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This investigation determined the effect of freezing and thawing on mortar bond strengths. Comparisons were made of a Type S portland cement-lime mortar without an air entraining agent and a companion mortar of the same cement-lime proportions with a purposefully added air entraining agent. The UBC Mortar Cement Test Method UBC 21-20, (formerly UBC 24-30) was used to construct prisms and test the mortar joints for flexural bond strengths. A series of six prisms were made for each mortar type, using the UBC standard concrete brick. Four sets of prisms for each mortar were made corresponding to: a control set (no freeze-thaw treatment), and prism sets for 5, 10 and 25 freeze-thaw cycles.
Each freeze-thaw cycle consisted of water saturation, draining, freezing for 12 h, and thawing at room temperature. Flexural bond strength data were obtained from 30 joints per prism set, in accordance with ASTM C1072 test method.
Results of this study indicate that air entrainment accelerates the loss of flexural bond strength of masonry composites when exposed to water saturated freeze-thaw conditions. Mortar freeze-thaw durability is not equivalent to masonry freeze-thaw durability, because there are mortar to masonry unit interfaces in masonry composites, and this is a significant weak link in masonry durability.
mortar, masonry, freeze-thaw, air entraining, flexural bond strength, water saturation, durability
Consultant Research Lime Chemist, Chemical Lime Co., Henderson, NV