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CHAPTER 2

Literature Review

2.1 Cement treatment of soft clay

2.1.1 Chemical reactions

The fundamental mechanism of cement-treated soil has been outlined by Schaefer et al.

(1997). Ordinary Portland cement (OPC) consists mainly of tricalcium silicate (C3S),

dicalcium silicate (C2S), tricalcium aluminate (C3A) and tetracalcium alumino-ferrite

(C4AF). In these chemical formulae, C represents CaO, S represents SiO2, A represents

Al2O3 and F stands for Fe2O3. In the presence of water, hydration reaction of cement takes

place rapidly, to produce primary cementitious products, which are hydrated calcium

silicates (C2SHx, C3S2Hx), hydrated calcium aluminates (C3AHx, C4AHx) and hydrated

lime (Ca(OH)2). The calcium silicate hydrates are the main cementitious products and the

hydrated lime is deposited as a separate crystalline solid phase. The cement particles bind

the adjacent cement grains together during hardening and formed a hardened skeleton. In

addition, the dissociation of hydrated lime results in increased concentrations of Ca2+

and

OH-, which accounts for the rise in pH value of the pore water. The strongly alkaline

condition promotes the dissolution of silica (SiO2) and alumina (Al2O3) from soil, which

then gradually react with the Ca2+

ions, forming the secondary cementitious products,

namely calcium silicate hydrate (CSH) and calcium alumina hydrate (CAH), which

hardened when cured to treat the soil. These secondary reactions are known as pozzolanic

reactions. Pozzolanic reactions further increase the strength and durability of cement-

treated soil due to the enhancement of the bonding among soil particles. Cement hydration

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and pozzolanic reactions can last for months or even years after the mixing and thus the

strength and stiffness of cement-treated soil are expected to increase with time. The above

reactions between cement, soil and water can be represented by Equations 2.1 to 2.4:

C3S + H2O C3S2HX (hydrated gel) + Ca(OH)2(primary cementitious products)

(2.1)

Ca(OH)2 Ca2+

+ 2 (OH)-

(hydrolysis of lime)

(2.2)

Ca2+

+ 2 (OH)-+ SiO2 (soil silica) CSH

(secondary cementitious product)(2.3)

Ca2+ + 2 (OH)- + Al2O3 (soil alumina) CAH

(secondary cementitious product)(2.4)

The equations above are only applicable to C3S present in OPC. Other main constituents

of OPC (i.e. C2S, C3A and C4AF) also undergo similar hydration and pozzolanic reactions

to produce cementitious materials.

The above discussions were on the main chemical reactions between cement, soil and

water. In the present study, the interest is on the possible effect of addition of some

chemical components (arising from IFA) onto these two chemical reactions.

2.1.2 Liquid limit and plastic limit of cement-treated clayConstant to slight decrease in the liquid limit (LL) of cement-treated Bangkok clay was

observed when cement content or curing time increases, as shown in Figure 2.1 (Uddin et

al., 1997). Figure 2.1 also shows that the plastic limit (PL) of cement-treated Bangkok

clay increases with cement content and curing time.

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Chew et al. (2004) noted that, LL of cement-treated Singapore marine clay (SMC)

decreases with curing time but remains significantly higher than that of the untreated

marine clay. As shown in Figure 2.2, LL increases significantly at low cement content (e.g.

10%) before dropping slightly at higher cement content. PL of cement-treated SMC

increases monotonically with curing time and cement content, with larger rate of increase

at low cement content. Chew et al. (2004) attributed this to the aggregation and

cementation of particles into larger sized clusters (Locat et al., 1990).

The trend of change in LL with cement/lime content and curing time seems to depend

heavily on the soil type. Sivapullaiah et al. (2000) reported an increasing trend of LL with

curing time on lime-treated black cotton soil. Immediately after addition of lime, LL of

Black Cotton Indian soil decreases with lime content until about 6% lime and stabilizes as

lime content further increases. However, as curing time is extended to 7 days, LL

increases with lime content until about 6% lime and decreases with further addition of

lime, as can be seen in Figure 2.3. As Figure 2.3 shows, immediately after addition of lime,

PL increases with lime content until 1% lime, decreases slightly with further addition of

lime and stabilizes as lime content is beyond 3.5%. As curing time is extended to 7 days,

PL increases with lime content until less than 4% lime and then stabilizes as lime content

further increases.

2.1.3 Pore size of cement-treated clay

Chew et al. (2004) noted that cement-treated SMC has a significantly higher proportion of

larger diameter pores than the untreated marine clay. Pore size also increases with cement

content and decreases slightly with curing time, as shown in Figure 2.4. Chew et al. (2004)

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suggested that the dissolution of the kaolinite and the flocculation process both lead to a

more open clay structure, with clay-cement clusters interspersed by large voids. The

reduction in pore size as curing time increases could be due to more deposition of CSH

and CASH on and around the flocculated clay clusters.

2.1.4 Unconfined compressive strength of cement-treated clay

The early research works carried out to understand the effects of the various factors on the

strength of cement-treated soil were based on the unconfined compressive (UC) strength

(qu) which is widely used as an index to quantify the effectiveness of the treatment method.

These factors include type of cement, cement content, curing time, type of soil, initial

water content, amongst others (Kawasaki et al., 1981; Taki and Yang, 1991; Chew et al.,

1997; Nagaraj et al., 1996; Uddin et al., 1997; Porbaha et al., 2000; Chew et al., 2004).

UC strength of cement-treated Bangkok clay increases with cement content and curing

time (Uddin et al., 1997), as shown in Figure 2.5. As shown in Figure 2.6, for cement-

treated SMC, the 7-day UC strength increases almost proportionally with cement content

(defined as the mass of dry cement over the mass of dry clay herein) throughout the range

of cement content investigated. However, for the 28-day samples, the strength gain is very

rapid when cement content is in the range of 5 to 50%. Beyond 50% cement content, the

strength gain moderates to a slower rate and then stabilizes (Chew et al., 2004). Figure 2.7

shows that UC strength of cement-treated Singapore marine clay is a function of

water/cement ratio and soil/cement ratio (Lee, 1999).

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2.1.5 Compressibility of cement-treated clay

The increase in gross yield stress (Hight et al., 1992) and reduction in compression indices

of soft clay due to the addition of cement have been well-documented (e.g. Uddin et al.,

1997; Balasubramaniam et al., 1999; Kamruzzaman et al., 2001). Uddin et al. (1997)

noted that increase in cement content results in an increase in gross yield stress and

reduction in compressibility of the soft Bangkok clay, especially from 0% to 5% cement

content, as shown in Figure 2.8. Kamruzzaman et al. (2001) noted that gross yield stress

increases with increasing cement content and curing time. As shown in Figure 2.9, the

swelling curves of cement-treated clay are almost parallel to the loading portions of the

initial part of the consolidation curves and they are not affected by cement content. The

swelling index (Cr) of the cement-treated clay is also observed to be much smaller than

that of the untreated soil and it decreases with increase in cement content. On the other

hand, the compression index (Cc) shows no significant change with cement content.

2.1.6 pH value of cement-treated clay

Rao and Rajasekaran (1996) found that the pH value of pore fluid of lime-treated clay

increases with curing time. Chew et al. (2004) noted that the pH value of cement-treated

SMC rises rapidly at low cement content but the rate of rise moderates at higher cement

content, as shown in Figure 2.10. Chew et al. (2004) attributed this stabilization of pH

value to the exhaustion of kaolinite rather than the exhaustion of lime. For cement content

of less than 20%, pH value decreases with curing time. At higher cement content (e.g.

30% onwards), curing time almost has no effect on pH value.

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2.1.7 Microstructural properties of cement-treated clay

Kezdi (1979) suggested that a soil-cement skeleton matrix may be formed owing to the

addition of cement with each skeletal unit consisting of a core of hydrated cement gel

(tobermorite gel) and secondary cementitious products (CSH and CAH) connecting the

adjacent clay particles. In addition, the inter-particle bond strength also increases as a

result of reduction of the diffused double layer and flocculation of the secondary

cementitious materials. A schematic diagram to illustrate the change in soil-cement

structures during hardening was proposed by Saitoh et al. (1985), as shown in Figure 2.11.

Immediately after mixing, cement slurry surrounds clusters of clay particles. The primary

hydration reactions involve the shell of cement slurry, which forms hardened cement

bodies. The pozzolanic reactions involve the inner clay particles, resulting in the

formation of hardened clay bodies.

As shown in Figure 2.12 (A), Locat et al. (1990) suggested that the microstructure of lime-

treated sensitive clay has an open micro-fabric, and individual particles and aggregates

could be clearly observed. Figure 2.12 (B) shows that, after the addition of quicklime and

10 days of curing, the clay flocculated into larger lumps. Figure 2.12 (C) shows the lumps

cemented together by the subsequent pozzolanic reaction products. Figures 2.12 (D-F)

clearly show the cementitious products, namely the platy CASH and the reticular CSH.

Kamruzzaman (2002) studied the microstructural characteristics of cement-treated SMC.

As shown in Figure 2.13 (a), remolded and untreated Singapore marine clay exhibits an

open type of microstructure, with the platy clay particles assembled in a dispersed

arrangement. Figures 2.13 (b) and (c) show the SEM images of 10% and 20% cement-

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of IFA are poorly graded, but the Brooklyn IFA clearly has a larger uniformity coefficient,

which indicates a larger range of particle sizes. The particle size of Senoko IFA is smaller

than that of Brooklyns IFA, which is in turn smaller than that of Tuas IFA. The ignition

loss for Tuas and Senoko IFAs is about 15%, suggesting that both contain significant

amount of organic compounds. Both the Tuas IFA and the Senoko IFA are alkaline but the

latter registers a significantly higher pH value.

The chemical compositions of both Tuas and Senoko IFAs are listed in Table 2.2. It

should be noted that, only cations present in IFA were reported. The predominant

chemical elements in both IFAs are silicon and calcium. Other major elements are

aluminum, ferrous, potassium, sodium and magnesium. There are also trace amounts of

heavy metals such as zinc, lead, nickel, chromium. Senoko IFA has higher calcium

content than that of Tuas IFA. The high levels of Ca and Si, which are the main strength-

contributing agents in Portland cement, seem to suggest that incineration fly ash can be

used as a cement admixture or pozzolanic material.

2.2.2 Strength properties

Goh and Tay (1993)investigated the use of 10% - 30% IFA to treat Singapore marine clay.

In addition, Goh and Tay (1993) also conducted tests to investigate the effect of adding

5% IFA into 5% cement/lime treated clay. Figure 2.14 shows the undrained shear strength

of the seven types of treated soils, normalized with the undrained shear strength of

untreated clay, versus curing time. By having IFA alone, the undrained shear strength

increases with curing time and IFA content. After 80 days of curing, the undrained shear

strength of the treated clay increases up to 1.9, 2.5 and 3 times of the untreated clay for the

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10%, 20% and 30% IFA mixes,respectively. Larger gain in strength is observed for both

cement-treated clay and lime-treated clay. Furthermore, the inclusion of 5% IFA

significantly increases the undrained shear strength of the 5% lime-treated clay. The

addition of 5% IFA into the cement-treated clay results in proportionally smaller strength

increase than the lime-treated clay. The above results indicate that IFA could be used as a

replacement material for lime or cement for soft clay treatment, provided that gain in

strength is only required in the order of two to three times. If substantially larger gains in

strength are required, IFA has to be used in combination with either cement or lime.

Moreover, the addition of IFA into cement- or lime-treated clay may have highly variable

effects.

Show et al. (2003) extended Goh and Tays (1993) investigation to higher IFA and cement

contents. As shown in Figure 2.15, there is clear gain in strength over curing time for all

the four treated samples. However, the addition of IFA to the cement-treated soil appears

to result consistently in a drop in the strength. Thus, in contrast to Goh and Tays (1993)

findings, the addition of higher levels of IFA into a cement-treated soil with higher cement

content appears to negate some of the strength improvement of the cement treatment.

2.2.3 Compression indexGoh and Tay (1993) noted that the compression index decreases with IFA content and

curing time, as shown in Figure 2.16. Show et al. (2003) noted that the compression index

decreases with curing time for all mixtures, as shown in Figure 2.17. In Show et al.

(2003)s study, all the treated soils have lower compression index than the untreated soil.

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However, for a given curing period, samples with IFA have higher compression index

than those treated purely by cement, especially for short curing periods.

2.2.4 Plasticity indexGoh and Tay (1993) notedthat plasticity index (PI) decreases with IFA content and curing

time, as shown in Figure 2.18. All the treated soils show decrease in PI compared to the

untreated clay. Goh and Tay (1993) noted that the mechanism of IFA-treated clay was

similar to that of lime-treated clay. Reduction in PI of IFA-treated could therefore be

attributed to flocculation. Figure 2.18 also shows that, in the case of specimens treated

with 5% cement, the addition of 5% IFA leads to a further decrease in PI.

Show et al. (2003) noted that PI decreases with cement content and curing time, as shown

in Figure 2.19. However, the inclusion of IFA into soil-cement mixes result in a larger PI

than those specimens treated with cement alone. Show et al. (2003) attributed this to the

reduction in the rate of hydration of cement but the mechanism was not clearly stated.

2.2.5 Some issues arising from the above research works

The above discussion shows that the results of Goh and Tay (1993) and those of Show et

al. (2003) indicate clearly opposite trends. In the case of Goh and Tay (1993), the addition

of IFA to the cement-treated soil leads to a further increase in strength together with a

decrease in compressibility and plasticity index. On the other hand, in Show et al.s (2003)

study, the addition of IFA to cement-treated soil leads to a decrease in strength together

with an increase in compressibility and plasticity index. Although both of these

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researchers claimed that IFA could function as a partial replacement of cement in the

mixture, the results showed the contradictory trends.

It is unclear as to why both studies show opposite trends. Many explanations are possible,

e.g. differences in the constituents of the two batches of IFA, as well as differences in IFA

and cement content. IFA contains significant amount of chemical compounds (e.g.

chlorides, carbonates and sulphates), heavy metals and organic compounds. Thus, these

components may alter the role of IFA in soil-cement mixes. However, the effect of these

chemical compounds on the properties of cement-treated clay has not been

comprehensively studied yet. Some other researches focused on the leachability of

cement-IFA-clay mixes as IFA could cause environmental pollution under some

unfavorable circumstances. Baur et al. (2001) noted that the salts from IFA could be a

bigger problem than the heavy metals, as cement stabilization could immobilize heavy

metals but it could not stabilize sulphate, chloride, and sodium and potassium compounds.

The uncertainty over the specific cause of the opposing trends observed by Goh and Tay

(1993) and Show et al. (2003) can be attributed firstly to the relatively narrow spectrum of

tests which had been conducted. In their studies, only changes in undrained shear strength,

compression index and plastic index of soil-cement mixes due to the inclusion of IFA

have been investigated. Furthermore, the effect of various factors (e.g. cement content,

IFA content and curing time) on the engineering properties and microstructural behavior

of cement-treated clay had not been investigated in detail. Finally, the effect of the

different chemical constituents in the IFA on the hydration and pozzolanic reactions had

not been studied.

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2.3 Cement-treated clay with chemical compounds

2.3.1 Cement-treated clay with monovalent alkali metal salts

Lambe and Moh (1957) and Lambe et al. (1960) carried out laboratory studies on the

effect of trace amounts of alkali metals on cement treated soils. Generally, among all the

alkali additives, sodium compounds were found to be most beneficial in terms of strength

enhancement, followed by potassium and lithium compounds, as can be seen from Figure

2.20.

In addition, Lambe et al. (1960) investigated the effects of 10 types of sodium compounds

on 11 different kinds of cement-treated soils. It was found that, for each sodium

compound, there is an optimum concentration which corresponds to 0.5-2.5% by weight

depending on the type of additives (Figure 2.21). As shown in Figure 2.22, for New

Hampshire silt (NHS) treated by 5% cement, sodium sulphate and sodium aluminate were

found to be most beneficial at their optimum concentrations, resulting in even higher

strengths than specimens with treated with 10% cement. Sodium metasilicate gave rise to

strengths comparable to those with treated with 10% cement. Sodium hydroxide and

sodium carbonate were less effective, but still provided significant strength improvement

compared to 5% cement-treated soil. The addition of sodium fluoborate only led to a

slight increase in strength. The other three sodium compounds (i.e. sodium fluosilicate,

sodium fluoride and sodium tetraborate) were found to be detrimental to soil-cement

mixes. This suggests that the effects of chemical additives probably depend not only on

the cation but also on the anion. Table 2.3 summarizes the compressive strength results of

three types of silty soils (i.e. New Hampshire silt (NHS), Massachusetts clayey silt (MCS)

and Vicksburg loess (VL)) treated with cement and sodium compounds.

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The addition of sodium compounds (e.g. sodium hydroxide, sodium sulfite, sodium

sulphate and sodium carbonate) into another three types of clayey soils (i.e. Illinois clay,

and Texas clays 1 and 2) treated with 5% cement did not, however, elicit a similar trend of

behaviour. It should be noted that Texas clays 1 and 2 were both montmorillonitic soils

and were slightly alkaline. As shown in Table 2.4, only sodium hydroxide was found to

improve the strength of soil-cement mixes, and all the other sodium compounds seemed to

have a negative effect on the strength of soil-cement mixes in this case.

Sodium compounds (e.g. sodium hydroxide, sodium metasilicate and sodium carbonate)

were also added into another three types of soils (i.e. Iraq clays 1 and 2, and Iraq clayey

silt) treated with 5% cement. It should be noted that the three types of soils all contained

fairly large amount of carbonates, and Iraq clays 1 and 2 were slightly alkaline. As shown

in Table 2.4, all the three sodium compounds added improved the strength of soil-cement

mixes. Sodium hydroxide proved to be the most effective additive.

Finally, sodium compounds (e.g. sodium hydroxide, sodium metasilicate, sodium sulphate

and sodium carbonate) were added into two types of sandy soils (i.e. Wisconsin sand 1

and 2) treated with 5% cement. As shown in Table 2.4, the addition of sodium hydroxide,

sodium metasilicate and sodium carbonate led to reduction in strength, possibly due to the

high organic content in both of these two soils. However, sodium sulphate added

significantly improved the strength of soil-cement mixes.

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Hence, it could be concluded that that the effects of sodium compounds on soil-cement

mixes varied with soil type, decreasing with increasing soil plasticity and/or organic

matter content (Lambe et al., 1960).

Moh (1962) extended the above investigation and proposed that the reactions taking place

in soil-cement mixes upon the addition of sodium compounds could be represented by

following equations:

With cement:

Na2X + C3S + H2O CSH (hydrated gel) + CaX + NaOH (2.5)

CSH + Na2X NCSH (hydrated gel) + CaX (2.6)

With soil:

2NaOH + SiO2 (soil silica) NSH (soluble) + H2O (2.7)

NSH + Ca2+ NCSH (hydrated gel)+Na+

Or CSH (hydrated gel) + Na+

(2.8)

in which X stands for the anion of the sodium compounds added and N denotes Na2O.

Moh (1962) noted that, regardless of the type of the anion of the sodium compounds

added, the following changes will take place in soil-cement mixes upon the addition of

sodium compounds: (a) increase in pH value, or increase in the available OH-

concentration; (b) apparent reduction in the calcium ion concentration; (c) increase in the

sodium-calcium ratio in the solution. These will ultimately lead to: (a) increased rate and

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extent of solubilization of soil silica; (b) retardation of precipitation of calcium silicate gel;

(c) formation of highly hydrated calcium silicate gels with sodium.

Davidson et al. (1960) and Kezdi (1979) noted that the addition of sodium chloride into

lime-treated clay resulted in a caustic reaction with the formation of sodium hydroxide.

Similar reaction was found in the mixture of lime-sodium chloride treated fly ash

(Narendra et al., 2003). It was suggested that the increase in the concentration of hydroxyl

ions caused more silica to be dissolved and hence be available for reactions with lime.

This led in turn to the formation of more cementitious products (e.g. voluminous sodium

calcium silicate hydrate).

2.3.2 Cement-treated clay with divalent alkali metal salts

Rajasekaran and Narasimha Rao (2000) noted that the addition of calcium chloride led to

a significant increase in strength of marine clay treated by quicklime columns, as shown in

Figure 2.23 (b). Calcium carbonate (CaCO3) was detected in the mixture. However,

CaCO3 was not perceived to impart significant improvement to the strength of soil.

Instead, it was proposed that the diffusion of additional calcium ions into the soil system

results in the crowding of the cations near the soil particles. This reduces the double layer

thickness of the soil particles, which was believed to enhance the strength of the soil

system. In addition, Rajasekaran and Narasimha Rao (2000) observed an increase in shear

strength of quicklime-treated clay when calcium sulphate was added, as shown in Figure

2.23 (c). However, the presence of ettringite was not detected.

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2.3.3 Cement-treated clay with sulphatesRajasekaran and Narasimha Rao (2000) noted that the addition of sodium sulphate led to a

significant reduction in shear strength of quicklime-treated clay, as shown in Figure 2.23

(d). It was suggested that the detrimental effect of sodium sulphate be due to the crowding

of monovalent cations around soil particles and the formation of ettringite which weakens

the soil system with time (Mitchell, 1986; Hunter, 1988).

Ettringite has been well known to be the cause of sulphate attack on concrete (e.g. Irassar

et al., 1996; Collepardi, 2003). Ettringite occupies a greater volume and results in

expansion of the concrete. Sulphate ions were reported to have a detrimental effect on the

strength of cement stabilized soil (e.g. Mehra et al., 1955; Cordon, 1962). Sherwood (1962)

observed cracking and swelling in 10% lime treated heavy clay immersed in the dilute

solutions of sodium sulphate or magnesium sulphate, and suggested that this is due to the

formation of ettringite. Mitchell (1986) noted that lime-treated sulphate-bearing clay

swelled and disintegrated after a few years when used for road construction.

Sivapullaiah et al. (2000) noted that formation of cementitious calcium silicate hydrate

was inhibited and ettringite/thaumasite was formed with the presence of sulphate in lime

stabilized black cotton soil. The sequence of reactions is simplified by Hunter (1988) as

follows:

Formation of ettringite:

6Ca2+

+ 2Al(OH)4

+ 4(OH)

+

3(SO4)2

+ 26H2O Ca6[Al(OH)6]2(SO4)326H2O (2.9)

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Formation of thaumasite:

Ca6[Al(OH)6]2(SO4)326H2O +

2H2SiO42

+ 2(CO32

+ O2) Ca6[Si(OH)6]2(SO4)3(CO3)2 +

2Al(OH)4

+ (SO4)2

+ 4OH

+

26H2O

(2.10)

While the negative effect of sulphate on cement/lime treated clay is well-documented,

some researchers (e.g. Kozan, 1960; Lambe et al., 1960; Mehta, 1983; Kamon and

Nontananandh, 1991) noted that ettringite could actually contribute to the strength

improvement. Kozan (1960) and Lambe et al. (1960) noted that small amounts of sodium

sulphate increased strength of certain type of cement stabilized soils. Mehta (1983) and

Kamon and Nontananandh (1991) noted that the long and needle-like ettringite (Type I)

was actually non-expansive. Instead, this hardened crystal intercrossed the soil particles

and filled up the voids.

This indicates that the role played by sulphate in soil-cement mixes will have to be

dependent on many factors, like soil type (i.e. soil chemical composition and physical

properties), sulphate concentration and metal cation type. Kinuthia et al. (1999) noted that,

when metal sulphates were added to lime-stabilized kaolinite, the cation exchange process

was dependent on the position of the sulphate metal cation in the lyotropic series. The

latter ranks the cations in the order of their ability to bond to the cation exchange face (Li+

< Na+

< K+

< Mg2+

< Ca2+

< Ba2+

< Al3+

< H+) (e.g. Cobbe, 1988; George et al., 1992).

2.3.4 Some issues arising from the above research works

Notwithstanding the extensive research works cited above, some issues relating to cement-

treated clay with IFA and cement-treated clay with small amount of chemical compounds

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remain unsolved. It is evident that, if the effect of IFA on cement-treated soil is to be fully

elucidated, further research should be carried out using a wider spectrum of test conditions

and over a larger range of cement, water and IFA contents, and there should also be

consideration on the physico-chemical reaction(s) between cement, clay and IFA. This

forms the theme of the first part of the present study. In addition, so far little or no

research has been carried out to examine the effect of small amounts of chemical

compounds on the engineering properties, physico-chemical and micro-structural behavior

of cement-treated Singapore marine clay. Thus, this forms the theme of the second part of

the present study. The two parts of the study are interconnected since the results of the

second part will be used to explain and predict the results obtained in the first part.

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Table 2.1 Physical properties of incineration fly ashes from Tuas & Senoko incineration

plant, Singapore, and Brooklyn, New York (after Poran and Ahtchi-Ali, 1989; Goh andTay, 1993; Show et al., 2003)

Properties

Tuas IFA,

Singapore

Senoko

IFA,Singapore

Brooklyn

IFA, USA

Specific Gravity 1.71 2.30 2.51

Effective size (mm)0.085-

0.180.005 0.02-0.04

Average uniformity coefficient 10.9 3.9 49

Average coefficient of curvature 1.5 0.975 10

Particle

size

distributionFines (%) 3-10 - 20

Loss on ignition (%) 15.0 15.72 -

pH value 9.4 11.05/11.14 -

Table 2.2 Chemical compositions of different IFAs (after Goh and Tay, 1993; Show et al.,

2003)

Concentration (% by weight)Chemical elements

Tuas IFA Senoko IFA

Silicon 42.00 34.60

Calcium 15.14 29.47

Aluminum 12.50 1.93Ferrous 3.30 1.98

Potassium 1.24 4.68

Sodium 1.19 1.10

Zinc 0.83 0.77

Magnesium 0.78 1.19

Lead 0.36 0.19

Copper 0.17 0.17

Manganese 0.11 0.33

Nickel 0.037 0.18

Chromium 0.023 0.05

Cadmium 0.0075 0.01

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Table 2.3 Compressive strengths of three cement treated silty soils with the addition of

various sodium compounds (after Lambe et al., 1960)

Cement content = 5%, dry cement weight by dry soil weight

Compressive strength, psiCombination

Additiveconcentration (%

by dry soil

weight)

Curing days

NHS MCS VL

7 110 300 180Control 0

28 180 375 260

7 165 805 3450.5

28 240 1370 390

7 260 815 340

Sodium

hydroxide1.0

28 360 1185 465

7 345 575 2600.5

28 500 800 2907 370 895 310

Sodiumcarbonate

1.028 375 1125 335

7 325 320 3300.5

28 410 500 300

7 260 685 305

Sodiumsulphite

1.028 445 1030 345

7 359 - 345Sodium

metasilicate1.0

28 - - -

7 260 - 2750.5

28 400 - -Sodium

sulphate 1.0 7 - 590 -

Note: New Hampshire silt NHS, Massachusetts clayey silt MCS, Vicksburg loess VL

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Table 2.4 Summary of the effects of sodium compounds on the compressive strength of

various 5% cement-treated soils (after Lambe et al., 1960)

Cement content = 5% (weight of cement over dry soil weight)

Effect of adding sodium compounds on different soilsSodiumcompounds

added NHS MCS VL IC TC1 TC2 IC1 IC2 ISC WS1 WS2

Sodium

sulphate - - - -

Sodiumaluminate

- - - - - - - - -

Sodium

metasilicate - - - - -

Sodium

hydroxide

Sodium

carbonate -

Sodiumfluoborate

- - - - - - - - - -

Sodium

fluosilicate - - - - - - - - - -

Sodium

fluoride - - - - - - - - - -

Sodium

tetraborate - - - - - - - - - -

Sodium

sulphite - - - - -

Note:

(1)New Hampshire silt NHS, Massachusetts clayey silt MCS, Vicksburg loess VL,Illinois clay IC, Texas clay 1 TC1, Texas clay 2 TC2, Iraq clay 1 IC1, Iraq clay

2 IC2, Iraq silty clay ISC, Wisconsin sand 1 WS1, Wisconsin sand 2 WS2

(2)NHS, MCS and VL are silty soils; IC, TC 1 and TC 2 are clayey soils; IC 1 and IC 2are calcareous soils.

(3) stands for the increase in strength due to the addition of sodium compound;stands for the decrease in strength due to the addition of sodium compound.

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Figure 2.1 (a) Effect of cement content on Atterbergs limits of cement-treated Bangkok

clay (after Uddin et al., 1997)

Figure 2.1 (b) Effect of curing time Atterbergs limits of cement-treated Bangkok clay

(after Uddin et al., 1997)

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Figure 2.2 Effect of curing time and cement content on Atterbergs limits of cementtreated Singapore marine clay (Wi = 120%) (after Chew et al., 2004)

Figure 2.3 Effect of lime content on Atterbergs limits of lime-treated black cotton soil

(after Sivapullaih et al., 2000)

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Figure 2.4 Effect of curing time and cement content on pore size distribution of cement-

treated Singapore marine clay (Wi = 120%) (after Chew et al., 2004)

Figure 2.5 Variation of unconfined compressive strength with cement content of cement-

treated Bangkok clay (after Uddin et al., 1997)

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Figure 2.6 Effect of cement content and curing time on unconfined compressive strength

of cement-treated Singapore marine clay (after Chew et al., 2004)

Figure 2.7 (a) Unconfined compressive strength of cement-treated Singapore marine clay

prepared from clay slurry (7 days of curing) (after Lee, 1999)

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Figure 2.7 (b) Unconfined compressive strength of cement-treated Singapore marine clay

prepared from clay slurry (28 days of curing) (after Lee, 1999)

Figure 2.8 Void ratio-axial stress relationship of cement-treated Bangkok clay (after 1

month curing time) (after Uddin et al., 1997)

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Figure 2.9 Effect of cement content and curing time on void ratio-vertical stressrelationship of cement-treated Singapore marine clay (Wi = 120%) (after Kamruzzaman et

al., 2001)

Figure 2.10 Variation of pH of cement-treated Singapore marine clay with cement content

and curing time (solid: water = 1:2.5, Wi = 120%) (after Chew et al., 2004)

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Figure 2.11 Schematic illustrations of cement improved soil (after Saitoh et al., 1985)

Figure 2.12 Scanning electron micrograph of Buckingham soil at the liquid limit: (A)

remolded, no lime; (B) 4% quick lime, 10 days of curing, showing lumps created by the

flocculation-agglomeration reactions; (C) neoformed phases; (D) platy CASH; (E) and (F)4% quick lime, 100 days of curing, platy CASH and reticular CSH (after Locat et al., 1990)

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(a) Untreated remolded Singapore marine clay

(b)10% cement treated SMC (Wi = 120% and curing time = 28 days)

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(c)20% cement treated SMC (Wi = 120% and curing time = 28 days)Figure 2.13 Scanning electron micrograph of untreated and cement-treated Singapore

marine clay (after Chew et al., 2004)

Figure 2.14 Effect of curing time on undrained shear strength of cement/lime-IFA-treated

soils (after Goh and Tay, 1993)

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Figure 2.15 Variations of undrained shear strength of cement-IFA-treated soils with time

(after Show et al., 2003)

Figure 2.16 Effect of curing time on compression index of IFA-stabilized soils (after Gohand Tay, 1993)

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Figure 2.17 Variations of compression index of cement-IFA-treated soils with time (afterShow et al., 2003)

Figure 2.18 Effect of curing time on plasticity index of IFA- and cement-stabilized soils

(after Goh and Tay, 1993)

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Figure 2.19 Variations of plasticity index of cement-IFA-treated soils with time (afterShow et al., 2003)

Note: 1. Cement content for all the treated samples = 5% based on dry soil weight

2. Additive concentration based on dry soil weight

3. All samples tested after 24 hours

Figure 2.20 Effect of alkali metal hydroxides on the strength development of cement-stabilized New Hampshire silt (after Lambe et al., 1960)

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Figure 2.21 Effect of type and concentration of additives on the strength of NewHampshire silt stabilized with 5% cement (after Lambe et al., 1960)

Figure 2.22 Effect of type of additives (at optimum concentration) on strength of New

Hampshire silt stabilized with 5% cement (after Lambe et al., 1960)

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(a) Quicklime column treated soil system (b) Quicklime-calcium chloride treated soilsystem

(c) Quicklime-calcium sulphate treated soilsystem (d) Quicklime-sodium sulphate columntreated soil system

Figure 2.23 Variation in strength with time for soils treated with quicklime and salts in

sea-water set-up (after Rajasekaran and Narasimha Rao, 2000)