Time-dependent changes in the strength of repair mortar used in the loss compensation of stone

Repair mortar and mixture of repair mortar with porous limestone sand aggregate were tested under laboratory conditions. Water absorption properties and micro-fabric analyses with a combination of strength tests were applied to assess the durability and compatibility of repair mortar with porous limestone. Uniaxial compressive strength and flexural strength were measured after 3, 7, 14, 28 and 90 days of casting. Durability was tested by comparing strength test results of samples kept air dry, water saturated, dried in drying chamber, freeze–thaw and non-standardized freeze–thaw cycles. The results indicate that with time various trends in strength were observed. In general, limestone aggregate content decreases more the compressive strength more than the flexural strength of the mortar. Standardized freeze–thaw tests of saturated samples caused a rapid material loss after 25 cycles, while freeze–thaw tests of undersaturated samples demonstrated that even after 100 cycles the test specimens still have a significant strength. Water-saturated samples that contain 50% of limestone aggregate have a 50% loss of strength in comparison with saturated repair mortar, while air-dry and water-saturated repair mortar has a minor strength difference after 90 days. The use of smaller amounts of porous limestone aggregate in repair mortar allow the preparation of repairs that are compatible with the monuments of Central Europe that were constructed from porous limestone.