Chemical stabilization with lime of expansive clays from northern morocco



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CHEMICAL STABILIZATION WITH LIME OF EXPANSIVE CLAYS FROM NORTHERN MOROCCO
Maissara. J, Karym, H, Chbihi, M. El M, Belaaouad S,
Moutaabbid M, and Bourakhouadar M, Benmokhtar, S

J. Maissara1, H. Karym1, M. El M. Chbihi1, S. Belaaouad1, M. Moutaabbid1, M Bourakhouadar2 and S. Benmokhtar1*,

1University of Casablanca, Laboratory of Chemistry and Physics of Materials LCPM, Faculty of Sciences, Department of Chemistry, Casablanca, Morocco

2University of My Ismail, Faculty of Sciences, Department of Chemistry, Meknes, Morocco
*Corresponding Author: E-mail: sbenmokhtar@yahoo.com

Abstract 

Lime has been used for many years to stabilize road beds and airfields. Lime’s use is especially valuable when expansive clays are encountered. Expansive clays have been known to crack concrete slabs or to create rough joints as the slabs heaved and then settled during wet and dry cycles. This paper aims to investigate the effect of hydrated lime on the strength and microstructure of lime of four soils of northern regions of Morocco: Kenitra, Sidi Kacem, Tangier and Tetouan and three of the most frequently occurring minerals in clay deposits, namely, Illite, kaolinite and montmorillonite. In order to illustrate such effect, a series of laboratory tests were conducted. Atterberg limits, X-ray diffraction, hydration heats and cementing heats obtained by micro-calorimetric measurements.

The results indicated that the addition of lime resulted in a reduction in the plasticity and an improvement in compaction properties and the amount of lime needed to modify a clay soil varies from 3 to 6 per cent,

Key words: Lime, Stabilization, clay, cementing heats, micro-calorimetric measurements.

1. INTRODUCTION

The Soils treatment by lime is often made to increase their resistance [1], to reduce or increase their permeability and for also to decrease their compressibility [2-4]. It is also used to minimize the sensitivity to changes in soil water content [5,6]. The technique of lime treatment is very old. It has been used by Chinese there are some thousands of years for the construction of the Chinese wall, then by the Romans for the establishment of the imperial roads. It was extensively used during the Second World War for road and runway construction. Its contemporary application in intensive form began in the US in the road sector and has been developed into Europe [7-9]. In Morocco, the lime treatment is also of ancestral empirical use. Today stabilization of clay soil by incorporation of lime is a technique widely used throughout the world to improve its use in construction. It is used in road construction to improve sub-bases and subgrades, for railroad and airport construction. Recently, various attempts have been made to streamline this technique [10-12]. When lime is added to a clay soil it has an immediate effect on the properties of the soil as cation exchange begins to take place between the metallic ions associated with the surfaces of the clay particles and the calcium ions of the lime. Clay particles are surrounded by a diffuse hydrous double layer which is modified by the ion exchange of calcium. This alters the density of the electrical charge around the clay particles which leads to them being attracted closer to each other to form flocs, the process being termed flocculation. It is this process which is primarily responsible for the modification of the engineering properties of clay soils when they are treated with lime [13-15]. All types of clay minerals react with lime. The addition of lime to the soil water system produces Ca2+ and OH-. In cation exchange, bivalent calcium ions (Ca2+) are replaced by monovalent cations. The Ca2+ ions link the soil minerals, thereby reducing the repulsion forces and the thickness of the diffused water layer. This layer encapsulates the soil particles, strengthening the bond between the soil particles. The remaining anions OH- in the solution are responsible for the increased alkalinity [16-18]. After the reduction in water layer thickness, the soil particles become closer to each other, causing the soil texture to change. This phenomenon is called flocculation-agglomeration [18,19]. The silica and alumina that exist in the soil minerals become soluble and free from the soil when pH exceeds 12.4. The reaction between the released soluble silica and alumina and the calcium ions from lime hydration creates cementitious materials such as Calcium Silicate Hydrates (C-S-H) and Calcium Aluminate Hydrates (C-A-H) [20,21]. These pozzolanic reactions can be clarified using the following chemical equations [22-24]:

Ca(OH)2 + SiO2 …………> CaO-SiO2 + H2O (1)

Ca(OH)2 + Al2O3 ………….> CaO-Al2O3-H2O (2)

Pozzolanic reactions are time dependent and require long periods of time (years) because such reactions are functions of temperature, calcium quantity, pH value and the percentage of silica and alumina in the soil minerals [20, 25].

The work presented in this paper is a contribution to the application of chemical stabilization techniques, by adding lime at different concentrations for Four different clays, in northern Morocco (Kenitra, Sidi Kacem, Tangier, Tetouan) and on the pure standards clays (montmorillonite, Illite, kaolinite) from Brussels Road Research Center. We will present the results for chemical analysis, physical-chemical. Secondly, the study examined the effects of thermal properties (heat of hydration and cementing) of the different types of clays. The effect of stabilization at hydrated lime Ca(OH)2 on the thermal parameters will also be highlighted. For practical and economic considerations, we limited ourselves in the scope of this research, at of the lime rates ranging from 0% to 10%.



2. EXPERIMENTAL

2.1. Materials used for study

Localization of the soils

All soils are extracted from northern Morocco (Kenitra, Sidi Kacem, Tangier, Tetouan) (fig.1). Our study was performed on the clay fraction between 0.5 and 2 μ of natural clays and and on the pure standards clays (montmorillonite, Illite, kaolinite) from Brussels Road Research Centre.



Fig. 1. Locations of the four sampling sites of the study.
Sample 1: PR 6 - PK 65 Kenitra.

Sample 2: CT 2309 - PK 1 Kenitra.

Sample 3: CT 2010 - KP 0 Sidi Kacem.

Sample 4: RS 612 - PK 10 Tangier.

Sample 5: RS 603 - 9 PK Tetouan.

The Natural clays were the subject of previous research in soil mechanics laboratory of the National Centre for Studies and Research Road of Morocco.



3. DISCUSSION OF TEST RESULTS

Our goal is to study the hydration, we submitted the samples to two types of analyzes:

a) Chemical analyzes for the determination of chemical elements in samples by atomic absorption.

b) Physico-chemical analyzes: as measuring the plasticity indices, X-ray diffraction to determine the nature of clay and thermal analysis by Calvet microcalorimetry which allowed us to follow the thermal evolution during hydration.



3.1 Chemical analysis

The dissolution has been realized using the method described previously by Karym and al [26]. 150 mg of each sample, previously dried at 110°C for 24 hours, were weighed and then introduced into a Teflon tube. They were then dissolved by the action of 15 ml of HF (28%) and 9 ml of HNO3 (68%) [27,28]. Dissolution was performed on a hot plate at maximum temperature of 240°C.



The chemical composition of natural clays studied (Table 1) was determined by atomic absorption (Perkin-Elmer spectrophotometer model 3110). From chemical analysis, the main mineralogical constituents of the soils are silica and alumina. As indicated in this table, It appears that silica dominates (40.9–53.8 wt%), followed by aluminum (18.5-25.2 wt%). The values ​​of the ratios SiO2/Al2O3 molar ("ki") and SiO2/(Al2O3 + Fe2O3) molar ("kj") vary respectively from 2.7 to 4.9 and from 2.3 to 3.7. These are very characteristic of clay minerals. The values ​​of "ki", slightly higher confirm the abundance of smectitic clays in these samples. This is in good agreement with the results of XRD. The iron oxide content (4-9% Fe2O3) shows their abundance in clay minerals and/or as free oxide. The MgO will vary between 0.7 and 1%. The Mg increase in samples 1 and 2 (1.07%) as well as potassium oxide (K2O 0.76 to 0.79%) indicates a greater proportion of clays 2: 1 (smectites) in these samples.

Table 1: Chemical composition of the clay fraction.

sample

Composition

SiO2

Al2O3

Fe2O3

CaO

MgO

Na2O

K2O

PF

1

40. 9

25.2

6.1

0.30

1.07

0.50

0.79

11

2

44.1

23.9

4.6

0.30

1.01

0.49

0.78

10.2

3

44.6

21.9

5.2

0.30

0.98

0.39

0.78

9

4

53.8

18.5

9.5

0.29

0.91

0.35

0.77

8.5

5

51.2

20. 5

6.0

0.27

0.78

0.23

0.76

9.8

3.2 Physicochemical analysis

3.2.1. Limit Atterberg

The natural clays studied have liquidity limits ranging between 57% and 63% and the plasticity indices that vary between 34% and 39% substantially higher (Table 2). They are therefore of very plastic clays [29], which was confirmed by the AASHTO classification (American Association of State Highway Officials). According AASHTO, clays are classified A7-6 (Table 3).



Table 2: Limits Atterberg natural clays.

sample

1

2

3

4

5

LL

60

61

63

57

59

LP

21

23

24

22

25

IP

39

38

39

35

34


Table 3: Classification of Natural clays.

sample

1

2

3

4

5

AASHO

A-7-6

A-7-6

A-7-6

A-7-6

A-7-6


3. 3. X-RAY DIFFRACTION

X-ray diffraction is one of the most widely used methods for clay minerals identification and studying their crystal structure within the soils.

The Clays studied have been identified at room temperature by X-ray powder using Philips PW 1065/40 goniometer with horizontal sample holder (mode θ/2θ, movable sample). It is provided with a monochromator graphite, the wavelength used is the copper Kα1/Kα2 (1,540560Å /1,544330Å). The analytical conditions were 40 kV, 40 mA, Ni filter, angular range from 2.5 to 70°2θ. The diffractograms X are isotypes, they reveal the presence of clay minerals and crystalline phases mainly as tectosilicates (quartz, feldspar, ...). For example, diffraction test carried out on sample 4, showed that the predominant clay minerals are smectic types; beside it reveals also the presence of Illite, quartz, and traces of kaolinite.

- The presence of montmorillonite characterized by reflections (060) to 1,49Å, (009) to 1,68Å, (200) 2,55Å, (110) and 4,47Å (001) to 12,50Å.

- The presence of crystalline phases in the form of impurities especially that of quartz located 4,16Å and 3,35Å.

3. 4. STUDY HEAT

Since water is the main factor agents can degrade the buildings, we found it necessary to conduct a study of the influence of water on the thermal properties of clays by measuring heat of hydration.

The hydration of the studied clays was followed by microcalorimetry type Tian-Calvet. It belongs to the family of heat flow microcalorimeters. Its two major advantages are firstly its high sensitivity (~1μW) and secondly its isothermal operating mode inhibits any change in the kinetics of temperature variations, the latter being kept constant at 25°C.

3. 4. 1. PURE CLAY

a) Pure montmorillonite Hydration

The thermogram recorded (Figure 2) at room temperature corresponds to an exothermic phenomenon, it shows the variation of heat flow vs. time. It has a rather unusual appearance because the hydration seems to perform two steps: after a maximum, the curve shows a plateau and an exponential descent. The measuring of the area bounded by the curve ABC and the basic line or "experimental zero" provide us the hydration heat release which is of


34 J/g.

thermog_montmo

Fig. 2: Hydration of montmorillonite at 25°C.

b) Hydration of pure Kaolinite

Contrary to what is observed with montmorillonite, we note that the nature of the clay has a marked effect on the kinetics of the reaction, and also on the amount of heat released. The thermogram (Figure 3) is different and has only one exothermic phenomenon less pronounced. The heat is 3.5 J/g.



c) Hydration of pure Illite

The thermogram has an identical appearance to that of kaolinite with a single maximum and a rapid response speed. The heat is 14.5 J/g illite.



thermogra_illiteFig. 3: Hydration of illite and kaolinite at 25 ° C.

d) Hydration of the Tangier sample

The heat is in the range of 26.1J/g clay. Heat of hydration of the calcium hydroxide used for this study was also determined; the value is 3.7J/g lime. We note that the montmorillonite has a much higher heat of hydration than the other two as it was predictable.



3. 4. 2. COMBINING CLAY - LIME

a) Heat of hydration

As part of this study, we limited ourselves at rates ranging from 0% to 10% (0%, 2%, 4%, 6%, 8% and 10%). In Table 5 below, we have grouped the results measures of hydration heat in depending of the content lime stallions performed on clays and the clay from Tangier to different percentages of lime. These results are obtained from the counting method of the experimental thermogram. The graphical illustration of these results is presented on Figure 4.

Table 5: Enthalpies of hydration Δ.h°hyd (J g-1) of the clays and clay mixtures - lime

Composition %

0

2

4

6

8

10

kaolinite

ΔH°hyd.

3.5

7.0

7.1

6.4

8.6

8.1

illite

ΔH° hyd.

14.5

31.5

33.6

33.5

34.8

32.4

montmorillonite

ΔH° hyd.

35

43.5

43.0

43.0

41.0

39.0

natural soil

ΔH° hyd.

26

34.1

34.3

34.6

26.3

26.4


hydratation

Fig. 4: Heat of hydration of lime-clay mixtures according to their composition in lime.

b) Heat of cementing

The results measurements of the cementing heat (Δ.h°cim.) reduced to 1g of the mixing in function of different percentages of lime performed on clays are summarized in Table 6. These results are illustrated by Figure 5.



Table 6 : Enthalpies of hydration Δ.h°cim (J g-1) of the clays and clay mixtures - lime



Composition %

0

2

4

6

8

10

kaolinite

ΔH°cim.

0

3.5

3.6

2.9

5.4

4.6

illite

ΔH° cim.

0

17.1

19.2

19.2

20.6

18.2

montmorillonite

ΔH° cim.

0

8.6

10.9

12.0

11.6

10.0

natural soil

ΔH° cim.

0

8.5

9.3

9.4

1.4

1.7

courbe cimentation

Fig. 5: Heat of cementing the lime-clay mixtures according to their composition in lime 4

4. DISCUSSION OF HYDRATION

a) Hydration of pure montmorillonite

The hydration reaction of the clay is performed in two successive steps (Figure 2): as soon as the first drop of water comes into contact with the clay, we observe a rapid initial exotherm which peaked in intensity in a few minutes, and then decreases exponentially, this first maximum is assigned at the exchangeables cations which hydrate and caused the opening of the leaves by acting as "wedges" used as a basis of development by hydrogen bonding of the monolayer film. The sudden decrease in the interlayer cohesion then causes the exponential drop on the thermogram. Our calorimetric data are consistent with crystallographic data of Calvet et al [30] and the data of the spectroscopic measurements of Roy et al. [21] The second exothermic phenomenon marked by a plateau and a slower descent relates to a complete filling of the interlayer space which involves lower energies than those required for the fixing of the first water molecules. Adsorption then occurs around of the water molecules constituting the interlayer blocks [31-32].



b) Lime Hydration with montmorillonite

Simultaneous analysis of Figures 4 and 5 (montmorillonite case) discloses:

Area I: The increasing of the energy manifest the penetration of some water molecules on surfaces interfoliar.

We can consider that 6% lime as the threshold needed to stabilize soil in which a montmorillonite is dominating.

Area II: The presence of a maximum between 2% and 6% lime can be interpreted by the fact that the cations Ca++ complete its sphere of hydration by forming the hexa-hydrates octahedric

c- Hydration of illite and kaolinite pure

For both phyllitic minerals, we observe only one maximum in calorimetry, which can be attributed to heat relative of the exchangeable cations which are hydrated and then involve around them a cooperative adsorption

d) Hydration of illite and kaolinite with lime

The curves of the illite and the kaolinite (Figures 4 and 5) shows that the amount of heat released is strongly influenced by the number of cations Ca++ added, thus obtaining a threshold from 4% Ca(OH)2 for the illite and a threshold from 2% Ca(OH)2 for kaolinite which considers the values needed to stabilize the illite and / or kaolinite.



e) Sample hydration (Tangier)

The thermogram obtained show only one maximum which can be attributed to the hydration of the exchangeable cations with a hydration heat between that of illite and montmorillonite.

f. Sample hydration (Tangier) with lime

The threshold is obtained for a percentage of 2% Ca(OH)2 (Figures 4 and 5), the curve shows a plateau which extends to 6% . It can be interpreted by the formation of a mineral complex of interbedded which keeps a constant heat. The decreased of energy then observed suggests that beyond this value, the addition of lime has no effect.



5- CONCLUSION

This paper evaluated the effect of lime on the swelling potential of Morocco expansive soil.

During this research, physicochemical characterization study was conducted on soils from four different sites in northern Morocco (Kenitra, Sidi Kacem, Tangier, and Tetouan) and on pure standards clays. The clay fraction of soils studied consists primarily of montmorillonite. A stabilization study in the lime by measuring the heat of hydration has highlighted the existence of one or two maxima that has granted the successive stages of the hydration of exchangeable cations during expansion of the sheets. The results demonstrate that a minimum of 2 to 3% of lime is required to stabilize both mechanically and hydraulically the clay used.

This work is only a first approach to the study of the interaction of lime and clay. Additional measures are planned on the kinetics of hydration, the systematic study of different clays and finally the influence of temperature.




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