Consolidating concrete vibration

11-Jul-2016 16:39 by 2 Comments

Consolidating concrete vibration

Along with the expense of repairing surface defects, it is difficult and sometimes impossible to make repairs match the color and texture of the surrounding concrete.By understanding the causes and using effective consolidation techniques, contractors can avoid repair costs and aesthetic disputes due to consolidation-related surface blemishes.

Kim Basham is president of KB Engineering LLC, which provides engineering and scientific services to the concrete industry.

When concreting resumes, place a short lift and thoroughly vibrate the two lifts together.

Honeycomb, subsidence cracks, cold joints and excessive surface air voids are common surface blemishes associated with ineffective concrete consolidation.

Revibration is not harmful, and it can mend subsidence cracks and reconsolidate concrete after delayed settlement has occurred.

If the vibrator can be inserted into the concrete and removed without leaving a hole, it is not too late to revibrate the concrete.

It is not possible to remove all the entrapped air bubbles; however, vibration should continue until the cessation of large air bubbles occurs.

Use the largest and most powerful internal vibrator, systematically vibrate the concrete area through the full depth of the lift being sure to penetrate the previously lift and limit the distance between insertions so the area visibly affected by the vibrator overlaps the adjacent just-vibrated area.

In addition to being unsightly, formed surfaces with blemishes may not conform to the requirements of the contract documents.

When this occurs, surface blemishes become defects and subsequently must be repaired.

Continue vibrating until the coarse aggregate particles become embedded, a thin film of mortar forms on the top surface and along the form faces, and large air bubbles stop escaping from the surface. When the vibrator is first inserted into the concrete, vibrator frequency drops but then increases and finally becomes constant when the concrete is free of entrapped air bubbles.

Many times, untrained operators only level the concrete and fail to complete the de-aeration phase of consolidation resulting in unwanted surface blemishes.

Cold joints are different than lift or layer lines.