1

Study on the action of cement grout on sandy soils when their mixture is

done mechanically

Henrique Oliveira1

1MSc Student, Instituto Superior Técnico, Av. Rovisco Pais, 1, 1049-001 Lisbon, Portugal;

henrique.oliveira@tecnico.ulisboa.pt

ABSTRACT: The work presented describes an experimental laboratory study that accomplished the physical and

mechanical characterization of three soil-cement mixtures, each with different cement dosage (150 kg/m3, 250 kg/m3

and 350 kg/m3) at 3,7,14 and 28 days of age. Specimens which intended to replicate the improved soil under in situ

conditions were prepared through mechanical mixing. The grout was also characterized in fresh and hardened state.

Geophysical tests were also used, which allowed the establishment of regression equations both to estimate the

mixtures’ mechanical properties and to detect the mixtures’ cement dosage. An improvement factor of several

mechanical properties was defined to quantify the influence of cement dosage.

Key-words: Ground improvement; soil-cement; mechanical mixing; Deep Mixing Method; mechanical properties;

geophysical tests

1. INTRODUCTION

Ground improvement through mechanical mixing, known as Soil Mixing (SM) involves disturbing the soil and mix it

with a binder. In one of its methods, the Deep Mixing Method, volumetric bodies with 3 to 50 meters length and

controlled geometries are produced. Due to the constrained conditions that soil-cement bodies are executed, the

precision and detail provided by the quality control and quality assurance procedures are very important to assure

the geometry, mechanical properties and homogeneity, specified by the geotechnical design (Masaki & Masaaki,

2013).

In this context, the main goals of this work are studying the influence of time and cement dosage on both the physical

and the mechanical properties of a sandy soil mechanically mixed with a cement grout, as well as studying the

application of geophysical tests to estimate the mechanical properties and cement dosage. Thus, it was designed a

work plan that integrated the preparation of specimens, which intended to replicate the improved soil under in situ

conditions, and the performance of several tests. The grout was also the subject of testing in fresh and hardened

state.

Physical characterization of soil-cement mixtures is presented through microscopic and macroscopic perspectives.

The mechanical behaviour of the soil-cement is characterized by presenting stress-strain experimental graphs for

each mixture, performing failure mode analysis and presenting the evolution of the mechanical properties through

time and the influence of the mixtures cement dosage on them. An improvement factor for each mechanical property

quantifies the effect of the cement dosage. Geophysical properties are also analysed from the perspective of time

and cement dosage influences, as well as its relation with the mechanical properties. Throughout the present work

regression equations are established in order to correlate the properties.

2

2. EXPERIMENTAL PROGRAM

2.1 MATERIALS AND METHODS

The soil subject to improvement was a non-plastic sandy soil (Néri,2013), classified as a silty sand-SM according to

the Unified Soil Classification System (86% of material with diameters between 0,074 mm and 4.76 mm and 14%

non-plastic fines), and with a specific gravity of solid particles, Gs of 2.64. The grain-size distribution curves are

presented in figure 1.

The soil-cement mixtures were prepared with 150 kg/m3, 250 kg/m3 and 350 kg/m3 of Portland Cement EN 197-1-

CEM I 42,5 R which corresponds to 10%, 17% and 23% of cement per mass of dry soil. Tap water was used and

water-cement ratio (0.6) was kept constant, as well as the solid soil dosage (1500 kg/m3), and therefore the dry

volumetric weight variations of the mixtures depend only on the presence of cement and its hydrated minerals. Giving

the fact that the soil-cement mixtures intended to replicate the improved soil under in situ conditions, the soil dosage

was estimated taking into account the usual values of dry volumetric weight of a sand (Maranha das Neves, 2006)

plus the disturbance to which the soil would be subjected to, in a mechanical mixing process. The soil-cement

formulation was done according to the relations presented in table 1.

The cement grout, which was also studied in the fresh and hardened state, was prepared using tap water and the

same water-cement ratio as in the mixtures.

Table 1 – Soil-cement mixtures formulation.

Soil-cement mixture

Cement 𝜸𝒉 w 𝜸𝒅

Per mass of dry soil

kN/m3 (%) kN/m3

150 kg/m3 10% 17.4 5.5 16.5

250 kg/m3 17% 19.0 8.6 17.5

350 kg/m3 23% 20.6 11.4 18.5

The preparation of soil-cement mixtures was done according to ASTM D1632-07 (2007). The mixtures were

performed mechanically and the specimens were prepared by compaction of the material within cylindrical moulds

(140 mm length and 70 mm diameter), which were manufactured by attaching a PVC tube to a ceramic base through

polyurethane glue. The compaction process was performed by light impact of a wooden tamping rod graduated with

four layers, 37.5 mm each. Each layer contained the same mass of material in order to improve homogeneity within

the specimen. The specimens were then submerged and maintained in a container filled with tap water until they

have reached the intended age to be tested. After their extraction, the specimens of 150, 250 and 350 kg/m3 soil-

cement mixtures exhibited visible differences, namely with regard to their colour, pores dimension at surface and the

perception of compaction layers (figure 2).

The specimen for the resistivity test was contained in a rigid cylindrical non-conducting material (PVC). Four steel

probe electrodes of equal length and equally spaced were inserted into the specimen while still in its fresh state,

along the longitudinal axis. The electrodes were then involved in plastic rubber (figure 3) to prevent contact with water

Sample 1 Sample 2

Grain size (mm)

0.01 0.1 1 10 100

Pe

rce

nt

fin

er

by w

eig

ht

50

70

90

0

10

20

30

40

60

80

100

Figure 1 – Grain-size distribution curves of the soil

(Néri, 2013).

3

during the submerged cure period. For the splitting tensile strength test, disk specimens were obtained by cutting the

cylindrical specimens in four approximately equal parts (figure 4).

Mechanical mixing Final mixture Tools for specimens’ compaction Compaction

Specimens after compaction Specimen extraction 150, 250 and 350 kg/m3 soil-cement specimens

Figure 2 – Preparation of mixtures and specimens.

Figure 3 – Specimen for resistivity test.

Figure 4 – Disk specimens production.

2.2 LABORATORY TEST PLAN

An extensive set of experimental tests was performed, including the characterization of the cement grout in the fresh

and hardened state (table 3) and the characterization of the soil-cement mixtures with different cement dosages

(table 4). With regard to fresh grout characterization, density, fluidity and exudation were studied, having the latter

been used for grout stability evaluation. For hardened grout characterization, physical, mechanical and geophysical

tests were performed at 3, 7, 14, 28 and 38 days of age, depending on the test. It was essentially performed the

same tests that were performed for soil-cement mixtures characterization.

The soil-cement mixtures test plan was established with the goals of performing the material’s physical, mechanical

and geophysical characterization at 3,7,14 and 28 days of age. Physical tests allowed macroscopic and microscopic

evaluation, whereas the performed mechanical tests followed the usual ASTM specifications (table 4, see also

Oliveira (2018)) and covered the most important mechanical properties used on the design of soil improvement

solutions (compression strength, stiffness and tensile strength). Geophysical tests, which are non-destructive

methods that may be used in the field for quality control purposes, were performed and their correlation with the

mechanical properties of the mixtures was studied, since the mixtures’ cement dosage has shown to be an influential

factor on the correlation.

70

mm

140 mm

V

I 32,5 mm

d=25 mm

Weighing container

Mould Adapter

cone

Knife Wooden tamping rod

4

Table 2 - Test plan for grout characterization.

Fresh grout Specification Hardened grout Specification

Density test NP EN 445 (2008) Physical characterization

Cone method NP EN 445 (2008) Porosity accessible to water RILEM (1980)

Grout spread method NP EN 445 (2008) Bulk Density No standard was used

Exudation test Kutzner (1996) Scanning electron microscope1 No standard was used

Mechanical tests

Splitting tensile strength ASTM D3967-95a (2001)

Unconfined compressive strength NP EN 12390 (2009); Gomes et al. (2010)

Geophysical tests

Resistivity2 BS 1377-3 (1990)

Ultrasonic pulse velocity ASTM C-597-09 (2009); UNE-EN 12504-4 (2006)

Impulse excitation of vibration ASTM C215-14 (2014); ASTM E 1876-15 (2015) 1Tests executed by external entities; 2Resistivity test was also performed on soil specimens.

Table 3 - Test plan for soil-cement mixtures characterization

Soil-cement

mixture (kg/m3) Curing age

Specification

150 250 350 3 7 14 28

Physical characterization

Porosity accessible to water - - - RILEM (1980)

Bulk Density No standard was used

Mercury intrusion porosimetry1 - - - ASTM D4404-10 (2010)

Scanning electron microscope1 - - No standard was used

Mechanical tests

Splitting tensile strength - ASTM D3967-95a (2001)

Unconfined compressive strength ASTM D2166/D2166M-13 (2013); NP EN 12390 (2009)

Geophysical tests

Resistivity - BS 1377-3 (1990)

Ultrasonic pulse velocity ASTM C-597-09 (2009); UNE-EN 12504-4 (2006)

Impulse excitation of vibration - ASTM C215-14 (2014); ASTM E 1876-15 (2015)

1Tests executed by external entities

3. RESULTS AND DISCUSSION

3.1 GROUT

Two samples of grout, M1 and M2 (table 4), were produced in order to evaluate their density and fluidity. The measure

of density resulted in a mean value of 1800 kg/m3. Fluidity was assessed right after production (t0 and a0) and 30

minutes later (t30 and a30). The results shown in table 4, allow considering that the fluidity of the grout remains

relatively constant through that period of time and from that perspective it was considered proper to be applied on

soil improvement. In regard to the initial values of fluidity, since in Deep Mixing the grouts’ w/c ratios range from 0.6

to 2.5, and there is a direct relation between w/c and fluidity (Ribeiro, 2008), it can be perceived that the present

grout is less fluid and more viscous that the generality of the grouts used in this context. The grout exudation was

also examined and it exhibited 2.8% after 2 hours, which is significantly inferior to the 10% limit referred by Kutzner

(1996) and therefor the grout can be considered stable.

Compressive strength tests were performed in a cylindrical hardened grout specimen for the purpose of being more

precisely compared with the soil-cement specimens, since geometry and dimensions were the same. The result at

28 days of age was 15.4 MPa. At 38 days of age half prims were tested according to Gomes et al. (2010), having

5

shown a compressive strength of 33 MPa and a tangent modulus of elasticity of 5.3 GPa. According to Xanthakos et

al. (1994), a cement grout with 0.6 w/c ratio, tested in half prisms specimens, has to achieve 25 MPa at 28 days of

age, and for that, it is assumed that the grout meets the requirements. Spitting tensile strength was also tested,

resulting in 1 MPa. This test tends to overestimate the real tensile strength in 10% (Mehta & Monteiro, 2014).

Table 4 – Fresh grout tests results: Density and fluidity.

Grout ID Density Flow time (s) Spread diameter (mm)

kg/m3 t0 t30 a0 a30

M1 1808 11.74 11.52 161 178

M2 1792 11.81 10.36 - -

Fluidity

Requirements1

t0 ≤ 25

t30 ≤ 25 and 1,2 t0 ≥ t30 ≥ 0,8 t0

a0 ≥ 140

a30 ≥ 140 and a0 ≥ a30 ≥ 0,8 a0

1requirements set out in NP EN 447.

Figure 5 – Evolution of exudation over time.

3.2 SOIL-CEMENT MIXTURES

3.2.1 PHYSICAL CHARACTERIZATION

The increment of the cement dosage has a direct effect on the porosity and bulk dry density of the soil-cement

mixtures. At 28 days of age it was observed a linear correlation between the cement dosage and the porosity (figure

6) and between the former and the bulk dry density (figure 7). The effect observed is caused by cement particles and

the subsequent hydrated products that fill the voids between the soil particles. By increasing the cement dosage, its

capacity of filling the soil voids is higher, thus densifying the solid structure of the soil-cement mixtures. Mercury

intrusion porosimetry, MIP provided further detail about the pore-size distribution of the soil and soil-cement mixtures

(figure 8). With increasing amount of cement it’s observed a growth of pores with less than 150 nm, and also a

reduction of the pores larger than 150 nm. The observations confirm that with higher cement dosages the porosity of

the mixtures tends to be dominated by capillary pores of the cement past due to the increasing occupation of the soil

voids by the hydrated cement.

Figure 6 – Porosity of soil and soil-

cement at 28 days of age.

Figure 7 – Bulk dry density of soil and

soil-cement a 28 days of age.

Figure 8 – MIP test in soil and soil-cement at

28 days of age.

Since cement is a binder, its presence among solid particles and its hydration process creates solid bonds between

the soil particles, hence reinforcing the interconnection of the mixtures solid structure. Figure 9 and 10 show SEM

photographs of the solid bonds and the hydration minerals such as ettringite and calcium hydroxide crystals, in soil-

cement mixtures at 3 days of age.

2,8

y = 0,023x + 0,0555R² = 0,99

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

0 30 60 90 120 150 180

Exudation (

%)

Time (minutes)

y = -0,0005x + 0,3299R² = 0,79

0%

10%

20%

30%

40%

50%

0 50 100 150 200 250 300 350

y = 0,0012x + 1,4947R² = 0,99

0,0

0,5

1,0

1,5

2,0

2,5

0 50 100 150 200 250 300 3500,00

0,05

0,10

0,15

0,20

0,25

0,30

0,35

0,40

1 100 10000

Soil

150 kg/m3

200 kg/m3

250 kg/m3

350 kg/m3

Pore diameter (mm)

Pore

-siz

e d

istr

ibutio

n

Cement dosage (kg/m3)

ρd (g/c

m3)

Cement dosage (kg/m3)

Poro

sity

(n)

Soil-cement Soil

6

Figure 9 – Evidence of solid bonds in 250 kg/m3 soil-cement

mixtures at 3 days of age.

Figure 10 – Ettringite and Hexagonal crystals of calcium

hydroxide in 350 kg/m3 soil-cement mixtures at 3 days of age.

3.2.2 MECHANICAL TESTS

Stress and axial deformation were measured during the unconfined compressive strength tests in order to study the

stress-strain behaviour of the soil-cement mixtures. Figure 11 illustrates the experimental stress-strain graphs of

each mixture at 28 days of age, whose progress is representative of the all the specimens tested. The range of the

graphs that refers to the small deformations, showed a curved shaped, and for that reason the stiffness of the material

was evaluated through the tangent modulus of elasticity Etg, which covers the linear segment of the graphs. It is

noticeable the increment of unconfined compressive strength (qu) and stiffness with the increase of cement dosage.

Failure modes of the mixtures at 28 days of age reveal substantial differences between them (figure 12). The most

noticeable aspects are crack propagation and their width. The 150 kg/m3 specimen has cracks mostly on its bottom

half, possibly due to significant contrast in regard to the compactness of each specimen layer, which together with

its low amount of cement, prevents its capability of transporting tension through all its length. The 250 kg/m3 and 350

kg/m3 specimens developed wider and longer cracks which revealed that crack propagation lasted longer, thus

increasing stiffness and qu. The observed behaviour with increasing cement dosage is due to the influence of the

hardened cement solid structure in the soil-cement mechanical behaviour. It is perceptible that 350 kg/m3 specimen

exhibits a failure mode which resembles that of the hardened grout specimen, in which stress accumulates on the

specimen’s central zone.

Figure 11 – Stress-strain graphs of soil-cement

mixtures at 28 days of age.

Figure 12 – Failure geometries of soil-cement (28 days) and hardened

grout (7 days) specimens tested in the compressive strength test.

The test results (figures 13 and 14) reveal that, although some dispersion is noted, as expected, both qu and Etg tend

to grow over time. The hydration process of the cement paste over time reinforces the adhesion forces of Van der

Waals, thus strengthening the bonds between the particles of the soil and the cement past and consequently

0,0

2,0

4,0

6,0

8,0

10,0

12,0

14,0

0 0,2 0,4 0,6 0,8 1

350 kg/m3

250 kg/m3

150 kg/m3

150 kg/m3 250 kg/m3 350 kg/m3 Hardened grout

σ (

MP

a)

εa (%)

Estimated progress

7

increasing qu. Another consequence of the hydration process is the reduction of the porosity of the cement paste,

which is the main factor for increasing the stiffness of the mixtures over time. Naturally, the evolution of both

properties over this period of time is greater in the mixtures with higher cement dosage because the influence of the

cement paste in the mixture mechanical behaviour is most prominent.

Figure 13 - Tangent modulus of elasticity through time.

Figure 14 - Compression strength through time.

The influence of cement dosage on the stiffness and compressive strength of the soil-cement mixture was quantified

by an improvement factor that was given by the ratio between the mean value of the mixture being evaluated and

the mean value of the 150 kg/m3 mixture. All four ages were analysed (figures 15 and 16). Due to the deviations

found in the results of the 350 kg/m3 mixture of Etg at 3 days and qu at 28 days, both were omitted from the graphs.

A logarithmic correlation between Etg and qu was found (figure 17) that is independent from age and cement dosage,

showing that is possible to estimate Etg from qu with a very acceptable level of accuracy.

Figure 15 – Improvement factor

for stiffness.

Figure 16 - Improvement factor for

unconfined compressive strength.

Figure 17 - Correlation between

compression strength and stiffness.

Tensile strength (σt), shows a similar trend to those obtained for the Etg and qu (figure 18). The result from the 350

kg/m3 mixture at 28 days was expected to be greater and the 250 kg/m3 mixture at 7 days exhibit higher values than

the ones obtained at 14 days, probably due to its lower water content (w), which shows the influence of this parameter

in σt.

Similary to what was done to Etg and qu, the influence of the cement dosage on σt was quantified by an improvement

factor (figure 19). The increment from 250 kg/m3 to 350 kg/m3 is substantially greater than the one from 150 kg/m3 to

250 kg/m3. Two values are marked with an (*) as their values were expected to be the ones inside the parentheses.

Lastly, in figure 20 it’s shown that σt and qu are correlated through a linear regression with r2=0.96, which is

independent from the cement dosage and age, thus demonstrating that the former can be estimate from the latter.

Etg = 53,349t0,499

RMSE=21

Etg = 450,65t0,3574

RMSE=187

Etg = 1269,1t0,1337

RMSE = 124

0

250

500

750

1000

1250

1500

1750

2000

2250

0 7 14 21 28

qu = 0,477t0,2933

RMSE=0,1

qu = 2,485t0,281

RMSE=0,6

qu = 5,4451t0,3855

RMSE=1,6

0

2

4

6

8

10

12

14

16

18

20

0 7 14 21 28

1,0 1,0 1,0 1,0

8,7

5,4 5,0

6,1

10,7

8,7

7,4

3 7 14 28

Impro

vem

ent fa

cto

r fE

tg

1,0 1,0 1,0 1,0

6,7

3,9

5,9 5,2

14,613,0

17,2

3 7 14 28

Impro

vem

ent fa

cto

r f q

u

Etg = 624,99ln(qu) + 177,93RMSE = 215

0

500

1000

1500

2000

2500

0,0 3,0 6,0 9,0 12,0 15,0 18,0

150 kg/m3

250 kg/m3

350 kg/m3

Etg (

MP

a)

qu (MPa) Age (days) Age (days)

Etg

(M

Pa

)

qu (

MP

a)

Age (days) Age (days)

150 kg/m3

250 kg/m3

350 kg/m3

8

Finally, the good correlations found show that the mechanical parameters are related with cement dosage and curing

time.

Figure 18 - Evolution of splitting tensile

strength through time.

Figure 19 - Improvement factor for

splitting tensile strength.

Figure 20 - Compression strength and

splitting tensile strength.

3.2.3 GEOPHYSICAL TESTS

In the impulse excitation of vibration test, the fundamental transverse and torsional resonant frequencies of the

specimens were assessed, which then allowed to compute the dynamic mechanical properties of the soil-cement

mixtures, namely the modulus of elasticity Ed, the distortion modulus Gd and the poisson’s ratio vd. The measurements

revealed to be extremely sensitive to the placement of the impact and the receiver sensor, thus causing excessive

variability. Despite this, it was possible to observe a linear correlation between the cement dosage of the mixtures

and each dynamic property, proving that the test is sensitive to cement dosage (Oliveira, 2018).

Ultrasonic pulse velocity (UPV) test was performed in all the specimens that were also tested to compressive

strength. The results show that UPV increases with time, following a similar trend for the three soil-cement mixtures,

whose measured values show little dispersion (figure 21). At three days, UPV values are quite high relatively to the

values at 28 days. The fast pace that UPV shows at early ages is due to the hydration process of cement, which

generates solid material that interconnects the solid particles of the soil, thus creating solid paths, which is where the

ultrasonic waves propagate faster (Panzera et al., 2011). The use of cement CEM I 42.5 R (NP EN 197-1) is also a

factor, since it quickly develops the hydration reactions at early ages. From 3 to 28 days, UPV continues increasing

due to the further solid trajectories created by the hydration products that gradually replace the water in the pores.

Yet the UPV evolution rate tends to decrease, since after a certain degree of solid connections are established, the

reduction of capillary porosity doesn’t have a proportional effect.

In figure 22, UPV correlation with qu was analysed and three regression curves were determined, each for a different

curing age. Mean values of UPV and qu for each dosage were used. For each curve, it’s notorious the influence of

the cement dosage in both properties, which is due to its intrinsic relation with the physical properties of the material.

With increasing cement dosage, the hydration products cause porosity to decrease (figure 6) and bulk dry density to

grow (figure 7), thus creating bonds between the solid particles that reinforce strength and enable a faster propagation

of UPV. Figure 23 show that UPV and Etg are correlated by a linear regression (r2=0.97). This means that both

properties are influenced by the same factor, namely the porosity.

σt = 0,4022t0,219

RMSE=0.10

σt = 1,5281t0,1085

RMSE=0.23

σt = 0,0878t0,3498

RMSE=0,02

0,0

0,5

1,0

1,5

2,0

2,5

3,0

0 7 14 21 28

1,0 1,0 1,0 1,0

3,6

4,8* (4,3)

3,2 2,8

12,313,1

9,87,5*(9,1)

3 7 14 28

Impro

vem

ent fa

cto

r fσ

t

σt = 0,1478qu + 0,0037R² = 0,96

0,0

0,5

1,0

1,5

2,0

2,5

0,0 3,0 6,0 9,0 12,0 15,0 18,0

150 kg/m3 250 kg/m3 350 kg/m3

qu (MPa)

σt (M

Pa)

σt (

MP

a)

Age (days) Age (days)

9

Figure 21 - Evolution of UPV through

time.

Figure 22 – UPV and unconfined

compressive strength correlated by age.

Figure 23 – Correlation between UPV

and stiffness.

Lastly, the resistivity test was performed in soil-cement specimens and also in three sandy-soil specimens, each with

different moisture content (dry, saturated and humid). Results show that dry soil exhibits apparent resistivity (ra) 60

times greater than saturated soil and 13 times greater than the humid soil, thus reflecting the influence of moisture

content in this property (Oliveira, 2018). This occurs because in materials such as sands or sand-cement mixtures,

the electric current flows mostly through interstitial water (electrolytic conduction).

For soil-cement, at 3, 14 and 28 days of age ra exhibited logarithmic correlation with the cement dosage (figure 24),

thus showing that it’s possible to analyse the cement dosage of a soil-cement mixture using electrical resistivity. The

results show that with increasing cement dosage, ra becomes higher. As electric current flows in the material through

the pores, porosity and pore connection are two key factors that control resistivity. As seen in the physical

characterization tests, the mixtures with greater cement dosage are less porous and their pore dimensions tends to

be controlled by small pores, which therefore reduces the pores connectivity.

The described physical effect that cement dosage has on soil-cement microstructure enables the correlation between

ra and qu. Three correlation curves were obtained that show that the resistivity can estimate the mechanical properties

of soil-cement (figure 25).

Figure 24 – Apparent resistivity and cement dosage

correlation for fixed age.

Figure 25 - Apparent resistivity and unconfined compressive

strength correlation for fixed age.

V = 1,2431t0,0856

RMSE = 0,15

V = 1,9785t0,1305

RMSE=0.26

V = 2,1145t0,1744

RMSE=0.52

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

0 7 14 21 28

3 days of agequ = 0,1592V4,1179

RMSE=0.9

14 Days of agequ = 0,192V3,4949

RMSE = 1.8

28 days of agequ = 0.3083V2,7652

RMSE=0.10

2

4

6

8

10

12

14

16

18

0,00 1,00 2,00 3,00 4,00

Etg = 835,83V - 1108,6R² = 0,97

0

500

1000

1500

2000

2500

0,00 1,00 2,00 3,00 4,00

3 days of agera = 24,268ln(x) - 115,85

14 days of agera = 15,401ln(x) - 73,351

28 days of agera = 15,286ln(x) - 70,73

0

5

10

15

20

25

30

150 200 250 300 350

3 days of agequ = 0,0408ra

1,6111

14 days of agequ = 0,0417ra

2,0802

28 days of agequ = 0,1377ra

1,4788

0

2

4

6

8

10

12

14

16

18

0 5 10 15 20 25 30 35

150 kg/m3 250 kg/m3 350 kg/m3 150 kg/m3 250 kg/m3 350 kg/m3 150 kg/m3 250 kg/m3 350 kg/m3

Age (days) UPV (km/s) UPV (km/s)

UP

V (

km

/s)

qu (

MP

a)

Etg (

MP

a)

150 kg/m3

250 kg/m3

350 kg/m3

Cement dosage (kg/m3) ra (Ω.m )

r a (

Ω.m

)

qu (

MP

a)

150 kg/m3

250 kg/m3

350 kg/m3

10

4. CONCLUSIONS

Considering the proposed goals of the present work, four main conclusions are established regarding the improved

silty sand. (i) the physical and mechanical behaviour of the silty sand mixed with cement was strongly influenced by

cement dosage; (ii) as expected, regardless of cement dosage the mechanical properties of soil-cement increased

with time; (iii) unconfined compression strength exhibit a satisfactory correlation with the tangent modulus of elasticity

and with the tensile strength, thus establishing equations that allow their estimation; (iv) the properties evaluated

using geophysical tests revealed to be strongly influenced by cement dosage, and consequently demonstrated a

satisfactory correlation with the mechanical properties, thus showing to be a solution with potential to be used as a

quality control resource in laboratory tests.

ACKNOWLEDGEMENTS

The author acknowledges professors Ana Paula Pinto and Rafaela Cardoso for supervising this work.

Acknowledgement is also due to OPWAY for providing the materials tested, and to Parque Escolar E.P.E. for the

funding.

REFERENCES

Gomes, Augusto, Ferreira Pinto, A. P. & Almeida, N. G. – Aulas de Laboratório MCII-10/11 – Módulo 6. Documento

de apoio à disciplina de Materiais de Construção II do Mestrado Integrado em Engenharia Civil. Lisboa : Instituto

Superior Técnico, 2010.

Kutzner, C. – Grouting of rock and soil. Rotterdam, The Netherlands : A. A. Balkema, 1996. ISBN 90 5410 634 4

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