Vibration is the most common consolidation technique, as it is used to densify the fresh concrete mass and to release excessive entrapped air. However, over-vibration causes water migration and water leakage from the formwork, which could result in low surface quality and reduced structural integrity. Ongoing research and practical experiences have demonstrated that over-vibration is a combination of extensive vibration time and excessive frequency, as a function of concrete workability. This session intends to inform contractors, concrete suppliers, engineers and architects of the recent developments made in the field, which are reflected in the upcoming revision of the ACI 309 main document.
Learning Objectives:
(1) Summarize the underlying theory for concrete’s response to vibration, particularly the importance of frequency and amplitude;
(2) Describe techniques to quantify the effect of vibration on different concrete mixtures;
(3) Calculate vibration parameters (frequency, amplitude and duration) for the concrete mix design;
4) Describe how vibration consideration during construction planning contributes to concrete quality.
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.
Vibration Theory and Reality: It is Not What You Think
Presented By: Paul Jaworski
Affiliation: Minnich Mfg
Description: Vibration performance in concrete mixtures has always been characterized in theory and not in practice. Because of the research effort conducted by the ACI 309 Concrete Consolidation Committee in revising its guidance document, it is all about science and measurements.
This segment will summarize vibration’s dynamics and compatibility through changes in workability that concrete processes present. How we look at vibration and workability controls for AI development in the future will be presented.
Vibration of Concrete… Going from Small Scale Mock-ups to the Real Deal!
Presented By: Jacob Borgerson
Affiliation: Wiss, Janney, Elstner Associates, Inc.
Description: The vibration of concrete is critical for the successful placement and finishing of concrete. In some instances, constructors and designers want an architectural off-the-form finish. This presentation will discuss the factors that influence the workability of concrete and potential concerns to consider when deciding to vibrate concrete. In addition, attendees will be introduced to various approaches for refining means and methods of vibration during the concrete placement. Examples will be used to illustrate the concepts presented.
Shaping Success - FRC Mixtures for Slip Forming of Bridge Railings
Presented By: Karoline de Sousa Felix
Affiliation: University of Florida
Description: During the construction of slip-formed concrete bridge railings, time and material costs associated with the installation of mild steel reinforcement are substantial. The use of fiber reinforced concrete (FRC) has therefore been investigated as a means of reducing construction costs by replacing mild steel reinforcement bars with distributed hooked-end steel fibers. Pendulum impact tests have demonstrated adequate performance of railings constructed using FRC. Because slip formed elements must retain their shape immediately after extrusion, very low slump mixtures are utilized. In conventional concrete slip forming, vibrators present in the forming equipment consolidate the low-slump mixture to an acceptable level. In FRC, however, the presence of steel fibers alters the fresh mixture properties, and influences the ability to achieve suitable consolidation. In this presentation, the authors will discuss the development of an FRC mixture design suitable for slip forming; the development of a fresh-mixture test that is expected to promote successful slip-forming; and tests of hardened FRC mechanical properties. Careful attention to aggregate gradation during mixture design is important in achieving a low slump material that consolidates well upon vibration yet retains its shape after form removal. To evaluate potential mixture designs, a new fresh mixture “pipe test” has been developed that simulates several aspects of slip forming: vibration, hydrostatic pressure, and form removal (extrusion).
Avoiding Failure in Slip Formed Concrete by Measuring Vibration Response
Presented By: Tyler Ley
Affiliation: Oklahoma State University
Description: It is widely known that the concrete mixture design impacts the ability to consolidate concrete with vibration, but little work has been done to quantify this. This presentation will introduce the Box Test and the Quake. These are simple tests to measure the response of the concrete to vibration. Both tests have been used with full scale airfield paving concrete mixtures to establish limits. This work will also present new guidance for concrete mixture design for airfield pavements based on the lessons learned from these tests.
Good Vibrations with your Contractor: Enhancing Concrete Quality through Effective Consolidation
Presented By: Eamonn Connolly
Affiliation: McHugh
Description: concrete structures. Furthermore, poor consolidation can lead to significant surface defects leading to expensive remediation and shortened service life. This presentation shows different examples of good and bad consolidation and its consequences on the finished concrete surface. It also shows the different causes of surface defects which can be attributed to insufficient vibration or over consolidation in combination. Attendees will gain valuable insights into best practices of concrete consolidation and practical applications to achieve superior results. This discussion aims to bridge theoretical understanding with real-world implementation, contributing to the advancement of quality and durability of concrete structures.
Not Too Fast, Not Too Slow
Presented By: Peter Taylor
Affiliation: National Concrete Pavement Technology Center
Description: The presentation will review work conducted investigating how vibration impacts fresh and hardened properties of a variety of mixtures, with a view to recommending what vibration parameters should be recommended, and how mixtures can be proportioned to be more resistant to damage incurred by poor vibration practices.
Producer Best Practices for Mix Workability
Presented By: Mike Baldoni
Affiliation: IMI
Description: There are several factors that can influence the vibration and consolidation of concrete. We will discuss all the factors that a ready mix producer can control and manage to ensure mix workability and performance.
Is ASTM C31 Still Adequate to Make Concrete Specimens in the Field?
Presented By: Dimitri Feys
Affiliation: Missouri S&T
Description: ASTM C31 has been proposed in 1917 based on the work performed by Abrams. In essence, the standard consolidation by rodding technique has not been changed since its inception in 1920. Consolidation procedures by interval vibration are in the standard for over 50 years. As concrete technology has significantly evolved over the last century, with the incorporation of supplementary cementitious materials, chemical admixtures, etc., is ASTM C31 still adequate?
Through an ACI Foundation CRC project, an investigation was made to evaluate the effect of different consolidation procedures on compressive strength and hardened concrete density, and their variability. Statistical analysis has shown that the rodding portion of ASTM C31 can be maintained for concrete mixtures with slump values between 4 and 10 inches, while doubling the number of layers for concrete mixtures with slump values below 4 inches showed in some cases a significant increase in strength. Internal vibration did not improve strength compared to rodding, and in many cases, a significantly lower strength was recorded while density followed a logical pattern. An increase in type 5 and 6 breaks was noted, indicating that internal vibration may segregate the concrete in the cylinder molds.