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OKONKWO, UGOCHUKWU NNATUANYA

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ABSTRACT

The frequent rises in the price of cement and other binders have resulted in the escalation of the cost of construction, rehabilitation and maintenance of roads. One of the possible ways of cost reduction is to convert waste bagasse residue into ash and use it as a supplement/partial replacement for cement. Therefore this study is an attempt to optimize bagasse ash content in cement-stabilized lateritic soil for low-cost roads. The bagasse ash and lateritic soil were characterized by carrying out Atomic Absorption Spectrometer and soil preliminary tests as well as X-ray diffraction respectively. Compaction test, California bearing ratio, unconfined compressive strength and durability tests were carried out on the soil stabilized with 2%, 4%, 6% and 8% cement contents and bagasse ash ranging from 0% to 20% at 2% intervals; all percentages of the bagasse ash and cement were by the weight of dry soil. Cost analysis was carried out for the constituents of the stabilized material and a model was formed for cost evaluation. Also three regression models were developed that involved relationships of cost of bagasse ash, cement content, optimum moisture content, California bearing ratio and unconfined compressive strength at 7 days curing period. The three regression models were used to form a non-linear model which was linearized and solved with the simplex method including sensitivity analysis on the objective function and the constraints. Attempt was also made to apply Scheffe’s regression method from obtained results. It was observed that the increase in bagasse ash content increased the optimum moisture content but reduced maximum dry density. On the other hand higher bagasse ash tremendously improved the strength properties of the stabilized matrix. The optimum contents for bagasse ash, cement and optimum moisture content for an economic mix were 14.03%, 4.52% and 22.46% respectively at a cost of 39.50 kobo for stabilizing 100 grams of the lateritic soil as against 43.52 kobo for stabilizing with only cement.

 

 

 

TABLE OF CONTENTS

 

TITLE PAGE                                                                                                                         i

CERTIFICATION                                                                                                     ii

APPROVAL PAGE                                                                                                   iii

DEDICATION                                                                                                           iv  

ACKNOWLEDGEMENTS                                                                                       v

ABSTRACT                                                                                                               vi

TABLE OF CONTENT                                                                                             vii

LIST OF TABLES

LIST OF FIGURES

LIST OF NOTATIONS

CHAPTER ONE    INTRODUCTION

  • Background of the Study 1
  • Statement of Problem 2
  • Aim and Objectives of the Study 3
  • Scope of the Study 3
  • Significance of the Study                4

CHAPTER TWO    LITERATURE REVIEW

  • Definition of Laterite 6

2.1.1 Formation of Laterite                                                                           9

2.1.2 Mineralogical Composition of Laterite                                                12

2.1.3 Uses and Economic Relevance of Laterites                                         13

2.1.3.1 Building Blocks                                                                                 13

 

2.1.3.2 Road Building                                                                                                13

2.1.3.3 Water Supply                                                                                      14

2.1.3.4 Waste Water Treatment                                                                      14

  • Ores 15
  • Definition of Soil Stabilization 19

2.2.1 Techniques for Soil Stabilization                                                           19

2.2.1.1 Stabilization by Compaction                                                               20

2.2.1.2 Mechanical Stabilization                                                                     21

2.2.1.3 Stabilizing by the Use of Stabilizing Agents                                      23

  • Soil Stabilizing Agents Available 23

2.3.1 Primary Stabilizing Agent                                                                      23

2.3.1.1 Portland Cement                                                                                 23

2.3.1.2 Lime                                                                                                    27

2.3.1.3 Bitumen                                                                                              28

2.3.2 Secondary Stabilizing Agents                                                                29

2.3.2.1 Blast Furnace Slag                                                                              29

2.3.2.2 Iron Fillings                                                                                         30

2.3.2.3 Rice Husk Ash                                                                                    30

2.3.2.4 Bagasse Ash                                                                                        31

  • Mechanisms of Stabilization 32
  • Mathematical Modeling 33

2.5.1 Mathematical Model-Building Techniques                                            39

  • The Non-linear Programming Modeling 41

2.6.1 Monomial and Polynomial Functions                                                    42

2.6.2 Previous Works on Optimization Techniques for Construction Materials           43

  • Classification of Soil 44

2.7.1 AASHTO Soil Classification System                                                    45

2.7.2 The Unified Classification System                                                        46

CHAPTER THREE: METHODOLOGY

  • Introduction 49
  • Characterization of the Lateritic Soil 49

3.2.1 Moisture Content Determination                                                           49

3.2.2 Liquid Limit                                                                                           50

3.2.3 Plastic Limit                                                                                           50

3.2.4 Linear Shrinkage                                                                                    51

3.2.5 Particle Size Analysis                                                                             51

3.2.6 Identification of Clay Mineral                                                               53

3.2.7 Classification of Soil                                                                              53

3.2.8 Compaction Test                                                                                    53

3.2.9 Specific Gravity of Solids                                                                     54

3.2.10 California Bearing Ratio                                                                      55

3.2.11 Unconfined Compressive Strength                                                      55

  • Characterization of Bagasse Ash 56
  • Test Requirements for the Stabilized Lateritic Soil 56

3.4.1 Unconfined Compressive Strength                                                        56

  • California Bearing Ratio 57
  • Durability Tests 58

3.5       Method of Formulation of Non-linear Programming Model                          58

  • Objective Function 58

3.5.2    Constraints                                                                                          60

  • Solution of Non-linear Programming Model 61
    • Sensitivity Analysis 63
  • Scheffe’s Simplex Regression Model 64

3.7.1 Determination of the Coefficients of the Polynomial Function            67

3.7.2 Validation of Optimization Models                                                       69

CHAPTER FOUR    RESULTS AND DISCUSSION

  • Presentation of Results 71
  • Soil Characterization 75
  • Characterization of Bagasse Ash 78
  • Stabilized Soil Tests 79

4.4.1 Compaction Characteristics                                                                   79

4.4.2 Strength Characteristics                                                                         81

CHAPTER FIVE   MODELING AND OPTIMIZATION OF BAGASSE ASH

CONTENT

  • Cost Analysis for the Stabilized Matrix 86

5.1.1 Cement Cost                                                                                          86

5.1.2 Projected Cost of Bagasse Ash                                                                         86

5.1.3 Cost of Water                                                                                        87

  • Cost of Lateritic Soil 87
  • Regression Models             88

5.2.1 Calibration and Verification of Models                                                 90

  • Non-linear Programming Model                                     92

5.3.1 Sensitivity Analysis                                                                               97

5.3.1.1 Sensitivity Analysis on Constraints                                                    98

5.3.1.2 Sensitivity Analysis on Objective Function                                        103

  • Application of Scheffe’s Simplex Regression Model 109

5.4.1 Determination of Densities of Materials                                              109

5.4.2 Formulation of Optimization Models                                                   110

5.4.3 Validation and Verification of the Scheffe’s Optimization Models    112

CHAPTER SIX   CONCLUSIONS AND RECOMMENDATIONS

  • Conclusion 118
  • Recommendations                                                             119

REFERENCES

APPENDICES

 

CHAPTER ONE

 

INTRODUCTION

  • Background of the Study

Bagasse-ash is an agricultural material obtained after squeezing out the sweet juice in sugarcane and incinerating the residue to ash. Bagasse is the fibrous residue obtained from sugarcane after the extraction of sugar juice at sugarcane mills or sugar producing factories (Osinubi and Stephen, 2005). The climatic and soil conditions favourable for the production of sugarcane are present in the Northern part of Nigeria and consequently, there is abundant production of it in the area. Sequel to the foregoing is massive generation of sugarcane residue waste which constitutes disposal problems and requires handling. There is yet no adequate awareness about the usefulness of the sugarcane residue in the country, in other words very little value has been attached to it.  In some cases, the residue is being utilized as a primary fuel source for sugar mills and also for paper production. However incinerating it to ash and adopting it as admixture in stabilized soils because it has been found to be a good pozzolana, adds to its economic value.

 

The major part of Nigeria is underlain by basement complex rocks, the weathering of which had produced lateritic materials spread over most part of the area. It is virtually impossible to execute any construction work in Nigeria without the use of lateritic soil because they are virtually non-swelling (Osinubi, 1998a). The climatic and geological position of Abia state with her alternating humid and dry periods enhanced the rich deposition and formation of lateritic soils which have been very often utilized as fill materials in road construction and other civil engineering works. These have shown promising potentials in the lateritic soils for road pavements in the stabilized form and prompted for more studies on them. In the past, several admixtures have been used on lateritic soil in the south east of Nigeria such as rice husk ash (Okafor and Okonkwo, 2009), and others. However, much has not been done with bagasse-ash on lateritic soil in the region.

 

  • Statement of Problem

Roads in Nigeria have not received adequate attention with regards to maintenance and even some rural areas are still inaccessible because of lack of motorable roads. These roads are classified as Trunks A, B and C which implies that the roads are managed and controlled by Federal, State and Local Authorities respectively. However this has not paid off in ensuring that the roads are sufficiently maintained and kept in good condition such that the users are not endangered in any way. In some cases they are left in a very deplorable state or a point where maintenance by mere cutting and patching bad portions cannot bring them to a satisfactory level to the users but might require total re-building.

 

One of the plausible reasons for allowing roads to deteriorate so much is that the cost of construction, maintenance and re-building has remained very high. The cost of materials is a vital component in the total cost of road work. Thus, if it is substantially reduced, the total cost of the road work would also be affected and consequently becomes affordable. Therefore efforts should be geared towards harnessing the natural potentials in the environment for use as construction materials to reduce the cost of road work to the most possible minimum.

 

  • Aim and Objectives of the Study

This work used bagasse ash (sugar-cane residue ash) as an admixture in cement- stabilized Ndoro Oboro lateritic soil for road construction works. The study is aimed at optimizing bagasse ash content in the cement-stabilized soil.

The objectives of this work were to:

  1. Characterize bagasse ash and lateritic soil.
  2. Examine the effects of bagasse ash on the compaction and strength characteristics of the cement-stabilized lateritic soil.
  • Develop relationships comprising cost of bagasse ash content, cement content, cement-stabilized lateritic soil compaction and strength characteristics.
  1. Calibrate and verify the model using experimental results.
  2. Develop a non-linear programming model for predicting the optimum content of bagasse ash.
  3. Optimize bagasse ash content in the cement stabilized lateritic soil and compare results with unoptimized solution.

 

  • Scope of Study

Soils have peculiarities, they vary in properties. In other words, no two soils can be similar in all properties but can behave alike in some cases. For example, peculiarities of structure may play more important role in cement stabilization than the Atterberg limits. Lateritic soils with the same and similar plasticity index may have completely different behaviours in mixing operations (Osinubi, 1998b). Osinubi (1998b) equally pointed out that one of the major problems confronting geotechnical engineers in the tropics is the fact that most local soils are not amenable to standard pretest preparations and testing procedures, resulting in variations of test results. These variabilities have been discussed by Gidigasu (1988). However, the differences in opinion are expressed over the understanding of engineering behaviour of residual soils. According to Vaughan (1985), the development of classical concepts of soil mechanics has been based largely on the investigation of sedimentary deposits of unweathered soils.  These concepts have been found to be inappropriate in describing the behaviour of residual soils and could lead to significant errors if inadvertently applied. Gidigasu (1988) concludes that classical soil-mechanics principles have failed in answering some of the geotechnical problems of  some soils formed under subtropical and tropical environments. In other words the results, model and recommendations are only limited to the  lateritic soil deposit in Ndoro in Ikwuano local government area of Abia State, which is stabilized with ordinary Portland cement as the binder and bagasse-ash as admixture. The tests that were carried out include compaction, California bearing ratio, unconfined compressive strength and durability tests which are the test requirements for stabilized materials.

 

  • Significance of the Study

Soil stabilization techniques for road construction are used in most parts of world although the circumstances and reasons for resorting to stabilization vary considerably. In industrialized, densely populated countries, the demand for aggregates has come into sharp conflict between agricultural and environmental interests. In less developed countries and in remote areas the availability of good aggregates of consistent quality at economic prices may be limited. In either case these factors produce an escalation in aggregate costs and maintenance costs. The upgrading by stabilization of materials therefore emerges as an attractive proposition (Sherwood, 1993).

 

The importance of cement stabilization of lateritic soils has been emphasized by researchers with soil-cement mixtures being used as sub-base or base courses of low-cost roads. However, excessive addition of cement becomes uneconomical; therefore the cheap agricultural waste (bagasse ash) becomes a partial replacement/supplement for the more expensive cement. Bagasse ash has been globally confirmed to be a good pozzolana because of its high silica content which indicates that there is a promising potential in the agricultural material to serve as an admixture. This would be one of the ways to guarantee the federal government’s efforts of meeting Millennium Development Goals of providing low-cost roads. The availability of good road networks becomes possible which would enhance the symbiotic relationship between the urban and rural areas for economic development.

 

The trade-off between cost effectiveness and the strength characteristics of the stabilized matrix resulting from the partial replacement/supplement of cement with the bagasse ash for road work should be balanced. Instead of going through a rigorous laboratory experiments with very many specimens in order to determine the optimum content of bagasse ash, a predictive model could be developed using relatively fewer observations. The model could also be useful in predicting other factors like the compaction and strength characteristics with variation in bagasse ash and cement contents.

 

Because of limited resources, there is a need to be very conscious not to be wasteful. The process of mathematical modeling and prediction puts a check on how effective limited field data are put to use in decision-making. In other words, it would be beneficial to predict the optimum amount of bagasse ash required with a certain amount of cement in the stabilized matrix to achieve the desired result with regards to the compaction and strength characteristics at minimum cost.

 

 

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