Track 1: Effects of Climate Change in Warm Weather Coastal Regions
APT Student Scholar Abstract and Application
Casein, an organic milk protein, was used extensively in masonry mortars from medieval times until the 18th century. It was understood to improve workability of the mortar, resulting in a pourable consistency, however, little information is available on its effects on material strength. Casein is non-toxic, has minimal environmental impacts, and has no reported health hazards beyond the lime powder of the mortar itself. Recent mortar conservation projects have proposed its use, notably on the buildings of Parliament, however, a debate exists on the value of this additive.
Mortar cubes conforming to relevant ASTM standards were cast for compressive and tensile tests, while square prisms were casted for flexural and shear tests. Brick-to-mortar bond strength tests were conducted both in flexure and in shear. Clay bricks intended for an historic retrofit application were used. It was found that adding 0.5% casein by mass resulted in a flowable mortar, however, a 75% reduction in strength resulted, even after 56 days. Contrarily, brick-to-mortar bond strength substantially improved. A casein content in excess of 0.5% prevented long-term curing of the masonry mortar; samples containing 1.5% casein by mass exhibited similar strengths after 7 days to that after 56 days.
Further tests were conducted reducing the water content while maintaining 0.5% casein by mass. This combination yielded the most optimal properties. It was found that reducing the water content by up to 18% resulted in a corresponding increase in material strength while maintaining the increased bond strength.
With masonry mortar repair techniques, it has been deemed critically important to appropriately specify the replacement mortar with a material strength compatible with both the brick and the original mortar. Casein protein acted as a superplasticizer, creating a liquid-like mortar if 0.5% casein by mass or more was added. A casein mortar would not be suitable for new construction or a complete re-build of an historic wall. However, the application of casein mortar is a plausible alternative for repointing existing mortar joints, as it has favourable flow properties, and the developed strength will eventually approach that of standard lime mortar. It may also be injected between mortar wythes as a means of stabilizing a multiple wythe masonry wall.