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

Ákos Török,Balázs Szemerey-Kiss

doi:10.1186/s40645-019-0282-1

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.

Highlights

Phase transition of water to ice causes severe damage to stones, causing frost damage which has been already described many years ago (Schaffer 1932)
Stone and mortar damage depends on relative humidity (RH), temperature, and pore structure in salt-rich environment (Linnow 2007), while in region, the damage is mainly controlled by the presence of the water, the porosity, the pore size distribution, and the saturation rate (Ruedrich et al 2011, Al-Omari et al 2015, Gökçe et al 2016)
Larger pores prevail in limestones while the pores of the mortars are in the lower size ranges (Table 2)

Summary

Introduction

Phase transition of water to ice causes severe damage to stones, causing frost damage which has been already described many years ago (Schaffer 1932). Stone and mortar damage depends on relative humidity (RH), temperature, and pore structure in salt-rich environment (Linnow 2007), while in region, the damage is mainly controlled by the presence of the water, the porosity, the pore size distribution, and the saturation rate (Ruedrich et al 2011, Al-Omari et al 2015, Gökçe et al 2016). Frost damage can lead to material loss, and in addition, it decreases the stone durability against other stress factors such as salts (Yu and Oguchi 2010). Larger pore size (1 μm) was found to be responsible for salt damage of porous stones (Benavente et al 2004). Natural stone and mortar durability are closely related

Results

Discussion

Conclusion