder required. Themethods of preparing and curing specimens of soil–binder mixtures directly influence the properties of the stabilisedsoils. The most common laboratory protocols used for preparing and curing the specimens of stabilised soil arepresented in this short review. The review focuses on several aspects such as homogenisation of the natural soil,mixing type and duration, mould type, moulding techniques and curing time and condition. This review can assistvarious construction projects that deal with soil improvement to choose an appropriate method for preparingand curing a soil–binder mixture to simulate the field conditions as much as possible and obtain uniformsoil–binder mixtures.
IntroductionFor soil stabilisation applications, the specimens of a soil–bindermixture are prepared in a laboratory according to a standardprocedure, which in principle should simulate the field conditions.These procedures vary between different countries; in addition,there are variations between different testing companies (Åhnbergand Holm, 2009; BRE, 2002; BSI, 2005; Carlsten and Ekström,1997; Kitazume, 2012). In Sweden, the specimens of soil–bindermixtures are prepared according to the common proceduredescribed by the Swedish Geotechnical Society (SGS) (Carlstenand Ekström, 1997) and the Building Research Establishment(BRE, 2002). In Japan, the specimens are prepared according tothe Japanese Geotechnical Society standard (Kitazume and Terashi,2013). These variations are related to differences in soil type, typeand procedure of soil stabilisation in the field and differences intraditional laboratory testing in general (Åhnberg and Holm, 2009).
Generally, the specimen of a stabilised soil is prepared in alaboratory according to a standard protocol, which normallyconsists of several steps. Firstly, natural soil is homogenised, andthen a cementitious binder is added in dry or in slurry form, and
the mixture is blended by hand or an electric blender for a certaintime. Then, the soil–binder mixtures are gradually filled as layersin a mould or tube according to the specified technique. Usually,five different moulding techniques can be used or combined toprepare a specimen, as summarised in the following (Kitazumeet al., 2015).
■ Tapping. For each layer, the mould is tapped (hit) against atable or the floor for a specified number of times until thespecimen height is subsequently filled.
■ Rodding. For each layer, the mixture is slowly tamped downfor a specified number of times using a rod to compact/smooth out each layer.
■ Dynamic compaction. Each layer is compacted by using aProctor hammer for specified drop height, weight and numberof blows to achieve standard compaction energy (600 kJ/m3)or according to the specified compaction energy.
■ Static compaction. Each layer is compressed by using aspecified static load for a certain time.
■ No compaction. The soil–binder mixture is filled in the mouldby either pouring or placing.
1
Table
1.Mostcommon
proced
ures
forho
mog
enisationof
naturalsoilp
riorto
treatm
ent,specim
enprep
arationmetho
dsan
dcurin
gcond
ition
s(con
tinue
don
next
page
)
Prep
aration
stan
dardsan
dreference
Naturalsoil
homogen
isation
method
Mixer
type
Mixing
duration
Specim
enmould
Number
of
laye
rsin
themould
Mouldingtech
niques
Curingco
nditions
TokyoInstitu
teof
Techno
logy,
Japa
n(Kita
zume
etal.,20
15)
Soilisho
mog
enised
bymixingwith
itsinitial
water
conten
t
Dom
estic
doug
hmixer
with
a50
00–
3000
0cm
3
mixingbo
wl
10min
with
occasion
alha
nd-m
ixing
Cylindrical
plastic
mou
lds
with
50mm
diam
eter
and
100mm
height
Threeto
six
layers
■Tapp
inga
■Ro
ddingb
■Dynam
iccompa
ctionc
■Staticcompa
ctiond
Sampleen
dsareprop
erly
sealed
with
specified
sealan
tsan
dstored
at20
±3°Cforspecified
timeat
95%
relative
humidity
Sapien
zaUniversity
ofRo
me,
Italy
(Grisolia
etal.,
2012
,201
3;Marzano
etal.,
2012
)
Thesoilisho
mog
enised
byremixingalon
e.Water
isad
dedat
thisstag
eto
adjustthesoilwater
conten
t
Hob
artmixer
10min
with
occasion
alha
nd-m
ixing
Cylindrical
plastic
mou
lds
with
50mm
diam
eter
and
100mm
height.T
helargestpa
rticle
containe
dwith
inthespecim
enshall
besm
allerthan
one-fifth
ofthespecim
endiam
eter
Threelayers
■Tapp
inga
■Ro
ddingb
■Dynam
iccompa
ctione
■Staticcompa
ctiond
■Nocompa
ctionf
Each
mou
ldiscoveredwith
asealan
tan
dstored
ina
specialcuringroom
at95
%relativehu
midity
topreven
twater
evap
orationfrom
the
specim
enUniversity
ofCoimbra,
Portug
al(Correia
etal.,20
13)
Thesoilisho
mog
enised
byremixingat
amixing
speedof
136revolutio
nspe
rmin
(rpm
).To
read
just
thesoilwater
conten
t,water
isad
ded
tothesoilas
aslurry
ofwater–bind
ermixture
Hob
artmixer
(mod
elN50
)3min
with
amixingspeed
of13
6rpm
Polyprop
ylen
erand
omcopo
lymer
pipe
s,with
50·8
mm
internal
diam
eter
and33
0mm
height.T
hehe
ight
ofthe
sampleis14
0mm,a
ndtheremaining
height
ofthemou
ldserves
asa
guideforthede
adload
,correspo
ndingto
avertical
pressure
of24
kPa.
Themou
ldha
stw
oho
lesne
arthetopto
allow
thesampleto
subm
erse
Sixlayers
(thickne
ss/
diam
eter
ratio
equa
lto
0·5)
■Staticcompa
ctiong
Ano
n-woven
geotextile
porous
disc
isplaced
atthebo
ttom
andtopof
themou
ld.S
amples
are
stored
at20
±2°Cfora
specified
time.
Avertical
pressure
of24
kPais
applieddu
ringcurin
g
SGS,
Swed
en(Åhn
berg
and
And
ersson
,20
11;C
arlsten
andEkström,
1997
)
Thesoilisfirst
homog
enised
thorou
ghly
bymixingthesoilalon
e
Dou
ghmixer
orkitche
nmixer
with
sufficien
tcapa
city
andrpm
5min
Themou
ldsused
areplastic
tube
scommon
lyused
for
piston
samplingin
Swed
en,w
ithadiam
eter
of50
mm
andahe
ight
of17
0mm
Four
tofive
layers
(abo
ut30
mm
thickn
ess
perlayer)
■Tapp
ingh
■Ro
ddingi
■Staticcompa
ctionj
Sampleen
dsareprop
erly
sealed
with
specified
sealan
tsan
dstored
at7°Cin
aclim
ate-
controlledroom
JGS08
21(JGS,
2005
),Kita
zume
andTerashi
(201
3)
Thesoilisho
mog
enised
bystirringitusingamixer.
Thesoilwater
conten
tis
adjusted
byad
ding
water
Dom
estic
doug
hmixer
with
a50
00–30
000cm
3
mixingbo
wl
10min
with
occasion
alha
nd-m
ixing
Specim
enmou
ldswith
50mm
diam
eter
and
100mm
height.T
hemaxim
umgrainsize
ofthesieved
sampleshou
ldbe
less
than
one-fifthof
theinne
rdiam
eter
ofthemou
ld
Threelayers
■Nocompa
ctionk
Sampleen
dsareprop
erly
sealed
with
specified
sealan
tsan
dstored
at20
±3°Cforaspecified
timeat
95%
relative
humidity
2
Geotechnical Research Briefing: Common laboratory proceduresto prepare and cure stabilised soilspecimens: a short reviewAl-Jabban, Laue, Knutsson and Al-Ansari
Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution
Table
1.Con
tinue
d
Prep
aration
stan
dardsan
dreference
Naturalsoil
homogen
isation
method
Mixer
type
Mixing
duration
Specim
enmould
Number
of
laye
rsin
themould
Mouldingtech
niques
Curingco
nditions
BRE(200
2)Th
esoilismixed
until
itbe
comes
visually
homog
enou
s
Dou
ghmixer
orkitche
nmixer
with
sufficien
tcapa
city
andrpm
5min
(dep
ending
onthesoil
type
)
Plastic
tube
sor
plastic-
coated
cardbo
ard,
50mm
diam
eter
and10
0mm
height
coated
with
oilo
rwax
ontheinne
rside
Four
layers
■Staticcompa
ctionl
Nostan
dard
specified
for
humidity.S
amples
are
stored
ataconstant
tempe
rature
of18
–22
°Cin
prop
erlysealed
cond
ition
sJacobson
etal.
(200
3)Th
econg
lomerateof
soilis
mixed
thorou
ghlyfor
3–4min
Kitche
nAid
doug
hmixer
with
ado
ughho
ok.
Outer
spindle
rotatin
gat
155rpm
andthe
inne
rspindleat
68rpm
3–5min
50mm
diam
eter
and
100mm
height
Four
layers
■Tapp
ing
■Staticcompa
ctionm
Cured
at10
0%relative
humidity
(moist
environm
ent)an
d20
±3°Cfor7,
14,2
8an
d56
d
Janz
and
Joha
nsson
(200
2),E
dstam
(200
0)
Thesoilisho
mog
enised
bymixingitalon
efor
2–6min.T
hisisno
rmally
done
theda
ybe
fore
the
stab
iliserisad
ded
Kitche
nmixer
orconcrete
mixer
4–10
min
Themou
ldsused
areplastic
tube
scommon
lyused
for
piston
samplingin
Swed
en,w
ithadiam
eter
of50
mm
andahe
ight
of17
0mm
Layer
thickn
ess
betw
een2
and4cm
after
compa
ction
■Tapp
ingn
■Staticcompa
ctiono
Thespecim
enscontaining
onlylim
earestored
atroom
tempe
rature
(+22
°C)for
thefirst10
dan
dtheremaining
timeat
+7°C.O
ther
specim
ens
arestored
ata
tempe
rature
of+7°Call
thetim
eASTM
D35
51-17
(ASTM,2
017),
ASTM
D51
02-
09(ASTM,
2009
),ASTM
(199
2)
Soilisair-driedfor24
han
dmixed
with
adry
bind
erfor1min
orun
tilthemixture
isho
mog
enised
visually
Mecha
nicalm
ixer
capa
bleof
prod
ucing
unifo
rman
dho
mog
eneo
usmixtures
5min
Mou
ldswith
aminim
uminside
diam
eter
50mm
andleng
th-to-diam
eter
ratio
sbe
tween2·0an
d2·5.
Thelargestpa
rticle
containe
dwith
inthe
specim
enshallb
esm
aller
than
one-tenthof
the
specim
endiam
eter
Atleast
threelayers
■Tapp
ingan
dkn
eading
■Dynam
iccompa
ctionp
Com
pacted
specim
ensare
curedin
anairtight,
moisture-proo
fcontaine
rat
atempe
rature
of23
+2°C
Fede
ralH
ighw
ayAdm
inistration
DesignMan
ual
(Bruce
etal.,
2013
)
Thesoilismixed
for
approxim
ately3min
atthelowestsettingof
the
mixer
(app
roximate
rotatio
nof
the
mixingtool
of10
0–17
5cycles/m
in).
Water
isad
dedto
adjust
thesoilwater
conten
t
Kitche
nmixer
with
asufficien
tcapa
city
10min
50by
100mm
plastic
mou
ldswith
lids
Threelayers
■Tapp
ing
■Ro
dding
Sealed
specim
ensarecured
unde
rcontrolled
cond
ition
sat
95–10
0%relativehu
midity
andat
aroom
tempe
rature
of20
–25
°C
3
Geotechnical Research Briefing: Common laboratory proceduresto prepare and cure stabilised soilspecimens: a short reviewAl-Jabban, Laue, Knutsson and Al-Ansari
Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution
Table
1.Con
tinue
d
Prep
aration
stan
dardsan
dreference
Naturalsoil
homogen
isation
method
Mixer
type
Mixing
duration
Specim
enmould
Number
of
laye
rsin
themould
Mouldingtech
niques
Curingco
nditions
Europe
anstan
dard
EN16
907-4
(CEN
,201
8)
Thesoilin
thefieldis
correctedto
thepa
rticle
size
distrib
utionbe
fore
adding
thebind
erby
blen
ding
thesoilalon
eto
breakup
largeblocks
orbo
ulde
rs
Mecha
nicalm
ixer
capa
bleof
prod
ucing
unifo
rman
dho
mog
eneo
usmixtures
Themixing
timeisno
tspecified
,but
theprod
uced
mixture
shou
ldbe
homog
enised
Differen
tmou
lddimen
sion
sareused
accordingto
the
compa
ctionmetho
dused
forprep
aringthesample
andthemaxim
umpa
rticle
size
perm
itted
inthe
sample.
Theleng
th-to-
diam
eter
ratio
ofthe
specim
enis2
Layers
■Proctoreq
uipm
entor
vibratingtable
compa
ctionq
■Vibratin
gha
mmer
r
■Vibrocompression
s
■Staticcompression
t
Inatempe
rate
region
,sampleen
dsareprop
erly
sealed
with
specified
sealan
tsan
dstored
inthe
airat
20±2°Cfora
specified
timeat
relative
humidity
>90
%.T
hesampleiscuredalso
inwater.O
ther
cond
ition
scanbe
adop
tedin
awarmer
orcolder
clim
ate
Fren
chstan
dard
NFEN
1328
6-53
(Afnor,2
005)
andthetechnical
guideby
Labo
ratoire
Cen
tral
desPo
nts
etCha
usses
(LCPC
,200
4)
Thesampleis
disinteg
ratedor
homog
enised
forseveral
minutes
Kitche
nmixer
with
enou
ghcapa
city
Themixing
timeisno
tspecified
,but
theprod
uced
mixture
shou
ldbe
homog
enised
Cylindricalsteelm
ould
with
differen
tdimen
sion
s(35×
70,5
0×10
0an
d10
0×
200mm).Th
eleng
th-to-
diam
eter
ratio
ofthe
specim
enis2.
Themou
ldha
sflan
gedpiston
s(plugs)from
both
ends.It
isused
toprod
ucea
specim
enwith
ade
nsity
grad
ient
such
asthe
density
inthecentralp
art
beingless
than
that
atthe
ends
One
layer
■Staticcompa
ctionor
compressing
the
specim
enfrom
both
side
sby
acompression
-testin
gmachine
with
asufficien
tforce.
The
additio
nalfl
ange
dpiston
partsare
removed
durin
gthe
compression
process
Thesampleissealed
and
curedat
controlroo
mtempe
rature
(20–
25°C
)
ASTM
(199
2)Th
esoilisair-driedfor24
hat
room
tempe
rature
and
mixed
with
adrybind
erfor1min
orun
tilthe
mixture
isho
mog
enise
dvisually.T
hesoilispa
ssed
throug
hsie
venu
mbe
r16
Han
d-mixingor
usinga
mecha
nicalm
ixer
Themixing
timeisno
tspecified
,but
theprod
uced
mixture
shou
ldbe
homog
enised
Cylindrical
steelm
ould
with
dimen
sion
sof
71×
299mm.T
hemou
ldha
sflan
gedpiston
sfrom
both
ends
tocompressthe
specim
ensan
dprod
uces
aspecim
enwith
dimen
sion
sof
17×
142mm.T
heleng
th-to-
diam
eter
ratio
ofthe
specim
enis2
One
layer
■Staticcompa
ction
■Dynam
iccompa
ctionp
Com
pacted
specim
ensare
curedin
amoist
room
4
Geotechnical Research Briefing: Common laboratory proceduresto prepare and cure stabilised soilspecimens: a short reviewAl-Jabban, Laue, Knutsson and Al-Ansari
Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution
Table
1.Con
tinue
d
Prep
aration
stan
dardsan
dreference
Naturalsoil
homogen
isation
method
Mixer
type
Mixing
duration
Specim
enmould
Number
of
laye
rsin
themould
Mouldingtech
niques
Curingco
nditions
BSI(19
90a,
1990
b)Th
eun
treatedsoilismixed
alon
eeither
byusinga
mecha
nicalm
ixer
orby
hand
Kitche
nmixer
with
asufficien
tcapa
city
10min
Tape
redmou
ldwith
two
steelp
lugs
with
the
followingdimen
sion
s:50
×10
0mm
forfine
-graine
dsoilan
d10
0×
200mm
formed
ium-
graine
dsoil
One
layerfor
a50
×10
0mm
specim
enan
dsix
layersfora
100×
200mm
specim
en
■Con
stan
tcompa
ction
effort
■For50
×10
0mm
specim
enu
■For10
0×20
0mm
specim
env
Specim
ensarecoated
with
wax
andcuredat
constant
tempe
rature
of20
±2°C
aForeach
layer,themou
ldistapp
ed50
times
againstthefloo
rbPerformed
usingan
8mm
dia.
steelrod
andtapp
ingdo
wn(30tim
es)the
mixture
with
therodforeach
layer
cEach
layeriscompressedby
theweigh
tof
arod(1·6
kg)a
ndcompa
cted
byafalling
weigh
t(0·6
kg)u
sing
aspeciala
pparatus.T
hefallhe
ight
issetto
10cm
,and
thenu
mbe
rof
blow
sisfive
dEach
layerisstaticallycompressedwith
avertical
pressure
of25
kPafor10
susingahe
avyrod
eEach
layeriscompa
cted
byafalling
weigh
t(1·5
kg)u
sing
aspeciala
pparatus.T
hefallhe
ight
issetto
10cm
andthenu
mbe
rof
blow
sto
five
fSimplyconsists
offilling
themou
ldby
either
pouringor
placingin
thecase
ofmixtureswith
ahigh
erconsistency
gForeach
layer,themixture
istapp
edby
hand
andstaticallycompressedwith
avertical
pressure
of10
0kPafor10
s.Fina
lly,the
surfaceislightlyscarified
andan
othe
rlayerisintrod
uced
hTapp
ingof
themou
ldispe
rformed
30tim
esforeach
oftheap
proxim
ately30
mm
thicklayers
ofthesoil–bind
ermixture
putinto
themou
ld.T
hefilling
ispe
rformed
infour
layers
iArodisused
tocompa
ct/smoo
thou
teven
lyeach
20–30
mm
thicklayerof
thesoil–bind
ermixture
byha
ndjEach
layerwith
abou
t30
mm
thickn
essisstaticallycompressedwith
avertical
pressure
of10
0kPafor5sto
sque
ezeou
tairpo
cketsfrom
each
layer
kForeach
layer,themou
ldislightlytapp
edag
ainstthefloo
r,hittingthemou
ldwith
amallet,an
dsubjectin
gthemou
ldto
vibration
lEach
layerwith
abou
t30
mm
thickn
essisstaticallycompressedwith
avertical
pressure
of10
0kPathreetim
esfor2sto
sque
ezeou
tairpo
cketsfrom
each
layer
mEach
layerwith
abou
t25
mm
thickn
essisstaticallycompressedwith
avertical
pressure
of10
0kPafor5–
10s
nA1kg
heavyload
isplaced
oneach
layer,an
dthemou
ldistapp
edthreetim
esag
ainstthefloo
roEach
layerwith
abou
t30
mm
thickn
essisstaticallycompressedwith
avertical
pressure
of10
0–20
0kPafor5–
10s
pEach
layeriscompa
cted
toachievestan
dard
compa
ctingeffortof
600kN
m/m
3accordingto
ASTM
D69
8-12
(ASTM,2
012).S
uitableforprep
aringaspecim
enat
thede
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5
Geotechnical Research Briefing: Common laboratory proceduresto prepare and cure stabilised soilspecimens: a short reviewAl-Jabban, Laue, Knutsson and Al-Ansari
Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution
Geotechnical Research Briefing: Common laboratory proceduresto prepare and cure stabilised soilspecimens: a short reviewAl-Jabban, Laue, Knutsson and Al-Ansari
Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution
Preparing and homogenising the natural soil before adding thecementitious binders represent the most common concern forobtaining a uniform soil–binder mixture. Disaggregating naturalsoil prior to treatment has many effects such as homogenising thesoil, reducing the variation in water content and obtaining smaller-sized particles by separating the agglomerated particles. Thisprocess could assist in obtaining a uniform distribution of thecementitious binders around soil particles. Table 1 summarises themost common procedures for homogenising natural soil prior totreatment, specimen preparation methods and curing conditions.The most common step in these procedures is that natural soil hasto be disaggregated and homogenised by remixing it alone beforeadding the stabiliser. Most of the standards do not specify the timerequired for the disintegration and homogenisation process becauseit can be influenced by several factors, such as the type andgradation, consistency limits, water content and organic content ofthe soil (Åhnberg and Holm, 2009; Bhadriraju et al., 2007; BRE,2002; Bruce et al., 2013; Carlsten and Ekström, 1997).
For the effect of mixing time after adding the cementitious binderon the obtained uniform soil–binder mixture, severalinvestigations have shown that the mixing time significantlyinfluences the properties of stabilised soils. Several factors controlthe uniformity of soil–binder mixtures, such as mixing time, typeof mixer used and the characteristics of the original soil, inaddition to the type, amount and form of the added binder (in dryor in a slurry form). Kitazume (2005) pointed out the influence ofmixing time and form of binder used on the unconfinedcompressive strength of the stabilised soil. These results werebased on the laboratory mixing tests by Nakamura et al. (1982).The laboratory tests were conducted according to the Japanesestandards for preparing the laboratory specimens (JGS, 2005) butusing different mixing times. Portland cement was added to thesoil in either a dry form or a slurry form with a water-to-cementratio of 100%. The results showed that the unconfinedcompressive strength of the stabilised soil significantly decreased,as the mixing time was decreased to shorter than 10 min,particularly for the case of when low binder amounts were used.The results also showed that adding the binder in a dry formrequired a longer mixing time compared with adding the binder inslurry form. The recommended mixing time to mix the soil andbinder is set as 10 min according to Japanese and Britishstandards (BSI, 1990a, 1990b; JGS, 2005). In contrast, inSweden, the recommended mixing time is set as 5 min and theproduced mixture should be visually homogenised (Åhnberg andAndersson, 2011; Carlsten and Ekström, 1997).
Several investigators have shown that different curing proceduressuch as curing time and curing temperature significantly influencethe strength and stiffness properties of stabilised soils. For theeffect of curing time, Kitazume (2005) pointed out the influenceof curing time and soil types on the unconfined compressivestrength of lime-stabilised soil based on the results from Terashiet al. (1977). The results showed that the strength properties oflime treatment are dependent on the soil type (lime is more
6
effective in clay) and the unconfined compressive strengthincreases almost linearly with the logarithm of the curing time.For lime treatment, 50–75% of the final shear strength is obtainedafter 1–3 months of curing, respectively, while 90% of stabilisedsoil shear strength is expected to be obtained after 1 year ofcuring (Broms, 2004: p. 263). For cement treatment, theimprovement in soil strength and stiffness increases as the cementcontent and curing time increases, and the major improvement insoil strength occurs during the first 28 d of curing (Hassan, 2009;Ho et al., 2017; Kang et al., 2017; Lorenzo and Bergado, 2006;Sariosseiri and Muhunthan, 2009; Subramaniam et al., 2016). Forthe effect of curing temperature, Kitazume (2005) mentioned thata higher strength can be obtained under a higher curingtemperature during short-term curing, and almost the same impactcan be obtained at a longer curing time for different soil–bindertreatments.
For soil stabilisation applications, choosing an appropriatelaboratory method for preparing and curing the specimens ofsoil–binder mixtures is considered highly important to simulatethe field conditions as much as possible. For instance, in shallowsoil stabilisation applications such as road projects where thestabilised soil in the field is usually compacted as layers using acompactor to obtain certain compacting efforts, the dynamiccompaction method is the most appropriate laboratory procedureto prepare the soil–binder mixture to simulate the desiredcompaction efforts. In contrast, for deep soil stabilisation, thecompaction efforts are less important compared with those forroad projects; therefore, the tapping or static compactiontechnique can be used. Moreover, choosing the appropriatemethod also depends on soil type, initial water content and thetype and amounts of binder used.
For deep soil stabilisation, a group of researchers studied theinfluence of different laboratory moulding techniques on the wetdensity and the unconfined compressive strength of stabilised soil(Kitazume et al., 2015). The study was a part of an internationalcollaboration between four organisations, the Tokyo Institute ofTechnology, the Sapienza University of Rome, the University ofCoimbra and the Swedish Geotechnical Institute. Details of theirstudies are presented in the first four methods mentioned inTable 1. Regardless of the soil type and the type and amount ofbinder used, they observed that the modelling techniqueconsiderably influenced the wet density and the unconfinedcompressive strength of stabilised soil. The liquidity index andthe undrained shear strength of the soil–binder mixture aftertreatment were used as indices to evaluate the results. They foundthat the tapping and rodding techniques were highly applicablewhen the undrained shear strength was less than 10 kPa or theliquidity index was larger than 1. The rodding technique washighly applicable when the undrained shear strength ranged from10 to 20 kPa or the liquidity index ranged between 0·5 and 1·0.Moulding with rodding and dynamic compaction were highlyapplicable when the undrained shear strength was larger than20 kPa or the liquidity index was smaller than 0·5.
Geotechnical Research Briefing: Common laboratory proceduresto prepare and cure stabilised soilspecimens: a short reviewAl-Jabban, Laue, Knutsson and Al-Ansari
Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution
ConclusionsThis short review presents the most common laboratory proceduresused to prepare and cure the specimens of soil–binder mixtures. Theaspects of the various laboratory procedures presented includehomogenisation of the natural soil, blending time, mould types andmoulding techniques and curing conditions (time and temperature).Different moulding techniques and curing conditions considerablyinfluence the properties of the soil–binder mixture. For soilstabilisation applications, choosing the appropriate method forpreparing and curing the specimens of soil–binder mixtures isconsidered highly important to simulate the field conditions as muchas possible, which subsequently reflect the strength and stiffness ofstabilised soil in the field site. Dynamic compaction and roddingmethods are more applicable for shallow soil stabilisation such asroad projects or when the soil shear strength is greater than 20 kPa.Static compaction and tapping methods are more applicable for deepsoil stabilisation or when the soil shear strength is lower than 10 kPa.
AcknowledgementsThe authors would like to acknowledge the Iraqi Ministry ofHigher Education and Scientific Research and the University ofBabylon for offering the opportunity to pursue this study throughtheir financial support.
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