Bitumen Stabilization of Laterite Pretreated With Heat as a Flexible Pavement Material

Bitumen Stabilization of Laterite Pretreated With Heat as a Flexible Pavement Material

Chapter One

Aim and Objectives

 Aim

The main aim of this study was to investigate the suitability of lateritic soil treated with heat and mixed with cutback bitumen, for use as subgrade materials.

Objectives

1. To determine the effect of heat on the Atterberg limit of the laterite
2. To determine the compaction characteristics of laterite treated with heat and cut-back
3. To determine the strength indices (UCS, CBR) of laterite treated with heat and cut-back
4. To determine the durability of laterite treated with heat and cutback bitumen.

CHAPTER TWO

LITERATURE REVIEW

Laterite and its Usage in Flexible Pavement Work

The most common residual soil profile is the lateritic weathering profile (Alhassan et al, 2012). Gidigasu and Kuma (1987) defined these soil profiles as those in which lateritic horizons exists or are capable of developing under favorable conditions. According to Gidigasu (1976) Laterite is defined as a soil group, which is commonly found in the leached soils of humid tropics and is formed under weathering systems that cause the process of laterization. Laterites are the most common tropically pedogenic surface deposits in Australasia, Africa and South America Gidigasu (1976). Osinubi (2004) asserted that the geotechnical characteristics and field performance of lateritic soils are influenced considerably by their pedogenesis, degree of weathering, morphological characteristics, chemical and mineral compositions as well as prevailing environmental conditions. Alhassan and Mustapha (2012) categorized lateritic weathering profile, derived from granite basement into three major horizons below the humus stained top soil: the first horizon is the sesquioxide rich lateritic horizon (sometimes gravelly and/or hardened in-situ as crust); the second horizon is the mottled zone with evidence of enrichment of sesquioxide sand; the third horizon which overlies the parent rock is referred to as the pallid or leached zone and contains rocks suffering from chemical and mineralogical changes, but retaining their physical appearance.

According to Maignien (1966) the term Laterite is derived from the Latin word ―later, meaning brick. It was first used in 1807 by Buchanan to describe a red iron-rich material found in the southern parts of India. Laterites are widely distributed throughout the world in the regions with high rainfall, but especially in the inter-tropical regions of Africa, Australia, India, South- East Asia and South America, where they generally occur just below the surface of grasslands or forest clearings. Their extension indicates that conditions were favorable for their formation at some point in time in the history of the world, but not necessarily simultaneously in all regions (Maignien, 1966).

Wild (2012) describes laterite as hard materials, rich in iron oxides. This hardness is retained even when the material is immersed in water. The iron occurs mainly as goethite, hematite and amorphous iron oxides. The material is usually coloured reddish brown with a moderately high density (2.5 to 3.6 g/cc) and usually contains secondary aluminum. The silica content is generally low, but some quartz and sometimes Kaolinite is present. Laterite often occurs on remnants and old land surfaces. Regrettably the word laterite has been used to describe a wide range of materials as noted by Wild (2012).

Furthermore, Fadamiro and Ogunsemi (2010) defined laterite as a porous soil ranging from soft earthly material to hard rock, which ranges in colour from white to dark red depending on the amount of iron in the soil. They explained that it is found below the earth surface and chemically made of silicate and alumina, which is formed by weathering of rocks, hence, giving rise to many variations of laterite in composition and properties.

According to Ola (1983) laterite is defined as the products of tropical weathering with red, reddish brown, and dark brown colour, with or without nodules or concreting and generally (but not exclusively) found below hardened ferruginous crust or hard pan.

Laterites vary in color, but are usually brightly colored. The shades most frequently encountered are pink, ochre, red and brown; however, some occurrences are mottled and streaked with violet,

and others exhibit green marbling. A single sample may exhibit a whole range of colors merging more or less perceptibly into one another in a variety of patterns and forms. Laterites owe their color to iron oxides in various states of hydration and sometimes also to manganese (Maignien, 1966).

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CHAPTER THREE

MATERIALS AND METHODS

Materials

The materials used for this study are as discussed below

Lateritic Soil

The laterite soil sample was collected from a borrow pit at Shika (Longitude 7° 31^’ 7^′’ E latitude 11° 13^’ 34^′’ N) along Zaria – Funtua road, Kaduna State, Nigeria. Disturbed samples were taken from a depth of between 1.5m to 2.0 m after removal of the top soil.

Cutback bitumen

Cutback bitumen used for the work was obtained from Mararaban Jos, along Zaria – Kaduna road, Kaduna State.

Methods

Laboratory tests performed on the samples were in accordance with BS1377 (1990) for the natural laterite and BS1924 (1990) for laterite treated with heat and admixed with cutback bitumen.

CHAPTER FOUR

RESULTS ANALYSIS AND DISCUSSIONS

 Properties of the Soil and Bitumen

The properties of the soil and bitumen used are discussed below

CHAPTER FIVE

SUMMARY,CONCLUSION AND RECOMMENDATION

Summary of Research Findings

1. The lateritic soil studied can be classifeid as an A-7-5 (11) and MH soil using AASHTO and Unified classification system respectively.
2. The percentage passing sieve size 0.002 mm (clay fraction) increased by 9.32 %, 48% and 45.64% when treated with heat treatment temperature at 200^oC, 400^oC and 600^oC respectively.
3. The use of heat at 200^oC, 400^oC and 600^oC showed decrease in liquid limits by 6.05%, 76% and 4.69% respectively, while Plastic limit increased with increase in heat treatment temperatures..The plasticity index value of laterite samples decreased from 13.41% to 8.33% which corresponds to showed decrease in PI by 37.88 %, 30.50% and 28.19% when treated with heat at 200^oC, 400^oC and 600^oC respectively .
4. The pretreatment with heat at temperature of 200^oC showed reduction in activity of the soil sample from 73 to 0.45 which corresponds to 42.46% reduction.This implies improvement in soil samples,because reduction in activity can results into reduction in changes in the volume of material during swelling or shrinkage that can lead to distress in pavement structure.
5. The moisture–density relationship of laterite subjected to heat treatment at different temperature and cutback bitumen mixtures at the West African Standard Compaction (WASC) energy, showed that Maximum Dry Density (MDD) generally decreased with bitumen content between 0 % and 6% bitumen content and increased between 6 and 9% bitumen content, at all heat treatment temperatures. Optimum moisture content (OMC) decreased with bitumen content at all heat treatment temperatures.

6. The maximum CBR value of 28. 52 % at West African Standard Compaction (WASC) energy, of laterite specimens, cured for 6 days and soaked for 24 hours, as specified by the Nigerian General Specification (Roads & Bridges) (1997), was obtained when laterite was treated with 6 % bitumen and subjected to heat treatment temperature of 400°C for one This correspond to 44.8% increase in strength
7. Since the values specified for CBR at the energy level of WASC for subgrade, sub-base and base course materials by the Nigerian code are 10, 30 and 80% respectively. The lateritic soil material can only be used as sub grade/fill material. Its usage as sub-base will require some further
8. Maximum 7 day UCS value of 23 kN/m² corresponding to 56.6 % increase in strength above values obtained with the natural laterite was obtained when laterite was subjected to heat at a temperature of 200^oC for one hour and treated with 3 % bitumen.
9. Highest resistance to loss in strength of 24.58% for WAS compaction energy obtained when laterite was subjected to heat at a temperature of 200^oC for one hour and treated with 3 % bitumen felt below allowable 80% resistance to loss in strength recommended by Ola (1975) though the immersion in water were above the recommended 4 days soaking period.

Conclusion

The following conclusions can be drawn from the study.

1. The use of heat improved the properties of the soil studied, because at 200^oC, 400^oC and 600^oC decrease in liquid limits by 6.05%, 7.76% and 4.69% respectively were observed, while Plastic limit increased with increase in heat treatment temperatures..The plasticity index value of laterite samples decreased by 37.88 %, 50% and 28.19% when treated with heat at 200^oC, 400^oC and 600^oC respectively . The decrease in liquid limits and plasticity index imply reduction in compressibility and increase in shear strength of the treated soil samples.
2. The moisture–density relationship of laterite subjected to heat treatment at different temperature and cutback bitumen mixtures at the West African Standard Compaction (WASC) energy, showed that Maximum Dry Density (MDD) generally decrease with bitumen content between 0 % and 6% bitumen content and increased between 6 and 9% bitumen content, at all heat treatment temperatures. Optimum moisture content (OMC) decreased with bitumen content, and heat treatment temperature.
3. Maximum 7 day UCS value of 23 kN/m² corresponding to 56.6 % increase in strength above values obtained with the natural laterite was obtained when laterite was subjected to heat at a temperature of 200^oC for one hour and treated with 3 % bitumen.
4. Highest resistance to loss in strength of 24.58% for WAS compaction energy obtained when laterite was subjected to heat at a temperature of 200° for one hour and treated with 3 % bitumen fall below allowable 80% resistance to loss in strength recommended by Ola (1978) though the immersion in water were above the recommended 4 days soaking period.

Recommendations

Based on findings from the study, heat at a temperature of 200^oC for one hour with 3 % bitumen content is suggested as treatment for the MH laterite studied before use in flexible pavement as sub grade/fill material and before use as a material under rigid pavement or under Airfield etc. Its usage as sub-base will require some further treatment.

Trial of higher grades in the series of cut-back bitumen for the stabilization be also considered in future research

REFERENCES

• AASHTO (2007). Standard specifications for transportation materials and methods of sampling and testing. 20th edition, American Association of State Highway and Transportation Officials (AASHTO), Washington D. C.
• Adebayo, F.F. and Jimoh, Y.A (2015). Production and Cost of Cold patch Road Mats with Bitumen Extracted from Nigerian Tar Sand. Nigerian Journal of Technology (NIJOTECH) Vol. 34 No. 2, pp. 245 – 253
• Alhassan, M. (2006). Classification of Minna Laterite. Proceeding of the 7^th Annual Engineering Conference, Federal University of Technology, Minna, Nigeria, pp. 40-44.
• Alhassan. M. and Mustapha, A. M. (2012). Clay Mineralogy of Lateritic Soils Derived from Granite Basement – A Case Study of Minna Lateritic Soils.
• Electronic Journal of Geotechnical Engineering, Oklahoma, USA, vol. 17(M), pp. 1897-1903.
• Alhassan, M., Mustapha, A. M. and Mesaiyete, E. (2014). Influence of Clay Mineralogy on Plasticity of Lateritic Soils. IOSR Journal of Mechanical and Civil Engineering. 11(3) version 4, pp.18-21.
• Amadi, A.A. (2011). Evaluating the Potential use of Lateritic Soil mechanically stabilized with quarry fines for construction of road bases. Nigeria Journal of Engineering Vol .17, No.2, pp1-12
• Arora, K.R. (2007). Soil Mechanics and Foundation Engineering. Standard Publishers Distributors, 1705-B, Nai Sarak, Delhi-110006. PP 383
• Austroads (2006). Guide to Pavement Technology Part 4D: Stabilised Material. Retrieved on 25 August 2015 from www.austroads.com.au PP 16
• BS 1377 (1990). Methods of Testing Soil for Civil Engineering Purposes. British Standard Institute, London.
• BS 1924 (1990). Method of Testing for Stabilized Soils. British Standard Institute, London.

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