UTILIZATION OF STEEL SLAG FOR STABILIZATION OF A LATERITIC SOIL

ABSTRACT

A lateritic soil classified as sandy clay or (CL) and A-7-6 (5) according to Unified Soil Classification System (USCS) and AASHTO classification system respectively, was treated with up to 10% pulverized steel slag (an industrial waste product) by dry weight of soil. Elemental and chemical analysis of the steel slag was determined using x-ray fluorescence spectroscopy. Tests were carried out to determine the index properties, compaction characteristics (maximum dry density, MDD and optimum moisture content, OMC), strength characteristics (California bearing ratio, CBR and unconfined compressive strength, UCS) and permeability of the natural and treated soil. Test results show that Atterberg limits (liquid limit, plastic limit and plasticity index) generally decreased, while specific gravity of soil – steel slag mixtures increased with higher steel slag content; MDD and OMC increased and decreased, respectively, with higher steel slag content. Generally, CBR and UCS increased up to 8% steel slag treatment of the soil. Permeability of soil – steel slag mixtures increased with higher steel slag content. Based on laboratory test results, an 8 % optimal stabilization of the A-7-6 soil with steel slag satisfactorily meets the Federal Republic of Nigerian General Specifications (Roads and Bridges) requirement for subgrade materials.

CHAPTER ONE

INTRODUCTION

1.1 Preamble

Many items discarded by people, organizations and companies have the potential to be reused for their original purposes or for new ones. Reuse allows people to get the most out of the products they buy and saves them money as well. Additionally, reusing products conserves natural resources and saves valuable landfill space. Use of environment-friendly materials in any industry is of paramount importance. According to Lim and Chu (2006), limited waste landfill space, increasing cost of waste disposal in combustion facilities and landfills, depletion of the natural resources, and the need for sustainable development have all amplified the need to reuse the materials that were once regarded as wastes as substitutes for natural resources.

1.2 Statement of the Problem

In the 1980’s, according to Coyne (2007), it became apparent that iron and steel plant wastes were a cause of concern due to, ground water contamination from stockpiling or land filling. As a result, restrictions were put on land filling and stockpiling of wastes and airborne emissions from plants and a new era of monitoring and control was established.

Over recent decades, studies have been carried out to explore all possible reuse methods of a wide range of waste materials. Up to now, construction waste (Osinubi and Edeh, 2011), blast furnace (Osinubi and Eberemu, 2006), coal fly ash (Osinubi and Amadi, 2003) and bottom ash (Osinubi, 2000a,b), have been accepted in many places as alternative aggregates in embankment, road, pavement, foundation and building construction. Metal industry slag, minestone and mining waste are generally suitable for recycling or reuse, and the use of these inorganic wastes as alternative materials in building, road and geotechnical constructions have been reported (Vazquez et al., 1991; Kamon and Katsumi, 1994; Kamon, 1997; Hartlén et al., 1997; Sarsby, 2000). The iron and steel industry involves a myriad of operations which generate vast volumes of air emissions, liquid effluents and solid wastes. Significant quantities of sludge and slag are generated as waste material or byproduct every day from steel industries. They usually contain considerable quantities of valuable metals and materials. It is generally possible to recover some values by physical or chemical mineral processing techniques. Transforming these solid wastes from one form to another to be reused either by the same production unit or by different industrial installation are very much essential not only for conserving metals and mineral resources but also for protecting the environment (Das et al., 2006).

Throughout history, there have been a number of materials used for stabilizing weak soils in order to improve their load-carrying ability. Some lateritic soils are known to have poor engineering properties such as high plasticity, poor workability, low strength, high permeability, tendency to retain moisture and high natural moisture content (Maigien, 1964). This research evaluated the use of steel slag for the stabilization of a lateritic soil.

1.3 Justification for the Study

The importance of lateritic soil as the most wide-spread construction materials for roads in Nigeria necessitates the need to search for alternative binders other than the existing ones such as cement, bitumen, and other chemicals considering their costs and, sometimes, scarcity (Mtallib and Bankole, 2011). According to Amu et al. (2008), lateritic soils are the most commonly used material for construction and rehabilitation of rural and urban access roads in Nigeria because they are most naturally occurring and their utilization is economically attractive.

According to van Oss (2003), approximately 10 to 12 million metric tonnes of blast furnace slag are produced each year in the US; worldwide, this number jumps to 150 to 180 million metric tonnes. Similarly, it is estimated that 9 to 14 million metric tonnes of steel slag are produced each year in the US, with the worldwide number ranging from 90 to 135 million metric tonnes per year.

These figures are very significant when compared with the total world steel production in 2005, which was given as 1130 million tonnes by Mahieux et al. (2009).

In Nigeria, it is estimated that 3.5 to 4.5 million metric tonnes of steel are produced per annum. This estimate was determined by collating the nominal steel production of steel plants in Ajaokuta, Delta steel, Jos, Katsina and Osogbo, as presented by Aderibigbe (2012). Assuming a 100 kg (0.1 tonne) of steel slag was produced simultaneously per ton of steel, then approximately 0.35 to 0.45 million metric tonnes of steel slag is generated per annum in Nigeria.

Generally speaking, however, the utilization rate or fields of application of steel slag are rather lower and limited.

It is desirable to increase the productive uses of steel slag. Unlike blast furnace slag, steel slag is less recycled, even in developed countries. Consequently, there is an increase in the volume of steel slag piles at dump sites or to be disposed-off in landfills.

1.4 Aim and Objectives

The aim of this research work was to use steel slag in the stabilization of lateritic soil.

The specific objectives of this study inclde:

• Determination of the elemental and chemical composition of the steel slag samples obtained;
• Determination of the engineering properties of the lateritic soil samples;
• Determination of the index, strength and permeability properties of the lateritic soil-steel slag mixtures; and
• Determination of the optimum steel-slag content (OSC) required.

1.5 Scope of the Study

The study was limited to the determination of the effect of adding up to 10 % steel slag on the properties of lateritic soil using Modified Proctor compaction energy with respect to compaction characteristics, Atterberg limits, shear strength characteristics and permeability. All tests were carried out in accordance with the procedures outlined in BS 1377(1990) and BS 1924(1990) for the natural and treated soils, respectively.

1.6 Significance of Study

Transforming industrial wastes into valuable materials or resources for further utilization is most desirable (Aguirre et al., 2009). The rate of reuse and recycling of solid wastes/by-products has increased dramatically in the past but considerable amounts are still being disposed to landfills Unlike most developed and some developing countries producing steel, Nigeria utilizes just a little of the waste it generates during the production of steel. A larger percentage of this waste is disposed off, even, in an environmentally-unfriendly manner (open dumping). According to Akinbinu (2010), major environmental concern in the iron and steel industry in Nigeria is associated with the management of the industrial wastes generated in their different processes since it is becoming increasingly difficult for safe disposal of these huge volumes. It is common knowledge that steel slag (a major waste generated when producing steel) has long been used in various applications in the construction industry such as aggregates in road construction, railway ballast and hydraulic protection structures. However, the free lime present in the steel slag causes expansion and therefore limits its application. Due to the steel slag having the presence of free lime and also the similar chemical composition and mineralogy to Portland cement; there is a great potential for furthering the usage of steel slag in the construction industry in the aspect of soil stabilization.

According to Ola (1975), stabilization of soil is employed when it is more economical to overcome a deficiency in a readily available material than to bring in one that fully complies with the requirements of specification for the soil. Lateritic soil is one of the most readily available soil types in Nigeria. Thus, the improvement of its engineering properties (high plasticity, poor workability, low strength, high permeability, tendency to retain moisture and high natural moisture content) via its mixing with steel slag will be a double-edge achievement. The cost of treating and disposing the vast number of steel slag stockpiles in the steel producing industry will be reduced while simultaneously reducing the construction cost of borrowing suitable soil materials or using expensive stabilizers.

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