Abstract

Oxidation of pyrite-rich, carbonaceous mudrocks used as fill beneath ground bearing floor slabs is currently causing significant problems to domestic and other properties in Ireland. Due to the precipitation of gypsum and other minerals the fill expands and this causes heave of slabs, together with distortion and cracking of the structure. Temperature is known to have an effect on both the rate and amount of this expansion; however, the full impact of human habitation on this process is not fully understood. The paper gives details of the development and testing of a system for monitoring temperature, humidity and pressure conditions within the material. This system is designed to minimise cost and disruption to the homeowner, whilst facilitating reliable measurements over period of 3 to 12 months.

1 Introduction

Oxidation of framboidal pyrite is knownto be the cause of several problems in ground engineering.A particular problem occurswhen sulfuric acid produced as part of the oxidation process reacts with calcium-bearing minerals also present in the parent rock. This can eventually lead to the expansive precipitation of sulfate minerals such as gypsum.

In Ireland, particularly in the Dublin area, pyriterich, Carboniferous age mudstone was extensively used in the late 20th Century as fill material beneath the ground supported concrete floor slabs of residential properties. Many of these properties are now showing evidence of damage such as uplift and cracking of the floor slab, which is attributed to heave of the fill material.

Although laboratory tests studying the nature and behaviour of the material are ongoing, little data currently exists detailing the behaviour of the material under field conditions. Information about the temperature and humidity conditions, both of which are recognised as key controlling factors of the reaction process, will assist with the interpretation of the lab tests and the relationships In addition the monitoring of temperature and humidity at various depths in the fill, it is also possible to record vertical stress conditions in the fill for periods between 3 and 12 months duration.

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