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The vibration of concrete is a critical step in concrete construction. The process eliminates air bubbles present in the freshly poured concrete and provides a compact concrete mass. Fresh concrete can be vibrated by hands or by concrete vibrating machines. Proper knowledge about different vibration methods and their applications can help in performing efficient concrete vibration.
Working of Concrete Vibrators
Concrete vibration is mostly performed by concrete vibrators that can either be electric or air-driven. The applications of concrete vibration are mainly categorized into:
- Formwork vibration
- Surface vibration
- Internal vibration
1. Formwork Vibration
Formwork vibration mounts the vibrators to the outside of the concrete forms. It is commonly used in precast concrete construction, For large area pours, the vibrators are spaced at a minimum distance of 6 feet.
2. Surface Vibration
Surface vibrators or jumpers are used to vibrate the concrete directly poured onto the surface. It is directed manually onto the surface to perform vibration. It provides a smooth surface and a nice appearance to the final concrete. This method is limited to slab construction with depth less than 6 feet.
3. Internal Vibration
Internal vibrators are the most commonly used vibrators in concrete construction. These are handled by a single operator. A probe-like internal vibrator is placed onto the wet concrete and slowly withdraws it after vibration.
Tips for Proper Concrete Vibration
In most cases, concrete is either under-vibrated or over-vibrated. Some important tips to be followed while vibrating concrete are:
- An internal vibrator must be withdrawn very slowly at a rate of 1 inch per second. If bubbles emerge at the concrete surface when the vibrator is withdrawn, it means more vibration is necessary.
- Quick vibration of concrete can result in structural failure once the concrete cures. If the concrete vibrator is used for a longer period, the aggregates and water can separate, leading to strength and aesthetic issues in the concrete.
- Always hold the vibrator in a vertical or nearly vertical position to maximize the effect of vibration.
- The concrete won't wait for sorting the equipment problems. So, always keep another vibrator as a backup if the first one fails.
- Excessive bending of the vibrator must be avoided as it would result in ruining the equipment.
- Do not use the concrete vibrator as a concrete placement tool. This mistake can result in an inconsistent surface along with other problems.
- Always make sure the concrete has not been vibrated previously by any co-workers before proceeding with vibration.
- The vibrator needle is fully inserted into the concrete and vibrated for at least 10 seconds. Make sure that the tip of the vibrator is fully submerged during vibration.
- The maximum rate at which a vibrator is pulled is 3 inches per second. Best results are yielded when the rate is 1 inch per second.
- If the first radius of vibration is R1, then the next vibration radius must include the first radius R1. Generally, as a thumb rule, the radius of action is four times the diameter of the vibrator tip.
- Stop the vibration when it does not result in the formation of any air bubbles on the surface or when a sheen surface is obtained.
- The vibrator must not be forced into the concrete as it may result in collision with the reinforcement.
- Always penetrate the previous lifts or layers of concrete to prevent cold joints. A minimum of 6-inch penetration is recommended.
- A low slump concrete requires more vibration. Therefore, never under vibrate a low-slump concrete.
- A lightweight portable vibrator can be used for small jobs.
Formwork vibration involves mounting the vibrators to the outside of the concrete forms. It is commonly used in precast concrete construction. For large area pours, the vibrators are spaced at a minimum distance of 6 feet.
Quick vibration of concrete can result in structural failure once the concrete cures. If the concrete vibrator is used for a longer period, the aggregates and water can separate, leading to strength and aesthetic issues in the concrete.