The behaviour of as-applied and artificially weathered silica–epoxy consolidants on a typical Mediterranean porous limestone : a comparison with TEOS

Abstract

A water based epoxy–silica consolidant and variants of the same consolidant containing silica nanoparticles (NP) were applied to Globigerina Limestone (GL) blocks by brushing and full immersion techniques. The consolidants were applied for their improved strength, toughness and adhesion to the stone surface. As-consolidated dried stone blocks were characterised (colour, total porosity, pore size distribution and microstructure) and their physical and mechanical properties assessed by a water uptake by capillary test, drilling resistance and resistance to salt crystallisation test. In another set of experiments, the consolidated limestone blocks were subject to 28 wet–dry cycles (8-h wet, 16-h dry) in a weathering chamber. The physical and mechanical properties of the weathered consolidated limestone blocks were then re-assessed. Parallel tests were also performed on tetraethyl orthosilicate (TEOS)-consolidated and untreated GL blocks. The water absorption coefficients of limestone blocks consolidated by brush-applied epoxy– silica dropped marginally. No significant changes to the water absorption coefficients were recorded after weathering. The drilling resistance curves showed a clear improvement of the mechanical properties of epoxy–silica treated GL, but the effects of the consolidants were reversed with weathering. The epoxy–silica consolidants reduced the resistance of GL to salt crystallisation. This resistance was partly restored after weathering, corroborating the drilling resistance results, and supporting the consolidation reversal hypothesis. Test results for the epoxy–silica consolidants applied by immersion showed similar trends, albeit complicated by pore blocking. The formation of an undesirable surface crust with epoxy–silica consolidants remains a pertinent issue with such hybrid materials. The behaviour of TEOS-consolidated GL was very different to the epoxy–silica consolidants and this can be traced to the hydrophobic nature of TEOS that persisted months after application.