Mechanical Properties of HPC with Expansive Additive and Shrinkage Reducing Admixture under Simulated Completely- Restrained Condition at Early Age Takafumi Noguchi The University of Tokyo, Japan Park Sun-Gyu Yonsei University, Korea Ippei Maruyama Hiroshima University, Japan

Background High-performance Concrete (Low W/C) High-performance Concrete (Low W/C) Self-desiccation Self-desiccation Autogenous Shrinkage Autogenous Shrinkage Under Restraint Condition Under Restraint Condition Cracking Cracking Influence on Durability & Aesthetic Influence on Durability & Aesthetic Use of Use of Expansive Addition Expansive Addition Shrinkage Reducing Admixture Shrinkage Reducing Admixture

Objective of Study Behaviour of Early Age HPC with and without Behaviour of Early Age HPC with and without Expansive Addition Expansive Addition Shrinkage Reducing Admixture Shrinkage Reducing Admixture Restraint Free Condition Restraint Free Condition Shrinkage Strain Shrinkage Strain Under Restraint Condition Under Restraint Condition Strain & Stress Strain & Stress Creep Behaviour Creep Behaviour Control of Autogenous Shrinkage Cracking Control of Autogenous Shrinkage Cracking

Variable Restraint Testing Machine Fresh concrete is cast into the framework of the testing machine. Specimen size is 1500 mm in length and 100 mm x 100 mm in cross sectional area The ends of specimen are fixed to the cross-head, which is fixed to the frame, by claws which hold the concrete specimen and are able to exert tensile or compressive force. The load through the specimen is monitored by a load cell with accuracy of 1 N. The longitudinal deformation of concrete specimen is monitored by four LVDTs with accuracy of μm. Experiment is commenced after the concrete setting.

Program Flow of Simulated Completely-Restrained Test Completely restrained condition is simulated by maintaining the total deformation of the specimen within a threshold, which is defined as the permissible change in the length of the specimen. There are two controlling triggers. stress One is stress trigger. strain Another is strain trigger. While repeating this process in VRTM, a completely-restrained condition is achieved and the stress generated by shrinkage is measured.

Mix Proportions of Concrete CompositionNHCEHCSHC Cement (kg/m 3 ) Expansive additive (kg/m 3 ) 0200 Shrinkage reducing admixture (kg/m 3 ) 006 Water (kg/m 3 ) Fine aggregate (kg/m 3 ) Coarse aggregate (kg/m 3 ) High-range water-reducing admixture (cement weight %)

Experiments Compressive Strength Compressive Strength Tensile Strength Tensile Strength Modulus of Elasticity Modulus of Elasticity Free Autogenous Shrinkage Free Autogenous Shrinkage Sealed with a polyester film at 20 ºC Sealed with a polyester film at 20 ºC Stress Development under Simulated Completely-Restraint Stress Development under Simulated Completely-Restraint Sealed with a polyester film at 20 ºC Sealed with a polyester film at 20 ºC Trigger of stress and strain : 0.01 MPa and 2 x Trigger of stress and strain : 0.01 MPa and 2 x 10 -6

Mechanical Properties of Concrete Compressive Strength (MPa) Tensile Strength (MPa) Modulus of Elasticity (GPa) (GPa) 1day3days5days1day3days5days1day3days5days NHC EHC SHC

Autogenous Shrinkage Autogenous shrinkages of NHC and SHC occurres at a rapid rate in the first few hours and the rate decreased afterward. In EHC, after a few hours expansion is observed. Expansive addition and shrinkage reducing admixture can obviously reduce the autogenous shrinkage of HPC.

Temperature Histories Almost constant temperature never causes significant expansion.

Strain under Simulated Completely-Restraint Deformation is well controlled within the range of the threshold value, 1  m. Tension Compression

Stress under Simulated Completely-Restraint Invisible Crack Tensile Strength of NHC at 1 day = 2.2 MPa (x 0.7 = 1.54 MPa) In EHC and SHC, lower tensile stress and no cracking.

Schematic Diagram for Creep Estimation Age Strain Strain Trigger Accumulation of Elastic Strain Free Autogenous Shrinkage Creep Strain ε i,creep = ε i,free - ε i,elastic Elastic Strain measured from the recovery cycles of VRTM

Creep Strain Creep is quite significant in the deformation of HPC at early age, corresponding to 90 % of the free shrinkage strain. Creep strain shows the tendency to increase rapidly immediately after the setting up to 10 hours. A considerable tensile stress in HPC can be relaxed under restraint at early age.

Creep Coefficient in Each Step ε i,co-creep = ε i,creep / ε i,elastic Creep coefficient of NHC is lower than those of EHC and SHC in the beginning. Tensile stress in restrained EHC and SHC is lower than that in NHC at early age.

Concluding Remarks (1st) The variable restraint testing machine can show how tensile stress and strain develop under restrained condition in HPC with and without expansive addition and shrinkage reducing admixture. The variable restraint testing machine can show how tensile stress and strain develop under restrained condition in HPC with and without expansive addition and shrinkage reducing admixture. The tensile stress in HPC with expansive addition or shrinkage reducing admixture under completely restrained condition at early age was lower than that of normal HPC. The tensile stress in HPC with expansive addition or shrinkage reducing admixture under completely restrained condition at early age was lower than that of normal HPC.

Concluding Remarks (2nd) Normal HPC shows larger creep strain but smaller creep coefficient than concrete with expansive addition or shrinkage reducing admixture. Normal HPC is sensitive to autogenous shrinkage cracking. Normal HPC shows larger creep strain but smaller creep coefficient than concrete with expansive addition or shrinkage reducing admixture. Normal HPC is sensitive to autogenous shrinkage cracking. Expansive addition and shrinkage reducing admixture make a crack prevention effect on HPC at early age. Expansive addition and shrinkage reducing admixture make a crack prevention effect on HPC at early age.