An experimental study on the effects of casein protein in unreinforced lime mortar specimens

Abstract

Casein, an organic milk protein, existed in masonry mortars from medieval times until the 18 th century. It was understood to improve workability of the mortar. Recent mortar conservation projects have proposed its use, however, little information is existent on its effects on strength, a critical property in repair of masonry mortars. Adding 0.25% casein by mass was insufficient to improve flow properties of mortar. It was found that adding 0.5% casein by mass resulted in a flowable mortar, however, a 75% reduction in strength resulted, while bond strength increased, after 56 days. Reducing the water by 18% resulted in a 50% reduction in strength from that observed in the control sample, while maintaining flowable properties. Reducing the water more than 27% yielded a rapidsetting, non-flowable mortar. The addition of casein is a plausible alternative for repointing existing mortar joints. It has favourable flow properties, as well as improved bond strength.iii

Influence of polar amino acids on the carbonation of lime mortars

“…Some previous studies showed that, the addition of protein-based additives such as animal blood, milk, egg white, animal glue, etc. into lime-based mortars can impart them with superior properties in both fresh and hardened state, such as increased workability [7,8], mortar strengths [9][10][11], water retaining capacity [9], water resistance [9,10,[12][13][14] and frost resistance [9]. Other studies, on the contrary, concluded that proteinaceous addition could have negative effects on mortar properties, such as decreased mortar strengths [7,8,[13][14][15] and water resistance [7].…”

“…into lime-based mortars can impart them with superior properties in both fresh and hardened state, such as increased workability [7,8], mortar strengths [9][10][11], water retaining capacity [9], water resistance [9,10,[12][13][14] and frost resistance [9]. Other studies, on the contrary, concluded that proteinaceous addition could have negative effects on mortar properties, such as decreased mortar strengths [7,8,[13][14][15] and water resistance [7]. Alonso et al [15] showed that 25% milk addition into lime mortar resulted in lower compressive and tensile strengths, while the 50% and 75% addition resulted in higher compressive and tensile strengths than specimen without organic addition.…”