Synopsis
When pyrite-rich calcareous aggregate oxidises beneath a ground floor slab, it can raise and crack the concrete floor. In addition, it has been found that when tightly compacted fill expands, it may grip the sub structure walls such that the whole superstructure is lifted off these support walls. During remediation of distressed buildings in Dublin, horizontal cracks more than 20mm wide have been seen in the concrete block sub-structure walls. These separation cracks normally reduce or close when the expanding fill is removed. Careful planning of the remedial works is required to avoid the development of differential stresses and prevent further cracking of the superstructure, particularly where this consists of semi-detached or terraced buildings.