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CROSS Safety Report

Preparation of holes in concrete for chemical anchors

Report ID: 1096 Published: 6 June 2022 Region: CROSS-UK


Overview

Reinforcement intended to be resin anchored into concrete was not anchored, because the resin did not cure, due to contamination within the holes.

Key Learning Outcomes

For the construction team:

  • Select the correct resin to suit the application and ambient fixing conditions
  • Strictly follow resin manufacturer's instructions for the drilling and cleaning of holes and use of resin
  • Be particularly careful to ensure the hole or fixing to be inserted is not contaminated
  • Deploy a regime of testing for anchors

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Works were being undertaken to a retaining wall that had moved due to increased loading on the retained side. Whilst carrying out a pre-pour inspection, a reporter noticed an issue with chemical resin that had been used to dowel in rebar to the wall. It was found that the resin had not set at all.

In the absence of a proper resin fixing for the dowel bars, the remedial detail would not have addressed the underlying problem with the retaining wall.

It transpires that the operatives on-site had not used a hand blower to clean the holes in the existing concrete but used a diesel air compressor which had been used to scabble the walls. Oil from the air compressor used for pneumatic tools contaminated the holes which in turn prevented the resin from curing.

The reporter concluded that the preparation of holes for resin fixed anchors is critical. Holes need to be appropriately located, drilled using the correct techniques, and cleaned fully, prior to installation of the resin anchor as per the manufacturer’s instructions.

Expert Panel Comments

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This is a fairly well-known issue and usually results from the poor preparation of the drilled holes and lack of cleaning before the application of resin. The design and installation of all resin fixings (including resin grouted rebar) should be treated as an engineered activity because of its complexity and safety-critical nature. CROSS would draw attention to the need for the correct design, specification, and execution assurance, including supervision, inspection, and testing, in strict adherence to the manufacturer’s installation instructions. BS 8539:2021 Code of practice for the selection and installation of post-installed anchors in concrete and masonry provides comprehensive guidance as does the Construction Fixings Association.

It can also be the case that a resin not suited to the end use application, or the ambient conditions during installation, can cause failures; the selection of a suitable resin is critical.

 

the selection of a suitable resin is critical

A regime of testing of the anchors, be it a torque or pull out should be undertaken to ensure that the anchors can be relied upon. It may be appropriate to start with say 10% testing and increase for high risk or incidence of failure.

CROSS has previously published a number of reports concerning epoxy fixings including Failure of epoxy resin bonded anchors in concrete .

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