@phdthesis{oai:sucra.repo.nii.ac.jp:00019700,
 author = {JOSHI, NIRMAL RAJ},
 month = {},
 note = {xvi, 205p, In many countries, severe deterioration of concrete structures has been observed instigated by expansion related to alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF). The past studies on ASR and DEF are mainly focused on the chemical and material aspects which have laid the ground for the formulation of various codes and guidelines. As a result, ASR and DEF can generally be avoided in the new construction. However, the safety and serviceability evaluation of the structures that have been infected remains dubious due to a lack of understanding of the mechanical behaviour of affected concrete. To address this gap of understanding, a study was initiated to carry out various laboratory experiments and numerical analysis related to change in the mechanical properties caused by expanding concrete.

 In the first part of the study, experiments were done to understand the interaction between restraints and DEF/ASR expansion. The external restraint could reduce the expansion by up to 45% while at the same time, restraining steel experienced stress of up to 132 N/mm². It was noticed that despite having a larger free expansion, the stress instigated by combined DEF and ASR (DA) expansion remained lower than due to DEF in restrained cases. Similar behaviour was found in reinforced concrete in which an internal restraint was provided by rebar. The rebar experienced a tensile strain of up to 0.05%, after which the strain gradually reduced indicating a deterioration of interface between concrete and rebar.

 To check the change in the bond due to expansion, a pullout test was conducted. The pullout strength slightly improved when expansion was small which is ascribed to the pre-stressing effect caused by the confinement from shear and main rebars. The large expansion deteriorated the pullout strength to about 60% of the original. After an expansion of about 0.5%, there was no significant drop in the pullout strength even though the compressive strength was reduced to 20% which indicated that the pullout strength is not directly related to the compressive strength.

 A small expansion in the ASR specimen improved the compressive strength. The dynamic Young’s modulus, however, deteriorated even at small expansion. This indicated that even though there is an increase in load capacity, there could be a larger deflection of structure that is affected by ASR. DEF and DA specimens had a larger expansion, and such effects were not observed. Their bond and compressive strength decreased rapidly with expansion. The expanded concrete also showed a large plastic strain which was attributed to the closing of pre-existing gaps in the direction of loading by X-ray CT. The failure of the highly expanded concrete was caused by the opening of cracks in the direction perpendicular to the loading.

 In the second part of the dissertation, a numerical modelling approach is proposed that can be used to evaluate the structural performance of expanding concrete. The model is a combination of Mazar’s model of concrete damage and the time-dependent expansion model of Larvae. The expansion-dependent variables such as the peak strength and elastic modulus were treated as a Gaussian function. The numerical model was implemented in Code Aster for FEM analysis. The model was fairly accurate at the lower expansion but at larger expansion, there was some deviation. The model needs to be further calibrated and fine-tuned to get better results.
 
 A numerical study was also done to highlight the effect of expansive concrete on the serviceability of a massive dam. This study is based on the work of previous researchers who had identified ASR expansion in the dam based on the petrographic analysis and had conducted a time-dependent FEM simulation. This study enhanced the previous study by incorporating probabilistic approaches for the prediction of dam deflection and stresses. A sensitivity analysis was also carried out to examine the effect of varying ultimate strain and time-dependent variables on dam behaviour. The maximum deflection was predicted to be 54―66 mm towards the upstream direction with a standard deviation of 28 mm at the age of 100 years. The principal stress distribution in the dam showed that it is predominantly in compression and safe against cracking at the current rate of reaction. It was predicted that some cracks may occur in the downstream face if the expansion continues., List of Figures.................................................................................................... vii
List of Tables.................................................................................................... xiii
List of abbreviations and symbols.................................................................................. xiv
1. Introduction...................................................................................................... 1
 1.1. Background..................................................................................................... 1
 1.2. Problem statement.............................................................................................. 3
 1.3. Objectives of research......................................................................................... 5
 1.4. Dissertation outline........................................................................................... 6
2. Literature review................................................................................................. 8
 2.1. A brief history of concrete deterioration...................................................................... 8
 2.2. Alkali-silica reaction......................................................................................... 9
  2.2.1. Factors Influencing ASR.................................................................................... 10
  2.2.2. Test method for ASR........................................................................................ 11
 2.3. Mechanical effect of ASR expansion............................................................................ 12
  2.3.1. Change in compressive strength............................................................................. 14
  2.3.2. Change in tensile strength................................................................................. 16
  2.3.3. Change in bond strength.................................................................................... 16
  2.3.4. Change in modulus of elasticity............................................................................ 17
  2.3.5. Change in shear strength................................................................................... 18
  2.3.6. Change in flexure strength................................................................................. 18
 2.4. Delayed ettringite formation.................................................................................. 18
  2.4.1. Factors influencing DEF.................................................................................... 19
  2.4.2. Test methods for DEF....................................................................................... 21
 2.5. Mechanical effect of DEF expansion............................................................................ 22
  2.5.1. Change in compressive strength............................................................................. 23
  2.5.2. Change in tensile strength................................................................................. 24
  2.5.3. Change in bond strength.................................................................................... 24
  2.5.4. Change of modulus of elasticity............................................................................ 24
  2.5.5. Change in shear capacity................................................................................... 25
  2.5.6. Change in flexure capacity................................................................................. 25
 2.6. Combination of ASR and DEF.................................................................................... 25
 2.7. Evolution of damage and mechanical tests...................................................................... 26
2.8. Numerical modelling of ASR and DEF....................................................................... 27
2.8.1. Numerical modelling of ASR................................................................................. 27
2.8.2. Model description............................................................................................... 27
2.8.3. Numerical modelling of DEF................................................................................. 29
3. Effect of internal restraints on ASR/DEF expansion............................................................... 34
 3.1. Background.................................................................................................... 34
 3.2. Methodology................................................................................................... 34
  3.2.1. Specimen dimension......................................................................................... 34
  3.2.2. Concrete................................................................................................... 35
  3.2.3. Steel...................................................................................................... 37
  3.2.4. Heat treatment for DEF sample.............................................................................. 37
  3.2.5. Measurement................................................................................................ 38
  3.2.6. ASR detection.............................................................................................. 39
 3.3. Results....................................................................................................... 39
  3.3.1. Evolution of strain in concrete............................................................................ 39
  3.3.2. Evolution of strain in steel............................................................................... 40
  3.3.3. Evolution of mass gain..................................................................................... 41
  3.3.4. Evolution of dynamic modulus of elasticity................................................................. 41
  3.3.5. Evolution of cracks........................................................................................ 42
  3.3.6. ASR distribution........................................................................................... 43
 3.4. Discussion.................................................................................................... 44
  3.4.1. Expansion behaviour........................................................................................ 44
  3.4.2. Effect of reinforcement in concrete expansion.............................................................. 44
  3.4.3. Relation between steel and concrete strains................................................................ 45
  3.4.4. Effect of reinforcement in mass gain....................................................................... 47
 3.5. Summary....................................................................................................... 47
4. Effect of external restraints on ASR/DEF expansion............................................................... 48
 4.1. Background.................................................................................................... 48
 4.2. Methodology................................................................................................... 48
  4.2.1. Specimen dimension......................................................................................... 48
  4.2.2. Concrete................................................................................................... 49
  4.2.3. Heat treatment for DEF sample.............................................................................. 50
  4.2.4. Application of restraint................................................................................... 51
  4.2.5. Measurement................................................................................................ 51
 4.3. Results....................................................................................................... 52
  4.3.1. Evolution of strain in the longitudinal direction.......................................................... 52
  4.3.2. Evolution of strain in the lateral direction............................................................... 54
  4.3.3. Evolution of strain in retraining steel.................................................................... 54
  4.3.4. Evolution of cracks........................................................................................ 55
 4.4. Discussion.................................................................................................... 56
  4.4.1. Expansion behaviour........................................................................................ 56
  4.4.2. Interaction between external restraint and concrete expansion.............................................. 57
  4.4.3. Strain from concrete and strain gauge...................................................................... 58
 4.5. Summary....................................................................................................... 60
5. Evolution of bond and compressive strength due to ASR/DEF expansion.............................................. 61
 5.1. Background.................................................................................................... 61
 5.2. Methodology................................................................................................... 61
  5.2.1. Specimen dimension......................................................................................... 61
  5.2.2. Concrete................................................................................................... 62
  5.2.3. Heat treatment for DEF sample.............................................................................. 64
  5.2.4. Conditioning of the specimens.............................................................................. 64
  5.2.5. Measurement................................................................................................ 65
  5.2.6. Strength test.............................................................................................. 66
  5.2.7. Sufficiency of coupler..................................................................................... 67
 5.3. Results....................................................................................................... 68
  5.3.1. Free expansion of cylinders................................................................................ 68
  5.3.2. Expansion in pullout specimens............................................................................. 69
  5.3.3. ASR distribution........................................................................................... 71
  5.3.4. Evolution of compressive strength.......................................................................... 71
  5.3.5. Incremental loading and internal damage.................................................................... 76
  5.3.6. Evolution of bond strength................................................................................. 80
 5.4. Discussion.................................................................................................... 84
  5.4.1. Comparison of the evolution of strain...................................................................... 84
  5.4.2. Interaction of ASR and DEF reaction and expansion mechanism................................................ 86
  5.4.3. Relation between bond strength and compressive strength.................................................... 87
  5.4.4. Relation between expansion and strength.................................................................... 88
  5.4.5. Evolution of damage in the affected concrete............................................................... 90
 5.5. Summary....................................................................................................... 91
6. Investigation in internal damage by X-ray CT..................................................................... 93
 6.1. Methodology................................................................................................... 93
  6.1.1. Specimens.................................................................................................. 93
  6.1.2. Mechanical tests........................................................................................... 94
  6.1.3. X-ray CT scan.............................................................................................. 95
 6.2. Specimen condition before the mechanical test................................................................. 96
 6.3. Measurement of elasticity..................................................................................... 97
 6.4. Crack characterization........................................................................................ 97
  6.4.1. Separation of cracks and air voids......................................................................... 98
  6.4.2. Crack volume............................................................................................... 99
  6.4.3. Crack width................................................................................................ 99
 6.5. Results...................................................................................................... 101
  6.5.1. Stress-strain relationships of concrete with DEF expansion under various compressive loading patterns..... 101
  6.5.2. Crack distribution and propagation after various loading.................................................. 103
  6.5.3. Crack volume and crack size based on X-ray CT scan........................................................ 106
 6.6. Discussion................................................................................................... 111
  6.6.1. Crack propagation......................................................................................... 111
  6.6.2. Distribution of cracks...................................................................................... 111
  6.6.3. Relating SDI and PDI with internal damage................................................................. 112
  6.6.4. Effect of sustained load.................................................................................. 114
  6.6.5. Changes in elasticity..................................................................................... 114
 6.7. Summary...................................................................................................... 115
7. Numerical modelling............................................................................................. 117
 7.1. Background................................................................................................... 117
 7.2. Time dependent expansion model of Larvie..................................................................... 117
 7.3. Strength model of Mazar...................................................................................... 117
  7.3.1. Change in peak strength................................................................................... 120
  7.3.2. Change in Young’s modulus................................................................................ 121
  7.3.3. Change in peak strain..................................................................................... 121
 7.4. Model implementation......................................................................................... 122
 7.5. Application of the model..................................................................................... 122
 7.5.1. Concrete prism with and without steel...................................................................... 122
7.5.2. Compressive strength of concrete cylinders at various ages.................................................. 125
7.5.3. Evolution of loading capacity of DEF affected beam.......................................................... 128
7.6. Summary....................................................................................................... 130
8. Case Study: Structural response of massive structure by internal expansion reaction............................. 132
 8.1. Background................................................................................................... 132
 8.2. Diagnosis of the problem..................................................................................... 133
  8.2.1. Petrographic analysis..................................................................................... 134
  8.2.2. Residual expansion test................................................................................... 137
 8.3. Numerical analysis for time-dependent deformation............................................................ 138
  8.3.1. Model implementation...................................................................................... 138
 8.4. Model calibration............................................................................................ 141
 8.5. Sensitivity analysis......................................................................................... 142
  8.5.1. Effect of elasticity...................................................................................... 142
  8.5.2. Effect of varying monthly temperature..................................................................... 143
  8.5.3. Effect of ambient temperature............................................................................. 144
  8.5.4. Effect of strain.......................................................................................... 146
 8.6. Deflection prediction........................................................................................ 146
 8.7. Crack susceptibility......................................................................................... 148
 8.8. Summary...................................................................................................... 150
9. Conclusion and recommendation................................................................................... 151
 9.1. Part A: Experimental works................................................................................... 151
 9.2. Part B: Numerical modelling for strength and serviceability evaluation....................................... 153
 9.3. Recommendation for future study.............................................................................. 154
References......................................................................................................... 155
Appendix........................................................................................................... 167
 A. Effect of cement type on the free expansion.................................................................... 168
 B. Photographs of specimens of Chapter 3 (Internal restrains)..................................................... 170
 C. Photographs of specimens of Chapter 4 (External restrains)..................................................... 175
 D. Photographs of specimens of Chapter 5 (Bond test).............................................................. 183
 E. Alternate analysis of prism based on random nodes ..............................................................193
 F. Sample script of Code-Aster used in Chapter 8.................................................................. 196
 G. List of some infrastructures infected by internal expansion reaction........................................... 203, 主指導教員 :  浅本晋吾准教授, text, application/pdf},
 school = {埼玉大学},
 title = {Study on mechanical deterioration and structural response due to internal swelling reactions of concrete},
 year = {2021},
 yomi = {ジョシ, ニルマ ラーズ}
}