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Workability Retention and Extension: Keeping Your Concrete Alive
Wednesday, October 20, 2021 1:00 PM - 3:00 PM
Many construction projects demand concrete mixtures with extended workability, and it is expected that this issue will become of even higher importance with the potential upcoming changes in ASTM C94 that will lift the 90-minute discharge limit for ready-mixed concrete. Attendees will understand the theoretical background and mechanisms behind concrete workability loss, including advancements in chemical admixture technology, industry practices, strategies, and tools available for design and control of concrete workability. Additionally, case studies of successful projects incorporating concretes with extended workability will be presented. Attendees will understand the theoretical background and mechanisms behind concrete workability loss, including advancements in chemical admixture technology, industry practices, strategies, and tools available for design and control of concrete workability. Additionally, case studies of successful projects incorporating concretes with extended workability will be presented. The target audience included concrete contractors, ready-mixed producers, designers, chemical admixture producers, and the research community.
(1) Identify key mechanisms and processes governing concrete workability loss;
(2) Describe various strategies and approaches for the design of concrete mixture with extended workability times;
(3) Explain tools, test methods and technologies available to the industry for workability control;
(4) Recognize limitations and potential problems associated with concrete workability extension.
This session has been approved by AIA and ICC for 2 PDHs (0.2 CEUs). Please note: You must attend the live session for the entire duration to receive credit. On-demand sessions do not qualify for PDH/CEU credit.
Impact of High-Range Water Reducer, Workability Retaining Admixture and Antifoaming Admixture on Fresh Properties of UHPC
Presented By: Jiong Hu
Affiliation: University of Nebraska-Lincoln
Description: Ultra-high-performance concrete (UHPC) has drawn considerable attention in the last decade due to its superior characteristics, such as self-consolidation nature and excellent mechanical and durability properties. However, it is often challenging to maintain appropriate UHPC workability over time to ensure success in construction. Different chemical admixtures such as high-range water reducer, workability retaining admixture, and anti-foaming admixtures have therefore been used to achieve desirable UHPC properties. However, the type and dosage of admixtures need to be carefully controlled to ensure an unsuccessful mix. This paper investigates the impact of chemical admixtures on fresh UHPC performance. Furthermore, the paper defines a practical way to assess the stability of the UHPC to prevent potential segregation during construction.
In-Transit Management of Slump
Presented By: Nathan Tregger
Affiliation: GCP Applied Technologies
Description: Retaining or extending slump for ready-mix applications is a challenging task that has a resulted in very sophisticated chemicals and formulations over the years. With the advent of IoT (Internet of Things), concrete trucks are now available with in-transit management systems which can measure, monitor, and manage slump during delivery through on-board water and admixture additions. Combined with current admixtures, synergistic effects can be achieved to minimize risk while maintaining target slumps at a lower dosage. Case studies will be presented to demonstrate current findings.
Admixtures for Use in Extended Slump Life Applications
Presented By: G Terry Harris
Affiliation: GCP Applied Technologies
Description: Chemical admixtures have been used for years to extend the slump life of concrete mixtures to meet the project demands. Depending on the application retarders, hydration stabilizers, high range water reducers, workability retaining admixtures or a combination of 2 or more of these are used. Case studies of the use of all of the admixtures are included in the presentation.
Improving the Lubrication, Stamina and Endurance of Concrete for Extended Workability Applications
Presented By: Oscar Antommattei
Affiliation: Kiewit Engineering Group Inc.
Description: One of the biggest challenges in concrete construction is the ability of the concrete to stay as workable as required to complete the placement of work. In many cases, concrete mixes need to be proportioned and enhanced to attain adequate workability and slump retention without causing detrimental effects that may affect the long-term performance of the concrete in-service. It is of great important to understand concrete demands to establish adequate lubrication, maintain proper stamina and develop endurance. This presentation will discuss different ways to assess, proportion and optimize concrete for extended workability applications such as drilled shafts or tremie placements including some lessons learned from case studies.
Extended Workability for Concrete: Goals and Challenges
Presented By: Jose Pacheco
Description: Modern construction often requires that concrete mixtures for special applications are designed with extended workability. Common industry practice to evaluate extended workability consists of measurements of a concrete slump or slump flow at time intervals. Performance requirements for initial, interval, and final slump and slump flow are defined at the discretion of the specifier but vary greatly from project to project. Along the slump or slump flow evaluation, determination of other fresh properties and hardened properties are often required as part of the extended workability performance testing. In some cases, however, challenges related to the extended workability performance can lead to constructability issues such as plastic shrinkage cracking. This presentation will cover the current standard of practice for extended workability evaluations, strategies to achieve workability extension without detrimental effects to the hardened concrete performance, and present case studies in which the intended evaluation resulted in very different field performance.