Testing and Modeling of Compressive and Tensile Viscoelastic Effects in High Performance Concrete

High performance concrete;Viscoelastic effect;Autogenous shrinkage;TSTM full restraint test;numerical modeling;Civil and Environmental Engineering;Engineering;Civil Engineering

Meng, BoMcCormick, Jason Paul ;

University of Michigan

关键词: High performance concrete;    Viscoelastic effect;    Autogenous shrinkage;    TSTM full restraint test;    numerical modeling;    Civil and Environmental Engineering;    Engineering;    Civil Engineering;   

Others  :  https://deepblue.lib.umich.edu/bitstream/handle/2027.42/150020/mengbo_1.pdf?sequence=1&isAllowed=y

瑞士|英语

来源: The Illinois Digital Environment for Access to Learning and Scholarship

【 摘 要 】

This thesis deals with experimental tests and numerical simulation of compressive and tensile viscoelastic behavior at later ages (since 7 days and curing at 20 °C) of high performance concrete (HPC), here defined as low water-cementitious ratio (0.35) concrete, which is cured under sealed moisture conditions.Previous studies have focused on early-age cracking, which is complicated by the rapid changing thermal effects. The viscoelastic effect starting from later ages (7 days), when the thermal effect is not major concern, still needs to be studied.The main objectives are to evaluate experimentally the compressive and tensile viscoelasticity effects on HPC, autogenous shrinkage stress development associated with full deformation restraint on the tensile cracking susceptibility, and to develop a modeling tool for incorporating effects of viscoelasticity in total stress analysis.HPC is studied for its popularity in structure and building. The experimental program can be split into three parts for creep, autogenous shrinkage and restraint net tensile stress evaluation and modeling respectively.The viscoelastic behavior under sealed condition of HPC is studied in this thesis for its prevalence in structure and buildings.Normal strength concrete is also studied for comparison. Basic creep under sealed condition is studied for HPC with w/c = 0.35. A rheological based model is used for simulating and predicting the basic creep of HPC under sealed condition due to its ability to capture underlying physical parameters. The relaxation under compressive mode is numerically simulated for investigating the contribution of relaxation in stress on the resistance to cracking. Viscoelastic creep modulus is defined in a similar way as elastic modulus for characterizing the resistance of concrete to be deformed viscoelastically in compressive mode due to external load. The effect of material parameters and aging on the viscoelastic modulus are also studied.Autogenous shrinkage tests under sealed condition for HPC and normal strength concrete (NSC) are conducted in a long-term study on the effect of water/cement ratio, aggregate contents and addition of LWA for internal curing. A direct approach for estimating the shrinkage stress under full restraint condition is proposed based on twin tests of free shrinkage and partial restraint autogenous shrinkage with reinforcement.The mitigation effect of LWA on shrinkage is directly shown by its significant effect on maintaining the internal RH concluded from internal RH and wrapping tests conducted in this research. For direct testing for net tensile stress development associated with full deformation restraint, a servo-hydraulic system known as a Temperature Stress Testing Machine, TSTM is implemented here for detailed long-term continuous measurement starting at the age of 7 up to 60 days. These results are augmented with free and restrained shrinkage tests. Shrinkage stress is shown to be significant and the major factor in viscoelastic stress contribution and is combined with elastic stresses for assessing crack susceptibility of HPC.Tensile viscoelastic effect on HPC is shown insignificant after early age (7 days) by TSTM test with LWA mitigation on shrinkage.Relaxation modulus as in plastics is not needed for the estimation of tensile stress of HPC with restraint.The addition of LWA is also proven to be effective for reduction in internal stress due to its mitigation effect in shrinkage.