Chapter 2. Heave Rates and Mechanism of Pyritic Expansion in Unbound Aggregates


Michael L. J. Maher
WSP Golder, Whitby, Ontario, Canada

Part of the book: Pyrite and Pyrrhotite: Managing the Risks in Construction Materials and New Applications

Chapter DOI:


The occurrences of crushed rock aggregates prone to causing pyritic heave in buildings are random but all too frequent. This Chapter focuses on the devastating pyrite crisis in Ireland that was first detected in 2007 but is still having financial consequences and impacting peoples’ lives, some 15 years later. We describe various tests conducted to simulate the heave mechanism in calcareous mudstone aggregate in a laboratory setting. A sample diameter of 600 mm seemed to provide the best compromise between achieving representative results with aggregate sizes up to 80 mm and manageable size for a laboratory setting. To provide context, we also present some case studies where heave in buildings was monitored, in one case for up to eight years. In the case of the Tober Colleen mudstone aggregates, the typical rates of recorded heave are 3 to 4 mm per year for an equivalent 500 mm of compacted fill. The results show that laboratory swell tests can simulate actual building heave but probably need to be run for at least one year. To obtain more insights into the mechanism of the heave, we examined the patterns of gypsum formation in individual coarse aggregate particles. We attempted to undertake some measurements of the magnitude of heave in individual aggregate laminations. We noted that the gypsum crystal cluster formation typically only occupies less than a quarter of the lamination surface area. The magnitude of particle expansion is determined by the number of open laminations present and the height of the tallest crystal clusters.

Keywords: pyritic heave, laboratory simulation, in situ heave monitoring


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