Anchoring to Concrete · ACI 318-19 Chapter 17 · ACI 355.4
To install epoxy anchor bolts correctly in RCC framing, you must understand both the ACI 318 design requirements and the product-specific field procedure from start to finish. Epoxy-bonded (adhesive) anchor bolts are the standard method for post-installing threaded rod and rebar dowels into hardened reinforced-cement-concrete (RCC) framing — column and beam extensions, machine bases, ledger connections, seismic retrofits, and dowelling new pours into existing structure.
Because the bolt’s entire capacity depends on a chemical bond formed on site rather than on a factory-controlled cast-in condition, ACI 318 treats adhesive anchor installation as a load-bearing construction activity, not a routine fixing job. This tutorial walks through the process end to end — design basics, tools, the drill-clean-inject-insert sequence, cure and torque, and the certified-installer/special-inspection requirements that ACI 318-19 attaches to this anchor type.
anchoring to concrete
qualification standard
cleaning cycles
horizontal sustained-tension anchors
Every number in this guide that varies by product — embedment depth, hole diameter, cleaning method, cure time, installation torque, edge distance and spacing — is set by the individual adhesive system’s ICC-ES Evaluation Service Report (ESR) and Manufacturer’s Printed Installation Instructions (MPII), not by ACI 318 itself. The code tells you what must be verified and who is allowed to install and inspect; the ESR/MPII for the specific product tells you the exact figures.
Treat every table below as illustrative of the pattern, and always pull the current MPII for the product actually being used before cutting a hole. This guide covers everything you need to correctly install epoxy anchor bolts — from substrate verification and design checks through post-cure torque and documentation.
1. Governing codes: ACI 318, ACI 355.4 and ICC-ES AC308
Three documents govern an epoxy-bonded anchor in the US code framework, and each does a different job:
| Document | Role |
|---|---|
| ACI 318-19, Chapter 17 | Design provisions for anchoring to concrete — cast-in, post-installed mechanical, and post-installed adhesive anchors. Covers strength design, applicable ductility/seismic categories, and construction requirements including installer certification (17.8.2) and inspection (26.13). |
| ACI 355.4 | Laboratory qualification standard for adhesive anchor systems — tension/shear capacity, sustained-load (creep) behaviour, cracked vs. uncracked concrete performance, and seismic qualification. Products don’t pass or fail ACI 318 directly; they’re tested to ACI 355.4 and the results become the design values in the product’s ESR. |
| ICC-ES AC308 | The acceptance criteria ICC-ES evaluation reports are written to, harmonized with ACI 355.4/ACI 318. The resulting ESR is the document a designer and inspector actually reference on a project — it lists characteristic bond stress, minimum embedment/edge distance/spacing, hole-cleaning method, and installation torque for that specific product. |
IBC adopts ACI 318 by reference for anchor design (IBC 1901.2) and separately requires special inspection of post-installed anchors under IBC 1705.1.1 / 1705.3. The full ACI 318-19 and ACI 355.4 standards are published by the American Concrete Institute; ICC-ES evaluation reports are searchable at ICC-ES.org.
2. How the bond works: failure modes and the bond-strength equation
A cast-in headed bolt develops most of its tension capacity through bearing on the head. An adhesive anchor has no head bearing on hardened concrete — its entire tension path is the shear bond between the cured adhesive and (a) the threaded rod/rebar surface and (b) the drilled concrete hole wall. ACI 318-19 Table 17.5.1.2 requires every adhesive anchor to be checked against the same failure-mode family as other post-installed anchors, plus one that’s unique to this anchor type:
| Failure mode | Governs when… |
|---|---|
| Steel strength (tension & shear) | Anchor rod/rebar yields or fractures — usually governs for short embedment or high-strength concrete. |
| Bond strength (adhesive–concrete interface) | Unique to adhesive anchors. Governs for typical embedments in normal-strength concrete; this is the failure mode this tutorial is really about. |
| Concrete breakout | A cone of concrete pulls out around the anchor group — governs near a free edge or with close anchor spacing. |
| Concrete pryout (shear) | Short, stiff anchors under shear can lever a breakout on the back side of the hole rather than shearing the rod. |
| Concrete side-face blowout | Deep embedment close to an edge; a wedge of cover spalls off sideways. |
The bond-strength check — ACI 318-19 Eq. 17.6.5.2a — is the equation that makes adhesive anchors different from every other anchor type in the chapter:
Nba = λa · τuncr or cr · π · da · hef
λa = lightweight-concrete modification factor (1.0 for normal-weight concrete) · τ = characteristic bond stress from the product’s ESR (uncracked-concrete value if the region is verified uncracked at service load, cracked-concrete value otherwise) · da = anchor outside diameter · hef = effective embedment depth. This basic value is then reduced by projected-area, edge-distance (ψed,Na) and, for anchors without supplementary confining reinforcement, splitting (ψcp,Na) factors before it becomes the anchor’s design bond strength, exactly parallel to the way concrete breakout strength is derived elsewhere in Chapter 17.
Why “cracked vs. uncracked” mattersThe characteristic bond stress τ used in the equation above can be two to three times higher for uncracked concrete than for cracked concrete in the same product’s own ESR. Unless the design has specifically verified the anchorage region stays in compression (or below the cracking moment) under service loads, ACI 318 requires the cracked-concrete value — which is also the only value most ESRs publish a seismic (SDC C–F) design strength for. Don’t upgrade to uncracked values without that verification in the calc package.
3. Design basics: embedment, edge distance and spacing
ACI 318 does not publish a universal embedment-depth table the way older rules-of-thumb (e.g. “8–12 bar diameters”) implied — effective embedment hef is a design output that falls out of the bond and breakout checks for the specific product, bar size, concrete strength and edge/spacing condition. That said, the shape of the requirement is consistent across every qualified system:
- Minimum embedment is set by the product’s ESR — commonly in the range of 4–6 anchor diameters as an absolute floor, with typical structural embedments landing at 8–12 diameters once bond and breakout are both satisfied.
- Minimum edge distance and spacing are also ESR values, not code constants; they’re driven by the same splitting (ψcp,Na) and breakout-area logic used for cast-in anchors, scaled to that product’s bond strength.
- Post-installed rebar dowels (epoxying new reinforcing steel into an existing RCC beam, column or slab to develop a splice) are designed under the same Chapter 17 adhesive-anchor bond provisions when treated as anchors, or under ACI 318 Chapter 25 development-length provisions using the product’s qualified bond values when treated as a development-length application — confirm which design basis the ESR supports before dowelling rebar rather than bolts. For rebar material grades and production, see our guide to how rebar is made and graded.
- Hole diameter and drill-bit type are matched to the anchor diameter in the ESR’s drilling table — oversizing the hole to “make it easier” reduces bond area and is one of the most common defects when contractors install epoxy anchor bolts in the field.
4. Certified installer and special inspection requirements
This is the requirement most often missed on RCC framing projects, and it’s written directly into ACI 318-19, not left to the ESR:
ACI 318-19 §17.8.2.4Adhesive anchors that resist sustained tension loads and are installed in a horizontal or upwardly inclined orientation must be installed by personnel certified through an applicable adhesive anchor installer certification program (the ACI/CRSI Adhesive Anchor Installer Certification program, or an equivalent recognized by the jurisdiction). Downward-oriented anchors resisting sustained tension, and anchors in any orientation not resisting sustained tension, fall outside this specific mandatory-certification trigger — but most specifiers require certified installers for all structural adhesive anchor work regardless, since it is the single biggest predictor of field bond-test failures.
Separately, IBC 1705.1.1 (referencing ACI 318 §26.13) requires special inspection of post-installed adhesive anchors on virtually every structural application. The level of inspection is tied to orientation and load type in the same way as the installer-certification trigger:
| Condition | Inspection level |
|---|---|
| Horizontal or upwardly inclined orientation, resisting sustained tension | Continuous |
| All other orientations / load conditions | Periodic (minimum), continuous where the AHJ or design documents require it |
“Sustained tension” typically means dead-load tension that’s present essentially all the time (e.g. a hanging mechanical support), as distinct from wind or seismic tension that’s transient — check the project’s inspection statement, since designers commonly specify continuous inspection more broadly for critical connections.
5. Tools and materials checklist
- Approved adhesive anchor system with current ESR and unexpired cartridge, matched dispenser tool and static mixing nozzle for that product
- Rotary hammer drill and carbide-tipped bit sized exactly to the product’s drilling table (a bit ground down from use runs undersize and must be rejected)
- Rebar locator / ground-penetrating radar or cover meter to scan the hole path and avoid cutting existing reinforcement
- Oil-free compressed air source (or manufacturer-approved vacuum system) meeting the ESR’s minimum pressure/volume for hole blow-out
- Correct-diameter nylon or steel wire brush as specified by the ESR (undersized brushes are a common defect — they don’t contact the hole wall)
- Depth gauge or marked drill bit / anchor rod to confirm hole depth and embedment depth by direct measurement, not by eye
- Calibrated torque wrench for post-cure tightening, plus washers and nuts matched to the anchor
- Anchor rod / threaded rod / deformed rebar of the specified grade, cut square, deburred, and free of oil, rust scale or coatings incompatible with the adhesive
- Installer certification card (where required) and an inspection/QA checklist with camera for photo documentation
6. How to Install Epoxy Anchor Bolts: Step-by-Step Procedure
The steps below show how to install epoxy anchor bolts following the generic pattern common to ICC-ES AC308-qualified systems. This sequence is not a substitute for the MPII of the specific product being used — hole-cleaning cycle counts, injection fill fraction, and cure/gel times in particular vary by product and must come from that document.
Step 1Verify the substrate and scan for existing reinforcement
Confirm the base material is within the ESR’s qualified range (normal-weight concrete, minimum specified compressive strength f′c, member thickness, cracked or uncracked condition, and installation temperature range). Scan every hole location with a rebar locator before drilling — cutting existing reinforcement to install a new anchor is a structural defect, not a tolerable installation shortcut, and is one of the most common causes of rework on RCC retrofit work.
Step 2Mark and drill the hole
Mark hole locations from the approved layout drawing and drill with a rotary hammer and the exact bit diameter listed in the product’s drilling table, to a depth equal to the required embedment plus the ESR’s allowance for drilling dust and tolerance. Hold the drill perpendicular to the surface (or at the specified angle for inclined installations) — an out-of-square hole reduces effective bond area on one side.
Step 3Clean the hole — brush and blow
Hole cleaning is the single step most correlated with adhesive anchor field failures, because drilling dust left on the hole wall coats the concrete and blocks bond formation. The generic AC308 cleaning sequence is a repeated blow–brush–blow cycle, done in the exact order and count specified by the ESR:
| Pass | Action | Purpose |
|---|---|---|
| 1 | Blow compressed air from the back of the hole outward, full depth, minimum dwell per ESR | Remove loose drilling dust |
| 2 | Scrub with the correct-diameter wire brush, full depth, specified number of passes | Break up dust bonded to the hole wall |
| 3 | Blow again, full depth | Remove dust loosened by brushing |
| 4 | Repeat brush and blow for the ESR’s specified total cycle count (commonly a total of two brush and two blow cycles for hand-cleaned holes) | Reach the bond-critical “clean and dry” condition the ESR was tested to |
Some qualified systems permit a single-step vacuum-assisted hollow drill bit (“SDS-plus/max hollow bit + vacuum”) in place of the brush-and-blow cycle — only use this method if the specific product’s ESR lists it as an approved alternative.
Step 4Prime the dispenser and check the mix
Fit the static mixing nozzle to the cartridge and discharge the first several strokes to waste (not into the hole) until the adhesive extrudes as a single, uniform colour with no streaking — streaking means the two components aren’t mixing 1:1 and the anchor will not achieve design bond strength. Many systems include a colour-change witness strip on the nozzle tip for exactly this check.
Step 5Inject the adhesive
Insert the nozzle to the back of the hole and inject while slowly withdrawing it as the adhesive fills, so the hole fills from the bottom up with no trapped air pockets. Fill to the fraction of hole depth specified in the MPII — commonly around half to two-thirds — leaving room for the anchor rod to displace adhesive upward without excessive waste when it’s inserted.
Step 6Insert the anchor
Push the anchor rod or rebar into the hole with a slow turning/rotating motion to work adhesive around the full circumference and up along the threads or deformations, to the embedment depth marked on the rod. Confirm adhesive squeeze-out at the hole mouth — its absence usually means the hole wasn’t filled enough in Step 5. For horizontal or overhead holes, hold or wedge the anchor in position until it will no longer sag under its own weight (well before full cure).
Step 7Respect gel time — do not disturb
Do not load, torque, or move the anchor during the adhesive’s gel time. Gel time and full cure time both shorten sharply as temperature rises and lengthen just as sharply as it falls — cold-weather installations frequently need a cold-temperature-rated adhesive formulation and a much longer wait before the next step.
| Base material temperature | Typical gel time | Typical full cure time |
|---|---|---|
| Hot (> 30°C / 86°F) | Minutes | Under 1 hour |
| Moderate (~20–25°C / 68–77°F) | 10–30 min | A few hours |
| Cold (near 0°C / 32°F) | Hours | Up to 24–72 hours, or requires a winter-grade adhesive |
Step 8Torque after full cure
Only after the MPII’s full cure time has elapsed, install the washer and nut and tighten to the installation torque listed in the product’s ESR using a calibrated torque wrench. Do not exceed the maximum torque — over-torquing a freshly-cured adhesive anchor can shear the bond before it reaches full strength, and re-torquing an anchor that’s already at the correct value serves no purpose and risks the same damage.
Step 9Document and inspect
Record hole diameter and depth, cleaning method used, adhesive lot number and expiration date, installer certification number, base material temperature, and final torque for each anchor (or each representative anchor in a large group, per the project’s inspection program). For anchors requiring continuous special inspection, the inspector must witness drilling through torquing in real time — it cannot be reconstructed from photos after the fact.
7. Common installation mistakes
- Skipping or shortening the brush-and-blow cycle, or using a worn/undersized brush that doesn’t contact the hole wall
- Drilling an oversized hole “to make insertion easier,” which reduces bond area below the qualified value
- Not discarding the first strokes of adhesive, so an unmixed slug of resin or hardener ends up in the hole
- Loading, torquing or disturbing the anchor before the temperature-adjusted cure time has elapsed
- Using an ESR’s uncracked-concrete bond value without verifying the anchorage region actually stays uncracked under service load
- Installing horizontal or upward sustained-tension anchors without a certified installer, or without continuous inspection
- Cutting or nicking existing reinforcement because the hole location wasn’t scanned first
- Mixing components from different lots, or using adhesive past its expiration or shelf-life date stamped on the cartridge
Installation QA checklist for epoxy anchor bolts
- Hole location scanned for existing reinforcement before drilling
- Bit diameter and hole depth match the product’s ESR/MPII exactly
- Hole cleaned with the specified brush-and-blow (or approved vacuum) cycle count
- Adhesive lot current, unexpired, and primed to a uniform colour before use
- Hole filled from the bottom up, correct fraction of depth, no trapped air
- Anchor inserted with a turning motion to full embedment depth, squeeze-out confirmed
- Anchor undisturbed through gel time; full cure time elapsed before torquing
- Torque applied with a calibrated wrench to the ESR value, not exceeded
- Installer certification confirmed for horizontal/upward sustained-tension work
- Inspection level (continuous vs. periodic) matched to orientation and load per ACI 318-19 §26.13
Key takeaways
- Epoxy anchor bolts carry load through adhesive bond, not head bearing — hole cleanliness and correct adhesive mixing matter as much as embedment depth when you install epoxy anchor bolts in RCC framing.
- ACI 318-19 Chapter 17 sets the design and construction framework; ACI 355.4/ICC-ES AC308 qualification and the product’s own ESR/MPII set every actual number.
- Horizontal or upwardly inclined anchors resisting sustained tension trigger both certified-installer and continuous-special-inspection requirements under ACI 318-19 §17.8.2.4 and §26.13.
- Cracked-concrete bond values are the default design basis unless the anchorage region is specifically verified to stay uncracked in service.
- The MPII for the specific adhesive system being installed always governs over any generic guide, including this one.
For other ACI 318-based structural design tools, see our ACI 318 Cantilever Retaining Wall Design Calculator and additional resources in the RCC & Structural section.
This article is an educational overview of ACI 318-19 Chapter 17 and ACI 355.4 as they apply to post-installed epoxy anchor bolts in reinforced concrete framing. It summarizes the general shape of the requirements and is not a substitute for the full text of ACI 318, ACI 355.4, the applicable building code, or the current ICC-ES Evaluation Service Report and Manufacturer’s Printed Installation Instructions for the specific adhesive anchor system used on a project. Anchor design, installer certification, and inspection requirements should always be confirmed with the project’s licensed structural engineer of record and the local authority having jurisdiction before installation.