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Self-healing of lime based mortars: microscopy observations on case studies

B. Lubelli1,2, T.G. Nijland2, R.P.J. van Hees1,2
1 Faculty of Architecture, Delft University of Technology, the Netherlands
2 TNO Built Environment and Geosciences, Delft, the Netherlands

Lime mortars have, up to a certain extent, a self-healing capacity which may contribute to their durability. Self-healing in lime mortars consists of a process of dissolution, transport and re-precipitation of calcium compounds to heal cracks and fissures. The spontaneous occurrence of self-healing in lime-based mortars is a well known phenomenon; to date, however, little research has been done on its occurrence in the practice. This study aims at gaining a better understanding of the self-healing mechanism in lime-based mortars through the investigation of case studies where self-healing has been observed. On the basis of the results obtained the relevance of the various controlling factors, the way in which they potentially interact, and how they affect the occurrence of self-healing is evaluated. Lime-based mortar samples collected from several case studies were studied. Thin sections were prepared and studied by means of Polarization & Fluorescence Microscopy (PFM). The influence of selected parameters (moisture content, degree of carbonation, binder-sand ratio, binder type, etc.) on the nature (calcium carbonate or calcium hydroxide) and crystal habits of the precipitated products has been investigated. The results obtained indicate that some recurrent patterns exist in the nature and the crystal habits of the re-precipitated products depending, among other factors, on the moisture content and on the degree of carbonation of the mortar.

Key words: Self-healing, lime mortars, calcite, portlandite, microscopy