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Kaolinite chemical composite and morphology in geotechnical engineering.

Introduction

The kaolinite is one of the important materials and could modify for finding appropriate construction material for solving geotechnical problem based on economically.

There is investigation on Thermal conductivity values, in the temperature range 300-1200 K, have been measured in air and at atmospheric pressure for a Kenyan kaolinite refractory with 0%-50% grog proportions. The experimental thermal conductivity values were then compared with those calculated using theoretical models. On the contrary, the conductivity values for the sample containing $ 40% decreased with increase in temperature in a manner consistent with the Eucken law (Kimani and Aduda, 2004). There is research on Physico-mechanical properties of fired clay bricks manufactured with different percentages of CBs are reported. The results show that the density of fired bricks was reduced by up to 30 %, depending on the percentage of CBs incorporated into the raw materials. Similarly, the compressive strength of bricks tested decreased according to the percentage of CBs included in the mix. The thermal conductivity performance of bricks was improved by 51 and 58 % for 5 and 10 % CBs content respectively (Aeslina Abdul Kadir et al., 2009). It has been reported on the deep clays exhibit pronounced strain anisotropy both during mechanical loading as well as during heating and cooling at constant stress in drained isotropic conditions. During mechanical loading vertical strain is larger than the horizontal one. During heating the vertical strain is larger than the horizontal one within the elastic range; the opposite is observed in the elasto-plastic range. The above described response can be interpreted adopting a consistent rotational, kinematic hardening thermo-elasto-plastic constitutive law (Hueckel and Pellegrini, 1996). In a scientific work it has been presented a new thermo-plastic mechanism for isotropic thermo-mechanical paths including thermal hardening. It is based on considerations of the thermal effect on void ratio. After a discussion of the experimental evidence, the formulation of the thermo-plastic yield mechanism is introduced. Typical features are analyzed and the responses of the model discussed. The proposed model is validated on the basis of experimental results on two different clays ( Laloui and Cekerevac, 2003). There is an investigation on thermal effects on the mechanical behavior of saturated clay. The study was performed on CM clay (kaolinite) using a temperature-controlled triaxial apparatus. Applied temperatures were between 22 and 90[degrees]C, The obtained results provide observations concerning a wide scope of the thermo-mechanical behavior of clays (Cane Cekerevac and Lyesse Laloui, 2004). Research interest in the thermo-mechanical behavior of soils is growing as a result of an increasing number of geomechanical problems involving thermal effects. These problems with nonisothermal situations are mainly encountered in the field of environmental geomechanics (Vulliet, et al., 2002). It has been reported the differences between kaolinite and smectite structures are notable, mainly as a result of the degree of weathering in the different compounds. Nevertheless, the kaolinite structure possesses great advantages in many processes due to its high chemical stability and low expansion coefficient. As a consequence of adsorption, the kaolinite structure and the soil solution pH will change. To analyze the adsorption behavior of kaolinite, Pb, Zn and Cd were studied at three different concentrations (1, 2 and 3 mmol/l) and over different periods of exposure (0.1, 1, 2, 4, 8, 12 and 24 h). The kaolinite retained up to 10.0 Amol/g of Pb, 8.40 Amol/g of Zn and 6.00 Amol/g of Cd when it was mixed with the 3 mmol/l concentrations of heavy metals. In each case, the adsorption eventually reduced the solution pH from 4.6 to 3.7. The changes in pH over time indicated both the release and retention of hydrogen ions by the mineral, probably involving the hydroxyl edge sites and exposed hydroxyl planes. The size of the atomic radii are 1.81, 1.71 and 1.53 A[degrees] for Pb, Cd and Zn, respectively, compared to the 0.79 A[degrees] for H. This difference, along with the differences in hydrated radii, will affect the structure of the clay causing stress in the molecule. Changes in the mechanical and chemical properties of the clay are discussed as the interactions of the heavy metal cations with the kaolinite could affect the structure of the kaolinite and influence properties such as swelling capacity, compaction capability and the double-layer behaviour. The kaolinite in this study contained some illite which may have increased the pH 7 cation exchange capacities to 17.8 mEq/100 g. using the adsorption data, the reactions at the clay water inter phase and the probable effects on the physical properties and structure of kaolinite are discussed. (Jorge, et al., 2003). It has presented that the thermal behavior of a formamide-intercalated mechanochemically activated (dryground) kaolinite was investigated by thermogravimetry-mass spectrometry (TG-MS) and diffuse reflectance Fourier transform infrared spectroscopy (DRIFT). After the removal of adsorbed and intercalated formamide, a third type of bonded reagent was identified in the 230-350[degrees]C temperature range decomposing in situ to CO and NH3. The presence of formamide decomposition products as well as CO2 and various carbonates identified by DRIFT spectroscopy indicates the formation of super-active centers as a result of mechanochemical activation and heat treatment (thermal deintercalation). The structural variance of surface species decreases with the increase of grinding time. The ungrounded mineral contains a low amount of weakly acidic and basic centers. After 3 hours of grinding, the number of acidic centers increases significantly, while on further grinding the super-active centers show increased basicity. With the increase of grinding time and treatment temperature the amount of bicarbonate- and bidentate-type structures decreases in favor of the carboxylate- and monodentate (Frost, et al., 2005). It has find in a scientific research work that Contact freezing of single supercooled water droplets colliding with kaolinite dust particles has been investigated. The experiments were performed with droplets levitated in an electrodynamic balance at temperatures from 240 to 268 K. Under relatively dry conditions (when no water vapor was added) freezing was observed to occur below 249 K, while a freezing threshold of 267K was observed when water vapor was added to the air in the chamber. The effect of relative humidity is attributed to an influence on the contact freezing process for the kaolinite-water droplet system, and it is not related to the lifetime of the droplets in the electrodynamic balance. Freezing probabilities per collision were derived assuming that collisions at the lowest temperature employed had a probability of unity. Mechanisms for contact freezing are briefly discussed (Svensson, et al., 2009). It is well established from the literature, experimental study and theory, about the effect of the heat on kaolinite characteristics and a number of theoretical and computational studies have been performed by various researchers to determine the clay behavior when submitted to the heat, it was understood that the clay behavior is changed due to application of thermal based on huge number of experimental and theoretical investigation executed but kaolinite mechanical behavior under the thermal for 6 hours from 100[degrees]C to 500 [degrees]C in increment of 100[degrees]C based on chemical element analysis, morphology in connection with triaxial experiments never has been documented. The purpose of the entire research exercise would be to (i) modification assessment of bentonite chemical element, morphology and mechanical properties under thermal (ii) formulate some useful guidelines in using kaolinite in the construction industry.

2. Methodology and Experiments:

Soil testing is an integral part of analysis and design in Soil Engineering. A proper evaluation of soil samples and determination of relevant soil properties simulating field-loading conditions are essential components of the practice of foundation engineering (Shamsher and Jain, 2002). Researches in unsaturated soil mechanics considerably developed in the past decades, through the simultaneous development of experimental investigations and theoretical analyses (Pierre Delage, 2002). To improvement of construction materials a series experimental on kaolinite submitted to heat for 6 hours from 100[degrees]C to 500[degrees]C in increment of 100[degrees]C executed. The main objective of the experiments was to analyze and development of ideal a construction material in the laboratory condition. The evaluation of both for the macro and micro of kaolinite characteristics have been taken systematically trough of laboratory testing. In the laboratory XRF, triaxial and SEM tests were conducted. The affect of heat on the kaolinite mechanical properties and morphology have been analyzed.

The triaxial test is a method for determination of shear strength of all types of soils under different drainage conditions, in this method cylindrical specimen submitted to the stress from all directions, this is subjected to confined pressure from the sides and also from the top gradually axial force applied up to shear failure of specimen. The axial force is the major stress and confides pressure is the minor stress and there is no shear stress from the sides. The total axial stress at the time of shearing is sum of major and minor stresses. Due to increasing axial stress the shear stress developed based on compressive stress.

The electron microscope is a scientific instrument for shape and size identification of the very fine scale objet that is a good representation and resolution of the three-dimensional particle it has more capability compare to light microscopes, the scanning electron microscopy (SEM) studies helps to understand the micro to macro surface features of the soil samples. The morphology of six kaolinite sample was studied using SEM. The SEM studies of the six soil samples of the investigations were carried out using instrument; JSM840A, JEOL-Japan. The SEM has been done to assessment of correlation between shape and size of soil particles with its mechanical properties.

The Terzaghi method has been used to calculation of soil foundation safe bearing capacity assumed depth of 1.5 m and widths of (2.5m) x (2.5 m). For all models, safe bearing capacity considered to assess soil foundation improvement thorough the interpreting of the suggested results. Formulas for calculation of safe bearing capacity are the following:

[q.sub.f] = 1.3C [N.sub.c] + [gamma]D[N.sub.q] + 0.4 [gamma]B[N.sub.[gamma]] (1)

[q.sub.nf] = [q.sub.f] - [gamma]D (2)

[q.sub.s] = ([q.sub.nf]/F) + [gamma]D (3)

Also [N.sub.q], [N.sub.c] and [N.sub.[gamma]] are the general bearing capacity factors, depend upon depth of footing and shape of footing and also [PHI], have been used from suggestion by the Terzaghi calculation method (Punmia, 1988).

Results and Discussion

When the heat is applied to the kaolinite unit weight is not significantly changed. The table 1 indicated that increasing heat not effected on improvement soil cohesion and could expect same for permeability. The soil internal angle of friction is increased. There is no linear correlation between increasing heat and angle of friction but this is positive correlation, observation of this phenomenon helps for prediction kaolinite behavior when is under heat and developing a code for all kind of clay for geotechnical engineering. In the room temperature kaolinite has 1360.63 KN/[m.sup.2] safe bearing capacity, when submitted to the thermal for 500 [degrees]C improved up to 4356.27KN/[m.sup.2].

Due to maintaining constant level of kaolinite cohesion at different levels of temperature could be understood that the chemical composite is not changed and only atomic structure may be changed and it is reason for kaolinite mechanical behavior when submitted to the heat.

The fig 2 indicated that stress-strain relationship of Kaolinte at different levels of temperature from triaxial test. When the heat is increased the stress-strain relationship raised but not linear and always increasing of heat not resulted of improvement of soil bearing capacity in this regard could bring example when soil is submitted to the 400[degrees]C.

The SEM photographs have clearly revealed that the surface morphology, shape and size of the minerals, which mechanically extracted from soils. In the Fig 3-8 indicated that the modification of soil morphology under all conditions are closely similar and there is not any significant change observed and also this kind of result is observed about soil chemical composite from the XRF experiment (table 2) it could be expected that the soil atomic structure is main reason for modifying Kaolinte properties subjected to the heat. The creation of heat on some part of structure foundation after construction could causes of differential settlement and structure instability.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

[FIGURE 5 OMITTED]

[FIGURE 6 OMITTED]

[FIGURE 7 OMITTED]

[FIGURE 8 OMITTED]

Conclusion:

* The heat up to 500[degrees]C has not changed kaolinte unit weight and cohesion

* The heat has direct correlation with modification of kaolinte angle of friction

* Improvement of kaolinte mechanical characteristics under heat is not due to changing chemical composite and morphology, the reason is due to alteration of atomic structure

* From this investigation understood that the weak soil could be modified based on using appropriate heat technique and chemical element, morphology and atomic structure investigation
Nomenclature

[PHI] (Degree)           = Angle of Friction.
C (KN/[m.sup.2])         = Cohesive of Soil.
OMC (%)                  = Optimum Moisture Content.
SBC (KN/[m.sup.2])       = Safe Bearing Capacity.
g (KN/[m.sup.3])         = Unit Weight.
[q.sub.f] (KN/[m.sup.2]) = Ultimate Bearing Capacity.
[q.sub.nf](KN/[m.sup.2]) = Net Ultimate Bearing Capacity.
[q.sub.s](KN/[m.sup.2])  = Safe Bearing capacity.
[N.sub.c]                = General Bearing Capacity Factor.
[N.sub.q]                = General Bearing Capacity Factor.
[N.sub.g]                = General Bearing Capacity Factor.
B (Meter)                = Width of the Foundation.
D (Meter)                = Depth of Foundation.
F                        = Factor of Safety = (3).
SEM                      = Scanning Electron Microscopy.


References

Kimani, J.N. and B.O. Aduda, 2004. Temperature Dependence of the Thermal Conductivity of A Grog Modified Kenyan Kaolinite Refractory, African Journal of Science and Technology (AJST), Science and Engineering Series, 5(1): 6-14.

Aeslina Abdul Kadir, et al., 2009. Density, Strength, Thermal Conductivity and Leachate Characteristics of Light-Weight Fired Clay Bricks Incorporating Cigarette Butts, World Academy of Science, Engineering and Technology, http://www.waset.org/journals/waset/v53/v53-170.pdf

Hueckel, T. and R. Pellegrini, 1996. A note on thermo mechanical anisotropy of clays, Engineering Geology, 41(1-4): 171-180.

Laloui, L., C. Cekerevac, 2003. Thermo-plasticity of clays: An isotropic yield mechanism, Computers and Geotechnics, 30: 649-660.

Cane Cekerevac and Lyesse Laloui, 2004. Experimental study of thermal effects on the echanical-behaviour of a clay, Int. J. Numer. Anal. Meth. Geomech., 28: 209-228. (DOI: 10.1002/nag.332).

Vulliet, L., L. Laloui, R. Harding, 2002. Environmental geomechanics: an introduction. In Environmental Geomechanics, Vulliet L, Laloui L, Schrefler B (eds). EPFL-Press: Lausanne, 3-12.

Jorge, C., Miranda. Trevinol, Cynthia A. Coles, 2003. Kaolinite properties, structure and influence of metal retention on pH, Applied Clay Science, 23: 133-139.

Frost, Ray and Horvath, Erzsebet and Kristof, Janos and Jakab, Emma and Mako, Eva and Vagvoelgyi, Veronika, 2005. Identification of superactive centers in thermally treated formamide-intercalated kaolinite, Colloid and Interface Science, 289(1): 132-138.

Svensson, E.A., et al., 2009. Freezing of water droplets colliding with kaolinite particles, Atmos. Chem. Phys., 9: 4295-4300.

Shamsher Parkash and P.K. Jain, 2002. Engineering Soil Testing, Published by Nem Chand & Bros, Civil Lines, Roorkee.

Pierre Delage, 2002. Experimental unsaturated soil mechanics, Proc. 3rd Int. Conf. on Unsaturated Soils, UNSAT, (3): 973-996. Juca JFT, De Campos TMP, Marino FAM, Recife, Brazil, Balkema.

Punmia, B.C., Soil Mechanics and Foundations, Madras, 1988.

Corresponding Author: Abdoullah Namdar, Islamic Azad University of Jolfa International Branch, Iran. E-mail: ab_namdar@yahoo.com

Abdoullah Namdar Islamic Azad University of Jolfa International Branch, Iran.
Table 1: the Kaolinit mechanical properties.

Model   Temperature   g                C                [PHI]
No      [degrees]C    (KN/[m.sup.3])   (KN/[m.sup.2])   [degrees]]

1       RT            13.4             80                0
2       100           13.1             80                7
3       200           13.5             80               10
4       300           13.3             80               15
5       400           13.3             80               13
6       500           13.1             80               20

Model   SBC
No      (KN/[m.sup.2])

1       1360.63
2       1967.68
3       2312.03
4       3130.27
5       2801.60
6       4356.27

Table 2: Chemical element in the Kaolinite at different level of
temperature.

Heat                 O       Al      Si      K      Fe
([degrees]C

25            Wt %   48.94   13.58   30.20   6.07   1.21
              At %   63.54   10.45   22.33   3.23   0.45
100           Wt %   47.58   13.39   30.40   6.92   1.71
              At %   62.48   10.43   22.74   3.72   0.64
200           Wt %   49.49   13.94   29.19   5.92   1.47
              At %   64.09   10.70   21.53   3.14   0.54
300           Wt %   38.38   14.24   37.48   6.85   3.06
              At %   53.42   11.75   29.71   3.90   1.22
400           Wt %   42.06   13.19   36.21   5.95   2.58
              At %   57.08   10.62   28.00   3.31   1.00
500           Wt %   45.29   13.66   32.71   6.34   2
              At %   60.12   10.79   24.86   3.46   0.77
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Title Annotation:Original Article
Author:Namdar, Abdoullah
Publication:Advances in Natural and Applied Sciences
Article Type:Technical report
Geographic Code:7IRAN
Date:Apr 1, 2011
Words:2833
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