Lime-earth mortars: characteristics and applications

Abstract Earth-lime mortars probably result from professional practices from the time when economical conditions enabled the addition of air lime to vernacular earth mortars, which are not durable when in contact with water. Previous studies have shown that the addition of low contents of air lime on earth mortars with dark colour, while turning the mortars water resistant, makes their colour lighter and weakens their mechanical characteristics. This study examines the partial weight replacement of lime by a local earth in air lime mortars with a 1:2 lime: sand volumetric proportion, corresponding to mortars with a 1:8 weight proportion, with replacements from 10 to 50%. The embodied energy of mortars is reduced by their formulation, and they are adequate for use as render in old buildings and also on new constructions with compatible characteristics. The results of the mechanical and physical characteristics, as well as on the reaction to sulphates attack, were particularly positive for a 10% lime replacement by earth, with variations between the assessed properties. Nevertheless, further research is still needed for a deeper knowledge of the characteristics of lime-earth mortars, widely used in the past, in order to optimise formulations to be applied in the present day.

摘要：石灰土砂浆（earth-lime mortars）的形成，大概率源自特定历史时期的工程实践——彼时经济条件允许向遇水不耐久的乡土土基砂浆（vernacular earth mortars）中掺入气硬性石灰（air lime）。已有研究表明，向深色土基砂浆中掺入少量气硬性石灰，虽可赋予其耐水性，但会导致砂浆颜色变浅，同时削弱其力学性能。本研究针对气硬性石灰与砂体积比为1:2（对应质量比1:8）的气硬性石灰砂浆，以当地原状土按10%至50%的比例等量取代石灰开展试验。该配方可降低砂浆的物化能（embodied energy），适用于古建筑抹灰作业，亦可用于性能匹配的新建建筑工程。力学、物理性能及抗硫酸盐侵蚀（sulphates attack）性能的测试结果显示，当石灰被土取代10%时，各项性能表现尤为优异，仅部分评估指标存在小幅波动。尽管如此，为优化适用于当代应用的配方，仍需开展进一步研究以深入了解这类曾被广泛使用的石灰土砂浆的性能特征。