EFFECT OF FLY ASH AND RICE-HUSK ASH ON LIME STABILIZATION OF EXPANSIVE SOILS FROM LOKPAUKWU AND AWGU, NIGERIA
Soil stabilization refers to the technique of altering the properties of a soil so as to improve its engineering performance. It aims at using chemical additives such as lime as a lone stabilizer or in combination with industrial residues (fly ash, rice husk ash, etc) to achieve this fit. This work investigates the effects of lime alone, lime-fly ash (LFA) and lime-rice husk ash (LRHA) blends in varying percentage mixtures on the engineering properties of expansive soils from Lokpaukwu (Ezeaku Formation) and Awgu (Awgu Formation) in Lower Benue Trough. The soils were stabilized with different percentages of lime (i.e. 2, 4, 6, 8, and 10%) and varying percentage ratio for lime-fly ash and lime-rice husk ash blends (i.e. 2 : 6, 2 : 8, 2.5:7.5, 2.5 : 10, 3 : 9, 3 : 12, 4 : 12, 4 : 16, 5 : 15 and 5:20).Liquid limit, plastic limit, linear shrinkage, compaction characteristics and California Bearing Ratio (CBR) tests were performed on the natural and lime-treated Lokpaukwu and Awgu soil samples while consistency limits and linear shrinkage tests only were performed on the lime-residue treated soil samples. Results of the study indicate that optimum reduction percentage of 24.14% and 30.56% (liquid limits), 72.22% and 74.42% (plasticity indices), 56.14% and 60.12% (linear shrinkages) and maximum percentage increase of 25.60 and 33.70 (Optimum Moisture Content (OMC)), 193.3 and 250 (unsoaked CBR), and 766 and 700 (soaked CBR) for Lokpaukwu and Awgu samples respectively were obtained on stabilizing the soils with 6% lime content. The results from lime-fly ash (LFA) and lime-rice husk ash (LRHA) blends indicate that liquid limits, plasticity indices and Linear Shrinkages decreased from 58 and 72 to 46 and 51, 36 and 43 to 11 and 12, 11.4 and 14.3 to 6.4 and 7.1, and from 58 and 72 to 45 and 51, 36 and 43 to 10 and 11, 11.4 and 14.3 to 6.4 and
7.1 for Lokpaukwu and Awgu samples respectively when treated with Lime-fly ash blend of 3 – 12% and lime-rice husk ash blend of 3 – 9%. It could be concluded that improving the characteristics of expansive soils by lime-fly ash blend or lime-rice husk ash blend is successful and provides immense environmental and economic benefits.
CHAPTER ONE INTRODUCTION
Background of the Study
Soil is the fundamental and most economical of construction materials. It bears the loads of structures and pavements transmitted through foundations and subbases respectively. Researchers have shown that the suitability of a soil as a construction material is a function of its geotechnical properties (Bowels, 1984 and 1988; Head, 1984; Venkatramaiah, 2012). The use of the existing soil at a construction site for engineering purpose may be hindered by poor engineering properties including poor bearing capacity, higher compressibility, and the alternate shrink and swell behaviour of expansive soils.
Expansive soils with potentials to change in volume in correspondence to a change in the moisture or suction condition of the soil (shrink or swell) are normally excluded as engineering construction materials because this volume change causes a resultant deformation, cracking and the eventual collapse of lightweight structures. Incidentally, the collapse of civil structures in some prominent towns in southeastern Nigeria have been associated with the occurrence of expansive clays in these towns (Okeke, 2008; Okeke and Okogbue, 2010)
Improvement of sites with weak or high compressible or high swelling or any other such problematic soils is commonly done by removing the problematic soils and replacing them with more competent ones such as compacted gravel, crushed rock, or lightweight aggregates to increase the load bearing capacity (Kukko, 2000). Although this is generally accepted as a good solution, the economic feasibility of an alternative construction material may not be guaranteed due to the excessive cost that may be incurred in long distance hauling of the alternative material, excavation of the insitu material and as well as refilling with the alternative material.
Also, rise in global population tends to exert pressure on land which is limited in supply (Oramah, 2006), resulting to a very high demand for the available land and consequent rise in its cost (Rama-Subbarao et al., 2011). Considering these factors improving the available soil at a site to meet the desired objective becomes the most viable alternative.
Soil improvement can be realized through several methods including the process of stabilization which aims at using chemical additives to achieve this improvement. Cement and lime are the most widely used stabilizing materials. However, the rise in the cost of these industrially manufactured soil improving additives (cement, lime, etc.) with a corresponding increase in the cost of construction on or with cement or lime stabilized soils has led to investigations and the subsequent adoption and usage of industrial wastes (rice husk ash, fly ash, kiln dust, etc.) as alternative materials for the total replacement (i.e. self cementitious e.g, Class C fly ash) or partial replacement (i.e. pozzolans) of cement and lime in engineering constructions (Uzal et al.; 2007; Sata et al. 2007; Yazici, 2008; Okafor and Okonkwo, 2009; Okeke and Enwelu, 2011; Baldino et al., 2014)
Industrial wastes such as fly ash and rice husk ash that accrues from the processing and, utilization of coal and rice abounds in Southeastern Nigeria due mainly to coal deposits and rice cultivation in the area. Harnessing these industrial wastes as soil treatment materials tend to provide an immense benefit to mankind as it reduces the cost of construction with stabilized soils, and as well as reduction in the environmental hazards caused by these wastes (Muntohar and Hantoro, 2000; Zumrawi and Hamza, 2014). Therefore, the whole process of soil stabilization with pozzolanic materials is invariably an industrial waste management strategy.
The long-term performance of any construction project depends on the soundness of the underlying soils (NLA, 2004). Expansive soil has been reported as a threat to engineering structures (Ola, 1987; Gutschick, 1967), and to occur mostly and extensively in tropical countries (Holtz and Gibbs, 1956; Katti, 1979; Ola, 1983; Garrido and Castenada, 1992; O’Connel and
Gourley, 1993; Uduji et al., 1994; Okeke, 2008; Lucian, 2008).
Immense damages to civil structures have been attributed to the occurrence of this soil in Nigeria and beyond (Skempton, 1954; Barber, 1956; Youssef et al., 1957; Hammer and Thompson, 1966; Jones and Holtz, 1973, US Army, 1983; Attewell and Taylor, 1984;). Okeke (2008) reported the occurrence of this problem soil in several towns of Southeastern Nigeria.
On the other hand, industrially developed and emergent nations of the world including Nigeria generate enormous industrial wastes, which constitute environmental hazards. The utilization of these industrial wastes for soil improvement has been identified as sustainable and cost effective method compared to the conventional method with lime or cement (Rama-Subbarao et al., 2011). In view of this, this work tends to investigate the stabilization of expansive soils – first with lime and secondly with industrial wastes as percentage substitutes for lime.
The study aims at utilizing the industrial wastes of Rice-Husk Ash (RHA) and Fly ash (FA) to improve and enhance the geotechnical properties of expansive soils in the study area in relation to their uses in engineering construction, thereby reducing the environmental hazards associated with the wrongful disposal of these wastes.
The specific objectives of the study are to:
- evaluate the effect of lime on the geotechnical characteristics of the expansive soils from Lopkaukwu and Awgu.
- evaluate the influence of rice husk ash on lime stabilization of the expansive soils.
- evaluate the influence of fly ash on lime stabilization of the expansive soils.
- determine the optimum contents for lime, lime-fly ash and lime-rice husk ash admixtures.
Justification of the Study
There have been cases of structural failures resulting from unstable foundation soils, as well as reports of huge volumes of industrial wastes dumped on open fields, constituting health and environmental hazards. It is against this backdrop that this project was conceived so as to reveal by concrete investigation, the efficacy of these industrial wastes in soil stabilization as an efficient waste management strategy.
Scope of the Study
The Study involved the collection of soil samples and soil additives including lime, rice-husk ash and fly ash.
It was limited to field sampling observations and laboratory analyses of the soil samples with reference to the various additives by measuring the necessary geotechnical properties (parameters); Attterberg limits (liquid limit, plastic limit and plasticity index), linear shrinkage, compaction characteristics (maximum dry density and optimum moisture content), and California bearing ration (CBR).