Internal mechanical vibration is the most consistent and effective method of consolidating concrete for Insulated Concrete Form (ICF) applications and therefore will be the focus of this entry.
Equipment
Low modulation (small movement) and high frequency (many times per minute) is the best method to vibrate within Insulated Concrete Forms (ICF). The most effective vibrator to achieve this result is an immersion type concrete vibrator with a 12’ (3.7m) flex shaft. The specific requirements differ slightly for different concrete core sizes. The following chart provides the recommended specifications for concrete vibrators used with ICF:
| Requirement | 4” & 6” | 8” & 10” |
| Maximum Vibrator Head Diameter | 1” (25mm) | 1.25” (38mm) |
| Frequency (vibrations/min) | 10000 | 9000 |
| Minimum Radius of Action (overlap) | 4” (100mm) | 6” (152mm) |
| Insertion on Center Spacing | 6” (152mm) | 9” (228mm) |
| Centrifugal Force | 220lbs (100kg) 2-4 yds3/hr |
500lbs (225kg) 2-5 yds3/hr |
| Compaction Rate | 1.5-3m3/hr | 1.5-3.8m3/hr |
Technique
The most important part of consolidation is proper technique. To vibrate properly, plunge the vibrator head to the bottom of the 4’ (1.2m) lift of concrete as quickly as possible and retract it slowly (approximately 3” (76mm) per second). Remove the vibrator head and re-insert it at a distance 1.5 times the radius of action. This will create an overlap with the previously vibrated area ensuring proper consolidation. When working on subsequent lifts, repeat the above method, but also penetrate into the top 6” (152mm) of the previous lift. This will fuse the lifts together, eliminating any pour seams or cold joints.
Keys to Success
For effective concrete consolidation, follow these three guidelines to ensure success:
1. Use a concrete mix with a slump of at least 6” (152mm).
2. Brace corners and lintels very well and vibrate them thoroughly.
3. Hire an experienced trained operator.