The VKelly test was developed to provide agencies and contractors a tool that reports how a slipform paving mixture responds to vibration.  It has been noted in the past that the slump test was useful, but did not provide a complete picture of the workability of a mixture.  Increased complexity of mixtures including the use of supplementary cementitious materials and chemical admixtures has reduced the usefulness of the information provided by the slump test.  In addition, current construction tools call for more information about all of the rheological properties of a mixture that are not fully described by the slump test.

Initial evaluation by agencies has shown that the VKelly does provide useful, numerical and repeatable data on how a mixture will perform in a paving machine and that it could distinguish between workability of mixtures with similar slumps.  It has also been used by contractors to develop mixture proportions that were reported to be successful in the field.  They were able to reduce the amount of cementitious materials in a mixture while improving workability without compromising engineering properties.

A number of rigs were sent to agencies around the country for them to evaluate.  Feedback indicated that while seemingly technically sound, the test was challenging to operate.

The aim of the work is threefold:

• Make the test more user friendly and portable
• Understand the science behind the method to guide mixture proportioning and field operations based on test results
• Broaden the applicability to include structural and pumping mixtures

The long-term vision of this work is to develop an understanding of how mixtures can be proportioned that are relatively insensitive to vibration abuse or are ideal for the vibration system planned for use on a given site.  In addition, it is desirable that a real-time test be available on a site so that as a mixture is delivered, it can be tested for workability variances due to batching or transport, thus providing the operator with guidance on how to tune the placing equipment for a truckload for a given workability. Data can also be provided to the batch plant to guide proportions for the next truck to maintain uniformity.

At present, the output from the method is a so-called VKelly Index that has been tested in the field to assess upper and lower limits for slipform paving. Initial laboratory test data using a smart vibrator that also reports the voltage required to maintain a constant vibration frequency also indicates the potential to assess a number of other mixture properties. Based on this information there is a need to fully understand the mixture and equipment factors that influence the rate at which the ball sinks under vibration and how it can be used to guide mixture proportioning and construction processes.

The overall scope is to refine the VKelly method and provide a cost effective, useful, operator friendly, portable, device that delivers a wealth of information about the fresh properties of a mixture before it is even unloaded from a dump truck.  It is the goal to extend the applicability of the method to be useful for structural concrete. Please refer to the expanded scope in the Documents section below for additional parameters and information.

Device Variables - Parameters that can be adjusted in the VKelly test include:

• Amplitude of the vibrator head.  In reality, this is not true, because most commercial vibrators operate with a fixed weight offset leading to amplitudes of around 2 mm.  Adjusting the equipment to vary this would be expensive.
• Vibrator frequency can be controlled using commercial devices.  It is desirable to stay within the range of recommended practice, although tests should be conducted over a range of frequencies to ascertain recommended limits.
• Etc.

Mixture Variables - A wide range of mixture variables needs to be tested to understand this method, and how a mixture response to vibration is affected by ingredients and proportions:

• Use of added water or WRA to adjust a mixture between the batch plant and the point of delivery
• The quality of the air void system including total air volume along with bubble size, spacing and stability
• The type and dosage of supplementary cementitious materials
• Etc.

Tests - It is proposed that the following tests be conducted on the various mixtures prepared using the various device parameters discussed above:

• Initial sink vs slump
• Rate of sink of VKelly balls under vibration
• ICAR rheology for structural mixtures
• Voltage curve of vibrator
• Standard fresh concrete characterization tests such as slump, SAM, bleed, segregation, and calorimetry

Analysis - All of the data collected will be cross-correlated to look for trends and relationships to understand how vibration affects a mixture, how mixture proportions influence responses, and which tests methods provide the necessary information to be useful.

At the end of the day, it is planned to refine the VKelly method and provide a cost effective, useful, operator friendly, portable, device that delivers a wealth of information about the fresh properties of a mixture before it is even unloaded from a dump truck.  It is the goal to extend the applicability of the method to be useful for structural concrete.

Desired total commitment from each partner is $20,000 split between FY22-24. This can be accomplished through two years at $10,000, one year at $20,000 or any other combination.

Will be pursuing a 100% SPR Part B waiver.

Additional partners are always welcome. Please reach out to the Lead Agency Contact at any time.