experimental investigation on curing time and stress … · 2013. 8. 27. · 2 md. kamal hossain is...

International Journal of Civil & Environmental Engineering IJCEE-IJENS Vol: 11 No: 04 34

119104-5858 IJCEE-IJENS © August 2011 IJENS I J E N S

Experimental Investigation on Curing Time and

Stress Dependency of Strength and Deformation

Characteristics of Cement-treated Sand and it's

Degradation Phenomena Abu Taher Md. Zillur Rabbi

1, Md. Kamal Hossain

2, Jiro Kuwano

3, Wee Boon Tay

3

Abstract— Soil stabilization with cement is a good solution for

the construction of subgrades for roadway and railway lines,

especially in transition zones between embankments and rigid

structures, where the mechanical properties of supporting soil

are very influential. In order to optimize the design of cement-

mixed soil structures, their behaviors need to be well understood;

especially the strength and deformation characteristics at very

small strains are of great importance. Similar to concrete

material, the strength of cement-mixed soil continues to increase

with time, thereby improving its strength and deformation

properties with time. On the other hand, in the field cementation

bonds in cement-mixed soils are formed under stress in case of

in-situ soil. However, in the past researches the cementation

bonds under stress was considered only by a few researchers.

This is an underestimation of the stress-strain behavior of

cement-mixed soil. This study investigates the influence of long

curing period (e.g. up to 180 days) and the stress condition

during curing stage on the strength and deformation

characteristics of cement-mixed sand. A series of consolidated

drained (CD) triaxial compression (TC) tests were performed

along with the small strain cyclic loading and bender element

tests at intervals during monotonic loading to determine the

elastic Young's modulus (Ev) at extremely small strain range and

shear moduli (Ghh, Ghv and Gvh) respectively. The test results

show that the curing stress and curing period both have a

significant influence in the peak strength, stiffness, Ev, and Gvh

value. Curing period also influences the value of shear moduli in

the two horizontal directions Ghh and Ghv. However, the influence

of curing stress on the Ghh and Ghv is not very clear. The

degradation phenomena of cementation bond were discussed

according to the test results obtained from the cyclic loading and

bender element test during shearing of cement-mixed sand.

This work was done in the Geosphere Research Institute of Saitama

University (GRIS) in order to update the Triaxial testing system and also as a part of first author’s Master’s by research. The financial support for his

Master’s Degree and therefore this research is from the Asian Development

Bank – Japan Scholarship Program (ADB-JSP) which is greatly acknowledged.

1 Abu Taher Md. Zillur Rabbi is an Assistant Professor of Department of Civil

Engg., Dhaka University of Engg. & Technology, Gazipur-1700, Bangladesh. (Corresponding author, Phone: +880-1712-526634, e-mail:

[email protected]) 2 Md. Kamal Hossain is a Professor of Department of Civil Engg., Dhaka University of Engg. & Technology, Gazipur-1700, Bangladesh. ( e-mail:

[email protected]) 3 Jiro Kuwano is a Professor of Geosphere Research Institute of Saitama University (GRIS), 255, Shimo-okubo, Sakura-ku, Saitama-shi, Saitama

University, Saitama 338-8570, Japan. 4 Wee Boon Tay is a Government employee of Singapore (formerly graduate

student of Tokyo Institute of Technology)

Index Term— cementation bond, triaxial test, buoyancy,

curing overburden stress, bender element, shear wave velocity,

Young’s modulus, shear moduli, phase transformation.

I. INTRODUCTION

Ground improvement by cement treatment has been widely

applied for structural foundations, excavation control,

reinforced soil wall construction, bridge embankments,

highway embankments and liquefaction mitigation. One of the

new cost effective methods, to construct important permanent

soil structures that allow only a limited amount of deformation

such as bridge abutment etc. is the use of compacted cement-

mixed soil as the backfill. After successful construction of the

first new type bridge abutment having the backfill of well-

compacted cement-mixed gravelly soil for a bullet train line

(Shinkansen) in 2003 at Kyushu, Japan [1]-[4], the use of

cement-mixed soil is gaining more acceptance throughout the

different parts of the world and it is widely used in several

ground improvement projects such as highway and railway

embankments. An example of the use of cement-mixed

geogrid reinforced embankments on both sides of a highway

flyover bridge in Utsunomya, Japan and the schematic

illustration of the reinforced soil embankment is shown in Fig.

1 [5]. The use of cement-mixed soil is found to be relatively

simple and economical compared to deep piling and the use of

reinforced concrete structures since less concrete is required.

Reliable evaluation of strength and deformation

characteristics of compacted cement-mixed soil is one of the

essential factors in order to design effectively and confidently

design such soil structures. Though there have been many

studies on cement-mixed soil using different types of soils [6]-

[10], the behavior has yet to be generalized. The effect of

curing conditions in terms of curing time and stress conditions

during curing are still poorly understood because sufficient

evaluation of these effects is extremely time-consuming and

so very difficult [5], [6], [9]. Moreover, with the use of

different testing techniques, there are discrepancies in the test

results.

Hydration of cement in cement-mixed soil continues over a

very long period [9] which therefore gives more resistance to

shearing. On the other hand, the cementation bonds in in situ

soil are formed under stress. However, it was found in the

literature that cementation bonds under stress has been

considered by only very few researchers. This leads to an

underestimation of the stress-strain-strength behavior of

cement-treated soil [6], [11].

mailto:[email protected]

mailto:[email protected]



II. OBJECTIVE

The objective of this study is to investigate the influence of

curing period (up to 180 days) and applied stress during

curing stage on the strength and deformation characteristics of

cement-mixed sand. To investigate the change of dynamic

shear modulus in the vertical direction (Gvh) and void ratio (e)

with curing period and application of curing stress is also

another objective of this study. The composition of cement-

mixed sand used in this study is the same as those used by

Kuwano [12] and Rabbi et al., [5].

III. MATERIAL AND METHODOLOGY

A. Specimen Preparation

In this study, Toyoura sand is mixed with high-early

strength Portland cement to improve its mechanical

properties.The amount of high-early-strength Portland cement

used is 60 kg/m3 of Toyoura sand, to achieve an unconfined

compressive strength of 500 kPa after 7 days of curing which

is typical in a method used for the highway embankment

introduced in Fig. 1. The component ratio is calculated such

that the wet density of cement-mixed sand ρt =1.6g/cm3, which

is in accordance with the soil characteristics of that used for

strengthening embankments using cement-mixed sand and

geogrids by Itoh et al., [13]. Wet density is the moist density

of the specimen just after preparing the specimen before

curing. It is the ratio of the total mass of cement, sand and

water to the total volume of the specimen. The properties and

the ratios of the raw materials used in cement-mixed sand are

shown in Table I. The composition of cement-mixed sand

used in this study is the same as that used in the study of

cement-mixed sand by Rabbi et al., [5]. As noted, the amount

of cement used is only 4.13% of the total weight of sand. This

is small compared to normal cement mortar (C/S=50%).

Moreover, the water-cement ratio used is about 242%, which

is higher compared to W/C<100% for cement mortar. This

amount of water was used to spread out the small amount of

cement and ensure that the hydration of cement occurs

throughout the specimen.

Specimens were cured for 4 different curing periods of 7,

28, 90 and 180 days in order to investigate the curing period

dependency of the stress-strain characteristics of cement-

mixed sand. For each curing period specimens were cured

under 2 different curing overburden stresses, σv of 0 kPa and

98 kPa, to investigate the stress dependency during the

formation of cementation bonds in curing stage on the

mechanical properties of cement-mixed sand. To compare the

test results of cement-treated sand with clean Toyoura sand,

one specimen prepared with untreated clean Toyoura sand was

tested in triaxial compression testing machine. The specimen

with clean Toyoura sand was prepared by pouring sand from a

funnel with a constant falling height to control uniform

density all through the specimen height. Density of the

specimen prepared with clean sand is 1.54 g/cm3 (Mg/m

3). All

the test cases are shown in Table II.

TABLE II

TEST CASES TO STUDY THE INFLUENCE OF

CURING TIME AND CURING STRESS.

Specimen

type

Curing

Overburden

stress

Curing

time

(days)

Effective

confining

stress (kPa)

Cement-

mixed sand

0 kPa

7 98

28 98

90 98

180 98

98 kPa

7 98

28 98

90 98

180 98

Clean sand - - 98

TABLE I PROPERTIES AND RATIO OF RAW MATERIAL

Specific gravity, Gs

Toyoura sand (S) 2.645

High-early-strength Portland

cement (C)

3.130

Water (W) 1.000

S C W C/S W/C

Ratio (%) 87.62 3.62 8.76 4.13 242

(b)

Fig. 1. Example of use of cement-mixed sand as reinforced soil wall (a) highway flyover bridge using reinforced soil wall in Utsunomya, Japan, (b)

Cross-section used for the reinforced soil wall in both side embankment.

(a)



Specimen was prepared using a method similar to that used

by Kuwano [12] and Rabbi [5]. Sand and cement were mixed

thoroughly together in a dry state. After that water was added

to the mixture and they were mixed thoroughly again. The

mixture was then compacted into moulds of height 170mm

and diameter 77mm to control the wet density of the specimen

1.6 g/cm3 (Mg/m

3). Compaction was done in 5 stages of about

the same amount of cement-mixed sand each time in order to

make uniform density although the specimen height. The

specimens were then wrapped with plastic wrapping sheet and

stored under constant temperature of 20ºC and humidity of

50% for the specified number of days before they were used

for experimental purposes. Specimens to be cured under stress

were set in a specially made consolidation apparatus as shown

in Fig. 2. The specimens were then loaded with the desired

amount of overburden stress immediately after the moulds

were filled. The loading was applied using air pressure in the

bellofram cylinder mounted on that special apparatus. The

whole process of preparation of specimen and the application

of curing stress is finished within 25 to 30 minute from the

time when water was first added to the sand and cement

mixture in order to avoid the disturbance of cementation

bonds beyond the setting time of cement. The change in shear

modulus in the vertical direction (Gvh) during the curing stage

for both the specimens cured without and under stress was

monitored using a pair of bender elements attached at the top

and bottom ends of the specially made consolidation apparatus

as shown in Fig. 2.

B. Triaxial Testing System

The triaxial testing machine used in this study has an

automatically control and measurement system. The triaxial

compression test system consists of 2 main parts, triaxial test

and bender element test. In triaxial test, output voltages from

all measuring sensors are converted into digital signals which

were recorded on the PC through a 16-bit AD converter. In

turn, the control signals from the PC are converted into

voltages for each control sensor, through a 12-bit DA

converter as shown schematically in Fig. 3 [14]. The vertical

strain was measured both externally using an outer LVDT and

locally using a pair of LDT and a pair of inner LVDT as

shown in Fig. 3. The Young’s modulus was determined from

small strain cyclic loading from the measurement of the LDT

as the LDT has a lower electrical noise level. Since, however,

the measuring range of the LDT is only 2.5%, the

measurements of inner LVDT are used as a supplement to the

LDT beyond the range of 2.5%. The measuring range of the

inner LVDT was 15%.

Introduced by Shirley and Hampton [15], bender elements

are currently a standard technique for deriving the elastic

Fig. 2. Consolidation mould for applying curing stress with BE monitoring.

Fig. 3. Schematic illustration of triaxial testing system (not in scale). (Chowaudhary et al., 2004)



shear modulus of soil at very small strains. In bender element

tests, the maximum shear strain was estimated by Dyvik and

Madshus [16] to be less than 10-5

so that the shear modulus G

determined is relevant to very small strains [17]. Bender

element systems can be set up in most laboratory apparatus,

but are particularly versatile when used in triaxial test as

described by Dyvik and Madshus [16]. Shear wave velocity is

calculated from the time taken for the shear wave to travel

from transmitter to receiver bender element and the distance

between the tip of the transmitter and receiver bender element

[19]. In the bender element test, a function generator sends out

a sine pulse wave, as proposed by Viggani & Atkinson [18], to

the transmitter at one end of the specimen. The receiver at the

other end of the specimen receives this wave. Both wave

patterns at the transmitter and receiver ends are outputted into

an oscilloscope screen. The time taken for sine pulse wave to

pass through the specimen is the time lapse between the start

of transmitting wave and the start of the receiving wave

pattern, as shown in Fig. 4.

In this experiment, 3 pairs of bender elements are used to

measure the shear wave velocity in 3 directions. Fig. 5 shows

the arrangement of bender elements used in this experiment.

The transmitting and receiving ends are denoted by (T) and (R)

respectively. The shear wave is denoted by Sij, where i refers

to the direction of propagation of shear wave and j refers to

the direction of motion of soil particles. Here, a pair of vertical

and two pairs of lateral bender elements were used to measure

the shear waves Svh, Shh, and Shv respectively. The distance

traveled by the shear wave is taken as the distance between the

tips of the transmitter and receiver bender elements, proposed

by Dyvik & Madshus [16].

The shear modulus is then calculated using the following

equations: 2

vhvh VG (1)

2

hvhv VG (2)

2

hhhh VG (3)

where, ρ: Density of specimen

Vvh, Vhv and Vhh: Shear wave velocity in the corresponding

direction of wave propagation.

Volume Change Mesurement using Digital Balance:

The volume change of the specimen during isotropic

consolidation and during monotonic loading was measured

using a digital balance with an accuracy of 0.0001g of weight

instead of the conventional double burette volume change

apparatus and a differential pressure transducer (DPT). The

main part of the digital balance is placed in a glass chamber

and it was connected to the body of the digital balance placed

outside of the glass chamber. A plastic pot with water was

placed over the main part of the digital balance and it was

connected to the specimen through a pipeline as shown in the

schematic triaxial test system in Fig. 3. The volume change of

the saturated specimen was measured by measuring the weight

of water goes in from plastic pot to the specimen or came out

from specimen to the plastic pot. The change of the weight of

water in the pot is a measure of the volume change of the

specimen during isotropic consolidation & shearing. A larger

schematic representation of the whole arrangement of the

digital balance system is shown in Fig. 6.

Effect of Buoyancy Force on Volume Change Measurement:

Fig. 4. Measurement of time taken by shear wave to pass through the

specimen.

Input wave

Output wave

Time taken

Shh(T)

Svh(T)

Shh(R)

Svh(R)

Shv(T)

Shv(R)

Fig. 5. Arrangement of Bender elements

Sensor of Digital

balance

Back

Pressure

Connected to

pressure gauge

Pot & Water

Body of the

digital balance

Oil

Pipeline

connected to the

specimen.

Fig. 6. Schematic illustration of digital balance setup for volume

change measurement.



During the triaxial test a backpressure of 200kPa to 300kPa

was applied to the specimen. Since the specimen was

connected to the water in the plastic pot placed over the digital

balance in the glass chamber, the chamber pressure was also

increased equal to the backpressure in order to avoid water

movement to or from the specimen due to pressure difference.

However, when the pressure in the glass chamber is greater

than the atmospheric pressure, it affects the air density i.e., the

air density increases as well as there introduces an extra

buoyancy force. This extra buoyancy force affects the

readings of the digital balance i.e., digital balance gives the

weight measurement less than the actual weight. In order to

check the effect the digital balance reading was recorded by

increasing the chamber pressure from 0kPa to 300kPa and the

results are shown in Fig. 7. The result shows that the weight of

the plastic pot with water with an initial weight of 155.5g is

reduced to 151.75g when pressure increased from 0kPa to

300kPa i.e., around 2.5% weight reduced. Therefore, we need

to consider the error in digital balance reading due to

buoyancy force and need a correction to be made to the digital

balance reading. Since the buoyancy force has an effect on the

self weight of the main part of the digital balance, readings are

also taken from the digital balance when no weight is over the

balance by increasing the pressure form 0 to 300 kPa. By

subtracting these two values we can get the weight which

containing the actual error due to the buoyancy forces. The

theoretical buoyancy force over an object given by the air

pressure can be calculated by using the equation:

gVFbuoyancy (4)

where, V is the volume of metal piece in cm3 on which

buoyancy force is acting, is the mass density of the air in

g/cm3, g is the acceleration due to gravity and Fbuoyancy is the

buoyancy force in Newton. And its mass equivalent in gram (g)

is V can be obtained by dividing the Fbuoyancy value by the

value of g. Air density can be determined using the following

equation:

T

p

273*05.287

325.101 (5)

where,

is the air density in g/cm3, p is the chamber

pressure in kPa, T is the temperature in degree Celsius.

In order to determine the effect of buoyancy force in the

digital balance reading and compare it with the theoretical

buoyancy force a piece of metal of known volume was placed

over the digital balance and the pressure inside the glass

chamber was increased from 0kPa to 300kPa at an increment

of 20kPa. Readings from the digital balance were recorded at

each pressure increment. Readings from the digital balance

were also taken by increasing the chamber pressure from 0 to

300kPa at an increment of 20kPa when there is no weight over

the balance in order to take into consideration of the effect of

buoyancy force on the digital balance itself. Actual error in

weight measurement from the digital balance can be obtained

by combining these two readings. This actual error in the

measurement was almost equal to the difference of the

theoretical bouyancy force due to the increase in chamber

pressure from the bouyancy force at 0kPa pressure on the

metal piece calculated using eq. (4) due to the increase of

chamber pressure from 0 to 300kPa as shown in Fig. 8.

Therefore, the error in the digital balance is due to the

buoyancy force only.

Correction for Buoyancy Force:

The above discussion implies that the volume change

measurement from the digital balance needs a correction. We

can correct this value using the following equation derived

based on the buoyancy force calculation equations (4) and (5):

VT

pwww bcor *

273*05.287

325.101

(6)

where, corw and w is the corrected weight and the weight

reading of balance at backpressure p respectively both in gram

0 50 100 150 200 250 300151

152

153

154

155

156

Chamber pressure (kPa)

Dig

ital

bal

ance

rea

din

g (

g)

Effect when mass over balance

Effect of empty balance

Combined effect

Fig. 7. Effect of buoyancy force on the digital balance reading.

0 50 100 150 200 250 300-0.02

0

0.02

0.04

0.06

0.08

Err

or

in w

eig

ht

dif

fere

nce

(g

)


Actual error in weight difference

Theoretical weight difference due to bouyancy

Fig. 8. Comparison of actual error in measured weight in digital balance

and calculated theoretical buoyancy effect on weight.

e digital balance reading.

0 50 100 150 200 250 300-0.1

-0.08

-0.06

-0.04

-0.02

0

wb=0.0003(p)+0.0008


Dig

ital

bal

ance

rea

din

g (

g)

No mass over Digital balance

Fig. 9. Effect of buoyancy force on the digital balance reading when no

weight over balance.



(g), p is the pressure in glass chamber or backpressure in kPa,

T is the experiment room temperature in degree Celsius (˚C),

V is the volume of the plastic pot and water containing it in

cm3, and bw is the balance reading in gram (g) at

backpressure p when balance is empty. The reading from the

digital balance when the balance is empty bw can be obtained

from the following equation which is obtained from the

readings obtained from digital balance when it is empty as

shown in Fig. 9:

0007.00003.0 pwb (7)

where, bw is in gram (g) and p is the back pressure in kPa.

C. Experimental Program

In this study, specimens were cured under two different

stresses of 0kPa and 98kPa in order to investigate the stress

dependency and for each curing stress 4 different curing

period of 7, 28, 90 and 180 days were considered in order to

investigate and time dependency of the strength and

deformation characteristics of cement-mixed sand. Specimens

were taken out of their moulds after their respective curing

days and saturated with de-aired water in the triaxial cell.

Backpressure and cell pressure were then applied up to

200kPa and 225kPa respectively, while the effective confining

stress was kept constant at 25kPa. In some cases, the

backpressure and cell pressure were increased up to 300 kPa

and 325kPa in order to get better saturation of the specimen.

Because, at high pressure the air bubbles inside the specimen

which cannot be removed from the specimen during the

application of vacuum pressure were diluted to water. The

specimens were then isotropically consolidated to an effective

confining stress of 98 kPa, followed by drained monotonic

loading. Young’s modulus Ev and shear modulli Ghh, Ghv and

Gvh were determined at each 50 kPa intervals during

monotonic loading using small strain cyclic loading and

bender element test respectively. In addition, Ghh, Ghv and Gvh

are also determined at each 10 kPa interval during isotropic

consolidation. In case of specimen prepared with clean

Toyoura sand, the specimen was isotropically consolidated to

an effective confining stress of 98 kPa, and then drained

monotonic loading was applied. The stress path for all the test

cases is shown in Fig. 10. The effective vertical and horizontal

stress are denoted by σv' and σh', respectively. The change in

shear modulus in vertical direction Gvh during curing stage is

also measured for specimens cured without and under stress

using a pair of bender elements attached in the special

consolidometer as shown in Fig. 2.

In all test cases, loading strain rate was kept constant at

0.01% /min. For cyclic loading, at each 50 kPa interval during

monotonic loading, 5 cycles with an amplitude of ±4 kPa were

used to produce small strain changes of about 10-5

to 10-4

.

Toyoura sand behalves elastically at strain levels of 10-6

to 10-

5. But at such low strain levels, interference of noise affects

the true value of Young’s modulus. Thus in this study, a

higher strain level is used as cement-mixed sand is much

stiffer than Toyoura sand. Properties of specimens are as

shown in Table III.

IV. MATERIAL AND METHODOLOGY

A. Stress-strain Relationship

Figs. 11 (a) and (b) shows the stress-strain relationships for

specimens cured without and under stress. It can be observed

that the deviator stress q increases with the axial strain εv,

reaches to peak and then reduces gradually. This brittle

behavior in the post peak region is more prominent in case of

specimens cured for longer periods of time. The cementation

bonds result in changes in the cement-mixed Toyoura sand

from a ductile to stiff brittle material, its strength increases by

a factor of approximately 4 over 180 days. The stiffness of

specimens increases notably with curing time regardless of the

availability of acting stresses during curing which is similar to

the results obtained by Rabbi [5]. On the other hand,

specimens cured under stress are noted to be stiffer than those

cured in the absence of stress, as shown in Fig. 12 which is

more clear than the results obtained by Rabbi [5]. This reflects

the coupled effect of the specimen becoming denser upon

loading during the initial curing stage and the hydration

process of the cement.

B. Peak Strength

TABLE III PROPERTIES OF SPECIMEN

Specimen

type

Curing

Overburden

stress

Curing time

(days)

Effective

confining

stress (kPa)

Wet density

before curing

(g/cm3)

Void ratio e

Cement-

mixed sand

0 kPa

7 98 1.612 0.795

28 98 1.630 0.794

90 98 1.622 0.794

180 98 1.622 0.793

98 kPa

7 98 1.620 0.791

28 98 1.630 0.790

90 98 1.640 0.790

180 98 1.630 0.789

Clean sand - - 98 1.54 0.718

Isotropic consolidation

σh′ = σv′

Monotonic loading +

Cyclic loading &

Bender element test

σv′

σh′ 98kPa

Fig. 10. Stress path for all the tests



Fig. 13 shows that the peak strength qmax increases with

curing time regardless of the availability of acting stresses

during curing. Peak strength increases with time and

specimens cured under stress are noted to have higher peak

strength during shearing than those cured in the absence of

stress. Although the peak strength is little less than that

obtained by Rabbi [5] the increasing trend shows similar

tendency as obtained by Rabbi [5]. This again shows the

acting stresses during curing enhances the formation of

cementation bonds and thus improves the specimen’s

resistance to shearing. The rate of increase in peak strength

with curing period for specimens cured without any stress and

under stress can be expressed by the following equations (2)

& (3) respectively, which are obtained directly from Fig. 13.

For specimens cured without stress

)log(16.3156.731max Tq (8)

And for specimens cured under stress

)log(60.4874.790max Tq (9)

where, maxq

Peak strength in kPa

and T Curing period in days.

The above equations show that the rate of increase in peak

strength is higher for the specimen cured under stress which

also coincides with the results obtained by Rabbi [5]. This

again shows that the curing stresses enhance the formation of

the cementation bonds and thus improve the shear strength of

specimen.

0 0.5 1 1.5 2 2.5 3 3.5 40

200

400

600

800

1000

1200

Axial strain, v (%)

Dev

iato

r st

ress

, q (

kP

a)

7 days 0kPa

28 days 0kPa

90 days 0kPa

180 days 0kPa

Curing stress = 98kPa

7 days 28 days90 days

180 days

Toyoura sand

Fig. 11(b). Stress-strain relationship for specimens cured under stress.

0 0.5 1 1.5 2 2.5 3 3.5 40

200

400

600

800

1000

1200

Axial strain, v (%)

Dev

iato

r st

ress

, q (

kP

a)7 days 0kPa

28 days 0kPa

90 days 0kPa

180 days 0kPa

7 days 90 days

180 days

28 days


Toyoura sand

Fig. 11(a). Stress-strain relationship for specimens cured without stress.

0 0.5 1 1.5 2 2.5 3 3.5 40

200

400

600

800

1000

1200

Axial strain, v (%)

Dev

iato

r st

ress

, q

(k

Pa)

7 days 0kPa

28 days 0kPa

90 days 0kPa

180 days 0kPa

7 days 0kPa

28 days 0kPa

90 days 0kPa

180 days 0kPa

Curing under stress

Curing without stress

Toyoura sand

Fig. 12. Stress-strain relationship for specimens cured without and

under stress.

1 5 10 50 100 500500

600

700

800

900

1000

1100

1200

qmax =731.56 + 31.16 ln (T)

qmax =790.74 + 48.60 ln (T)

Curing stress = 0kPaCuring stress = 98kPa

Curing period, T (Days)

Pea

k s

tren

gth

, q m

ax (

kP

a)

Fig. 13. Peak strength variation with curing time.

0 0.5 1 1.5 2 2.5 3 3.5 4-2

-1.5

-1

-0.5

0

0.5

1

1.5

2

Axial strain v (%)

Vo

lum

etr

ic s

train

v (

%)

7 days 0kPa

28 days 0kPa

90 days 0kPa180 days 0kPa

7 days 98kPa28 days 98kPa90 days 98kPa180 days 98kPa

Cured without stress

Cured under stress

Fig. 14. Volume change behavior for specimens cured without and

stress.



C. Volume Change Behavior

As mentioned earlier, the volume change of specimen was

measured using a digital balance and corrected for the effect

of buoyancy force due to the increase in backpressure using

equations (6) and (7). Fig. 14 shows the relationship between

volumetric strain and axial strain during shearing for

specimens cured without stress and under stress. Here, the

positive and negative value of the volumetric strain indicates

the dilative and contractive behavior respectively. It is

observed that specimens become less compressive and more

dilatant with longer curing times.

As expected, specimens cured under stress are more

dilatant than those cured without stress. This also agrees with

the results obtained by Rabbi [5]. However, the reverse is seen

in specimens cured for 90 days and 180 days specimens. The

concentration of strain at the slip surface may result in the

concentration of the volume change around the slip surface,

making the specimen as a whole less dilatant.

D. Small Strain Cyclic Loading

Young's modulus Ev is dependent on the loading stress σ'v

and the void ratio e of specimen. The following equation can

be used to represent Ev (e.g. [20], [14]):

vh n

r

v

n

r

hv

r

v

ppeFC

p

E

'' (10)

where e

eeF

1

17.2)(

2

Cv, nh and nv are constants and can be obtained from

experimental data, while pr is the reference stress. In this study,

the reference stress pr is taken as 1 kPa. Since the void ratio, e

is almost same for all the specimens, F(e) is constant for all

specimens. Also, since the effective confining stress, σ′h is

constant for all the specimens, Equation (10) can be expressed

in the form n

vv AE , where A and n are constants. This is

a straight line when Ev and σ'v are plotted in logarithmic scale.

Therefore, Ev is plotted against vertical effective confining

stress, σ'v in a logarithmic scale, as shown in Fig. 11.

Fig. 15 shows the change in Ev during the monotonic

loading for specimens cured without stress and under stress. It

can be observed that Ev increases with σ'v and follows eq. (10).

Ev drops when vertical effective stress σ'v is about 50% to 60%

of its peak value which is similar to the Young’s modulus

obtained by Rabbi [5]. This may be explained as follows: Ev

increases when specimens become stiffer with increases in the

vertical contact forces between the sand particles during

monotonic loading, but it decreases when the cementation

bonds start to break down.

It is found that the Young's modulus increases notably with

the curing period, regardless of the availability of curing stress.

Also, it is quite apparent that specimens cured under stress

have a higher Young's modulus, regardless of the number of

curing days. The rate of increase of Ev with σ'v, however, is

higher for specimens cured in the absence of stress. This

shows that specimens cured without stress are more

compressive. However, the rate of increase in Ev obtained by

Rabbi [5] is lower than that obtained in the current study.

E. Bender Element Test

As is the case with the Young's modulus, the shear modulus,

G is dependent on the vertical effective stress σ'v, the

horizontal effective stress σ'h and the void ratio e of specimen.

The following equation can be used to represent G (e.g. [20],

[14]):

cba n

r

c

n

r

b

n

r

a

r pppeCF

p

G

''' (10)

C, na, nb and nc are calculated from experimental data,

while pr is the reference stress，σa’ is the principle stress in

the direction of shear wave，σb’ is the principle stress in the

direction of soil particle movement，σc’ is the principle stress

in the direction perpendicular to both directions of shear wave

and soil particle movement. Reference stress pr is taken as

1kPa similar to Young’s modulus. Rewritting the equations in

terms of σ’v and σ’h for triaxial test, we have the following

equations:

100 200 400 1000 2000

500

1000

5000

Effective vertical stress 'v (kPa)

Young's

modulu

s E

v (

MP

a)

7 days 0kPa28 days 0kPa90 days 0kPa180 days 0kPa7 days 98kPa28 days 98kPa90 days 98kPa180 days 98kPa

Fig. 15. Elastic Young’s modulus variation with effective vertical stress (log scale).



hn

r

hhh

r

hh

peFC

p

G

' (12)

vh n

r

v

n

r

hhv

r

hv

ppeFC

p

G

'' (13)

hv n

r

h

n

r

vvh

r

vh

ppeFC

p

G

'' (14)

In this study, the void ratio e is almost constant for all the

specimens and the effective confining stress, σ′h is also

constant for all the specimens. Therefore, equations (6) to (8)

can be generalized as mvBG , where B and m are

constants. This is also a straight line when G and σ'v are

plotted on a logarithmic scale, as shown in Figs. 16 to 18.

Change of Gvh during Curing

The change in the shear modulus in the vertical plane Gvh

and change in void ratio e during the application of curing

stress and also during the entire curing stage is shown in Fig.

19. The results show that as the void ratio decreases during the

loading stage, Gvh increases; however, as time passes, Gvh

continues to increase even when void ratio remains almost

constant. Similar to Rabbi et al., [5] this can be explained by

the strengthening of the cementation bonds due to the

hydration of cement. This is also true for specimens cured

without stress (clear dots). This observation, i.e. the Gvh of

specimen cured under stress is higher than that of cured

without stress, again shows the coupled effect of loading

during the initial curing stage and the hydration process of

cement which is similar to the results obtained by Rabbi [5].

In the specimens cured without stress, Gvh approaches the

Gvh of the specimen cured under stress as time passes.

Compared to the results obtained by Rabbi [5], the difference

between the Gvh value of two specimens are found lower in the

current study as curing time increases to 180 days. Due to the

time constraints of this study, whether or not the Gvh of the

specimen cured in the absence of stress actually increases to

the level of that cured under stress with time was not able to

be observed.

10 20 50 100 200 500 1000 2000

400

1000

20007 days 0kPa28 days 0kPa90 days 0kPa180 days 0kPa7 days 98kPa28 days 98kPa

'h = 'v 'h < 'v

7 days

28 days

90 days

180 days


Shea

r m

od

ulu

s G

hh (

MP

a)

Fig. 16. Variation of Ghh with effective vertical stress.

10 20 50 100 200 500 1000 2000

400

1000

20007 days 0kPa28 days 0kPa90 days 0kPa180 days 0kPa7 days 98kPa28 days 98kPa90 days 98kPa180 days 98kPa

'h = 'v 'h < 'v

7 days

28 days

90 days

180 days


Sh

ear

mo

du

lus

Gh

v (

MP

a)

Fig. 17. Variation of Ghv with effective vertical stress.

10 20 50 100 200 500 1000 2000

400

1000

2000


'h = 'v 'h < 'v

7 days

28 days

90 days

180 days


Shea

r m

od

ulu

s G

vh (

MP

a)


Fig. 18. Variation of Gvh with effective vertical stress.

Gvh (

MP

a)

Curing stress of 0kPa Curing stress of 98kPa

0

1000

2000

30007 28 90180Days:

10-1 1 10 102 103 104 105 106 107

Void

rat

io e

Time (min)Curing stress (kPa)

0 20 40 60 800.785

0.79

0.795

0.8

Fig. 19.. Change of Gvh and void ratio during curing stage.



Change of Gvh during Shear Loading

Figs. 16 – 18 show the change in the shear moduli Ghh, Ghv

and Gvh respectively with vertical effective stress σ'v in both

isotropic consolidation and triaxial compression stages for

specimens cured in the absence of stress and under stress

during curing. For all the specimens, Ghh, Ghv and Gvh increase

with the n power of σ'v which follows eq. (12) to (14) and it

drops when σ'v reaches about 40% to 60% of its peak value.

As the specimens become denser during monotonic loading,

shear moduli increase and then drop when the cementation

bonds start to break. This is similar to what occurs in the case

of the Young's modulus. Shear moduli Ghh, Ghv and Gvh of

cement-mixed sand increase with time regardless of the

availability of curing stress, which is the same as that for

stiffness, peak strength and elastic modulus. By comparing the

difference in shear modulus Gvh between specimens cured

without and under stress, as shown in Fig. 15, it can be noted

that specimens cured under stress have a higher Gvh, than

those cured without stress, regardless of the number of curing

days. On the other, there is no apparent difference in Ghh or

Ghv, as observed in Figs. 17 and 18 respectively. The higher

value in Gvh of specimens cured under stress can be attributed

to the coupled effect of overburden stress and formation of

cementation bonds as discussed earlier. On the other hand,

since the consolidation curing apparatus only allowed

overburden stress to be exerted in the vertical plane,

significant effect might not be seen in Ghh and Ghv, as

compared to isotropic loading. It is also observed that the rate

of increase of Gvh with σ'v is slightly higher for specimens

cured without stress, which is also similar to what was found

in the case of the Young's modulus.

F. Phase Transformation Points

The points where Ev and Gvh, Ghv and Ghh changes their

phase from increasing to decreasing tendency is introduced

here as phase transformation points for Young's modulus

(PTPEv) and phase transformation for shear moduli (PTPGvh,

PTPGhv, PTPGhh) respectively. The phase transformation points

for Ev, Gvh, Ghv and Ghh is determined by drawing two straight

lines in the initial and final straight portion of the Ev- σ'v and G

- σ'v curves respectively when they are plotted in log-log scale

as shown in Fig. 15 and Figs. 16 to 18 respectively for Ev, Gvh,

Ghv and Ghh respectively. Crossing points of these two lines is

taken as phase transformation points for Ev and corresponding

G value. The detail description of determination of Phase

transformation points is described in Rabbi et al., [5].

In Figs. 20 and 21 the phase transformation points for Ev

(PTPEv), Gvh (PTPGvh), Ghv (PTPGhv), Ghh (PTPGhh) volume

change (PTPv) and peak strength (qmax) is plotted in stress-

strain field for specimens cured without and under stress

respectively. With the increase in curing period, the deviator

stress for the PTPqmax and PTPv states is higher. The phase

transformation point for volume change is taken where the

volumetric strain curve changes their phase from compressive

to dilatant behavior. It can be observed that PTPEv and PTPG

obtained first during shear loading. Following that, phase

transformation points for volume change PTPv and qmax is

obtained which is similar to the case of Rabbi [5]. It can also

observe that PTPEv and PTPGvh are found almost at the same

axial strain level of 0.2% to 0.3% irrespective of curing stress

and curing period before PTPv and qmax. This result is almost

similar to that obtained by Rabbi [5] which strengthens the

point of discussion that the degradation of cementation bond

starts after a certain level of axial deformation due to the

relative displacement of particles. This amount of relative

displacement causes the cementation bond starts to break

down but this relative displacement level is not enough to

cause the specimen shows dilatancy. Breakage of cementation

bond occurs at relatively small strain level and is a

predominant factor to reduce stiffness of cement-mixed sand.

V. CONCLUSIONS

-Addition of a small amount of cement (4.13% by weight)

with Toyoura sand gives a much higher strength than fresh

sand alone, about 4 times after 180 days.

-Curing stress increases the stiffness, peak strength, Young's

modulus Ev and shear modulus in vertical plane Gvh

irrespective of curing period. However, shear moduli in other

two directions (Ghv and Ghh) do not show apparent increase

with the application of stress during curing stage.

-Curing period increases considerably the stiffness, peak

strength, Young's modulus and shear moduli (Gvh, Ghv and Ghh)

irrespective of the availability of curing stress.

0 0.5 1 1.5 20

200

400

600

800

1000

1200

Axial strain a (%)

Devia

tor

stre

ss q

max (

kP

a) PTPqmax ('h = 0kPa)

PTPv ('h = 0kPa)PTPEv ('h = 0kPa)PTPGvh ('h = 0kPa)PTPGhv ('h = 0kPa)PTPGhh ('h = 0kPa)


Curing period 7, 28, 90, 180 days

Fig. 20. Phase transformation points (PTP) plotted in stress-strain

field for specimens cured without stress.

0 0.5 1 1.5 20

200

400

600

800

1000

1200

Axial strain a (%)

Dev

iato

r st

ress

qm

ax (

kP

a)

PTPqmax ('h = 98kPa)PTPv ('h = 98kPa)PTPEv ('h = 98kPa)PTPGvh ('h = 98kPa)PTPGhv ('h = 98kPa)PTPGhh ('h = 98kPa)


Curing period7, 28, 90 & 180 days

Fig. 21. Phase transformation points (PTP) plotted in stress-strain field

for specimens cured under stress.



-Gvh increases during the application of curing stress as void

ratio decreasing. It is also noted to increase with time even

though void ratio remains constant. However, the curing

period should be further increased in order to investigate

whether the shear modulus value become equal or not for both

the specimens cured without and under stress. -Phase transformation of Ev and Gvh occurs almost at the

same level of axial strain of 0.3% to 0.4%. This might be due

to degradation of cementation bond starts from that level of

axial deformation due to the relative displacement of particles.

Further investigation is required and therefore recommended

in order to establish this point e.g., observation of microscopic

view of the cement bonds between particles at that level of

axial strain and also at initial and final stage of application of

loading to the specimens.

ACKNOWLEDGMENT

The first author acknowledge to the Foreign Student Office

(FSO) for giving assistance and guidelines for his Master’s

study in the Saitama University of Japan. The valuable

discussion and suggestions with Assistant Professor Dr.

Shinya Tachibana of Geosphere Research Institute of Saitama

University (GRIS) is also acknowledged. The first author

acknowledges the valuable time and the guidelines of Dr.

Jianglian Deng, JSPS Post Doctoral Fellow of IIS, Tokyo

University for teaching him the triaxial testing system with

very sensitive and modern automatic triaxial apparatus. He

also acknowledges the help of his colleagues Mr. Takeuchi

Yasunary, Mrs. July win and the undergraduate student of

Saitama University Mr. Tomonori Masaki for their help and

mental support during the triaxial test.

REFERENCES [1] H. Aoki, T. Yonezawa, O. Watanabe, M. Tateyama and F.

Tatsuoka, ‖Results from full-scale loading tests on a bridge abutment

with backfill of geogrid-reinforced cement-mixed gravel‖, Geosynth. Engg. Journal., Japanese chapter of International Geosynthetics

Society, 2003, Vol. 18, pp. 237-2428 (in Japanese).

[2] K. Watanabe, M. Tateyama, G. Jiang, F. Tatsuoka and T. N. Lohani, ‖Strength characteristics of cement-mixed gravel evaluated by

large triaxial compression tests‖, Proc. Of 3rd International Conference

on Pre-Failure Deformation Characteristics of Geomaterials (eds. By Di Bendetto et al.) Lyon, Balkema, 2003, Vol. 1, pp. 683-693.

[3] F. Tatsuoka, H. Nawir and R. Kuwano, ―A modeling procedure of

shear yielding characteristics affected by viscous properties of sand in

triaxial compression‖, Soils and Foundations, 2004, Vol. 44, No. 6, pp.

83-99.

[4] L. Kongsukprasert, F. Tatsuoka & H. Takahashi, ―Ageing and viscous effects on the deformation and strength characteristics of cement-mixed

gravelly soil in triaxial compression. Soils and Foundations, 2005(b),

Vol. 45, No. 6, pp. 55-74. [5] A. T. M. Z. Rabbi, J. Kuwano, J. Deng and W. B. Tay, ―Effect of

curing stress and period on the mechanical properties of cement-mixed

sand‖, Soils and Foundations IS-Seoul Special Issue, 2011, Vol. 51, No. 4 (to be Published).

[6] N. C. Consoli, G. V. Rotta and P. D. M. Prietto, ―Influence of curing

under stress on the triaxial response of cemented soils, Geotechnique,2000, Vol. 50, No. 1, pp. 99-105

[7] N. C. Consoli, D. Foppa, L. Festugato, & K. S. Heineck, ―Key

parameters for strength control of artificially cemented soils‖. J. Geotech. Geoenviron. Eng., 2007, Vol. 133, No. 2, pp. 197-205.

[8] L. Kongsukprasert, F. Tatsuoka & M. Tateyama, ―Several factors

affecting the strength and deformation characteristics of cement-mixed gravel‖. Soils and Foundations, 2005(a), Vol. 45, No. 3, pp. 107-124.

[9] L. Kongsukprasert, F. Tatsuoka, & M. Tateyama, ―Effects of curing

period and stress conditions on the strength and deformation characteristics of cement-mixed soil‖. Soils and Foundations, 2007,

Vol. 47, No. 3, pp. 577-596.

[10] T. N. Lohani, L. Kongsukprasert, K. Watanabe and F. Tatsuoka, ―Strength and deformation properties of compacted cement-mixed

gravel evaluated by triaxial compression test‖, Soils and Foundations.

2004, Vol. 44, No. 5, pp. 95-108.

[11] T. Taguchi, M. Suzuki, T. Yamamoto, H. Fujino, S. Okabayashi & T.

Fujimoto, "Influence of consolidation stress history on unconfined

compressive strength of cement-stabilized soil," Technical Report, Department of Engineering, Yamaguchi University, 2002, Vol. 52, No.

2, pp.87-92 (in Japanese).

[12] J. Kuwano and W. B. Tay, "Effects of curing time and stress on the strength and deformation characteristics of cement-mixed sand," Soil

Stress-Strain Behavior: Measurement, Modeling and Analysis (Ling,

H.I., Callisto, L., Leshchinsky, D. and Koseki, J. eds.), Springer, 2007, pp.413-418.

[13] H. Itoh, T. Saitoh, J. Kuwano & J. Izawa ―Development of

reinforcement wall using cement-mixed soil and geogrids.‖ Geosynthetics Technical Report, 2003, No. 11, pp.42-49.

[14] S. K. Chaudhary, J. Kuwano & Y. Hayano, ―Measurement of quasi-

elastic stiffness parameters of dense toyoura sand in hollow cylinder apparatus and triaxial apparatus with bender elements.‖ Geotechnical

Testing Journal, 2004, Vol. 27, No. 1, pp. 23-35.

[15] D. J. Shirley, and L. D. Hampton, ―Shear-wave measurements in laboratory sediments.‖ J. Acoust. Soc. Am., 1977, Vol. 63, No. 2, pp.

607-613.

[16] R. Dyvik and C. Madshus, ―Lab measurements of Gmax using bender elements.‖Proceedings of Advances in the Art of Testing Soils Under

Cyclic Conditions, V. Khosla, ed., ASCE Annual Convention, Detroit, Michigan, 1998, pp. 186-196.

[17] G. Viggani and J. H. Atkinson, ―Stiffness of fine-grained soils at very

small strains‖, Geotechnique, 1995(b), Vol. 45, No. 2, pp. 249-265. [18] G. Viggiani & J. H. Atkinsion, ―The interpretation of bender element

tests.‖ Geotechnique, 1995(a), Vol. 45, No. 1, pp. 149-155

[19] S. Mulmi, T. Sato, & R. Kuwano, ―Performance of plate type piezo-ceramic transducers for elastic wave measurements in laboratory soil

specimens‖. Seisan-Kenkyu, IIS, University of Tokyo, 2008, Vol.60,

No.6, pp. 43-47. [20] B. O. Hardin, and G. E. Blandford, ―Elasticity of particulate materials,‖

Journal of Geotechnical Engineering, ASCE, 1989, Vol. 115, No. 6, pp.

788-805.

ABOUT THE AUTHORS

Abu Taher Md. Zillur Rabbi is a member of Institute of Engineers,

Bangladesh (IEB), Japanese Geotechnical Society (JGS). He is an Assistant Professor in the department of civil engineering in Dhaka University of

Engineering & Technology (DUET), Bangladesh. He received B. Sc. Eng.

(Civil) from RUET, Rajshahi, Bangladesh in 2003 and M. Sc. Eng. (Civil & Geotechnical) from Saitama University, Japan in 2010. He has born in

Nilphamari district of Bangladesh in February 01, 1980. His research interest

includes soil improvement, laboratory based element and model tests of soil, small strain stiffness properties, dynamic properties of soil, geotechnical

earthquake engineering.

Dr. Md. Kamal Hossain is a Fellow of Institute of Engineers, Bangladesh (IEB). He is a Professor of department of civil engineering in Dhaka

University of Engineering & Technology (DUET), Bangladesh. He received

B. Sc. Eng. (Civil) from BUET, Bangladesh in 1993 and M. Sc. Engg. (Civil & Transportation) from the same University in 1997 and Ph. D. in 1999 from

UKM Malysia.. He has born in Khulna district of Bangladesh in December 01,

1968. His research interest includes soil improvement, laboratory based element and model tests of soil, small strain stiffness properties, dynamic

properties of soil, geotechnical earthquake engineering.

Dr. Jiro Kuwano is a Professor of the Department of Civil and

Environmental Engineering, Geosphere Research Institute of Saitama

University, Saitama, Japan. Prior to that he also have experience in teaching and research in Asian Institute of Technology (AIT), Tokyo Institute of

Technology (TIT), IIS-University of Tokyo. He is a member of ASCE, JSCE,

JGS, and many more renound organization. He supervised the first author’s Master’s thesis during Master’s study in Saitama University. His research

interest is Geotechnical earthquake engineering, reinforced soil, liquefaction

of soil etc.

Mr. Wee Boon Tay is a Government employee in Singapore. He is a national

of Singapore. He finished his B.Sc Engg. In Nanyang Institute of Technology, Singapore and finished his Master’s study in Tokyo Institute of Technology

(TIT), Tokyo, Japan. His research interest is the improved soil using binding

material.

experimental investigation on curing time and stress … · 2013. 8. 27. · 2 md. kamal hossain is...

Documents