Freeze-thaw durability of repair mortars and porous limestone: compatibility issues

Abstract

Freeze-thaw cycles can cause considerable damage to porous materials and thus have an adverse effect on the durability of mortars and porous stone. To assess the behavior and frost resistance of two types of porous limestone, three commercially available repair mortars and four mixtures of laboratory-prepared repair mortars were subjected to freeze-thaw cycles according to EN 12371. During the test, samples of stone and mortar were bonded together and the weight loss was continuously monitored. The adhesion bond between the stone and the mortar was also observed during the cycles. Petrographic analysis and thin sections were also made before and after the freeze-thaw test. The pore size distribution (mercury intrusion porosimetry, MIP) of mortars and stones was also measured. The test showed that most of the repair mortars were damage more than porous limestone due to frost action. Two exceptions are two commercial available repair mortars. These mortars were able to keep the adhesion with the stone, and the frost did not modify significantly the cubic shape of the test specimens, only rounding of the edges was observed. All other samples were broken during the frost tests; stone/mortar interface was dismounted. Other typical damage features such as delamination, blistering, powdering, and granular disintegration were also observed leading to the gradual surface loss of the material. Our tests proved that low pozzolanic cement content in mortars decreases the material durability. According to the pore size distribution (MIP), the small pores (around 0.1 μm) control the weathering behavior of tested porous materials.

Effect of water saturation on strength and deformability of building calcarenite stones: Correlations with their physical properties

“…In this line, the calcarenites cemented by smaller calcite grains and with higher pore size (BC-Y1 and BC-Y2) exhibit greater strength reductions due to water saturation than the varieties cemented by greater calcite grains and with lower pore diameters (BC-BL, BC-BG and BC-DM). These results are in agreement with those found by Török [49], Papay and Török [50] and Török and Szemerey-Kiss [51], [52], who observed that the limestones cemented by fine grained micrite calcite are more water sensitive in terms of strength and durability than those cemented by micro-sparitic calcite. In addition, they also found the existence of a close relationship between the pore structures and the mechanical properties of Hungarian limestones.…”

Characterization of Historic Binders and Stones of a Ruined Medieval Church (Hungary)

“…The pore structure also influences the water absorption and thus the frost resistance of the stone [20]. The differences in the porosity of stone and mortar, the compatibility [5] might lead to differential weathering and loss of stone material. The different moisture content of different lithotypes suggests that the porosity and poresize distribution of various limestone types are different, and thus their resistance against freeze-thaw related weathering is also different.…”

“…17), while in medieval lime-based mortars quartz grains dominate. These differences can also contribute to the differences in durability [1,5].…”

“…Choosing an incompatible repair material can result not only in the failure of the repair [5] but also the accelerated deterioration of the adjacent materials [6,7,8].…”

Rock Features and Alteration of Stone Materials Used for the Built Environment: A Review of Recent Publications on Ageing Tests

“…Sometimes pore characteristics are associated with other textural features. For example, images of study by Török and Szemerey-Kiss [79], showed that a coarser limestone which was less porous and presented a higher percentage of fine pores presented higher erosion than a finer limestone that was more porous and had a higher percentage of the higher radii pores (in freeze-thaw tests with stone and mortars, where, hence the possibility of some salt contribution could be pondered). Bioturbation in limestones has been reported to be susceptible to salt weathering erosion because of the association with iron oxides and porosity [71].…”