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Home > Events > Conventions > Current Convention > Sessions and Events
C = Duke Energy Convention Center; H = Hyatt Regency Cincinnati
Measurement and Prediction of Early-Age Properties of High-Performance Concrete for Durability and Crack Resistance, Part 2 of 3
Wed, October 23, 2019 8:30 AM - 10:30 AM, C-Junior Ballroom B
This session will present latest developments on high-performance concrete (HPC). Presentations will review material requirements for achieving HPC (e.g. low water-cementitious ratio, SCM and internal materials and replacement levels, air-void characteristics for salt scaling and internal frost resistance, etc). Crack resistance due to volume changes from thermal, creep and shrinkage effects will be discussed. Measurement and prediction of stress development for crack resistance in HPC associated with deformation restraint will be presented. Designers, contractors, educators, engineers, material suppliers, and students will benefit from attending this session.Learning Objectives:(1) Stress development from shrinkage restraint;(2) Embedded sensors for monitoring stresses;(3) Chloride ingress and crack size effects on service life;(4) New bond-slip model for uniaxial tension analysis.
Shrinkage-Induced Tensile Stress Development in High Performance Concrete under Partial and Full Deformation Restraint-Is Stress Relaxation Fictitious or Real?
Presented By: Will Hansen
Affiliation: University of Michigan
Description: Autogenous shrinkage is intensified in high performance concrete (HPC) of low water-binder (W/B) ratio (relative to conventional concrete) and addition of SCM’s. The early age cracking problem in HPC has become important due to the increased use of these materials (Bentz et al. 2001; Kovler et al. 1993; Toma et al. 1999; RILEM Report 2003). The reasons were generally attributed to the higher chemical shrinkage, finer pore structure, removal of calcium hydroxide as a shrinkage restraint, and a reduction in pore humidity associated with pozzolanic reactions. Tension members are subjected to elastic and viscoelastic stresses, which are typically restrained. While creep is assumed to cause stress relaxation, shrinkage will increase stress if restrained, thus resulting in a complex total stress development, which in turn has significant influence on occurrence and timing of tensile cracking in HPC. The role of elastic and shrinkage stress development of HPC members is investigated experimentally based on fully restrained relaxation tests (TSTM) and partially restrained shrinkage tests.
Monitoring Early-age Temperature and Shrinkage of Ultra-High-Performance Concrete with Distributed Fiber Optic Sensors
Presented By: Weina Meng
Affiliation: Stevens Institute of Technology
Description: Ultra-high-performance concrete (UHPC) has a low water-to-cementitious materials ratio (w/cm < 0.25) and can develop larger autogenous shrinkage compared with conventional concrete. Significant shrinkage can lead to cracking, which in turn can compromise mechanical properties and durability. The standard shrinkage evaluation method recommended by ASTM is to measure the length change of a cylinder specimen cast in a corrugated plastic tube and calculate the average strain. This standard method does not consider possible nonuniform shrinkage, which may be generated by cracks or thermal gradients in the specimen. In this study, distributed fiber optic sensors based on Rayleigh scattering are used to monitor temperature and strain distributions in cost-effective UHPC. Slab specimens measuring 305 mm by 305 mm by 100 mm were prepared and instrumented with distributed temperature and strain sensors at different depths. Non-uniform temperature and strain distributions are measured from the distributed fiber optic sensors and used to analyze the effect of temperature gradient on the shrinkage of UHPC. This study develops an effective tool for evaluating spatially-distributed shrinkage in UHPC and provides new insights into shrinkage characteristics of UHPC. The effectiveness using saturated lightweight sand to reduce autogenous and drying shrinkage was evaluated with sand substitutions of up to 60% by volume of the total sand. The effect of using saturated lightweight sand on the variations in in-situ relative of IHPC and the development of mechanical properties and shrinkage at early age at determined.
Modeling the Effects of Cracks on Chloride Ingress and Corrosion
Presented By: Neal Berke
Affiliation: Tourney Consulting Group, LLC
Description: Service life model based on diffusion of chlorides into concrete are widely used to predict service life of reinforced concrete structures. However, most of the models do not address chloride ingress into cracks, or the effect of crack size, concrete, and reinforcing properties on the ingress of chloride into the cracks and subsequent corrosion of steel. In this presentation, chloride ingress at cracks formed in flexure is compared to that in uncracked concrete. The cementitious matrix and type of reinforcing bar present are shown to play significant roles in the ingress of chloride at the cracks. A methodology for modifying probabilistic service life models to address cracking is presented.
Effect of Age on the Development of Bond by Simulation of Tensile Stiffening Effect
Presented By: Barzin Mobasher
Affiliation: Arizona State University
Description: A nonlinear finite difference tension stiffening model for reinforced concrete and textile reinforced composites is used to assess the effect of bond development as a function of age and curing period. The geometrical input parameters include sample dimensions, geometry, and reinforcement ratio. The material models are described by free form functions, providing flexibility in modeling of longitudinal reinforcement, interface, and matrix elastic and tensile strength. The matrix is assumed to be brittle in reinforced concrete and post crack response is attributed to tension stiffening. Equivalent material properties at macroscopic level can be obtained from calibration of test results available in literature. By simulating the tensile behavior of experiments conducted in uniaxial tension, cracking criteria as well as evolution of crack spacing can be compared with the composite systems’ performance in terms of overall load-displacement response. Several independent experimental sets of data were used in the simulations: a steel reinforced concrete tension member, steel and GFRP reinforced concrete tension members, AR-glass textile reinforced concrete, as well as recycled aggregate concrete materials. The equivalent bond-slip model, in which the bond-slip and its development with the duration of the curing of the sample are them investigated. Results provide a general overview of how this test can be used to measure bond parameters for engineering design purposes.