APPLICATION PRACTICES
GOOD VIBRATIONS
Researching vibration energy transfers to help track better vibration field practices. BY PAUL JAWORSKI
PHOTOS COURTESY OF MINNICH MANUFACTURING
M
embers of the American Concrete Institute (ACI) are working to bring more understanding about the use of vibration energy to the industry to improve outcomes for contractors. At the just-concluded ACI Fall Convention, promising research was presented to the Consolidation Technical Committee that can be used to capture and gather data for the purpose of machine learning during the vibration of concrete pavements. Members of the committee have been busy for the past four years gathering and testing quality control methods to offer more predictable outcomes in vibrating various concrete mixtures across several construction applications. With ACI 309 Consolidation Guidance document being re-written, the members have been engaged in producing a new document that will offer contractors a better understanding of vibration energy and how to limit the amount of surface damage from over-vibration. Since the concrete industry is focused on carbon-neutral initiatives, which includes producing concrete mixtures that use Type 1L cement, the committee has stepped up the urgency to update its guidance document. Vibration research for the document has been concentrating on the challenges of placing pumpable mixtures without separating available mix water and a more advanced testing platform targeted at machine-learning methods in placing concrete pavement mixtures. The effort has been focused on construction case studies using controlled frequency vibration (CFV) that applies the same vibration energy to the concrete, and more importantly maintains a frequency, despite any concrete load changes. The method has led to specifications that set maximum allowable limits to vibration frequency in pavements to limit any concrete distresses from frequency over-vibration. New limits to vibration frequency will result in a maximum frequency for commercial applications, especially pumpables. In 2021, Iowa State University released a study of the effects
of vibration on mixtures by looking at vibration energy transfers to clinically verify what the field studies have been empirically telling us about frequency over-vibration: the quality of concrete surfaces is usually compromised with vibrator frequency. Iowa State researchers used a fixed frequency and output of force during vibration that can be tracked through the concrete. This revealed important factors that outline the behaviour of frequency and the material separation that it causes (see Chart on Page 34). The energy transfers reveal how to meet consolidation standards in concrete mixtures while limiting the issues that come with over-vibration of low-viscosity mixtures. In a sustainable model, vibration energy is the easiest piece of the puzzle to control. The researcher simply chooses a fixed vibrator frequency that matches the workability of concrete at pre-construction trials during mock-ups. In both pavements and pumpable mixtures, just the frequency control and reduction in frequencies has shown a marked improvement in limiting the damage that high frequency does to most concrete mixtures. Once the vibrator is set at a frequency, the control of vibration process turns to evaluating the variability challenges in the workability associated with concrete production. on-sitemag.com / 33
