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Founded in 1904 and headquartered in Farmington Hills, Michigan, USA, the American Concrete Institute is a leading authority and resource worldwide for the development, dissemination, and adoption of its consensus-based standards, technical resources, educational programs, and proven expertise for individuals and organizations involved in concrete design, construction, and materials, who share a commitment to pursuing the best use of concrete.
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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 3 of 3
Wed, October 23, 2019 11:00 AM - 1:00 PM, 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) Assess advanced materials for crack mitigation;(2) Develop mix optimization for setting and crack control;(3) Describe the new test method for paste setting and strain development;(4) Explain how moisture gradient measurements for shrinkage and curling assessment are used.
Early Age Response of Cementitious Matrices Influenced by Phase Change Materials (PCMs): Implications on Crack Resistance
Presented By: Aashay Arora
Affiliation: Arizona State University
Description: The heat released during the hydration of cement at early-ages is well understood to be a reason for early-age cracking of restrained concrete elements such as pavements and bridge-decks, while diurnal changes in temperature can cause thermal fatigue and associated cracking in mature concrete at later ages. The addition of phase change materials (PCMs) has been proposed as a means to mitigate such cracking in cementitious materials. The success of PCMs in these applications is ensured by their ability to absorb heat from their surroundings at temperatures in excess of their phase change temperature (TPC,°C), and desorb such heat at temperatures inferior to their phase change temperature. This presentation will elucidate: (i) the thermal effects of PCMs at early ages in hydrating cementitious systems through experiments and numerical simulations, (ii) the mechanisms by which small dosages of PCMs enhances the cracking resistance (as compared to a plain cement paste or composites containing similar dosages of stiffer (e.g., quartz) inclusions, even independent of their concurrent heat sorption-desorption effects, and (iii) temperature and thermal strain results from field placement of pavement sections containing PCMs in Phoenix, Arizona. It is expected that the experimental and simulation results help design of PCM-cement composite systems in order to gain maximum benefits towards enhanced durability of concrete.
Setting Time and Cracking Potential of Concrete Mixtures with Variable Packing Density of Aggregates
Presented By: Jan Olek
Affiliation: Purdue University
Description: The volumetric changes are probably the most important causes of concrete cracking since they typically occur at early age, when the resistance of concrete to tensile stresses is relatively low. The presentation will examine the cracking potential of concrete mixtures optimized with respect to the paste-aggregate void saturation ratio and the aggregate packing density. Four different aggregate blends, with packing densities representing gradations ranging from well-graded to gap-graded were used to prepare concretes meeting the specification for concrete paving mixtures. The setting time of the mixtures was evaluated using the method of Time Domain Reflectometry (TDR) and their cracking potential was evaluated using the restrained shrinkage method (AASHTO PP34). The results indicated that although both, the paste-void saturation ratio and aggregate packing density, influenced the cracking potential of the mixtures, the influence of paste volume saturation ratio was more dominant. The TDR method was also found to be a viable option for monitoring the setting time of mixtures.
Measuring Early Age Strain and Setting Time of Cement-based Paste with Admixtures
Presented By: Akthem Al-Manaseer
Affiliation: San Jose State University
Description: Determination of the initial set time of cement-paste mixtures using a new test method for measuring early-age strain was investigated in this work. Volumetric strain versus time curves of six batches of the same paste mixture were tested at two different ambient temperatures. The data demonstrated an extended initial set time for the batches tested in the cooler ambient temperature. Correlation was found between the slopes of the volumetric strain versus time curves for four mortar mixtures and the initial setting time for the same mixtures obtained by using the ASTM C403 needle penetration test method. Therefore, both the initial set time and early-age strain data were simultaneously obtainable for paste specimens tested with this new method.
Examining the Role of Moisture Gradients for Shrinkage and Curling
Presented By: Mehdi Moradilo
Affiliation: Oregon State University
Description: This presentation uses neutron radiography as a method to measure moisture gradients in drying concrete. This will be related to the shrinkage, curling and cracking of concrete. The role of mixture composition and degree of hydration will be assessed along with the role of Shrinkage reducing admixtures and internal curing.
Evaluation of High Early Strength Concrete Repair Slab Cracking Mitigation Methods
Presented By: Dhanushika Gunatilake
Affiliation: University of South Florida
Description: Jointed plain concrete pavement (JPCP) replacement slabs are often made of high early strength (HES) concrete characterized by high cement content and low w/c ratio, which can result in higher temperature rise and increased autogenous shrinkage. Consequent early-age volume changes elevate the cracking risks in repair slabs, when restrained. This study investigated the effects of base restraint minimization on reducing concrete early-age cracking potential. The effect of two base friction reducing media at the slab-base interface namely, double layers of polyethylene and geotextile fabric was studied. Field concrete slabs of 12x15x1 ft, instrumented with concrete stress meters and thermocouples were used to measure the in-situ stress and temperature development. Finite element modeling was performed for further understanding of early-age cracking mechanism(s) of slabs. A discussion will be given on the benefits and mechanisms of action of each cracking mitigation option.