In short
Post-installed rebar continues the reinforcement of an existing member and is designed to EN 1992-1-1 with the product's bond values (EOTA TR 023), or, for products assessed to EAD 332402, with the bond-splitting method of EOTA TR 069. A bonded anchor is a fastening designed to EN 1992-4. Both need a suitable ETA and correct drilling, cleaning and injection.
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Extending a slab, adding a wall to an existing raft, strengthening a column or connecting a new staircase all involve fixing new steel into old concrete. Two families of solution use the same injection mortars and look almost identical on site, but they are designed in different ways: post-installed rebar and bonded anchors. Choosing the wrong design approach is a serious error. This guide explains the difference, which design documents apply, and what installation quality involves.
What is the difference between post-installed rebar and a bonded anchor?
Post-installed rebar acts as reinforcement: the bar laps with existing bars or is anchored within the existing member, and the reinforcement carries the force onward. A bonded anchor acts as a fastening: the load goes into the surrounding concrete, which in the usual case must resist it without relying on reinforcement. EN 1992-4 does allow supplementary reinforcement to take concrete failure modes where it is designed for that purpose.
This difference determines everything else. In a rebar connection the design assumes the existing reinforcement and the concrete between the bars form a load path, as in a strut-and-tie model. With TR 023 the checks are the bond along the embedded length, concrete cover, bar spacing and the force transfer to existing bars. With TR 069 the anchorage is checked for steel yielding, concrete cone and bond splitting, so edge distance and cover also matter for rebar. In an anchor design the checks include combined pull-out and concrete failure, concrete cone breakout, splitting, edge breakout under shear and pry-out, all of which depend strongly on edge distance, spacing and member thickness.
| Aspect | Post-installed rebar | Bonded anchor |
|---|---|---|
| Structural role | Reinforcement continuity or anchorage | Fastening of a fixture or base plate |
| Typical applications | Slab and wall extensions, new elements cast against existing, column and beam strengthening | Steel base plates, brackets, façade and MEP supports, handrails |
| Design basis | EN 1992-1-1 with EOTA TR 023, or EOTA TR 069 (bond-splitting method) | EN 1992-4 |
| Governing checks | TR 023: bond, anchorage and lap length, cover, spacing, load path into existing reinforcement. TR 069: steel yielding, concrete cone, bond splitting | Steel, combined pull-out and concrete, concrete cone, splitting, edge breakout, pry-out |
| Typical embedment | Long. Often tens of bar diameters | Shorter. Set by the anchor design |
| European assessment | ETA to EAD 330087 (for TR 023) or EAD 332402 (for TR 069) | ETA to EAD 330499 (bonded fasteners) |
Which design documents apply?
Three documents cover most cases. EN 1992-4 covers fastenings such as bonded anchors. EOTA TR 023 covers post-installed rebar designed like cast-in bars to EN 1992-1-1, for both end anchorage and lap splices. EOTA TR 069 is an alternative design method, based on bond-splitting behaviour, for post-installed rebar end anchorage and moment-resisting concrete-to-concrete connections. Lap splices are designed to EN 1992-1-1 with the applicable post-installed rebar ETA. The product's European Technical Assessment must cover whichever method you use.
- EN 1992-4:2018 (Eurocode 2, Part 4): design of fastenings for use in concrete, covering cast-in and post-installed anchors, including bonded anchors. The product values come from the anchor's ETA.
- EOTA TR 023: the design basis for post-installed rebar connections to EN 1992-1-1, used with products assessed to EAD 330087. The bar is treated like a cast-in bar. Anchorage length (EN 1992-1-1, 8.4) and lap length (EN 1992-1-1, 8.7) are calculated using the design bond strength from the product's ETA. This bond strength may be lower than for cast-in bars, depending on the product, drilling method and concrete class. Minimum anchorage and lap lengths follow EN 1992-1-1 (Eq. 8.6 and Eq. 8.11), with any increase the ETA requires. Minimum concrete cover depends on the drilling method, the use of a drilling aid and the embedded length, and is given in TR 023 and the ETA.
- EOTA TR 069: a design method for the anchorage length of post-installed rebar that combines EN 1992-1-1 with EN 1992-4 principles. It checks three failure modes (steel yielding, concrete cone and bond splitting) and the lowest resistance governs. Bond-splitting resistance depends on concrete cover and is taken from the product's ETA. Because bond resistance is related to the actual cover, the required anchorage length can be shorter than to EN 1992-1-1 where cover is generous. TR 069 can be used only with products assessed to EAD 332402. An assessment to EAD 330087 alone is not sufficient. It applies to normal-weight, non-carbonated concrete from C20/25 to C50/60.
TR 069 covers end anchorage and moment-resisting concrete-to-concrete connections, not lap splices. For any reinforcement connection, designers should also check the parts of EN 1992-1-1 that apply: cover for durability and bond (4.4.1), bar spacing (8.2), transverse reinforcement at laps (8.7.4), shear transfer at the interface between old and new concrete (6.2.5, which may require a roughened surface), and whether the existing member has enough capacity to take the new forces.
End anchorage or lap splice: which applies?
If the new bar overlaps an existing bar that continues the tension, it is a lap splice. If the new bar has to develop its force within the existing concrete with no existing bar to transfer to, it is an end anchorage. Identify which case you have before choosing a design method.
| Situation | Typical case | Design reference |
|---|---|---|
| Slab extension where new top and bottom bars overlap existing slab bars | Lap splice | EN 1992-1-1 (8.7) with the product's post-installed rebar ETA (EOTA TR 023) |
| Column jacketing or thickening with bars lapped alongside existing column bars | Lap splice | EN 1992-1-1 (8.7) with the product's post-installed rebar ETA (EOTA TR 023) |
| New wall or cantilever slab anchored into an existing wall or foundation, where the bar cannot be lapped, including moment-resisting connections | End anchorage | EN 1992-1-1 (8.4) via EOTA TR 023, or EOTA TR 069 where the product is assessed to EAD 332402 |
| Steel bracket or base plate fixed to concrete | Fastening, not rebar | EN 1992-4 |
Moment connections, such as a cantilever balcony or a retaining wall added to an existing footing, need particular care. The existing member must have reinforcement placed to take the tension and compression forces from the new element. A long post-installed bar cannot make up for an existing member that has no suitable reinforcement.
What does installation quality involve?
Installation quality means following the manufacturer's instructions from the ETA exactly: approved drilling method, specified hole diameter and depth, the full cleaning sequence, void-free injection from the bottom of the hole, and undisturbed curing for the specified time at the actual concrete temperature. Bond values in the ETA are valid only when all of these are met.
- Locate existing reinforcement with a cover meter or scanner before drilling. Agree with the engineer of record what to do if a bar is hit. Do not cut existing reinforcement without approval.
- Drill using a method the ETA permits: hammer drilling, hollow drill bit with vacuum extraction, compressed-air drilling, or diamond core drilling where assessed (some products need the hole roughened after core drilling). Use a drilling aid or guide for long holes to keep them straight and maintain the edge cover; the minimum cover in the design depends on whether one is used.
- Clean the hole exactly as the instructions specify, typically repeated cycles of blowing with oil-free compressed air and brushing with a brush of the correct diameter. Some ETAs allow a reduced procedure with hollow drill bits. Dust left in the hole is one of the most common causes of reduced bond.
- Check hole condition. Dry, wet or flooded holes each have to be covered by the ETA, and bond values may differ between them.
- Inject from the bottom of the hole using mixer extensions and piston plugs for deep or overhead holes, so that no air is trapped. Discard the first mortar from each new cartridge as instructed.
- Insert the bar clean and free of oil, marked for the embedment depth, with a slight twisting motion, within the working (gel) time. Check that mortar appears at the hole mouth.
- Do not disturb or load the bar until the specified cure time for the concrete temperature has passed. Cold concrete greatly extends cure time.
On critical work, installers should be trained on the specific product, and the installation should be supervised and recorded. Site proof testing may be specified. Its extent and loads are set by the engineer and the specification.
How do you check that a product is approved?
Check that the mortar has a current European Technical Assessment covering the intended use (rebar connections, anchors, or both) and the intended design method, and that the ETA covers your bar diameters, embedment depths, drilling method, hole condition, temperature range and any seismic or fire requirements.
- EAD 330087 is the assessment document for systems for post-installed rebar connections with mortar. It gives the bond values used with TR 023.
- EAD 332402 is the assessment document for post-installed rebar connections with improved bond-splitting behaviour. It gives the bond-splitting values needed for TR 069.
- EAD 330499 is the assessment document for bonded fasteners for use in concrete. It gives the performance values used with EN 1992-4.
- Seismic performance: anchors may be assessed for seismic performance categories C1 and C2. For rebar, use seismic bond values only if the ETA states them. Use only what the ETA covers.
- Fire: some ETAs include bond resistance at elevated temperature. Fire design is possible only where the ETA provides these values.
- Service temperature and working life: the ETA defines the in-service temperature ranges and the assumed working life. Check both against the project.
Epoxy and vinyl ester (hybrid) mortars differ in cure speed, working time, temperature range and approved uses. See epoxy vs vinyl ester anchors for a comparison.
What are the most common mistakes?
Typical errors are designing an anchor case as rebar (or the reverse), using bond values or a design method the ETA does not cover, cutting or skipping hole cleaning, and loading the bar before the mortar has cured.
- Treating a short bar near an edge as a rebar connection when no reinforcement load path exists.
- Using a product's anchor ETA values for rebar design, or the reverse.
- Designing to TR 069 with a product assessed only to EAD 330087.
- Using TR 069 outside its scope, for example in carbonated concrete or outside C20/25 to C50/60.
- Ignoring the existing member's capacity to take the new forces.
- Substituting a different mortar on site without redesign. Bond values and installation rules are product-specific.
- Drilling with a method or into a hole condition the ETA does not cover.
- Using the cure times for warm conditions when the concrete is cold.
How SHM360 helps
AnchorDesign360™ is SHM360’s tool for post-installed connections in existing concrete. It works in three steps: design, compare, choose.
- Design. Model the connection and check it to the right document: base plate anchors to EN 1992-4, post-installed rebar end anchorage and lap splices to EOTA TR 023, and end anchorage and moment-resisting connections to EOTA TR 069 where the product is assessed for it. Each check uses the product’s own ETA data.
- Compare. Run the same design across injection mortars from different manufacturers and see side by side which products work for your case and how they perform.
- Choose. Select the product that suits the job, with the design basis behind the choice.
Frequently asked questions
What is the difference between post-installed rebar and a bonded anchor?
Post-installed rebar is designed as reinforcement: it laps with existing bars or is anchored in the existing member, and the reinforcement carries the force onward. A bonded anchor is designed as a fastening to EN 1992-4, where the concrete around the anchor must resist the load and edge distance, spacing and member thickness govern.
When is TR 023 used and when is TR 069 used?
EOTA TR 023 covers post-installed rebar designed like cast-in bars to EN 1992-1-1, for both end anchorage and lap splices, with products assessed to EAD 330087. EOTA TR 069 is an alternative method for end anchorage and moment-resisting concrete-to-concrete connections that checks steel yielding, concrete cone and bond splitting; it does not cover lap splices. It can be used only with products assessed to EAD 332402, in non-carbonated concrete from C20/25 to C50/60, and can give shorter anchorage lengths where cover is generous.
Which approval does a post-installed rebar mortar need?
In Europe, look for a European Technical Assessment (ETA) issued against EAD 330087 for design to TR 023, and against EAD 332402 if you intend to design to TR 069. Bonded anchor use is assessed separately, under EAD 330499. The ETA states the permitted bar sizes, drilling methods, hole conditions, temperatures and bond values.
Why is hole cleaning so important for post-installed rebar?
Drilling dust left in the hole coats the wall and reduces the bond between mortar and concrete. The bond values in an ETA assume the cleaning procedure in the manufacturer's instructions was followed exactly.
Can post-installed rebar be installed in wet or water-filled holes?
Only if the product's ETA covers that hole condition. Some mortars are assessed for dry and wet concrete, fewer for flooded holes, and bond values may be reduced.
This article is general technical information, not project advice. Your project specification, the applicable standards and the engineer of record govern.
