Influence of freeze–thaw cycles on mechanical properties of historical brick masonry

• Stronger bond between bricks and mortar is formed by “weaker” mortar M3a compared to M1.
• After freezing and thawing, UV is significantly reduced, indicating the damage of specimens.
• Influence of freeze–thaw cycles on mechanical properties of brick masonry as a composite is evaluated.
• By triplets, angle of internal friction is reduced after freezing and thawing indicating the damage.
• By wallets, freeze–thaw damage reflects in reduction of stiffness but has no significant effect on compressive strength.

The research presented in this paper focuses on influence of freeze–thaw cycles accompanied by simultaneous moistening on mechanical properties of historical brick masonry. In order to evaluate the rate of reduction in mechanical properties of the masonry due to freezing and thawing, a series of brick wallets built of solid brick and lime mortar or lime-slag mortar representing an actual building envelope was subjected to testing. Besides testing the wallets and triplet specimens as a mortar–brick composite, mortar prisms and brick units were also tested separately. Wallets built with either of analysed types of lime-based mortar were able to withstand 50 freeze–thaw cycles without any effect on their mechanical properties. After 150 freeze–thaw cycles, the damage of brick surface and mortar joints increased, but had no significant effect on the compressive strength of the wallets. However, in case of wallets built with lime-slag mortar, freeze–thaw damage reflected in the reduction of modulus of elasticity. The results indicate that both tested mortar types have the potential in reconstruction and repair works carried out on historical masonry in areas exposed to freezing and thawing.

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