Chemical anchors for rebar and bolts
Epoxy anchoring adhesive allows starter bars and bolts to be bonded into concrete with high load capacity and fast installation, making it especially suitable for renovation, vertical extension and structural strengthening projects.
When a slab needs to be extended, a beam added or heavy equipment installed on an existing structure, drilling and bonding rebar with chemical adhesive has almost entirely replaced the traditional method of breaking out concrete to splice reinforcement. The anchor does not crack the surrounding concrete the way mechanical expansion bolts can.
How chemical anchors work
The adhesive is injected into the drilled hole, and then the rebar or threaded rod is inserted. Once cured, the adhesive fills the gap between the steel and the hole wall, transferring load through adhesive bond and mechanical interlock with the roughness of the concrete. The load is distributed along the embedment depth rather than concentrated at the bolt head.
Comparing anchoring adhesive types
| Adhesive type | Cure time at 20 °C | Load capacity | Applications |
|---|---|---|---|
| Pure epoxy | Approx. 7 – 12 hours | Very high, stable over the long term | Structural rebar, deep holes |
| Epoxy acrylate | Approx. 1 – 2 hours | High | Bolt anchoring, fast-track schedules |
| Polyester | Approx. 30 – 60 minutes | Medium | Light loads, solid brick, masonry walls |
Correct installation procedure
- Drill the hole to the correct diameter, typically 4 to 6 mm larger than the bar diameter.
- Blow out the dust and brush the hole with a dedicated brush, repeating at least twice.
- Dispense and discard the first portion of adhesive until the color is uniform.
- Inject adhesive from the bottom of the hole until it is about two-thirds full.
- Rotate the bar slightly while inserting it to the design depth, and do not disturb it until the adhesive has cured.
Hole cleaning is the decisive step. Residual dust can reduce anchor capacity by 40 to 60% compared with published values.
Anchor quality testing
Once the adhesive has reached full strength, the supervising engineer typically selects a random percentage of anchors for on-site pull-out testing with a hydraulic jack. Acceptance records should include the adhesive lot number, installation temperature and pull test results.
Temperature has a strong effect on cure time. In winter in Northern Vietnam, when concrete is only about 10 °C, the waiting time can be twice as long as under standard conditions. Conversely, at midday in summer, working time is shortened, so workers need to have the bars ready and work quickly after injecting the adhesive. Holes with standing water also require an adhesive grade approved for installation in wet holes.
Contact AMS Vietnam for advice on selecting anchoring adhesive and calculating rebar embedment depth for your renovation project.
