Early age creep and shrinkage of emerging concrete materials

concrete volume change;tensile creep;autogenous shrinkage;restrained cracking;self-consolidating concrete (SCC);shrinkage reducing admixtures (SRA);high-performance concrete (HPC)

D'Ambrosia, Matthew

关键词: concrete volume change;    tensile creep;    autogenous shrinkage;    restrained cracking;    self-consolidating concrete (SCC);    shrinkage reducing admixtures (SRA);    high-performance concrete (HPC);   

Others  :  https://www.ideals.illinois.edu/bitstream/handle/2142/29427/D%27Ambrosia_Matthew.pdf?sequence=1&isAllowed=y

美国|英语

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

【 摘 要 】

Concrete pavements and structures are especially vulnerable to cracking at early age. Thevolumetric instability of concrete at early age is a frequent cause of cracking. The primarycomponents of volume change are external drying shrinkage, autogenous shrinkage, and thermaldilation. When concrete is restrained, tensile stress develops due to shrinkage and increases theprobability of cracking. Early age properties, such as tensile creep, are not well understood andthe availability of literature on the subject is limited. The goal of this research is to improve theunderstanding of early age behavior in emerging materials in order to improve long termdurability.The early age volume changes of self-consolidating concrete (SCC), high-performanceconcrete (HPC), and concrete with shrinkage reducing admixture (SRA), or shrinkage-reducedconcrete (SRC) were studied in order to understand mechanical behavior and develop guidelinesfor practice. A restrained uniaxial testing frame was previously developed for the purposes ofunderstanding of early age mechanical properties and it was used to explore the role of tensilecreep for relaxation of shrinkage stress in materials that are outside the scope of many currentprediction models and design guidelines. Tensile creep was compared to compressive creep andup to a tenfold increase was observed, indicating an urgent need for updating models. Otherobservations, such as non-linearity of creep at early age and under restrained conditions, led tonew insights regarding the use of superposition for long term deformations. Experimentalcharacterization of early age behavior aided the development of a new modeling approach basedon the utilization of relative humidity (RH) as the driving force for shrinkage. This approachwas validated using new experiments developed to characterize tensile creep and autogenousshrinkage, and results demonstrate that RH is a powerful parameter for modeling shrinkage stressdevelopment and drying gradients.Based on the experimental work and modeling efforts, practical guidelines weredeveloped for specifications, mixture proportioning, and acceptance testing, and mitigationstrategies were suggested to minimize the potential for shrinkage cracking. Improvements werealso suggested for existing prediction models to account for early age behavior. These researchcontributions enable practitioners to implement new concrete materials technology and realizethe benefits of innovative concrete materials without sacrificing long term durability.