1 Introduction 1 1.1 Early-age Cracking of Modern Concrete . 1 1.1.1 Significance of Early-age Cracking 1 1.2 Causes of Early-age Cracking 2 1.3 Measures for Controlling Early-age Cracking of Concrete 3 1.3.1 Mitigating the Drop in Internal Relative Humidity . 3 1.3.2 Controlling the Change of Temperature 4 1.3.3 Decreasing the Early-age Shrinkage . 4 1.3.4 Increasing the Tensile Strength . 5 1.4 Objectives and Scope . 6 References 9 2 Techniques and Methods for Evaluating the Early-age Cracking Resistance of Modern Concrete 13 2.1 Introduction . 13 2.2 Early-age Internal Relative Humidity in Concrete . 13 2.2.1 Test Device andMethod . 13 2.2.2 Calculation of Internal Relative Humidity Decrease Rate 15 2.3 Early-age Autogenous Shrinkage . 15 2.3.1 Test Device andMethod . 15 2.3.2 Calculation of Autogenous Shrinkage 16 2.4 Early-age Mechanical Properties . 18 2.4.1 Compressive Strength . 18 2.4.2 Tensile Strength 19 2.4.3 Static Elastic Modulus . 19 2.4.4 Dynamic Elastic Modulus 20 2.4.5 Bond Behavior . 22 2.5 Early-age Tensile Creep . 23 2.5.1 Test Device andMethod . 23 2.5.2 Calculation of Tensile Creep . 26 2.5.3 Calculation of Tensile Creep Coefficient . 27 2.5.4 Calculation of Specific Tensile Creep 27 2.6 Early-age Cracking Resistance Under Circumferential Restrained Condition . 27 2.6.1 Test Device andMethod . 27 2.6.2 Calculation of Residual Stress 30 2.6.3 Calculation of Stress Rate 30 2.6.4 Calculation of Cracking Potential . 31 2.6.5 Calculation of Stress Relaxation 31 2.7 Early-age Cracking Resistance Under Uniaxial Restrained Condition . 34 2.7.1 Test Device andMethod . 34 2.7.2 Calculation of Temperature History . 35 2.7.3 Calculation of Creep 36 2.7.4 Calculation of Cracking Resistance 36 References 37 3 Evaluation on Early-age Cracking Resistance of Concrete . 41 3.1 Introduction . 41 3.2 Internal Relative Humidity in Early-age Concrete . 42 3.2.1 Internal Relative Humidity . 42 3.2.2 Critical Time of Internal Relative Humidity . 44 3.2.3 Internal Relative Humidity Decrease Rate 45 3.2.4 Moisture Diffusion 47 3.2.5 Prediction Models for Internal Relative Humidity 48 3.3 Early-age Cracking Resistance of Concrete with Different Water-to-Cement Ratios Under Circumferential Restrained Condition . 57 3.3.1 Mechanical Properties . 57 3.3.2 Free Shrinkage . 58 3.3.3 Steel Ring Strain . 59 3.3.4 Residual Stress . 60 3.3.5 Stress Relaxation . 61 3.3.6 Cracking Resistance . 64 3.4 Early-age Cracking Resistance of Concrete with Different Water-to-Cement Ratios Under Uniaxial Restrained Condition . 65 3.4.1 Temperature History 65 3.4.2 Autogenous Shrinkage . 67 3.4.3 Restrained Stress . 68 3.4.4 Tensile Creep 71 3.4.5 Cracking Resistance . 73 3.5 Early-age Cracking Resistance of High Performance Concrete with Different Curing Temperatures Under Uniaxial Restrained Condition . 74 Contents ix 3.5.1 Autogenous Shrinkage . 74 3.5.2 Ratio of Stress to Tensile Strength . 82 3.5.3 Cracking Resistance . 84 3.6 Summary . 85 References 86 4 Early-age Cracking Control on Concrete with Fly Ash 91 4.1 Introduction . 91 4.2 Mechanical Properties 92 4.2.1 Compressive Strength . 93 4.2.2 Tensile Strength 96 4.2.3 Tensile Young's Modulus 100 4.3 Early-age Cracking Resistance of High Performance Concrete with Fly Ash Under Circumferential Restrained Condition . 105 4.3.1 Free Shrinkage . 105 4.3.2 Steel Ring Strain . 106 4.3.3 Residual Stress . 107 4.3.4 Stress Rate . 109 4.3.5 Stress Relaxation . 110 4.4 Early-age Cracking Resistance of High Performance Concrete with Fly Ash Under Uniaxial Restrained Condition . 111 4.4.1 Autogenous Shrinkage . 112 4.4.2 Temperature History 113 4.4.3 Restrained Stress . 114 4.4.4 Tensile Creep 118 4.4.5 Cracking Resistance . 119 4.5 Summary . 120 References 121 5 Early-age Cracking Control on Concrete with Ground Granulated Blast Furnace Slag . 125 5.1 Introduction . 125 5.2 Mechanical Properties 126 5.3 Early-age Cracking Resistance of High Performance Concrete with Ground Granulated Blast Furnace Slag Under Circumferential Restrained Condition . 128 5.3.1 Free Shrinkage . 128 5.3.2 Steel Ring Strain . 128 5.3.3 Residual Stress . 129 5.3.4 Stress Rate . 130 5.3.5 Cracking Potential 131 5.3.6 Stress Relaxation . 132 x Contents 5.4 Early-age Cracking Resistance of High Performance Concrete with Ground Granulated Blast Furnace Slag Under Uniaxial Restrained Condition . 133 5.4.1 Temperature History 133 5.4.2 Autogenous Shrinkage . 134 5.4.3 Restrained Stress . 135 5.4.4 Cracking Resistance . 138 5.5 Summary . 139 References 140 6 Early-age Cracking Control on Concrete with Silica Fume 143 6.1 Introduction . 143 6.2 Mechanical Properties 144 6.3 Early-age Cracking Resistance of High Strength Concrete with Silica Fume Under Uniaxial Restrained Condition 146 6.3.1 Temperature History 146 6.3.2 Autogenous Shrinkage . 148 6.3.3 Tensile Creep 150 6.3.4 Restrained Stress . 152 6.3.5 Cracking Resistance . 154 6.4 Summary . 155 References 155 7 Early-age Cracking Control on Concrete with 3D Hooked-End Steel Fiber 159 7.1 Introduction . 159 7.2 Mechanical Properties 160 7.3 Tensile Creep of 3D Hooked-End Steel Fiber Reinforced Concrete Under a Constant Tensile Load . 164 7.3.1 Tensile Creep of Concrete with Different Contents of 3D Hooked-End Steel Fiber 164 7.3.2 Tensile Creep of Concrete with Different Thermal Treatment Temperatures . 168 7.3.3 Prediction Model for Early-age Tensile Creep . 170 7.4 Early-age Cracking Resistance of High Strength Concrete Reinforced with 3D Hooked-End Steel Fiber Under Uniaxial Restrained Condition . 175 7.4.1 Temperature History 175 7.4.2 Autogenous Shrinkage . 177 7.4.3 Restrained Stress . 180 7.4.4 Cracking Resistance . 182 7.5 Early-age Cracking Resistance of 3D Hooked-End Steel Fiber Reinforced Concrete Under Different Curing Temperatures 184 7.5.1 Temperature History 184 7.5.2 Autogenous Shrinkage . 186 Contents xi 7.5.3 Restrained Stress . 189 7.5.4 Tensile Creep 191 7.5.5 Cracking Resistance . 194 7.6 Summary . 195 References 196 8 Early-age Cracking Control on Concrete with 5D Hooked-End Steel Fiber 199 8.1 Introduction . 199 8.2 Mechanical Properties 200 8.3 Early-age Cracking Resistance of Concrete with 5D Hooked-End Steel Fiber Under Circumferential Restrained Condition . 201 8.3.1 Steel Ring Strain . 201 8.3.2 Residual Stress . 203 8.3.3 Free Shrinkage . 203 8.3.4 Stress Rate . 204 8.3.5 Cracking Potential 204 8.3.6 Stress Relaxation . 205 8.4 Early-age Cracking Resistance of Concrete with 5D Hooked-End Steel Fiber Under Uniaxial Restrained Condition . 208 8.4.1 Temperature History 208 8.4.2 Autogenous Shrinkage . 209 8.4.3 Restrained Stress . 212 8.4.4 Cracking Resistance . 214 8.5 Summary . 216 References 216 9 Early-age Cracking Control on Concrete with Polypropylene Fiber . 219 9.1 Introduction . 219 9.2 Mechanical Properties 220 9.3 Early-age Autogenous Shrinkage of High Strength Concrete with Polypropylene Fiber . 222 9.3.1 Temperature History 222 9.3.2 Autogenous Shrinkage . 222 9.3.3 Ultrasonic Velocity 225 9.3.4 Prediction Model of Autogenous Shrinkage Strain Based on Ultrasonic Velocity . 228 9.4 Early-age Tensile Creep of Concrete with Polypropylene Fiber . 231 9.4.1 Autogenous Shrinkage . 231 9.4.2 Tensile Creep 232 9.4.3 Mechanism of Polypropylene Fiber Reinforcement 234 9.4.4 Modeling of Creep of Fiber Reinforced Concrete 236 xii Contents 9.5 Early-age Cracking Resistance of High Strength Concrete with Polypropylene Fiber Under Circumferential Restrained Condition . 238 9.5.1 Free Shrinkage . 238 9.5.2 Steel Ring Strain . 239 9.5.3 Residual Stress . 239 9.5.4 Stress Rate . 240 9.5.5 Cracking Potential 241 9.5.6 Stress Relaxation . 242 9.6 Early-age Cracking Resistance of High Performance Concrete with Different Amounts of Polypropylene Fiber Under Uniaxial Restrained Condition . 243 9.6.1 Temperature History 243 9.6.2 Autogenous Shrinkage . 244 9.6.3 Restrained Stress . 245 9.6.4 Compressive and Tensile Creep . 247 9.6.5 Cracking Resistance . 249 9.7 Early-age Cracking Resistance of High Performance Concrete with Different Polypropylene Fiber Lengths Under Uniaxial Restrained Condition . 250 9.7.1 Temperature History 250 9.7.2 Autogenous Shrinkage . 251 9.7.3 Restrained Stress . 252 9.7.4 Tensile Creep 254 9.7.5 Cracking Resistance . 256 9.8 Summary . 257 References 258 10 Early-age Cracking Control on High Strength Concrete with Polyvinyl Alcohol Fibers 263 10.1 Introduction . 263 10.2 Mechanical Properties 264 10.3 Early-age Cracking Resistance of High Strength Concrete with Polyvinyl Alcohol Fibers Under Circumferential Restrained Condition . 267 10.3.1 Residual Stress . 268 10.3.2 Stress Rate . 268 10.3.3 Stress Relaxation . 269 10.3.4 Cracking Potential 270 10.4 Early-age Cracking Resistance of High Strength Concrete with Polyvinyl Alcohol Fiber Under Uniaxial Restrained Condition . 273 10.4.1 Temperature History 273 10.4.2 Autogenous Shrinkage . 273 10.4.3 Restrained Stress . 276 Contents xiii 10.4.4 Compressive and Tensile Creep . 279 10.4.5 Cracking Resistance . 282 10.5 Summary . 283 References 283 11 Early-age Cracking Control on High Strength Concrete with Nano-CaCO3 . 287 11.1 Introduction . 287 11.2 Mechanical Properties 288 11.3 Early-age Cracking Resistance of High Strength Concrete with Nano-CaCO3 Under Circumferential Restrained Condition . 290 11.3.1 Free Shrinkage . 290 11.3.2 Residual Stress . 291 11.3.3 Cracking Potential 292 11.3.4 Stress Relaxation . 293 11.3.5 Tensile Creep 295 11.3.6 Relationship Between Relaxation and Creep 295 11.4 Early-age Cracking Resistance of High Strength Concrete with Nano-CaCO3 Under Uniaxial Restrained Condition . 298 11.4.1 Temperature History 298 11.4.2 Restrained Stress . 299 11.4.3 Autogenous Shrinkage . 300 11.4.4 Tensile Creep 301 11.4.5 Cracking Resistance . 304 11.4.6 Simplified Stress�CStrain Failure Criterion 305 11.5 Summary . 308 References 308 12 Early-age Cracking Control on High Strength Concrete with Crystalline Admixture 311 12.1 Introduction . 311 12.2 Mechanical Properties 312 12.3 Early-age Cracking Resistance of High Strength Concrete with Crystalline Admixture Under Circumferential Restrained Condition . 315 12.3.1 Free Shrinkage . 315 12.3.2 Residual Stress . 316 12.3.3 Stress Rate . 317 12.3.4 Cracking Potential 319 12.3.5 Stress Relaxation . 320 12.4 Summary . 321 References 322 13 Early-age Cracking Control on Concrete with MgO Compound Expansive Agent . 325 13.1 Introduction . 325 13.2 Deformation of Concrete 326 13.2.1 Free Strain . 326 13.2.2 Autogenous Strain 328 13.3 Restrained Stress of Concrete 331 13.3.1 Restrained Stress . 331 13.3.2 Stress Relaxation and Ratio of Stress to Tensile Strength . 333 13.4 Early-age Creep Behavior . 335 13.4.1 Compressive Creep . 335 13.4.2 Tensile Creep 337 13.5 Cracking Resistance 338 13.5.1 Parameters for Evaluating Cracking Resistance 338 13.5.2 Evaluation of Cracking Resistance 341 13.6 Simplified Stress�CStrain Cracking Criterion 342 13.7 Summary . 344 References 344 14 Early-age Cracking Control on Concrete with Temperature Rise Inhibitor . 349 14.1 Introduction . 349 14.2 Mechanical Properties 350 14.3 Early-age Cracking Resistance of High Strength Concrete with Temperature Rise Inhibitor Under Uniaxial Restrained Condition . 351 14.3.1 Temperature History 351 14.3.2 Restrained Stress . 352 14.3.3 Autogenous Shrinkage . 353 14.3.4 Tensile Creep 356 14.3.5 Cracking Resistance . 360 14.3.6 Simplified Stress�CStrain Failure Criterion 361 14.4 Summary . 364 References 364 15 Early-age Cracking Control on High Strength Concrete with Shrinkage Reducing Admixture 367 15.1 Introduction . 367 15.2 Mechanical Properties 368 15.3 Early-age Cracking Resistance of High Strength Concrete with Shrinkage Reducing Admixture Under Circumferential Restrained Condition . 370 15.3.1 Free Shrinkage . 370 15.3.2 Steel Ring Strain . 371 15.3.3 Residual Stress . 372 15.3.4 Stress Rate . 372 15.3.5 Cracking Potential 373 15.3.6 Stress Relaxation . 375 15.4 Early-age Cracking Resistance of High Strength Concrete with Shrinkage Reducing Admixture Under Uniaxial Restrained Condition . 377 15.4.1 Temperature History 377 15.4.2 Autogenous Shrinkage . 378 15.4.3 Tensile Creep 380 15.4.4 Restrained Stress . 382 15.4.5 Cracking Resistance . 383 15.5 Summary . 384 References 384 16 Early-age Cracking Control on Concrete with Reinforcing Bars . 387 16.1 Introduction . 387 16.2 Early-age Bond Behavior Between High Strength Concrete and Reinforcing Bars . 388 16.2.1 Relationship Between Bond Strength and Age 388 16.2.2 Relationship Between Bond Strength and Concrete Strength . 392 16.2.3 Prediction Model for the Slip Corresponding to Bond Strength . 396 16.2.4 Prediction Model for Bond Stress�CSlip Relationship Between Reinforcing Bars and High Strength Concrete . 397 16.3 Early-age Cracking Resistance of Reinforced High Strength Concrete Under Uniaxial Restrained Condition . 401 16.3.1 Temperature History 401 16.3.2 Autogenous Shrinkage . 403 16.3.3 Restrained Stress . 406 16.3.4 Tensile Creep 408 16.3.5 Cracking Resistance . 408 16.4 Summary . 409 References 410 17 Early-age Cracking Control on Concrete with Internal Curing 413 17.1 Introduction . 413 17.2 Early-age Cracking Control on Concrete with Internal Curing by Super Absorbent Polymers . 414 17.2.1 Mechanical Properties . 414 17.2.2 Temperature History 416 17.2.3 Autogenous Shrinkage . 418 17.2.4 Restrained Stress . 419 xvi Contents 17.2.5 Tensile Creep 421 17.2.6 Cracking Resistance . 423 17.3 Early-age Cracking Control on Concrete with Internal Curing by Pre-wetted Lightweight Aggregates 424 17.3.1 Mechanical Properties . 424 17.3.2 Steel Ring Strain . 428 17.3.3 Residual Stress . 429 17.3.4 Stress Rate . 430 17.3.5 Stress Relaxation . 431 17.3.6 Tensile Creep 432 17.3.7 Relationship Between Relaxation and Creep 434 17.4 Summary . 435 References 436