Minerals commonly found in mine waste, such as pyrite (or mundic as it is also known), can decay over time and cause a slow chemical reaction which can result in concrete deterioration. This can lead to powdering and crumbling, and may cause weakening of a mass of concrete or mortar and structural failure in rare cases.
Building materials containing mundic were also transported and used outside mining areas. Blocks containing mundic were mixed with other blocks, and now appear across housing estates and sometimes in patches within individual properties, small developments or extensions.
What does a Mundic test do?
By analysing samples of concrete taken from the property by various methods the presence of substances known to cause problems can be confirmed. The analysis process is as follows;
Stage One, involves detailed examination of core samples under a low power microscope. To a trained petrographer, identification of the aggregate type can be made from this inspection and, in the majority of cases, a classification for the concrete can be determined. It must be stressed that approximately 75% of properties tested will pass the Stage One analysis, receiving a Group A classification.
Stage Two analysis involves the core sample being cut into wafer-thin segments for a further examination under a high power microscope and possibly subjected to a range of ancillary analytical techniques. Stage Two analysis is not included in the initial Stage 1 cost and is only carried out if a Stage 1 test is inconclusive.
Stage Three involves the sample being subjected to an accelerated weathering test under environmentally controlled conditions in an attempt to activate a reaction between the aggregate and cement binder. This test takes place over several months.
How We Can Help ?
If the presence of Mundic is suspected and/or testing is required we can provide a Chartered Building Surveyor and will carry out the analysis on the surveyors behalf. Wheal Jane Consultancy offer analytical petrographic services to Chartered Building Surveyors. We can undertake all stages of Mundic testing and provide advice on the process if required.