How should concrete be prepared prior to repair?
The preparation of the existing concrete for repair is very important to ensure the durability of the performance.
This phase involves removing all deteriorated and damaged concrete until a solid surface is obtained for the repair material to properly bond to.
If this preparation is not done properly, regardless of how well the other steps are performed, the repair will likely fail prematurely.
It is therefore important to ensure that the prepared surface can achieve a superior level of adherence to the chosen repair mortar.
In accordance with the standard EN 1504, this should be 2 N/mm² for a R4 mortar and 1.5 N/mm² for the R3 mortar.
This phase is so important, so a clear and concise description of the substrate preparation process should be provided.
Then, this preparation will need to be checked and evaluated during the repair execution phase to ensure that the specified surface roughness and strength requirements are met.
In this regard, the following actions should be assessed. Surface layers must be removed in such a way that the steel reinforcement is not damaged and structural elements are not unnecessarily disturbed in their core.
Accordingly, as recommended by EN 1504, it is always advisable to remove the concrete behind the rebar, leaving a space of +/- 1 cm.
This way, there will be a higher degree of homogeneity in the remaining concrete.
Moreover, the static suitability of the structure must not be compromised in any way when removing surface layers of concrete.
Special attention must be paid to this aspect when it comes to thin-walled components.
The substrate (concrete and reinforcement) must be inspected after pre-treatment (visual inspection, acoustic tracking, tear tests, etc.).
Additionally, cracks found in affected areas must be documented.
Cracks less than 0.3 mm in width don’t need to be filled in in any special way.
Cracks in the base concrete that are larger and possibly statically significant must be assessed separately and, if required, rehabilitated.
Anyhow, the steps to follow in the preparation of the concrete surface are the ones in the table below.
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