ABSTRACT
Artificial Intelligence (AI)-based bi-input predictive models have been executed to forecast the bulk density, linear and volumetric shrinkages and desiccation cracking of HSDA-treated black cotton soil (BCS) for sustainable sub-grade construction purposes. The BCS was characterized and classified as A-7 group soil with high plasticity and poorly graded condition. Sawdust ash was obtained by combusting sawdust and sieving through 2.35 mm aperture sieve. It was further activated by blending it with pre-formulated activator material (a blend of 8M NaOH solution and NaSiO2 in 1:1 ratio) to derive HSDA. The HSDA was further used in wt % of 3, 6, 9, and 12 to treat the BCS. The treated samples were compacted in the standard proctor moulds, cured for 24 hours and extruded. The desiccation tests were then performed on the prepared specimens by drying them at a temp of 102°C for 30 days and behavioural changes in weight, height, diameter, average crack development, etc. were taken throughout the period. Multiple data sets were collected for the references test, and treated specimens of 3, 6, 9, and 12% wt HSDA of the soil for 30 drying days. XRF, XRD and SEM tests were also conducted to determine the pozzolanic strength via the chemical oxide composition, three chemical moduli (TCM) and the micro structural arrangement of the experimental materials and the treated BCS. The XRF tests showed that the experimental materials had less pozzolanic strength, which improved with the treated blends thereby forming stabilized mass of BCS. Also, it showed the silica moduli of the TCM dominated the stabilization of the soil with HSDA. SEM tests showed increased formation of ettringite and gels with the addition of the HSDA. The data collected was subjected to MLR analysis for the four outcomes, BD, CW, LS and VS of the HSDA-treated BCS. The MLR performed with an accuracy of 69% for BD, 75% for CW, 95% for LS and 96% for VS. The addition of the various percentages of admixture (HSDA) improved the measured parameters as compared to the control soil thereby improving the stability of the soil.
TABLE OF CONTENTS
Title Page i
Declaration ii
Certification iii
Dedication iv
Acknowledgement v
Abstract vi
List of Tables vii
List of Figures viii
CHAPTER 1: INTRODUCTION
1.1 Background of Study 1
1.2 Statement of the Problem 5
1.3 Aims and Objectives 5
1.4 Significance of the Study 6
1.5 Scope of the Study 6
CHAPTER 2: LITERATURE REVIEW
2.1 Pavement Foundation 7
2.2 Soil Desiccation 7
2.2.1 Dry soil layer 9
2.2.2 Drying 9
2.2.3 Shrinkage 10
2.2.4 Cracking 11
2.2.5 Black cotton soil 13
2.3 Soil improvement 14
2.3.1 Saw dust ash 15
2.4 Activated Ash 15
2.4.1 Sawdust ash treated soil 17
2.4.2 X-ray diffraction 18
2.5 Scanning Electron Microscope 19
2.6 X-ray Florescence Test 20
2.7 Multiple Linear Regression 22
2.8 Cronbach’s Alpha 22
2.9 Swell Index Test 22
2.10 Sieve Analysis Test 23
CHAPTER 3: METHODOLOGY
3.1 Sample Collection 24
3.2 Materials 24
3.2.1 Soil 24
3.2.2 Saw dust 25
3.2.3 Hybrid sawdust ash (HSDA) 25
3.3 Laboratory Tests 27
3.3.2 Moisture content 29
3.3.3 Specific gravity 29
3.3.4 Sieve analysis test 33
3.4.4 Atterberg limit 35
3.4.1 Liquid limit 36
3.4.2 Plastic Limit 36
3.4.3 Shrinkage limit 36
3.3.4 Plasticity index 36
3.4.5 Plasticity 36
3.4.6 Consistency index 37
3.4.7 Liquidity index 37
3.4.8 Determination of liquid limit of soil 38
3.4.10 Determination of plastic limit of soil 38
3.4.9 Procedure 39
3.5 Proctor Soil Compaction Test 42
3.5.1 Apparatus 42
3.5.2 Proctor soil compaction test procedure 42
3.5.3 Calculation 44
3.6 California Bearing Ratio (CBR) Test 44
3.6.1 Apparatus for CBR test 45
3.6.2 Procedure of california bearing ratio test 45
3.6.3 Calculation 46
3.7 X-ray Diffraction 47
3.7.1 Principles of X-ray diffraction 47
3.7.2 Equipment of X-ray diffraction 47
3.7.3 X-Ray diffraction analysis 48
3.8 Scanning Electron Microscopy 49
3.8.1 Principles of scanning electron microscopy 49
3.8.2 SEM equipment 49
3.8.3 Working mechanism of SEM equipment 51
3.8.4 Specimen preparation for SEM 52
3.8.5 Image treatment and analysis in SEM 53
3.8.6 Advantages and applications of scanning electron microscopy 53
3.9 X-ray fluorescence analysis (XRF) - 54
3.9.1 Shrinkage 56
3.9.2 Cracking 56
3.9.10 Swell Index Test 56
CHAPTER 4: RESULTS AND DISCUSSION
4.1. Preliminary Results and Discussions 57
4.2. Black Cotton Soil Treatment and Desiccation Results and Analysis 58
4.3. Multi linear Regression Model 66
4.3.1. MLR predictive models for bulk density, crack width, linear,
shrinkage and volumetric shrinkage 73
4.4. Scanning Electron Microscopy and X-Ray, Diffraction Tests Results 76
CHAPTER 5: CONCLUSION AND RECOMMENDATION
5.1. Conclusion 84
5.2. Recommendation 86
References 87
Appendices 92
LIST OF TABLES
Table 4.1: Summary of the basic properties of the BCS 58
4.2 Table 4.2.1: Desiccation tests results of the untreated black
cotton soil 59
4.2 Table 4.2.2 Desiccation tests results of the 3% -hybrid saw dust ash treated black cotton soil 60
4.2 Table 4.2.3: Desiccation tests results of 6% -Hybrid Saw Dust
Ash Treated Black Cotton Soil 61
4.2 Table 4.2.4: Desiccation tests results of the 9%- hybrid saw dust ash treated black cotton soil 62
4.2 Table 4.2.5: Desiccation tests of the 12%- hybrid saw dust ash
treated black cotton soil 63
4.3 Table 4.3.1: The used database 67
4.3 Table 4.3.2: Statistical analysis of collected database of parameters 71
4.3 Table 4.3.3: Pearson correlation matrix of parameters 71
4.3 Table 4.3.4: Performance accuracies of the developed models 76
LIST OF FIGURES
3.1. Location Maps for soil collection 24
3.2. Formulation for activator for NaOH(aq) – NaSiO 26
3.3. HSDA-treated specimen extrusion and measurement 27
3.4 HSDA-treated compacted and extruded specimens oven drying at 102oC 28
3.5 HSDA treated black cotton soil crack development under drying at 102oC 28
3.6. Liquid limit apparatus 38
3.7 Grooving tools 40
3.8 Closing of groove 41
3.9 Principle of X-ray diffraction analysis- 47
3.10. XRD spectrometer 48
3.11 A schematic diagram of micro-focused XRF
equipment 55
4.2 Figure 4.2.2: Weight of Specimen showing Desiccation properties of 0% & 12% 64
4.2 Figure 4.2.3: Crack Width showing Desiccation properties of 0% & 12%68 65
4.2 Figure 4.2.4: Volumetric Shrinkage showing Desiccation properties of 0% & 12% - 65
4.2 Figure 4.2.5: Linear Shrinkage showing Desiccation properties
of 0% & 12% 66
4.3 Figure 4.3.1 Distribution histograms for input (in blue) and outputs (in green) 72
4.3 Figure 4.3.2 Relation between predicted and calculated (BD) values using the developed MLR models 74
4.3 Figure 4.3.3 Relation between predicted and calculated (CW) values using the developed MLR models 74
4.3 Figure 4.3.4 Relation between predicted and calculated (LS) values using the developed MLR models 75
4.3 Figure 4.3.5 Relation between predicted and calculated (VS) values using the developed MLR models 75
4.4 Figure 4.4.1 Micropores configuration of BCS, NaOH, and HSDA-treated BCS 77
4.4 Figure 4.4.2 Micro-spectral/micrographs of untreated BCS 55 wt % Kaolinite and 50 wt % Quartz 79
4.4 Figure 4.4.3 Micro-spectral/micrographs of NaSiO2 26 wt %
scapolite, 27 wt % Quartz, 15 wt % Nahcolite, and 16 wt % Alum-(Na) 79
4.4 Figure 4.4.4 Micro-spectral/micrographs of NaOH 2 wt % Natrolite 80
4.4 Figure 4.4.5 Micro-spectral/micrographs of SDA 64 wt % Calcite, 11 wt % Quartz, and 29 wt % Lime 80
4.4 Figure 4.4.6 Micro-spectral/micrographs of HSDA 73 wt % Calcite, 54 wt % Quartz, and 25 wt % Dolomite 81
4.4 Figure 4.4.7 Micro-spectral/micrographs of 3 wt % HSDA treated BCS; 64 wt % Quartz, and 51 wt % Kaolinite 81
4.4 Figure 4.4.8 Micro-spectral/micrographs of 6 wt % HSDA treated BCS; 55 wt % Quartz, and 38 wt % Kaolinite 82
4.4 Figure 4.4.9 Micro-spectral/micrographs of 9 wt % HSDA treated BCS; 47 wt % Quartz, and 46 wt % Kaolinite 82
4.4 Figure 4.4.10 Micro-spectral/micrographs of 12 wt % HSDA treated BCS; 74 wt % Quartz, and 41 wt % Kaolinite, 17 wt % Goethite, and 8 wt % Calcite 83
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF STUDY
Desiccation is a state or process of extreme dryness. It usually comes with cracks and shrinkage of the soil. Loss of water from the soil causes desiccation cracks on the surface of the soil and this is a common phenomenon in nature. To a large extent, how the soil behaves during desiccation affects the performance of soil in various geotechnical, geological and environmental applications.
According to (Morris et al. 1992), the presence of cracks in soils would generally increase the compressibility and reduce the overall mechanical strength. Cherktkov (2000), is of the opinion that the hydraulic properties of soils are influenced directly by crack networks in soil. Similarly, other researchers have found that, the hydraulic conductivity of cracked soils is typically several orders of magnitude greater than that of uncracked soil (Albrecht et al. 2001).
Desiccation is therefore a serious issue to tackle when designing and constructing low permeable structures like clay buffers and barriers for nuclear waste isolation, liners and covers for landfill, etc. Desiccation cracking is mainly due to water loss by evaporation which results in the generation of soil suction. Cracking is likely to occur if the surface tensile stress induced by increasing suction exceeded the bonding strength of soil grains (Corte et al. 1960).
However, when the soil is not dried but very soft, it also poses difficulties working on it. In such case the soil will have to be modified to attain the required properties that will enable it
to be worked upon and the engineer therefore resort to soil stabilization admixtures that could reduce the moisture content of the soil and equally reduce the level of desiccation or dehydration to a level that can allow the soil to be worked with or worked on.
Given the expansion of cities towards the limited available lands, most of these available lands are dominated by clay or expansive or lateritic soils which often cause problems to construction as a result of its swelling nature when wet and shrinkage/cracks when dry, and in some cases these areas are waterlogged. As this may adversely affect structures founded upon them or constructed of them (Shawl et al. 2017). There is need to control the moisture content of such soils to make it suitable, to be able to work on such soils for the proposed project.
According to (Shawl et al. 2017), soils containing large quantities of clay and silt are the most burdensome to the engineer. These materials exhibit marked changes in physical properties with changes in water content, a hard, dry clay, for example. This may be suitable as a foundation for heavy loads so long as it remains dry, but it may become unstable when wet whereas many of the fine soils shrink on drying and expand on wetting. Also, this may negatively affect structures founded upon them. Even when the water content does not change, the properties of fine soils may vary significantly askatcn their natural condition in the ground and their state after being disturbed.
For any construction to take place in such soils, the engineer is left with the option of making the soil suitable for the intended job having in mind the safety, quality, economical aspect etc. This is to achieve the desired goals but most times the rate at which the same soils dried up, also poses difficulties working on them.
Soils are stabilized either by compaction or use of admixtures (lime and cement) to improve the strength and durability of such soils in a bid to make the soil desirable for any construction. Especially for pavement foundation, it is imperative to keep the soil desiccated to a certain level and this could be achieved when saw dust ash is introduced to the soil to replace cement in controlled percentages.
According to A. Sabbat, and S. Pati, (2014), recently, the use of solid waste is being practiced everywhere to improve different types of soils to suit its differing requirement. Similarly, the use of biomass ashes emanating from agricultural sources in modifying soil has been a welcomed development in civil engineering practice.
Saw Dust Ash (SDA) or wood dust is one of such Agricultural waste that has found wide application in the manufacture of concrete and not long ago, it has been used in the stabilization of clay soils. Different works were carried out on the use of SDA either alone or combined with primary binders on the various geotechnical properties of soil (Shawl et al. 2017).
(Butt et al. 2016) and (Raheem et al. 2012) showed SDA as a pozollanic substance because of its siliceous content. As such SDA will work better when combined with primary binder instead of using it alone to stabilize soils. It is clear that researchers have adopted SDA in stabilizing soils mainly as a stand-alone stabilizer and get good results.
But using SDA, one is likely to face the problem of what quantity or percentage of SDA can be used be it alone or in combination with other binders in stabilizing a particular soil in order to achieve the required properties that could be sufficient to make the soil suitable for the proposed construction job.
Therefore, this study is aimed at determining the volume that could be used to estimate the percentage of HSDA that can be needed in a clay soil to modify its properties without losing it bearing capacity while maintaining adequate moisture in the soil and at a minimal cost.
When there is a reduction in the soil’s moisture content during desiccation, the soil will shrink as air penetrates into the soil pores thereby increasing the soil matrix suction and causes the formation of tensile stress to be restrained. The formation of desiccation can affect the permeability and compressibility of the soil as well as it strength. As the soil re-hydrate after a period of desiccation, it will swell resulting in ground heave. This off and on circulation of water into the soil causes instability of the earth slopes and also causes cracks on structures leading to foundation failures.
In soft clayey soils, Saw Dust Ash (SDA) can be used in place of cement either completely or partially to reduce the clayey content in such soils during road construction and still maintaining the safety, durability of the road at a minimized cost. Reducing the cost of construction and lengthening pavement life can help in maintaining the road network. (Shawl et al. 2017).
It is therefore necessary to generate a means of controlling the moisture content of the soil and observe the behaviour of the soil when treated with HSDA either to reduce the clay content or maintain a proper level of desiccation within the soil for it to be worked upon.
If the moisture of the soil is not controlled, dehydration becomes a problem in clay soils mostly in dry season. It is on this note that this work will be carried out on various controlled percentages of Saw Dust Ash that could be used to stabilize clay soil to give it the required properties.
1.2. STATEMENT OF THE PROBLEM
Saw Dust Ash has been found to possess some characteristics that makes it function like cement when converted to ashes and used to stabilize clay or lateritic soils, but not much has been said about the behaviour of the Saw Dust Ash treated soils used in place of cement, whether the addition of SDA to soils, causes total or partial desiccation of the soil layers or not. And nothing has been done to guide the users on the percentages of SDA to be used to achieve the required soil properties without always going through the regular laboratory practical before commencing the project at hand.
Even though the use of SDA as a soil modifying agent has been confirmed to yield good results, the addition of SDA in huge quantity to the soil may trigger desiccation in such soils. After desiccation has taken place, if re-hydration takes place in such soil, the soil can swell which will bring about ground heave and in the end causes damages to foundation.
1.3. AIMS AND OBJECTIVES
Aim
The aim is to study the effect of desiccation on Hybrid Sawdust Ash (HSDA) Treated black cotton soil for pavement foundation.
Objectives
The objectives are;
a. To prepare Hybrid Saw Dust Ash by combining 8M of sodium hydroxide (NaOH) solution and sodium silicate (NaSiO2) to create an activator.
b. To characterize the Lateritic soil, Saw Dust Ash (SDA) and the Hybrid Saw Dust Ash.
c. To conduct scanning electron microscopy, x-ray fluorescence and x-ray diffraction test which studies the microstructure of the Hybrid Saw Dust Ash treated soil.
d. Evaluating the volumetric shrinkage, linear shrinkage and crack width potential of the hybrid saw dust ash treated soil.
e. Modelling of the volumetric shrinkage, linear shrinkage and crack width using Artificial Intelligence.
1.4. SIGNIFICANCE OF THE STUDY
It has been noted that the use of SDA in place of cement or lime in road construction can reduce the cost by about 30 to 50%, increase structural integrity, loading capacity, and life of road. This work will make it easier and saves time in estimating the percentage of HSDA that should be added to the clay soil to be able to control the soil’s moisture content, prevent or reduce total desiccation and still achieve the required properties that is desirable to stabilize the soil without always going through laboratory experiment to enable the engineer to estimate the proper percentage of HSDA needed.
1.5. SCOPE OF THE STUDY
This research will focus on material characterization and the desiccation of Black Cotton soils that are treated with HSDA, their behaviours when used for soil stabilization. In order to achieve the above the following tests will be conducted under laboratory condition; sieve analysis, compaction, Atterberg limits, California Bearing Ratio (CBR), Unconfined Compression Test (UCS), linear and volumetric shrinkage, and Cracking, X-ray Diffraction, x-ray florescence and scanning electron Microscopy.
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