Title Page

Contents

SUMMARY 23

CHAPTER 1. INTRODUCTION 28

1.1. Background 28

1.2. Scope 29

CHAPTER 2. EVALUATION OF ELASTIC WAVES PROPAGATING THROUGH CONTROLLED LOW-STREGNTH MATERIALS 32

2.1. Introduction 32

2.2. Experimental Studies 33

2.2.1. Material 33

2.2.2. Specimen Preparation and Properties 34

2.2.3. Embedded Piezoelectric Transducers 35

2.2.4. Test Setup for Wave Measurement 36

2.3. Experimental Results 38

2.3.1. Compressional and Shear Waves 38

2.3.2. Frequency Analysis 39

2.4. Discussion 40

2.4.1. Comparison between Compressional and Shear Wave Velocities 40

2.4.2. Connectivity of Particles 42

2.4.3. Boundary Effect 44

2.5. Conclusions 47

CHAPTER 3. SIZE EFFECT OF ALUMINUM CHIPS IN CHEMICALLY-INDUCED FOAM CEMENT 64

3.1. Introduction 64

3.2. Experimental Study 66

3.2.1. Tested Materials 66

3.2.2. Sample Preparation and Experimental Procedure 66

3.3. Experimental Results 69

3.3.1. Volume Expansion with Time 69

3.3.2. Terminal Volume Expansion 70

3.3.3. Pore Size Distribution - Aluminum Chip Size 72

3.3.4. Pressure Response 73

3.4. Analyses and Discussion 75

3.4.1. Pressure Prediction 75

3.4.2. Emerging Gas Bubbles - Pore Formation and Evolution 76

3.5. Conclusions 79

CHAPTER 4. EVALUATION OF VOLUMETRIC, STRENGTH AND STIFFNESS CHARACTERISTICS OF EXPANDABLE FOAM GROUT 92

4.1. Introduction 92

4.2. Expandable Foam Grout 94

4.2.1. Materials 94

4.2.2. Foaming Mechanism 95

4.2.3. Mixing Process 96

4.2.4. Hydrogen Gas Pressure 97

4.3. Experimental Setup 98

4.3.1. Flow Test 98

4.3.2. Expansion Test 98

4.3.3. Unconfined Compressive Test 99

4.3.4. X-ray Computed Tomography (CT) Imaging 99

4.3.5. Elastic Wave Measurements 101

4.3.6. Electrical Resistivity Monitoring 102

4.4. Experimental Results 104

4.4.1. Flowability 104

4.4.2. Volumetric Change 104

4.4.3. Stress-strain Curves 106

4.4.4. Pore Distribution 107

4.4.5. Elastic Wave Velocities 108

4.4.6. Electrical Resistivity 109

4.5. Analyses and Discussion 110

4.5.1. Air Bubble Generation 110

4.5.2. Electrical Resistivity during Expansion 112

4.5.3. Wave-based Estimations 113

4.5.4. Resistivity-based Estimations 118

4.5. Summary and Conclusions 120

CHAPTER 5. EVALUATION OF STRENGTH AND STIFFNESS OF EXPANDABLE FOAM GROUT USING UNCONFINED COMPRESION APPARATUS 148

5.1. Introduction 148

5.2. Expandable Foam Grout 151

5.2.1. Materials 151

5.2.2. Mix Design 152

5.3. Experimental Setup 153

5.3.1. Flowability 153

5.3.2. Unit Weight 154

5.3.3. Unconfined Compressive Test 155

5.4. Results and Discussion 156

5.4.1. Flowability 156

5.4.2. Air Contents and Expansion Ratio 157

5.4.3. Unconfined Compressive Strength and Elastic Modulus 159

5.5. Summary and Conclusions 166

CHAPTER 6. EVALUATION OF INTERFACIAL CHARACTERISTICS BETWEEN SOILS AND CONTROLLED LOW-STRENGTH MATERIALS USING DIRECT SHEAR APPARATUS 186

6.1. Introduction 186

6.2. Matenals 187

6.2.1. Controlled Low-strength Material (CLSM) 187

6.2.2. Soils 189

6.3. Direct Shear Test 189

6.3.1. Test Condition 189

6.3.2. Sand-CLSM Interface 190

6.3.3. Weathered Soil-CLSM Interface 191

6.4. Analyses and Discussion 192

6.4.1. Peak Shear Stress 193

6.4.2. Maximum Dilation 194

6.4.3. Maximum Contraction 195

6.4.4. Friction Angle 195

6.5. Summary and Conclusions 197

CHAPTER 7. EVALUATION OF INTERFACIAL CHARACTERISTICS BETWEEN SOILS AND EXPANDABLE FOAM GROUT USING DIRECT SHEAR APPARATUS 216

7.1. Introduction 216

7.2. Materials 218

7.2.1. Expandable Foam Grout (EFG) 218

7.2.2. Soils 219

7.3. Direct Shear Tests 220

7.4. Shear Stress-displacement Behavior 222

7.4.1. Expandable Foam Grout 222

7.4.2. Interface between EFG and Poorly Graded Sand 223

7.4.3. Interface between EFG and Well Graded Sand 224

7.5. Shear Strength and Interface Friction Characteristics 225

7.5.1. Expandable Foam Grout 225

7.5.2. Interface between EFG and Poorly Graded Sand 226

7.5.3. Interface between EFG and Well Graded Sand 227

7.5.4. Comparisons 227

7.6. Summary and Conclusions 229

CHAPTER 8. SUMMARY AND CONCLUSIONS 249

REFERENCES 259

VITA 281

List of Tables

Table 2.1. Grading properties for fines aggregate. 49

Table 2.2. Mixed proportion by weight for CLSM. 50

Table 2.3. Properties of CLSM mixtures. 51

Table 2.4. Summary of the coefficients of the relationship between shear wave velocities and time. 52

Table 3.1. Sample preparation - Mass-based mixing ratios for cement paste mixtures. 82

Table 4.1. Chemical components of the ordinary Portland cement and admixture used in this study with comparison to bentonite. 122

Table 4.2. Dynamic properties of the EFG with the curing time. 123

Table 5.1. Chemical components of admixture and bentonite. 168

Table 5.2. Mix proportion of EFG. 169

Table 5.3. Model parameters for the relationship between imconfined compressive strength and curing time at different admixture-cement ratios. 170

Table 5.4. Model parameters for the relationship between elastic modulus and curing time at different admixture-cement ratios. 171

Table 5.5. Model parameters for the relationship between miconfined compressive strength and admixture-cement ratio on each curing time. 172

Table 5.6. Model parameters for the relationship between elastic modulus and admixture-cement ratio for each curing time. 173

Table 6.1. Chemical compositions of the CSA cement and fly ash. 199

Table 6.2. Mixed proportion by weight of the CLSM. 200

Table 6.3. Interface friction angles and coefficient of determination with curing time. 201

Table 6.4. Summary of the parameters of the friction angle models with curing time. 202

Table 7.1. Index properties of sands. 232

Table 7.2. Test plans for first and second mode direct shear tests. 233

Table 7.3. Friction angles and cohesions for EFG with curing time in 1st mode direct shear tests. 234

Table 7.4. Friction angles and coefficient of determinant for EFG-poorly graded sand interface with curing time in 2nd mode direct shear tests. 235

Table 7.5. Internal friction angles of sands. 236

Table 7.6. Friction angles for EFG-well graded sand interface at three different densities in 2nd mode direct shear tests. 237

List of Figures

Figure 2.1. Schematic drawings of embedded transducers: (a) piezo disk element; (b) bender element. The unit is millimeters. 53

Figure 2.2. Schematic drawings for test set-up: (a) side view of the container; (b) top view of the container and the measurement system for elastic waves. The BE and... 54

Figure 2.3. Compressional wave signals according to fine contents: (a) FC ＝ 10%; (b) FC ＝ 50%; (c) FC ＝ 90%. The inverted triangles denote the estimated first arrival times. 55

Figure 2.4. Shear wave signals by square input according to fine contents: (a) FC ＝ 10%; (b) FC ＝ 50%; (c) FC ＝ 90%. 56

Figure 2.5. Frequency response curves of shear waves in case of fine contents of 50%: (a) 1 h; (b) 6 h; (c) 24 h; (d) 72 h. The inverted triangles denote the estimated... 57

Figure 2.6. Resonant frequency of shear waves estimated from the received signals by BEs. 58

Figure 2.7. Shear wave signals by sinusoidal input with resonant frequency according to fine contents: (a) FC ＝ 10%; (b) FC ＝ 50%; (c) FC ＝ 90%. The inverted triangles denote the estimated first arrival times. 59

Figure 2.8. Evolution of compressional (Vp) and shear (Vs) wave velocities: (a) up to 72 h; (b) up to 12 h.[이미지참조] 60

Figure 2.9. Variation in shear wave velocities according to fine content, x- and y-axes are scaled logarithmically. 61

Figure 2.10. Interference of compressional and shear waves: (a) travel paths of waves in the container; (b) critical boundary width (bc) estimated by wave velocities. 62

Figure 2.11. Shear waves selected in case of fine contents of 50%. The bc₁ and bc₂ denote the travel times of compressional waves reflected at short and long... 63

Figure 3.1. Scanning electron microscope SEM images for aluminum chips with different sizes. Table summarizes the aluminum content estimated from energy-dispersive X-ray spectroscopy EDS. 83

Figure 3.2. Normalized volume expansion versus elapsed time. (a) Cement-water-aluminum mixtures for different aluminum mass ratios. Mixtures: aluminum mean grain size d₅₀＝0.29 mm; (b) Cement-water-aluminum-bentonite mixtures for five different bentonite mass ratios.... 84

Figure 3.3. Normalized terminal volume expansion VT/Vo after 24 hours in terms of initial mixture volume at time t ＝ 0. (a) Cement-water-aluminum mixtures for different aluminum mass ratios FAl with two mixing methods (stirring and shaking); (b) Cement-water-almninum-...[이미지참조] 85

Figure 3.4. X-ray CT images and normalized cumulative pore size distributions extracted from the CT images for cement-water-alumimim-bentonite specimens... 86

Figure 3.5. Pressure using gram of pure aluminum for the cement-water-aluminum specimens with five different aluminum mean grain sizes d₅₀. All mixtures: water-... 87

Figure 3.6. Terminal pressure PT per gram of aluminum versus aluminum mean grain size d₅₀. The black dotted line indicates a model that anticipates the terminal pressure...[이미지참조] 88

Figure 3.7. Normalized volume expansion versus elapsed time in a closed system. The normalized volume expansion Vt/Vo is normalized mixture volume at a given...[이미지참조] 89

Figure 3.8. Time-lapse CT images during pore formation and evolution in a cement-water-aluminum-bentonite specimen. Mixture: water-cement ratio Mwater/Mcement＝ 100%, aluminum mass ratio MAl/Mcement＝ 4%, and bentonite mass ratio Mbent/Mcement＝ 8%, and aluminum chip...[이미지참조] 90

Figure 3.9. Conceptual drawing of volume expansion mechanisms in a gassy cement mixture. 91

Figure 4.1. X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDS) results for the admixture: (a) XRD, (b) EDS for silicate (SiO₂), and (c) EDS for... 124

Figure 4.2. Foaming procedure of aluminum: (a) Al in air, (b) Al2O3 film under alkali conditions, and (c) Al under alkali conditions. 125

Figure 4.3. Expansion ratio of EFG with diflferent admixture contents. 126

Figure 4.4. Variation of hydrogen gas pressure generated from the EFG with respect to curing time. 127

Figure 4.5. X-ray CT images: (a) original, (b) contrast-enhanced, (c) cropped, and (d) binary. 128

Figure 4.6. Schematic drawing of the measurement system for the elastic waves and electrical resistivity. 129

Figure 4.7. Relationship between the resistivity (res) and electrical resistance (Rc).[이미지참조] 130

Figure 4.8. Temperature effect on the electrical resistance at res ＝ 2 Ω·m.[이미지참조] 131

Figure 4.9. Expansion test results with the curing time. 132

Figure 4.10. Unit weight with the curing time. 133

Figure 4.11. Stress-strain curves with the curing time. 134

Figure 4.12. Results of the unconfined compressive tests with the curing time: (a) static elastic modulus and (b) unconfmed compressive strength. 135

Figure 4.13. Binary images along the height and with the curing time. H indicates the height from the bottom of the cell. Note that the diameter of all specimen are 30 mm. 136

Figure 4.14. Porosity distribution with the curing time. 137

Figure 4.15. Typical waveforms with the curing time for (a) compressional waves and (b) shear waves. The ▲ mark denotes the first arrival of the compressional or shear wave. 138

Figure 4.16. Compressional and shear wave velocities with the curing time. 139

Figure 4.17. Electrical resistivity with the curing time up to (a) 24 h and (b) 30 d. 140

Figure 4.18. Resistivity, temperature, and expansion ratio with the curing time at early ages. 141

Figure 4.19. Relationship between the unconfined compressive strength and wave velocities. 142

Figure 4.20. Relationship between the unconfined compressive strength and dynamic moduli. The lines denote the exponential functions for dynamic moduli. 143

Figure 4.21. Relationship between the static elastic modulus and the (a) elastic-wave velocities and (b) dynamic moduli. The lines denote the exponential and linear... 144

Figure 4.22. Poisson's ratio estimated from the elastic wave velocities. 145

Figure 4.23. Relationships between the electrical resistivity and either the static elastic modulus (Es) or unconfined compressive strength (fc).[이미지참조] 146

Figure 4.24. Relationship between the dynamic moduli and electrical resistivity. The lines denote the exponential functions for dynamic moduli. 147

Figure 5.1. Energy dispersive x-ray spectroscopy spectrum for a particle in admixture. Ca, O, Na, Al, and Si indicate calcium, oxygen, sodium, aluminum, and silicon, respectively. 174

Figure 5.2. Procedure of flow test: (a) filling a cylindrical mold with the mixture; (b) removing the mixture surrounding the mold; (c) lifting up the mold. 175

Figure 5.3. Variation in flow consistencies of EFG with respect to admixture-cement ratio. 176

Figure 5.4. Variation in unit weights of EFG with respect to admixture-cement ratio. 177

Figure 5.5. Variation in material properties calculated from the unit weights with respect to admixture-cement ratio: (a) air contents; (b) theoretical expansion ratio. 178

Figure 5.6. Stress-strain curves with respect to admixture-cement ratio at 28 d of curing. 179

Figure 5.7. Wriation of unconfined compressive strength with respect to curing time. AD/C denotes the admixture-cement ratio. 180

Figure 5.8. Variation of coefficient α with respect to admixture-cement ratio. 181

Figure 5.9. Variation of modulus of elasticity with respect to curing time. AD/C denotes admixture-cement ratio. 182

Figure 5.10. Variation of coefficient c with respect to admixture-cement ratio. 183

Figure 5.11. Variation in EFG properties with respect to admixture-cement ratio: (a) unconfined compressive strength; (b) modulus of elasticity. 184

Figure 5.12. Relationship between measured and estimated engineering properties: (a) unconfined compressive strength; (b) modulus of elasticity. 185

Figure 6.1. Pictures of the CLSM for: (a) flow test; (b) unconfined compressive strength test. 203

Figure 6.2. Properties of the CLSM along the curing time: (a) unit weight; (b) compressive strength. 204

Figure 6.3. Grain size distribution curves of the two soil types used in this study. 205

Figure 6.4. Schematic drawings of the direct shear test for evaluating the interface friction between the CLSM and soils: (a) side view; (b) plane view of the lower box. 206

Figure 6.5. Shear stress curves for the sand-CLSM specimens during shearing on: (a) 0.5 day; (b) 1 day; (c) 3 days; (d) 7 days, σn denotes the normal stress applied on the...[이미지참조] 207

Figure 6.6. Normal displacement curves for the sand-CLSM specimens during shearing on: (a) 0.5 day; (b) 1 day; (c) 3 days; (d) 7 days. ▼ indicates the... 208

Figure 6.7. Direct shear test results for the weathered soil-CLSM specimens during shearing on 3 days: (a) shear stress; (b) normal displacement. 209

Figure 6.8. Example of determination of peak shear stress in the sand-CLSM specimen on 7 days: (a) shear stress, (b) normal stress; (c) stress ratio. 210

Figure 6.9. Peak stresses along the curing time under three different normal stresses of: (a) 25 kPa; (b) 50 kPa; (c) 100 kPa. 211

Figure 6.10. Maximum dilation of the sand-CLSM specimens during shearing under two different normal stresses. 212

Figure 6.11. Maximum contraction under three different normal stresses: (a) sand-CLSM specimens; (b) weathered soil-CLSM specimens. 213

Figure 6.12. Peak shear versus normal stresses on 0.5 day. 214

Figure 6.13. Variation of friction angles along the curing time. 215

Figure 7.1. Images of expandable foam grout with curing time. 238

Figure 7.2. Particle size distribution curves for two sands used in this study. 239

Figure 7.3. Schematic drawing of direct shear testing apparatus with test specimens: (a) direct shear testing apparatus; (b) EFG (first mode) specimen; (c) EFG-sand... 240

Figure 7.4. Shear stresses of EFG at different curing time in 1st mode direct shear tests: (a) 3 days; (b) 28 days, σn indicates the normal stress. 241

Figure 7.5. Shear stresses at EFG-poorly graded sand interface at different curing times in 2nd mode direct shear tests: (a) 3 days; (b) 30 days. 242

Figure 7.6. Shear stresses at EFG-well graded sand interface at 3 days with different unit weights in 2nd mode direct shear tests: (a) 15.5 kN/㎥; (b) 16.5 kN/㎥; (c) 17.4kN/㎥. 243

Figure 7.7. Shear strength versus normal stress in the EFG at different curing times in 1st mode direct shear tests. The dashed lines indicate the linear Mohr-Coulomb... 244

Figure 7.8. Shear strength versus normal stress at EFG-poorly graded sand interface at different curing times in 2nd mode direct shear tests. The dotted line indicates a... 245

Figure 7.9. Shear strength versus normal stress at EFG-well graded sand interfece at different curing times in 2nd mode direct shear tests: (a) 3 days; (b) 7 days. 246

Figure 7.10. Variation of friction angles with curing time. 247

Figure 7.11. Images of shear planes of EFG specimens after curing time of 14 days in 2nd mode direct shear tests: (a) before shearing; (b) after shearing under σ＝35kPa;... 248

This research explores characteristics of high flowable and cementitious materials, such as controlled low-strength materials (CLSMs) and expandable foam grout (EFG), which are suitable materials to fill underground cavities considering the condition in urban areas. For the CLSMs, an elastic wave measurement system is designed to monitor their hydration process. For the EFG, various engineering properties are evaluated to consider implications by chemical reaction in cement paste containing aluminum chips. Direct shear tests are performed to evaluate shear strength and behavior at interface of underground cavities filled with both materials.

For the evaluation of elastic wave characteristic of CLSMs, two types of embedded piezoelectric transducers to controlled low-strength material (CLSM) are applied and the elastic wave characteristics are monitored during the hydration process. The CLSM mixture is composed of silica sand, calcium sulfoaluminate cement, fly ash, and water, and then, the CLSM mixture is prepared with three different fine contents. Using piezoelectric disk and bender elements installed in cuboid containers, the compressional and shear waves are measured from hour 1 to hour 74. The monitoring results show that during the hydration process, the evolution of shear wave velocities obtained from the bender element is less variable than that in compressional wave velocities obtained from the piezoelectric disk element. As a power function, the shear wave velocities increase with an increase in the elapsed time. As the fine content of the CLSM mixture increases, the water content required for flowability of the CLSM mixture increases and then the shear wave velocities decreases. The results demonstrate that the high water content of the CLSM mixture less develops the interconnection of the cementitious particles at very early stage of the hydration. The geometric boundary condition of the container is considered as an aspect of the estimation of the shear wave velocity by the bender element. This study demonstrates that the embedded elastic wave transducers may be effectively used for monitoring the hydration process of CLSM.

For the exploration of the effect of aluminum chip sizes on engineered behavior of expandable gassy cements, volume expansion, pressure development, and pore formation and evolution are evaluated. Normalized terminal volume expansion appears to be a function of aluminum mass ratio, bentonite mass ratio, and aluminum chip size. X-ray CT images clearly capture that the finer aluminum chip results in the more significant volume expansion and creates smaller pores. On the other hand, increased chip sizes lead to fracture-like pores; yet, pieces of aluminum chips remain inactive due to the incomplete reaction between hydroxide ions and aluminum chips (aluminum chips for d50 ＝ 0.64 and 2.00 mm). Pressure generated from the chemical reaction depends not only on the aluminum size, but also its purity and mass. Time-lapse CT images clearly show the sequence of internal pore formation and development. Associated phenomena include gas bubble nucleation, individual bubble growth, pore expansion, coalescence, collapse and repetition of overall events. Engineering designs that use chemically-induced gassy cement should consider the mechanisms to prevent gas release and fracture.

For evaluation of the volume, strength, and stiffness of the EFG during curing various testing methods are performed. Flow, expansion, and unconfined compressive tests are conducted to investigate the fundamental material properties of the EFG. X-ray computed tomography is performed to verify the pore distribution of the EFG. Elastic waves and electrical resistivity are monitored to estimate the stiffness and strength characteristics of the EFG. The results show that EFG has high flowability, expanding within four hours depending on the temperature. The X-ray computed tomography images indicate a heterogeneous pore distribution in the EFG. A series of relationships between static and dynamic properties based on the elastic wave velocities and electrical resistivity are established. Furthermore, elastic wave measurement and electrical resistivity monitoring may be useful for estimating the volume, strength, and stiffness characteristics during curing.

To evaluate the strength and stiffness of expandable foam grout (EFG) as a repair material, the unconfined compressive strength tests are performed. EFG consists of water, ordinary Portland cement, and admixtures. EFG was prepared at a fixed water-cement ratio of 100% and different admixture-cement ratios (AD/Cs), ranging from 0 to 8%. The unit weights of EFGs with different AD/Cs at the slurry and expanded states are measured, and the air contents for both states and the theoretical expansion ratio (ER) are subsequently estimated. Stress-strain curves are obtained using unconfined compressive strength tests to evaluate the unconfined compressive strength and modulus of elasticity. The experimental results show that the air content in the slurry state gradually increases with the AD/C, while the air content in the expanded state and the ER rapidly increased and then converges. The strength and modulus of elasticity increased with curing time, whereas they decreased with increasing AD/C. Based on logarithmic and exponential regression models, the relationships between the strength/modulus, curing time, and AD/C are established with high values of the coefficients of determination. Thus, the relationships proposed in this study can be effectively used to predict the strength and modulus of EFG with respect to curing time and AD/C.

For assessment of the interface friction characteristics between the CLSM and soils based on curing time, gradation, and normal stress, the direct shear test apparatus is used. The CLSM is composed of fly ash, calcium sulfoaluminate cement, sand, silt, water, and accelerator. To investigate the engineering properties of the CLSM, flow and unconfined compressive strength tests are performed. Poorly and well graded sands are selected as the in-situ soil in combination with the CLSM. The direct shear tests of the CLSM and soils are performed under three normal stresses for four different curing times. The test results show that the shear strengths obtained within 1 day are higher than those obtained after 1 day. As the curing time increases, the maximum dilation of the poorly graded sand-CLSM specimens under lower normal stresses also generally increases. The maximum contraction increases with increasing normal stress, but it decreases with increasing curing time. The shear strengths of the well graded sand-CLSM interface are greater than those of the poorly graded sand-CLSM interface. Moreover, the friction angle for the CLSM-soil interface decreases with increasing curing time, and the friction angles of the well graded sand-CLSM interface are greater than those of the poorly graded sand-CLSM interface. The results suggest that the CLSM may be effectively used for trench backfilling owing to a better understanding of the interface shear strength and behavior between the CLSM and soils.

To investigate the shear strength characteristics of expandable foam grout (EFG) and the interface between EFG and two types of sands, a series of direct shear tests is conducted using EFG specimens prepared under different conditions of curing time and unit weights of sand. After three days of curing, the shear stress curves of EFG and EFG-sand interface obtained at three normal stresses indicate brittle behavior and ductile behavior, respectively. Friction angles of the EFG increase with curing time, while those of the EFG-sand interface remain almost constant. The interface friction angles between the EFG and sands are smaller than or equal to the internal friction angles of the sands. Therefore, the shear strength of the EFG-surrounding soil interface should be given more attention than the high shear strength of the EFG, to fill underground cavities.