Study of the mechanical behavior of masonry repair lime-based mortars cured and exposed under different conditions

Abstract

Specimens of aerial and hydraulic lime-based mortars to be used in restoration works were prepared, hardened and subjected to different environments in order to study their mechanical behavior and durability. Outside exposure, weathering cycles in a climatic chamber, SO2-rich environment, freezing–thawing cycles and indoor exposure were selected to expose (as control group) the mortars.

Flexural and compression strength tests were performed at 7, 14, 21 and 28 days. Porosity values and SEM/EDAX analysis were used to evaluate the microstructural changes.

Flexural strength has been strongly influenced by the RH of the environments. Outside exposure improves, in general, the compressive strength, whereas SO2 chamber only provides the strength in hydraulic specimens. Porosity reduction has been related with a strength increment.

In climatic chamber, the porosity increment matches a gradual higher degree of alteration. A strength reduction has been determined through a fracture mechanism using the cracks of climatic alteration. In SO2 chamber, sulfation appears as a surface phenomenon, giving gypsum in aerial specimens and gypsum and syngenite in hydraulic specimens, as SEM/EDAX confirms. Freezing–thawing cycles showed a high destruction capacity. Hydraulic specimens endured better durability tests than aerial specimens: a discussion on the mortar durability was also introduced.