A Performance-Based Approach to Hot Weather Concreting, Part 1 of 2
Tuesday, November 10, 2015 8:30 AM - 10:30 AM, GOVERNOR'S SQUARE 12
This session focuses on new developments, common practices, innovative technologies, and challenges related to design, construction, and performance of concrete in hot weather.
By attending this session, attendees will be able to:
1. Identify options for dealing with placing, finishing, and curing concrete in hot weather;
2. Learn about new ideas and innovative technologies available to improve concrete performance in hot weather;
3. Understand common construction practices and challenges with concrete in hot weather; and
4. Recognize benefits of knowing ways to optimize design and construction of concrete in hot weather.
Model for Early-Age Rate of Evaporation of Cement-Based Materials
Presented By: Mehdi Bakhshi
Affiliation: AECOM
Description: Early-age cracking affects the structural integrity of concrete structures and, if not inhibited, would lead to a reduction in service life. Plastic cracks are observed in the first few hours after placing the concrete, a time period well within the initial stages when the drying process is controlled by the rate of evaporation of concrete surfaces, which is roughly constant and similar to the rate of evaporation from water surfaces. In the absence of a theoretical method, this rate is commonly estimated using a nomograph based on Dalton’s law. A fluid mechanics-based approach for water evaporation based on the boundary-layer theory, mass transfer, diffusion, and convection is presented. A parametric study is conducted on the effect of boundary-layer temperature, wind speed, relative humidity, and evaporation characteristic length on the calculated evaporation rates. Predicted evaporation rates are verified by recent experiments. Results show that given appropriate environmental parameters, evaporation rates can be predicted with a good degree of accuracy.
Dealing with Hot Weather Concrete: Specifications, Materials, Operations and Other Challenges
Presented By: Oscar Antommattei
Affiliation: Kiewit Corp - Kiewit Infrastructure Engineers Co
Description: Placing concrete in hot weather conditions is known to pose unique challenges. Specifications can include restrictive and prescriptive requirements that result in additional challenges to the field operations. Technologies available to the concrete industry facilitate concrete construction in hot weather. Recent developments in admixtures can also be beneficial in improving concrete performance in hot weather. Concrete mixture proportions must be designed to meet specified requirements, but also to properly perform in the field and meet construction demands. This presentation provides fundamental knowledge and experiences to consider for concrete in hot weather.
Specifying, Proportioning and Producing Rapid Strength Concrete with Consideration for Ambient Conditions
Presented By: Boris Stein
Affiliation: Twining Inc
Description: Proper preservation and rehabilitation strategies extend service life of concrete pavements and structures and are essential for enhancing sustainability of concrete transportation infrastructure. The use of rapid strength concrete (RSC) for these purposes allows for minimizing the impact on traffic. Acquired experience suggests that for the best quality and longevity RSC must be designed for: (i) constructability; (ii) required rate of strength gain; (iii) ambient conditions during construction and exposure conditions in-service; (iv) early age volume changes; (v) permeability; and (vi) durability. The paper discusses (i) principles of specifying , proportioning and producing of RSC with consideration for the impact of ambient conditions on constructability and pace of construction, (ii) summarizes laboratory and field data addressing impact of ambient conditions on performance of RSC; (iii) discusses best practices; and (iv) illustrates recommended approaches with case studies of specific projects.
Using Workability Retaining Admixtures in Hot Weather Concreting
Presented By: G Terry Harris
Affiliation: W R Grace & Company
Description: Historically increased dosage rates of Retarding or Extended Set Control admixtures were used to extend slump life in hot weather. Now, workability retaining admixtures allow us to extend the slump life in concrete mixtures without extending the set time significantly. Recently these workability retaining admixtures were used in drill shaft concrete to extend the slump life without excessive retardation.
How Does Hot Weather Placement Impact Transport, Durability, and Performance Specifications
Presented By: W Jason Weiss
Affiliation: Purdue University
Description: High temperature curing (at 50 ± 2 °C) was evaluated in comparison to conventional curing for use in a Nernst-Planck service life prediction model (Stadium®). Curing at 50 °C accelerated the hydration reaction as expected. When the samples were stored in lime water, the microstructure formed at the higher temperature showed an increase in total porosity, chloride diffusion coefficient, and permeability at the same maturity. The impact of these inputs was assessed for service life prediction for the example used here resulted in a prediction of corrosion initiation times that were approximately 30 % earlier than those predicted using samples moist cured at 23 ± 2 °C. The results indicate however that the moisture conditions dramatically impacted the influence of temperature as samples with a higher degree of saturation were more prone to damage caused by high temperatures presumably due to the coefficient of thermal expansion of the water.
To Register: www.concrete.org
