1.0 Introduction
1.1 Background of the Study
Mechanical stabilization is accomplished by mixing or blending soils of two or more gradations to obtain a material meeting the required specification. The soil blending may take place at the construction site, a central plant or a borrow area. Additive stabilization is achieved by the addition of proper percentages of cement, lime, fly-ash, bitumen or combination of these materials to the soil. The selection of the type and determination of the percentage of additive to be used is dependent upon the soil classification and the degree of improvement in the soil quality desired. Modification stabilization refers to the stabilization process that results in improvement in some properties of the soil, but does not by design result in a significant increase in soil strength and durability (Afjman, 1994). Lime, basically is derived from the process of burning limestone at temperature above 900oC and the lime produced as a result of the above decomposition, is generally referred to as quicklime. The quicklime is subsequently slaked with water to produce hydrated lime (Mukerji and Strulz, 1988). Mukerji and Strulz (1988) also pointed out the fact that the production of lime kilns is a more than 2000 years old technology, believed to have been developed by the Romans around 300 B.C. Lime is also obtained as a by-product in the form of lime sludge (which contains calcium carbonate and various impurities) from sugar manufacture, and form acetylene and paper industries. The building lime is used for preparing building mortars, concrete, binders and for manufacturing artificial stones, slabs and miscellaneous building parts (Kumar, 1987). Lime plays an important role in soil stabilization, mortar for brick bonding, production of block, renders and in lime paints (Vazquez, Marquez and Macias, 2005). Lime is used as stabilizer in construction with clayey soils, because the lime reacts with clay to form a binder and when it is mixed with a pazzolana (rice husk ash, fly ash, blast furnace slag e.t.c.) to produce a hydraulic binder, which can partially or completely substitute cement, depending on the required performance (Mukerji and Strulz, 1988). The chemical process of lime burning shows that the main constituent in the raw material (lime stone) is necessarily calcium carbonate (CaCO3) and lime stone can have CaCO3 contents exceeding 98% (as in chalk and various types of shells and coral) or as low as 54% (in pure mineral dolomite) (Mukerji and Strulz, 1988).
Different types of stabilizers have been used in different parts of the world to enhance the engineering properties of laterite (Moh, 1962). The most common ones are cement, lime and bitumen and the choice of a particular stabilizer depends on the soil type and degree of effectiveness of the stabilizers (Rahaman, 1968). Mustapha (2006) defined soil stabilization as the treatment of soils to enable their strength and durability to be improved such that they become totally suitable for construction beyond their classification if left untreated. Stabilization as viewed by Afjman (1994) is the process of blending and mixing materials with a soil to improve certain properties of the soil. Afjman (1994) further explained that stabilization process may include the blending of soils to achieve a desired gradation or the mixing of commercially available additives that may alter the gradation, texture or plasticity or act as a binder for cementation of the soil. Stabilization can be used to function as mechanical stabilization, additive stabilization or modification.
It has been reported by Craig (2005) that to the Civil Engineer, soil is any un-cemented or weakly cemented accumulation of mineral particles formed by the weathering of rocks, the void space between the particles containing water and/or air. Craig (2005) further explained that the weak cementation can be due to carbonates or oxides precipitated between the particles or due to organic matter. Soil is naturally occurring materials that are used for the construction of all except for the construction of surface layers of pavements (i.e. concrete and asphalt) and these are subject to classification tests (ASTM D 2487) to provide a general concept of their engineering characteristics (Afjman, 1994).
According to Williams (2006) clay is sticky and plastic-like to handle when wet, the individual particles are extremely small and can only be seen with the aid of an electron microscope. The three main soil texture classifications are: sandy, silt and clay. Sandy soils are coarse-textured, clay soils are fine-textured and silt soils are intermediate in texture (Williams, 2006). Clay minerals all have a great affinity for water, some swell easily and many double in thickness when wet, while most have the ability to soak up ions (electrically charged atoms and molecules) from a solution and release the ions later when conditions change (Nora,1999). Compare to other soil types, clay soil particles are small in size and have very large surface area relative to their volume, this large surface is highly reactive and has the ability to attract and hold positively charged nutrients ions (Pidwirny, 2006). Before clay soil can be stabilized with lime the plasticity index (PI) must be measured, when the plasticity index is at least 10, according to the Atterberg limits (Consistency limits), the soil can be stabilized with lime (Vazquez, et al, 2005). Vazquez et al (2005) shows that the Atterberg limit expresses the difference between the liquid limit and plastic limit in soils and that if plasticity index is less than 12, means a low plastic soil and if plasticity index is greater than 40 means a very high-plastic soil (almost liquid).This research work intends to proffer solution to problem associated with wall constructed with unstabilized red clay bricks.
Therefore, in Nigeria where the research was carried out, the activities that was conducted is to know the Lime and Fly Ash Stabilization on Brick Produced using Red Clay.
1.3 Statement of Problem
Weathering of rocks and soil is the primary way that clays and clay minerals form at the earth’s surface today. The weathering process involves physical disaggregation and chemical decomposition that change original minerals to clay minerals; weathering is uneven, and many stages of breakdown may be found in the same clay sample (Nora, 1999). Clay soil can be easily sticky when mixed with water. The individual particles of clay are much smaller than those of sand. Locally, clay soils have been used in many ways in Sokoto state. For instance, in making bricks, used as mortar in block laying, plastering and rendering of wall surfaces. The clays in use as explained above had been applied directly after mixing with water only. In most villages in Sokoto State, the red clay bricks, used in construction of walls are not usually stabilized. Even those that were stabilized were not done according to the required standard. Cement is commonly used as stabilizer but is being applied in small quantities. Thus, due to the fact that the red clay soil is not usually stabilized or not adequately stabilized, most of the walls constructed with the red clay bricks experienced cracking, seasoning swelling and even collapse of the entire wall. This is because the bricks were not produced in accordance with the standard specification. And since the cost of purchasing lime is cheaper than cement, therefore, lime was adopted as stabilizer for this research work. If the strength of the clay is enhanced by stabilizing it with lime, these problems of cracking and collapsing of wall can be checked. Moreover, this study established the effect of lime stabilization on brick made with “Sokoto red clay soil”.
1.4 Aim and Objectives of Study
The aim of the study is to scrutinize the Lime and Fly Ash Stabilization on Brick Produced using Red Clay. In achieving this aim, the following specific objectives were laid out as follows:
- To determine the physical properties of Sokoto red clay soil.
- To produce brick samples made with stabilized Sokoto red clay soil.
- To test the brick samples for mechanical properties.
- To determine the optimum level of lime stabilization required in the case of “Sokoto” red clay soil.
1.5 Justification of the Study
Clay soils are deposited in large quantities in almost all the local government areas in Sokoto State, Nigeria (Field survey, 2009). Sokoto state has very good quality limestone deposited in more than three local governments in the state. Presently, cement is being manufactured in the state since early 1980s at “Kalambaina” in Wamakko local government due to large quantities of limestone deposited in the area compare to other local governments (CCNN, 2010). However, it was observed that due to the quality of the limestone in Sokoto State, the red clay soil in the area perhaps possess some qualities which can make it suitable for building construction when well treated. Therefore, this brought about the reason for this research work.
Blocks and bricks are two major material used for construction of wall. Lot of researches have been carried out on the sandcrete block (either hollow or solid) such as partial replacement of cement to make block, compressive strength sandcrete block, an assessment of the quality of sandcrete hollow block production of different block industries in a state, preliminary study of properties of compressed building blocks stabilized with rice husk ash, soil blocks admixed with bitumen and ordinary Portland cement for building construction etc. Blocks are more common in used for wall construction than bricks. Probably, that is the reason why researchers focused more on it than brick. More research works have not been documented on how to improve strength characteristics of clay bricks. Also, in Sokoto state, blocks are common in use for construction of wall compare to brick. However, red clay soil is deposited in large quantities in Sokoto State, may be that is the reason why most of the walls of buildings in the villages are constructed by red clay bricks. Hence, it is imperative to look inwards on how to improve the strength properties of the red clay bricks.
1.6 Scope of Study
The study focuses on the Lime and Fly Ash Stabilization on Brick Produced using Red Clay. Physical properties of the soil were examined before used. After the bricks were produced and cured accordingly, the samples were tested for mechanical properties.
1.7 Limitations of the Study
Red Clay Soils used for this research were sourced by method of disturbed sampling. And that the soil was removed at about 300mm depth from the top most part of the soil. The soil below 300mm depth perhaps possesses physical properties different to the surface part of the soil. Thus, this study only covered the physical properties of the top most part of the soil.
The brick samples were cured by spraying water on the samples every 24 hours before covering with sacks. There is possibility that some portion of the water might not get to the whole part of the samples compared to the specimens immersed in curing tank. Hence, the curing method adopted may have influence on the strength properties of the bricks.
