1. Anchor
Channel Systems
2. HAC
Portfolio
3. HAC
Applications
11.5.6 CONCRETE CONSOLIDATION
7. Anchor Channel
Design Code
8. Reinforcing
Bar Anchorage
9. Special Anchor
Channel Design
10. Design
Software
14. Design
Example
The Process of Concrete Consolidation
When concrete is first poured, entrapped air can occupy up
to 20% of the concrete volume (1). The amount of entrapped
air varies depending on the concrete’s workability. As a rule of
thumb, concrete compressive strength improves by about 5%
for every 1% of air removed (3). Figure 11.5.6.2 illustrates the
decrease in strength of the designed concrete compressive
strength per percentage of entrapped air. Proper concrete consolidation helps avoid air pocket
formations, honey combs, and removes the entrapped air in the
concrete. Adequate concrete consolidation helps ensure the
concrete will reach its designed properties as well as helping
the concrete reach its designed strength. Moreover, adequate
concrete consolidation helps enhance the bond of the concrete
with the reinforcing bars and increases the general durability
of the concrete. Finally, it helps decrease the permeability and
helps minimize it’s shrinkage and creep characteristics. Figure
11.5.6.4 provides pictures of jobsites with proper concrete
consolidation at the anchorage zone. Although there are different ways to consolidate the concrete,
the most effective way to remove entrapped air is vibration.
Vibration consists of subjecting freshly placed concrete to rapid
vibratory impulses which liquefy the mortar and significantly
reduce the internal friction between aggregate particles (1).
Figure 11.5.6.5 illustrates a construction member vibrating the
concrete at the anchorage zone using a standard immersion
vibrator.
Figure 11.5.6.2 — Loss of Concrete Compressive Strength Through Increase
in Entrapped Air (2).
Concrete Consolidation
Figure 11.5.6.5 – Construction Member Vibrating the Concrete at the
Anchorage Zone.
Concrete consolidation is defined as the process of removing
entrapped air from freshly placed concrete. Several methods and
techniques are available, the choice depending mainly on the
workability of the mixture, placing conditions, and degree of air
removal desired. Some form of vibration is usually employed (1).
Figure 11.5.6.3 — Pouring and Vibrating Concrete at the Edge of the Slab.
Figure 11.5.6.4 — Pictures of Conditions with Proper Concrete
Consolidation at the Anchorage Zone.
Cast-In Anchor Channel Product Guide, Edition 1 • 02/2019
361
Water
Cement
Sand (small aggregate)
Rock (large aggregate).
Per ACI 309R-05, the procedure for internal vibration shall be as
follows (1):
• Concrete should be deposited in layers compatible with the
work being done.
• The maximum layer depth should be limited to 20”.
• The depth of the layer should be nearly equal to the vibrator
head length.
• The layer should be as level as possible so that the vibrator is
not used to move the concrete laterally, as this could cause
segregation.
• The vibrator should be systematically inserted vertically at a
uniform spacing over the entire placement area.
• The distance between insertion should be approximately
1-1/2 times the radius of influence and should be such that
the area visibly affected by the vibrator overlaps the adjacent
just-vibrated area.
Consolidation via standard immersion vibrators is best
described as consisting of two stages — the first comprising
subsidence or slumping of the concrete, and the second a
de-aeration (removal of entrapped air bubbles). The two stages
may occur simultaneously, with the second stage underway
near the vibrator before the first stage has been completed at
greater distances (2). Figure 11.5.6.6 illustrates the two-stage
process to best consolidate concrete. If in doubt, always err
on the side of more vibration.
Concrete is the combination of four basic components:
360
13. Field Fixes
Purpose of Concrete Consolidation
Concrete
When mixed together, hydration, or curing, occurs, where the
cement paste acts as a glue binding all of the surrounding
aggregates. When concrete is poured, it contains entrapped air.
If the entrapped air is not removed and the concrete is hardened
in this way, it will negatively impact the expected properties of
the concrete. Moreover, it will create serviceability, esthetics,
and other issues such as subsidence cracking, and placement
lines (1).
12. Instructions
for Use
Entrapped Air in Concrete
Figure 11.5.6.1 — Pictures of Conditions with Improper Concrete
Consolidation at the Anchorage Zone.
•
•
•
•
11. Best
Practices
Proactivity goes a long way. Implementing best practices
that ensure adequate concrete consolidation will ensure the
anchorage will perform the way it was designed. During pre-
construction meetings, emphasize the importance of
adequate concrete consolidation at the anchorage zone,
especially if the cast-in anchor is near a confined space or
congested zone. Try it out in your next project!
6. Loading
Air pocket formation occurs due to improperly or no concrete
consolidation. Repairing cured concrete with entrapped air
is time-consuming, tedious, and can turn out to be quite
expensive. Adopting best practices to ensure proper concrete
consolidation is performed at the anchorage zone is one
of the most effective ways to minimize field issues due to
improper concrete consolidation. A couple of extra seconds
at each connection point can pay dividends, avoid additional
coordination and additional work to an already complex and
fast-track work environment where the project’s schedule leaves
room for a minimal margin of error.
5. Base material
The combination of new construction practices, new
technologies, and more sophisticated designs is allowing for
the construction of buildings in record times. Spans get longer,
columns get smaller, slabs get thinner, and lighter construction
materials are used. As a result, the construction process has
become more complex and best practices have evolved to
solve the disputes of modern business. A common field issue
encountered in building construction is the formation of air
pockets (entrapped air) in the concrete at the anchorage zone.
4. Design
Introduction