Investigation of the Impacts of Nonpolar Amino Acids on Air Lime Mortars

Natural protein-based additives have been frequently added to lime-based mortars to enhance their properties. However, the possible mechanism underlying this effect is not well understood. All proteins are built up by the basic units of amino acids, which may be viewed as a useful starting point for the research topic. The present study focused on the impacts of nonpolar amino acids on air lime mortars. The results obtained from the present study highlighted that some nonpolar amino acids (represented by glycine, alanine, valine and proline) decrease mortar water retention, decrease consistency, delay and prolong setting, increase compressive strength, and decrease water absorption. However, other nonpolar amino acids (such as leucine, isoleucine, phenylalanine and tryptophan) showed almost opposite results. The addition of all the nonpolar amino acids slowed mortar drying and carbonation, decreased the carbonation degree, inhibited calcite formation, and tended to form metastable calcium carbonate phases, such as vaterite. Studying the effects of single amino acids on lime mortars could contribute to the design of repair mortars with more specific requirements, and the results of the present study could open up a series of future topics to be investigated.