Post-Installed Adhesive Anchor Per ACI 318 Chapter 17 and ICC-ES AC308
Why this matters
Post-installed anchors carry structural loads in commercial concrete: column base plates retrofitted to existing slabs, machinery anchors, seismic upgrade anchors, facade attachment, and crash-rated bollard anchorage. ACI 318-19 Chapter 17 unified the design rules for both cast-in and post-installed anchors; ICC-ES AC308 is the acceptance criteria for adhesive (epoxy and vinyl-ester) post-installed anchors and is the source of the Evaluation Service Report (ESR) numbers cited in every spec. The ESR is non-optional: it documents the embedment, the substrate, the installation procedure, and the design values. A contractor installing an anchor outside the ESR conditions has produced a non-conforming installation even if the hardware looks perfect.
What an ESR delivers
The ESR is issued by ICC-ES, IAPMO-UES, or DrJ Engineering for a specific anchor product. It states: characteristic bond strength in cracked and uncracked concrete, applicable temperature range, minimum and maximum embedment, minimum edge distance and spacing, hole-cleaning procedure, installation temperature window, and required installer certification (if any). The engineer of record's calculation uses the ESR values to derive the design tension and shear capacity per ACI 318-19 Chapter 17.
Hole cleaning is the most-failed step
The number-one field failure mode for adhesive anchors is incomplete hole cleaning. Drilling produces a dust paste in the hole; if the adhesive bonds to the dust instead of the substrate concrete, the anchor pulls out at a fraction of the ESR rated capacity. The ESR mandates a specific cleaning sequence; a typical sequence is:
- Blow out the hole with compressed air (oil-free) for the prescribed number of strokes.
- Brush the hole with a wire brush sized to the hole diameter for the prescribed number of strokes.
- Blow out the hole again for the prescribed number of strokes.
Some products require a 3-blow / 3-brush / 3-blow cycle; others require 4 / 2 / 4. The ESR is the source. Skipping the brushing or using a worn brush is the single largest field-defect mode.
Drilled-hole tolerances
The hole diameter and depth are specified by the ESR. Drilling oversize (more than 1/16 inch oversize on common diameters) reduces the adhesive bond area; drilling undersize means the rod will not fit. Drilling deeper than the ESR maximum embedment can place the anchor in zones the ESR did not characterize. Set the drill bit's depth stop to the ESR-specified embedment plus the dust-cleanout allowance.
Cracked vs uncracked concrete
ACI 318-19 Chapter 17 differentiates cracked and uncracked concrete because the bond strength of adhesive in a cracked tension zone is lower than in an uncracked zone. The structural engineer's calculation tells the contractor which condition applies. Most ESRs publish two characteristic bond strengths; the lower (cracked) value applies under: tension on the anchor, concrete tension zone of a flexural member, or seismic design category C / D / E / F. The uncracked value applies only where the engineer demonstrates the concrete remains uncracked under all design load combinations.
Sustained tension loads
ACI 318-19 Section 17.5.2.2 requires special design considerations for adhesive anchors in sustained tension (long-term tension load greater than 60 percent of the short-term tension capacity). This was a response to the 2006 Boston Big Dig ceiling collapse where adhesive anchors holding suspended ceiling panels failed in sustained tension; ACI 318-19 prohibits adhesive anchors in sustained tension for overhead installations unless the engineer specifically designs for creep and the installer is qualified per the ACI/CRSI Adhesive Anchor Installer Certification.
Installer certification
Under ACI 318-19 Section 17.5.2.4, adhesive anchors in sustained tension for overhead installations require certified installers (ACI/CRSI Adhesive Anchor Installer Certification or equivalent). The certification is anchor-product agnostic and is held by the individual installer. Project specifications increasingly require the certification on all overhead and all sustained-tension applications.
Special inspection
IBC Chapter 17 (Special Inspections) requires continuous special inspection for adhesive anchors in tension in cracked concrete under most circumstances. The special inspector documents the installation parameters: hole diameter, depth, cleaning method, adhesive lot number, ambient temperature, anchor torque (if applicable), and curing time before load application.
Adhesive cure time before load application is temperature-dependent. The ESR's cure-time table is the source. Loading an anchor before the cure is complete (typical full-cure times range from 4 to 72 hours depending on temperature and adhesive chemistry) produces a partial-strength anchor. On cold-weather installations the cure time can exceed the project schedule's expectation; plan accordingly.
References
- ACI 318-19 Building Code Requirements for Structural Concrete, Chapter 17
- ICC-ES AC308 Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements
- ICC-ES AC193 Acceptance Criteria for Mechanical Anchors in Concrete Elements
- ASTM E488 Standard Test Methods for Strength of Anchors in Concrete Elements
- ASTM E1512 Standard Test Methods for Testing Bond Performance of Adhesive-Bonded Anchors
- ACI/CRSI Adhesive Anchor Installer Certification Program
- IBC 1705 Special Inspections
- Hilti HIT-RE 500 V3 ESR and Installation Instructions
- Simpson Strong-Tie SET-3G Adhesive ESR