What Is Rebar Epoxy Anchoring?
Rebar epoxy anchoring — also called post-installed reinforcement or rebaring — is the process of drilling holes into existing hardened concrete and bonding reinforcement bars (rebar) using a two-component epoxy adhesive. This creates a structural connection equivalent to cast-in-place reinforcement.
This technique is essential whenever new concrete elements must be connected to existing structures: extending floor slabs, adding shear walls, connecting new beams to existing columns, or strengthening existing members with additional reinforcement.
When Is Post-Installed Rebar Needed?
Common project scenarios that require rebar anchoring include building extensions where new slabs connect to existing structures, structural modifications such as new openings cut into existing walls requiring reinforcement, seismic retrofit where additional reinforcement is needed in existing members, construction errors where rebar was omitted or placed incorrectly, and phased construction where joints between pour stages need continuous reinforcement.
Embedment Depth: The Critical Design Parameter
The embedment depth determines the anchor's load capacity. Insufficient embedment leads to pull-out failure; excessive embedment wastes material and drilling time.
General guidelines for tension connections:- Minimum embedment: 10 times the bar diameter (10d)
- Recommended embedment: 12-15d for standard applications
- High-seismic zones: 15-20d or as specified by the structural engineer
Bond Strength: Real Test Data
The performance of a rebar anchor depends on the bond strength between the adhesive, the rebar, and the concrete. Our epoxy anchor adhesives achieve the following characteristic bond strengths:
| Concrete Grade | XQ-ZJ-E585 (Epoxy) | XQ-ZJ-V390 (Vinyl Ester) |
|---|---|---|
| C20 | ≥ 12 MPa | ≥ 10 MPa |
| C30 | ≥ 14 MPa | ≥ 12 MPa |
| C40 | ≥ 16 MPa | ≥ 14 MPa |
| C50 | ≥ 18 MPa | ≥ 16 MPa |
These values mean that in C30 concrete with our standard epoxy, a M16 rebar at 200mm embedment can resist approximately 110 kN in tension — exceeding the yield force of the rebar itself (approximately 80 kN for grade 400 steel).
Hole Preparation: Where Most Failures Originate
In our 20 years of experience, over 80% of anchor failures can be traced back to inadequate hole preparation, not adhesive performance. The bonding surface inside the drilled hole must be clean, dry, and free of drilling dust.
Step-by-step hole preparation:- Blowing with mouth instead of pump (insufficient pressure, introduces moisture)
- Skipping the wire brush step (leaves a film of fine dust bonded to the hole wall)
- Drilling with water without proper drying afterward
- Reusing holes that have been drilled for weeks (dust re-settles and moisture absorbs)
Rebar Preparation
The rebar surface also needs attention. The bars must be degreased and free of loose rust. For ribbed (deformed) rebar, the ribs provide excellent mechanical interlock with the adhesive, and no additional surface preparation is needed beyond removing contamination.
For smooth round bar, the adhesive bond relies entirely on chemical adhesion, so surface preparation is more critical. Light sandblasting or mechanical abrasion improves bond performance significantly.
Injection Procedure
Cure Time and Loading
Our epoxy anchors (XQ-ZJ-E585) reach full design strength after 24 hours at 25°C. Temperature significantly affects cure time:
| Temperature | Load-Bearing Time | Full Cure |
|---|---|---|
| 35°C | 4 hours | 12 hours |
| 25°C | 12 hours | 24 hours |
| 15°C | 24 hours | 48 hours |
| 5°C | 48 hours | 96 hours |
For cold weather applications, our fast-set vinyl ester (XQ-ZJ-VF650) provides significantly shorter cure times.