From the Portland Cement Association:

Bugholes in concrete: Causes and Cures.

Causes

Perhaps the most influential cause of bugholes is improper vibration. Consolidation, usually through vibration, sets the air and water bubbles into motion. A proper amount of vibration sends both entrapped air and excess water to the free surface of the concrete – either vertically winding through the matrix or laterally in a direct route to the form wall. Improper vibration will either insufficiently liberate the voids or over-consolidate the concrete resulting in segregation and bleeding. (See ACI 309 for a full description of consolidation using vibration.)

Another factor that promotes bughole formation is the form material itself. Nonpermeable forms (i.e. polymer impregnated wood and steel) and the use of form-releasing agents can restrict the movement of the air voids between the concrete-form interface that is necessary for bughole reduction. It is imperative that when form-releasing agents are used, they are used according to the manufacturer’s recommendations and used only with specified form material.

Mix design can also be considered a significant contributor to bughole formation. Mix designs vary widely in their use of aggregate type, size, and grading and their use of admixtures and air-entrainment. A sticky or stiff mixture that does not respond to consolidation can be directly linked to increased surface void formation.

Cure

(1) Proper consolidation. Vibration should be completed with each lift of concrete placed. As successive lifts are placed, the vibrator should penetrate the previous lift, working the entrapped air towards the form and then vertically up the sides.

(2) Permeable Forms. When impermeable forms are used, more vibration is necessary to move the air voids to the free surface of the concrete. The use of permeable forms has been shown through research to reduce bugholes significantly by allowing escaping air to move through the form to the ambient air. Choosing the proper form releasing agent in the proper amount can also improve the surface quality.

(3) Mix design. Workable, flowing mixtures are easier to place and consolidate and therefore reduce the risk of bughole formation. Concrete with an optimally graded aggregate that avoids excessive quantities of fine aggregate, properly proportioned cement content, and any admixture that provides increased flow, workability, or ease of consolidation contributes to bughole reduction. Self-consolidating concrete (SCC) is becoming increasing popular for industries (precast especially) to improve surface quality.

Bugholes as surface defects are not detrimental to structural concrete from a durability standpoint. Nevertheless, with the increased use of structural concrete in finished construction, surface quality is increasingly important. Through careful selection of materials, quality workmanship, and dutiful supervision, surface voids can be minimized.

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Read the article at cement.org.

Is a new infrastructure law possible for 2020?  As Congress reconvenes after the Martin Luther King, Jr. holiday the House is expected to unveil a new infrastructure spending bill.  In addition to funding for roads and bridges, the House bill is also expected to address other sectors such as water resources, energy, broadband, pipeline safety and climate.

On January 16th, Nancy Pelosi confirmed that the House will unveil infrastructure legislation when the chamber returns the week of January 27th, 2020.  “It’s pretty exciting, something we talked about during the campaign, and something the president talked about as a priority during the campaign,” the Speaker said during her weekly press conference. “We thought we would be able to move in a positive way on this, so far they have not come on board.  However, we decided now we just have to go forward. We do believe now with the passage of the U.S.-Mexico-Canada agreement that they might be interested in cooperating in other ways.”

Learn how to properly use internal concrete vibrators with these simple and easy to understand tips.

Vibrating concrete has many benefits such as:  Increasing the compessive strength of the concrete, increasing the bond between the concrete and the rebar and reducing the permeability of the cured concrete.    In addition, proper vibration also decreases cold joints, honeycombing and removes entrapped air making for a more attractive and structurally sound finish.    Using the simple steps listed below, even first time users of concrete vibrators can get a great finish with consistent results.

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How to use poker vibrators, how to use concrete vibrators, how to use internal vibrators, how to use cement vibrators.

Cold weather is here and with it comes the headaches associated with materials becoming stuck and frozen inside of bins and hoppers.  Though material flow problems can happen at any time during the year, outdoor bins and hoppers really begin to suffer as temperatures plummet.  Damp materials that flow well in the summer can freeze as solid as a rock during the winter.  A common solution to restoring flow is to bang on the outside of the hopper with a sledge hammer.  However, using a hammer can damage the bin wall and cause even more flow problems as the hammer marks give the material inside more places to hang up .  Flow problems due to hopper damage will continue even as temperatures warm.

A simple solution for these flow problems is to use an external vibrator on the outside of the hopper.  To be effective, however, a vibrator must be properly sized for the application.  A vibrator that is too small will not produce the desired results.  A vibrator that is too large can damage the hopper itself and may even cause the vibrator to fail prematurely.  By using our bin/hopper sizing sheet below, Denver Vibrator will be able to accurately size your application to make sure your external bin vibrator is the right one for your application.  Simply print off the work sheet, fill in the necessary information that is relevant to your application and return to us by fax or email.

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Please note that if the sizing sheet does not download the first time, try hitting your refresh button on your browser.

External electric vibrator, external air vibrator, ball vibrator, piston vibrator, hydraulic vibrator, hopper shaker, hopper vibrator, bin shaker, bin vibrator.

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Denver Concrete Vibrator is please to announce that we will be attending The Precast Show in Fort Worth, Texas.  The show dates are March 5th, 6th and 7th.  Please visit theprecastshow.org for event hours and schedule.

The Precast Show is the largest precast-specific trade show in North America and the one place where you can find the industry’s most important suppliers and foremost equipment experts under one roof.  The Precast Show is sponsored by the National Precast Concrete Association and the Precast Prestressed Concrete Institute with additional collaboration from the Canadian Precast Prestressed Concrete Institute and the Cast Stone Institute.

If you would like to attend, Denver Concrete Vibrator has a limited number of free Guest Passes available,  The guest pass entitles you to free admittance to the show including 3 days of access to the trade show floor with accompanying food and beverage,  product demonstrations and more.  Contact us and get your free pass today (while supplies last).

Stop by our booth and see some of our more popular products and take advantage of our show specials.   Booth number 1751.

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