Good planning is a perquisite to helping off-setting perils that may lie ahead, hence Jamie Squires, Product Manager at global building products manufacturer Sika, offers some sound, preparatory advice in relation to concrete repair, as well as a proven, long-term repair and protection solution.
Corrosion, either as a result of chloride or carbonation contamination, is a major contributor to concrete debilitation. If not diagnosed early enough and effectively dealt with, the consequences of such damage can have serious structural implications. By getting the pre-project basics right; however, the first step to successful concrete repair has been taken.
Pre-project checklist
Before any work is carried out, it’s essential to check the right tools and products are available to do the job. This means ensuring said tools are in excellent condition – clean and well-maintained. In terms of concrete removal, only defective areas highlighted by a supervising officer or qualified engineer should be removed, and as with any repair project, only use clean, potable water when required.
It’s essential to avoid contaminating mixture with other chemicals or mixing powders from different products. It’s also not advisable to add more water than recommended. In addition, mixing and applying product in direct sunlight should be avoided.
Substrate priming
For the all-important substrate preparation, defective concrete should be marked and removed accordingly. For small patch repairs, a hammer and chisel will likely suffice. A hammer drill should be used on larger areas, whilst even larger sites might best be treated with a high-pressure water jetting.
Concrete should be removed to a minimum of 15mm behind the reinforcing bars. Cut the sides to a minimum of 90° to avoid undercutting and maximum of 135° to reduce de-bonding around edges. The substrate should be sound and devoid of loose material before repairs continue. If the substrate appears cracked, immediately inform a supervisor.
For the reinforcement preparation, remove all tie wires, mortar/concrete, rust/scale and any other loose material. This can be completed with a steel wire brush or hand/power tools – a technique is applicable only in carbonated concrete and under environmental constraints where abrasive blast cleaning or high-pressure water jetting cannot be carried out. Ideally, the steel should appear bright and in accordance with SA2 ½.
Repair solution
With the concrete primed, sacrificial anodes represent an effective and sustainable long-term solution to the debilitating effects of chloride contamination. They are particularly suited to the repair of bridges and buildings in large suburban areas where carbonation is more prevalent. Indeed, where environmental and safety grounds play a significant role in deciding on an appropriate refurbishment solution, the anodes system scores highly over grit and water blasting.
Galvanic, sacrificial anodes comprise a zinc core encased by a small, cementitious shell which can be installed within the perimeter of repair sites to prevent incipient anodes developing, or outside the repaired area to protect the reinforcement in chloride – infused concrete. The anode is quickly and easily fastened to exposed steel reinforcement in repair sites or cored and grouted holes within concrete, yet outside the repaired area. Once installed, the anode’s zinc core corrodes sacrificially to protect the surrounding rebar.
Sika’s embedded galvanic anodes provided the rapid, corrosion control system for the long-term protection of a major transport link.
Case study – Tickton Flyover:
Tickton Flyover, which carries a vital ‘A’ road over the River Hull in North Yorkshire, was found to be at risk of corrosion due to signs of chloride in its concrete columns and beams. A proven solution was required to prevent corrosion forming on the steel rebar and maintain the flyover’s structural integrity. It led to the specification of Sika Galvashield CC100 anodes.
Nearly 1000 anodes were used in the flyover’s repair. These were tied at intervals to the reinforcement and charged using a Sika Galvashield Anode Connection Kit. Sika Galvashield Embedding Mortar was used to repair drill holes created to install the anodes.
The flyover’s repairs were completed in September 2018. Thanks to Sika Galvashield’s ingenious technology, this vital transport link has been long-term protected against the perils associated with chloride and carbon-induced corrosion.
Good preparation paid fair dividend in lieu of installing Sika’s proven, high-performance total control management system. Each process was vital for the restoration of this crucial transportation link and its long-term protection against the perils associated with concrete corrosion.
