The Effect Of Adding Iron Powder On Atterberg Limits Of Clay Soils

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1 International Research Journal of Applied and Basic Sciences 2012 Available online at ISSN X / Vol, 3 (11): Science Explorer Publications The Effect Of Adding Iron Powder On Atterberg Limits Of Clay Soils 1 Arash Barazesh, 2 Hamidreza Saba, 1 Mehdi Gharib 1. Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran 2. Amirkabir University of Technology, Tehran, Iran Corresponding Author Arash Barazesh ABSTRACT: The increasing cost of building soil structures has made engineers use local materials to avoid transporting large volumes of construction materials. Soil stabilization is the process of changing soil properties to improve strength and durability. By adding natural or artificial materials, it can improve the shear strength of the soil and, as a result, increase its bearing capacity and reduce foundation settlement. Different materials such as lime, Portland cement, and fly ash have been used for stabilization of fine-grained and expansive soils. However, due to the growing population of the world and increasing human needs, there is an increasing accumulation of industrial and agricultural wastes. Wastes and garbage have become one of the main problems of modern societies and there is a large body of research dedicated to how these wastes can be safely reused. One of the industries that allow for the reuse of wastes is the construction industry. In the present research, iron powder, as a waste, is combined with clay soils in order to examine its effects on the atterberg limits of the soils. Five different types of soil with initial plasticity indices of 26, 31, 35, 39, and 49 are used for this experiment. Plasticity indices (i.e. liquid limit, plastic limit, and plasticity index) of the sample soils combined with different percentages of waste iron powder will be examined and compared with the plasticity of the original soils. Keywords: Clay Soil, Soil Stabilization, Wastes, Iron Powder, Atterberg Limits INTRODUCTION Expansive soils are considered problematic in geotechnical engineering since they undergo large volume changes due to seasonal variations in moisture. Clay soils are one type of expansive soil and usually have problems such as high subsidence and low shear strength. Expansive soils can be found in many regions of the world, especially in arid and semi-aridlands. Vast areas in Africa, Asia, and America are covered with expansive soils (Chen, 1988). In most of these areas, high-plasticity clay soils are among the most economical and most accessible materials for construction of road embankments, airports, pavements, and other engineering structures. On the other hand, seasonal variations in moisture have surfaced the swelling and shrinkage ability of these soils. Movement of foundations as a result of frequent swelling and shrinkage of clay soils leads to irremediable cracks and deformations in the structures built on them. Some examples of the annual cost of damage to buildings and light structures by expansive soils are $1000million in the USA, $150 million in the UK, and at least $4 million in South Africa (Gourley, 1993). Research in Iran has also shown that expansive clay soils cover vast areas of West and Northwest Iran and one of the most important factors in destruction of the concrete lining of irrigation canals in regions such as Khuzestan and Mugan (Baroutkoub & Rahimi, 1992). Clay soil stabilization is one of the ways of addressing these problems. Soil stabilization involves activities through which the engineering characteristics of soils. It increases soil strength, decreases its swelling and permeability, and increases its efficiency. There are various soil stabilization methods but they can generally be divided into two categories: chemical stabilization and physical (and mechanical) stabilization. Chemical stabilization involves improvement of characteristics of soils, especially aggregate soils, by adding certain materials. Different materials such as lime, Portland cement, and fly ash have been used stabilization of fine-grained and expansive soils. Physical stabilization, on the other hand, refers to improvement of soil characteristics without any change in is chemical properties. There are different methods of physical stabilization of soils one of which is reinforcement. Measures of Potentially Expansive Soils

2 Intl. Res. J. Appl. Basic. Sci. Vol., 3 (11), , 2012 There are several ways for visual identification of potentially expansive soils (Wayne, 1984): Wide and deep shrinkage cracks occurring during dry periods Soil rock-hard when dry, but very sticky and soft when wet Damages on the surrounding structures due to expansion of soil Driving Factors of Soil Expansion The driving factors of soil expansion can be divided into three main categories (Nelson, 1992): 1. Soil characteristics 2. Environmental factors 3. The state of stress SOIL IMPROVEMENT METHODS Increasing cost of building soil structures has made engineers use local materials in order to avoid transporting large volumes of construction materials. However, the natural soil in the site of operation is not always suitable for bearing a structure (Terzaghi et al., 1996). To prevent future problems, it is imperative to use certain methods for improving the condition of the soil. Soil improvement involves the in situ improvement of soil characteristics in order to reuse the soil in a geotechnical structure. What follows are some of the methods for soil improvement (Tahuni, 1994 & 1999): Compaction Grouting Excavation and replacement Physical and chemical changes Reinforcement Biological methods Soil stabilization is the most widely used soil improvement method which improves soil characteristics by creating physical and chemical changes in the soil. Of course, it must be noted that it is necessary to examine fine-grained soils and their behavior. The geotechnical engineer must choose the best soil improvement method with respect to all the technical and economic issues, the manpower and machinery, personal experience, and results of experiments. Soil Stabilization Soil strength depends on the contact between soil particles and it can be improved at microscopic and macroscopic scales. At the microscopic scale, resistance is increased by creating link between the particles which can be done by soil stabilization methods. At the macroscopic scale, the link between particles is reinforced using certain equipment and this method is usually referred to as soil reinforcement. There are both physical and chemical stabilizers. Chemical stabilizers stabilize and strengthen soils by creating reactions and transforming the structure and link between soil particles. Through these reactions, soil particles form a new material with new characteristics. Lime and cement are two of these stabilizers. Physical stabilizers such as polymeric materials and ionic stabilizers usually increase the cohesion between particles and thus increase soil strength. Different admixtures can be used in soil stabilization, the commonest of which are (Al-Rawas, 2002; Yazici, 2004): Lime Cement Fly ash Lime-fly ash mix Chlorides and salts Mixture of lime and polymer fibers Lime-microsilica mix Waste materials The type of stabilization depends on the geotechnical characteristics of the soil and how much they need to be improved. These characteristics may include strength, plasticity, permeability, durability, stability, fatigue, etc. Nowadays, one of the common and acceptable methods of soil improvement is to use waste materials, for they are not only economical, but also help in protecting the environment. Waste materials such as fly ash, glass, plastics, blast furnace slag, rice husk ash, scrap tire rubber, waste iron powder, egg shells, and other pozzolanic materials have been used to improve the geotechnical characteristics of soils (Ali et al., 1992; Lazarov & Moh, 1970; Muntohar, 2009; Rahman, 1987).

3 Intl. Res. J. Appl. Basic. Sci. Vol., 3 (11), , 2012 Using admixtures decreases the plasticity index of soils which in turn reduces moisture and, as a result, swelling of the soil. The most important effect of adding these materials is that they increase the efficiency of the soil, reduce e its expansion and shrinkage, and increase its compressive and tensile strengths. In the present article, waste iron powder has been used for stabilization of expansive soils. Numerous tests are carried out on samples of soil mixed with different percentages of iron powder (1-25 percent by weight) and the effect of iron powder on the atterberg limits of the soils is examined. METHODOLOGY The tests in this research are carried out in accordance with ASTM standards. The purpose of these tests is to examine the effect of iron powder on the characteristics of the studied soils. Laboratory tests are an important way of identifying the physical and mechanical characteristics of soils and predating their behavior under various conditions. The tests (ASTM D4318) examine atterberg limits and the procedure is as follows. First, to examine the effect of iron powder on the plasticity indices of the soil, liquid limit and plastic limit tests were run using sample soils with initial plastic indices ices of 26, 31, 35, 39, and 45 and different percentages of admixture (1-25 percent by weight). RESULTS The Effect of Admixtures on the Plasticity Indices of the Soil The following figures display the results of running liquid limit and plastic limit tests on sample soils with different plasticity indices, stabilized with different percentages of iron powder. Figure 1. The effect of adding different percentages of iron powder on the plasticity indices of the sample soil with an initial plasticity index of 26

4 Intl. Res. J. Appl. Basic. Sci. Vol., 3 (11), , 2012 Figure 2. The effect of adding different percentages of iron powder on the plasticity indices of the sample soil with an initial plasticity index of 31 Iron Powder Percentage Figure 3. The effect of adding different percentages of iron powder on the plasticity indices of the sample soil with an initial plasticity index of 35 Figure 4. The effect of adding different percentages of iron powder on the plasticity indices of the sample soil with an initial plasticity index of 39 Figure 5. The effect of adding different percentages of iron powder on the plasticity indices of the sample soil with an initial plasticity index of 45

5 Intl. Res. J. Appl. Basic. Sci. Vol., 3 (11), , 2012 DISCUSSION AND CONCLUSION By running atterberg limits tests, we examined the effect of adding different percentage of iron powder to sample soils with different plastic indices. Atterberg limits tests were performed on soil samples and different percentages of iron powder and the results of the tests were displayed in diagrams. A. Soil sample with an initial plasticity index of 26 Adding different percentages of iron powder to this sample reduces its liquid limit; the more the iron powder percentage, the less will be the liquid limit. Adding iron powder to this sample reduces its plastic limit. With lower percentages of iron powder, there is a sharp decline in the plastic limit of the soil, but by adding to the percentage of iron powder, gradually the plastic limit reaches a moderate level. Mixing iron powder with this type of soil reduces its plasticity index. There will be more reduction in the plasticity index of the soil as the percentage of iron powder increases. B. Soil sample with an initial plasticity index of 31 Adding different percentages of iron powder to this sample reduces its liquid limit. This index continues its downward trend and has its lowest value upon adding 25 percent by weight of iron powder. Comparing the maximum and minimum changes in Figure 2 reveals that there is not much difference between these values and there is absolute certainty that adding iron powder reduces the plastic limit of this soil sample. Adding low percentages of iron powder to this soil leads to no dramatic changes in plasticity index, but from 13 percent by weight of iron powder on the changes can clearly be seen and higher percentages of the admixture leads to considerable reduction in the plasticity index of the sample soil. C. Soil sample with an initial plasticity index of 35 Adding different percentages of iron powder to this sample reduces the liquid limit of the soil. However, it must be noted that in these set of tests the slope of the diagram is rather moderate, signifying the lack of any dramatic change in the obtained values. The plastic limit of the sample soil decreases by adding any percentage of iron powder, but this reduction is very moderate. However, even this slight change indicates the effect of iron powder on the plastic limit of the soil. Adding different percentages of iron powder to the third soil sample reduces its plasticity index. As higher percentages of the admixture are added to the sample, there is more decrease in the soil s plasticity index. D. Soil sample with an initial plasticity index of 39. Adding different percentages of iron powder to this sample reduces its liquid limit. There is no considerable change in the plastic limit of this sample as higher percentages of iron powder are added and the diagram has a moderate slope. After some slight changes, the plastic limit of the soil reaches its original value when higher percentages of iron powder is added, indicating the lack of any significant change in the plastic limit of this soil sample. Adding iron powder to this sample reduces its plasticity index by about 28 and this decrease can be seen with all the percentages of the admixture. E. Soil sample with an initial plasticity index of 45 Adding different percentages of iron powder to this sample reduces its liquid limit. There is also a significant decrease in the plastic limit of the soil as different percentages of iron powder are added. There is more decrease at the lower percentage of the admixture and the downward trend moderately continues until the end of the test. At the lower percentages of iron powder, there is a dramatic increase in the plasticity index, but this changes as higher percentage of iron powder is added to the soil and this index follows a downward trend. Considering the results, the following conclusions can be made regarding the effect of adding iron powder to sample soils with initial plasticity indices of 26, 31, 35, 39, and 45: 1. Adding iron powder to the sample clay soils decreases their plasticity index. 2. Adding different percentages of iron powder to the sample soils decreases their liquid limit. The more the percentage by weight of the admixture, the less will be the liquid limit of the soils. 3. Adding iron powder to the soils leads to slight decrease in the plastic limit of the soils. There is a sharp decrease at the beginning stages of adding iron powder and the changes follow a moderate trend as higher percentages of iron powder is added to the soils. In general, there are moderate changes in the plasticity index of all the sample soils.

6 Intl. Res. J. Appl. Basic. Sci. Vol., 3 (11), , 2012 REFERENCES Ali FH, Adnan A, Choy CK Geotechnical properties of a chemically stabilized soil from Malaysia with rice husk ash as an additive". Geotechnical and Geological Engineering, 10(2): Al-Rawas AA, Taha R, Nelson J, Al-Shab BT, Al-Siyabi H A comparative evaluation of various additives used in the stabilization of expansive soils. Geotechnical Testing Journal, GTJODJ, ASTM, 25(2): Baroutkoub S, Rahimi H A study of the reasons for the destruction of concrete linings in Khuzestan Province. Master s thesis, University of Tehran. Chen FH Foundation on expansive soils. Second edition, Elsevier Science Ltd, New York. Gourley CS, Newill D, Schreiner HD Expansive soils: TRL s research strategy. In: Proceedings of the First International. Symposium on Engineering Characteristics of Arid Soils, City University, London. Lazarov RC, Moh ZC Stabilisation of deltaic clays with lime-rice husk ash admixtures. Proceedings of the 2 nd Southeast Asian Conference on Soil Engineering, Singapore, pp Muntohar AS Influence of plastic waste fibers on the strength of lime-rice husk ash stabilized clay soil.civil Engineering Dimension, 11(1): Nelson J, Miller DJ Expansive soils:problems and practice in foundation and pavement engineering. John Wiley and Sons. Rahman MA Effects of cement-rice husk ash mixtures on geotechnical properties of lateritic soils. Proceedings of The Japanese Geotechnical Society, 27(2): Tahuni S Principles of geotechnical engineering. Second edition. Terzaghi K, Peck RB, Mesri G Soil mechanics in engineering practice. Third edition, John Wiley and Sons, New York. Wayne AC Construction on expansive soils in Sudan. Journal of Construction Engineering and Management, 110(3): Yazici V Stabilization of expansive clays using granulated blast furnace slag (GBFS), GBFS-lime combinations, and GBFS Cement. Middle East Technical University.