ABSTRACT
Clay soil collected along Gwagwalada – Garki road was characterized and classified as A-7-6 soil according to American Association of State Highway and Transportation Officials (AASHTO) soil classification system. The clay was treated with 0, 2, 4 and 6% cement which was admixed with 0, 3, 6, 9, 12 and 15% Calcium Carbide Residue (CCR). Unconfined Compressive Strength (UCS) test was used as evaluation criterion to measure the effect of CCR on the cement stabilized clayey soil. Results showed significant increase in UCS with increase in cement and CCR. In the absence of cement, the UCS was observed to increase from 71 kN/m2 at 0% CCR to 602 kN/m2 at 15% CCR and 90 day curing. At 6% cement, the UCS increased from 473 kN/m2 at 0% CCR to 3589 kN/m2 at 15% CCR and 90 day curing. This UCS strength has satisfied the strength required for a soil material to be used as base course for high trafficked road bases. It was also observed that 12 – 15% CCR is the optimal content required for efficient stabilization of clayey soils.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Background to the Study
Expansive clays are common for swelling, shrinkage and other forms of weaknesses which make it difficult as materials to support civil engineering structures or to be used in construction of some civil engineering structures including pavements. In a region where clay soils are the dominant soil materials available, stabilization of the clay soil to meet the requirements is inevitable. Many researchers (Khajuria and Chopra, 2019; Abdullah et al., 2017; Du et al., 2019; Xiao et al., 2019; Pourakbar et al., 2016) have used different additives to improve the strength and durability of weak clay soils.
Fine-grained soils without stabilization are unsuitable for earth structures and pavement. The chemical stabilization is one of the extensively used techniques to improve the engineering properties of fine-grained soils. Portland cement is commonly used for this stabilization in most areas. The resistance to compression and consequent strength development increase with increasing curing time. However, the high unit cost and energy intensive process of Portland cement is driving a search for alternative cementitious additives. For fine-grained soils, which contain high natural Pozzolanic materials, silica rich materials can be used to produce a moderately high strength geo- material (Horpibulsuk et al., 2011; Songsuda et al., 2013).
Cement stabilization is one of the extensively used techniques to rectify the deficiencies in engineering properties of expansive soils, especially for pavement applications. An advantage of cement stabilization is that the required strength can be attained in a shorter period. The effect of moisture content, replacement ratio, compaction effort, curing period, and cement content on the engineering characteristics and microstructure of cement aided soils is widely being researched (Deng et al., 2012; Venkatesh et al., 2018).
Clays exhibiting poor engineering properties such as low strength, high compressibility, and high shrinkage/swelling potential pose a major challenge to several construction and geotechnical engineering applications (Chen et al., 2017). Chemical stabilization is commonly used to improving engineering properties of problematic soils. Several recent studies have shown that CCR stabilization can improve strength characteristics, dispersibility, and swelling potential of problematic soils (Arulrajah et al., 2016).
Calcium carbide residue (CCR) is a by-product of the acetylene production process that contains mainly calcium hydroxide Ca(OH)2. Compared to hydrated lime, CCR has similar chemical and mineralogical compositions. The Ca(OH)2 contents are approximately 96.5% and 76.7% for hydrated lime and CCR respectively, CaO contents are 90.13% and 70.78% for the hydrated lime and the CCR, respectively. The high Ca(OH)2 and CaO contents of CCR indicates that it can react with Pozzolanic material such as Coconut Shell Ash and produce a cementitious material. The production of CCR is best described by the following equation (Balarabe and Mary, 2015):
CaS2 + 2H2O → C2H2 + Ca(OH)2
This study is therefore aimed at determining the effect of CCR on cement stabilized clay soil.
1.2 Statement of the Research Problem
The increasing world population, especially in developing nations has led to increasing demand for roadways, railways, housing facilities and other infrastructures. Soil with higher stability is required to bear the weight of these structures; generally speaking, the stability of any construction related structure indirectly or directly depends on the soil stability.
Clayey soils swell or increase in volume in tropical rainy seasons on imbibition of water, and shrink or reduce in volume because of evaporation of water in dry seasons. As a result of the alternate swelling and shrinkage of clay soils, structures such as foundations, pavements, residential buildings, constructed on it experienced severe damage.
Also, in developing countries like Nigeria, there are many acetylene gas production units and PVC chemical plants, which produce CCR in huge amounts. It is usually dumped in the landfills and causes environmental problems to landfills due to its alkalinity. Therefore, the use of CCR to stabilize soil will reduce the problem of waste disposal.
1.3 Aim and Objectives of the Study
Aim
The aim of this work is to investigate the sustainable use of calcium carbide residue to enhance the strength of cement stabilized clay soil in road construction.
Objectives
To achieve the above aim, the following objectives are to;
i. determination of index properties of Clay soil samples.
ii. determination of Microstructural analysis of the clay using XRD, XRF and SEM.
iii. determination of Unconfined Comprehensive Strength of untreated clay and clay treated with varied composition of cement and Calcium Carbide Residue.
iv. determination of effect of calcium carbonate residue on cement stabilized clay.
1.4 Scope of Work
The scope of the study focuses on the laboratory tests on clay soil collected from Bako village along Gwagwalada – Garki road using the methods highlighted in BS 1377, (1990). Index properties tests such as natural moisture content, specific gravity, particle size distribution, liquid limits test and plastic limit tests to be carried out on the untreated expansive clay soil. Other engineering properties tests such as Compaction characteristics and Unconfined Comprehensive Strength (UCS) to be carried out on the untreated expansive clay soil and clay soil treated with cement and calcium carbide at cement replacement of 0, 2, 4 and 6% and Calcium Carbide replacement of 3, 6, 9, 12 and 15% concurrently.
1.5 Justification of Study
In order to address the above problems of changes in volume of Clay soils for construction activities in our society and other environmental problems relating to the disposal of waste industrial by-products like Calcium Carbide while reducing costs of construction, Calcium Carbide Residue will be used to stabilized Clay Soil in this research work because of the material constituent compositions which can replace cement without much utilization of energy, with lower temperature rise and improvement in durability and strength.
The findings of this research work will therefore add more knowledge on the existing literatures and will act as a supportive insight for further research on the use of Calcium Carbide Residue as a clay soil stabilizing material.
In addition, the use of Calcium Carbide Residue is not common in the Nigerian construction sector. This study will be able to enhance the understanding on the suitability of Calcium Carbide Residue as cement replacement material for stabilization.
This material content is developed to serve as a GUIDE for students to conduct academic research
SUSTAINABLE USE OF CALCIUM CARBIDE RESIDUE TO ENHANCE THE STRENGTH OF CEMENT STABILIZED CLAY SOIL IN ROAD CONSTRUCTION
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