CROSS Safety Report
Unstable concrete blocks
This report is over 2 years old
Overview
A reporter from a consulting firm was called to a site where the blocks in a retaining wall were found to be expanding and falling apart.
Key Learning Outcomes
For the construction team:
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It is good practice to procure blocks (and other materials) that comply with British Standards from a manufacturer who can give a quality assured history of the product and its constituents
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Quality control and competent supervision on site can help to ensure that the structure is built in accordance with the design
Full Report
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A reporter from a consulting firm was called to a site where the blocks in a retaining wall were found to be expanding and falling apart. After consultation with an expert, it was decided the cause was most likely to be faulty aggregate that was expanding when wet. Having established that the client was not to blame for the faults the reporter had no further input in this case.
The firm was however subsequently asked to look at a site where concrete blocks from the same manufacturer have been used in a 2m high retaining wall, precast concrete floors and 2m deep foundations to the internal walls of two of the houses.
The blocks used in the retaining wall were showing the same problem as seen in the initial job. The image (Figure 1) is of one of the remaining pallets on site illustrating blocks that have been soaked after a period of wet weather.
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Expert Panel Comments
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This looks like a severe case of reactive aggregates where blocks are completely breaking up. This type of progressive cracking can occur when there is a high moisture contents (e.g. blocks get wet on site during storage or in a partially constructed situation). It emphasises the point of procuring blocks (and other materials) that comply with British Standards from a manufacturer who can give a quality assured history of the product and its constituents. Once built in it is very difficult to rectify these situations. The standards which apply depend upon the application for which the blocks are to be used. CROSS is keen to hear of similar examples in order that a broader picture may be established.