The rate at which roads fail in Nigeria should worry any responsible citizen. Considering the enormous resource expended to construct a kilometer of road, it is heart breaking when the same road fail barely six (6) months after construction. For in the life of our dear country, the all important economic theory of opportunity cost is applicable just as it is elsewhere in the world. Stabilization is a viable alternative to achieving a durable road construction regime. Soil stabilization is not new, even in this part of the world, but as dynamic as the world is, more cost effective and less problematic means of stabilization is being researched or reviewed daily. Bitumen stabilized materials (BSM) either as subgrade or road base is still new or nonexistent in this part of the world. In some part of Africa especially Southern Africa it is already in use to construct rural roads without any further surfacing. The cohesion between the bitumen and the soil particles brings about a decrease in moisture and an increase in density and ultimately results in a durable road. For this research, soil sample was obtained from a supposed problematic soil along KM 105 Port Harcourt –Aba, expressway, Umuahia. The soil was analysed for Atterberg’s limits, compaction (moisture-density relationship) and California bearing ratio at 6%, bitumen content. It was analyzed for compaction and CBR again to compare with the result obtained prior to stabilization. A further stabilization was done with 8% bitumen content and another with 10% bitumen content and in both cases moisture-density test and CBR test performed. The results showed a significant positive improvement in the index properties of the soil, but also showed a decline in CBR value as the bitumen content increased from 6% to 10%.Thus there was need to get the optimum quantity, and so I had to carry out same procedure this time with 2% and 4% bitumen content and the results showed 4% bitumen content as the optimum.
TABLE OF CONTENTS
Title Page i
Certificate of approval v
1.0 Introduction 1
1.1 Historical Background 1 – 2
1.2 Research Problem 2
1.3 Objective of Research 3
1.4 Significance of Study 3
1.5 Scope of study 3
1.6 Limitation of the Study 3
2.0 Literature Review 4
2.1 Related Works 4-5
2.2. Subgrade 7
2.2.1. Subgrade Performance 7-8
2.3. Stiffness/Strength tests 9
2.3.1. California Bearing Ratio 9-10
2.3.2. Elastic Modulus 11-12
3.0. Materials and Methods 13
3.1. Soil (Subgrade) 13
3.1.1 Particle Size Distribution 13
3.1.2. Atterberg’s Limits Test 13-14
3.1.3 .Compaction 14
3.1.4 .California Bearing Ratio Test 14
3.2. Bitumen 14-16
3.3. Method Adopted for Stabilization 16
4.0. Results and Discussion 17
4.1 .Particle Size distribution 17
4.2. Atterberg’s Limits 17-19
4.3. California Bearing Ratio 20-21
5.0. Conclusion and Recommendations 22
5.1 Conclusion 22
5.2 Recommendations 22
1.1 HISTORICAL BACKGROUND
Road design and construction is as old as man found it necessary to move from one location to another. Biblical references to roads and paths are numerous and can be found in many chapters of the bible. It is believed in some quarters that the first pathways were trails made by animals. Others believe that some roads originated from following animal trails. By about 10,000 BC, rough pathways were used by human travelers. The world’s oldest known paved road was laid in Egypt between 2600 and 2200 BC.
In ancient times, transport by river was far easier and faster than transport by road, especially considering the cost of road construction and the difference in carrying capacity between carts and river badges. From about 312 BC, the Roman Empire built straight strong stone Roman roads throughout Europe and North Africa, in support of its military campaign. At its peak, the empire had about 29 major roads connecting it and moving out of Rome which covered about 78 kilometers.
In the 8th century AD, many roads were built throughout the Arab Empire. The most sophisticated roads were those in Baghdad, which were paved with tar. Tar was derived from petroleum, accessed from oil fields in the region, through the chemical process of destructive distillation. (Wikipedia). Roads and highways can be paved by concrete or asphalt. The former is known as a rigid pavement while the latter is Flexible pavement. Pavement is the durable surface material laid down in an area intended for vehicular or foot traffic.
Asphaltic concrete has been widely used since the 1920’s. The viscous nature of the bitumen binder allows asphalt concrete to sustain significant plastic deformation, although fatigue from repeated loading over time can cause failure to this surface.
Concrete surfaces (specifically, Portland cement concrete) are formed using a mix of Portland cement, coarse aggregate, sand and water. In virtually all modern mixes there will always be admixtures added to increase workability, reduce the water content, and mitigate harmful chemical reactions and to increase strength.
There also abound cases in practice where composite surface is the solution. Composite surface combine Portland cement concrete and asphalt. There are usually found more in road rehabilitation than in new construction. Road construction the world over would have been reduced in cost by at least 40% if there were no poor subgrade in existence. Again, the long term performance of any construction project, especially roads depends on the nature of the underlying soils.
A subgrade is considered unsuitable for construction purposes if after a geotechnical survey of the soil in question, certain properties of the soil such as its bearing capacity etc are not in tandem with the minimum required for structural purposes. Because our project will not be situated in the air, and has some economic, social and other numerous reasons why it has to be situated in a particular locality, we may refer to stabilizing the soil. This is with a view to improve the characteristics of the soil and to make it suitable for engineering purposes.
We are mindful of the various types of stabilization, processes involved, stabilizing agents used and perhaps the method adopted for the attainment of the set target. This work is aimed at providing to the audience the use of bitumen as an agent for the stabilization of poor subgrades and the attendant benefits thereof.
Bituminous stabilization is generally accomplished using bitumen. The type of bitumen to be used depends upon-
(i) The type of soil to be stabilized
(ii) Method of construction
(iii) Weather condition
As a general rule, the most satisfactory results are obtained when the most viscous liquid bitumen that can be readily mixed into the soil is used.
1.2 RESEARCH PROBLEM
The cost of road construction will be reduced significantly if subgrade is good. Poor subgrade if not considered appropriately during design stage leads to expensive pavement laid over poor subgrade.
The aim of this research is to introduce bitumen (sourced locally) as a stabilizer /stabilizing agent to improve poor subgrade thus leading to more economically and technically efficient roads.
1.3 OBJECTIVES OF RESEARCH
The objectives of this research work include the following.
i To obtain the particle size of the soil chosen to confirm its grading zone.
ii To determine the Atterberg’s limits of the soil. Its moisture-density relationship and CBR values.
iii Identify a bitumen (stabilizer) that is readily available for the stabilization from the various classification of bitumen.
iv Determine maximum dry density, optimum moisture content and CBR values of stabilized soil.
v Compare soil properties before and after stabilization.
1.4 SIGNIFICANCE OF STUDY
Bitumen as a stabilizer is still in infant stage in Nigeria whereas in some part of Africa and the western world it is in advanced stages and being used to enhance subgrade and to build more economical roads.
1.5 SCOPE OF STUDY
This research work focuses mainly on the use of bitumen as a stabilizer for the fine grained soil identified and tested in this work.
1.6 LIMITATIONS OF THE STUDY
This research is limited to the use of bitumen found in the market and does not cover its origin or production. However its availability is guaranteed.
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