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）的出现大概率源于特定时期的行业实践——彼时经济条件允许在乡土土砂浆（vernacular earth mortars）中掺入气硬性石灰（air lime），而未掺石灰的乡土土砂浆遇水后耐久性极差。已有研究表明，向深色土砂浆中掺入少量气硬性石灰，虽可提升其耐水性，但会使砂浆色泽变浅，同时削弱其力学性能。本研究针对石灰-砂体积比为1:2（对应质量比1:8）的气硬性石灰砂浆，以本地土料按10%至50%的质量占比部分替代石灰开展试验。该砂浆配方可降低材料隐含能（embodied energy），适用于古建筑修复抹面，亦可用于性能匹配的新建建筑。力学、物理性能及抗硫酸盐侵蚀（sulphates attack）性能的测试结果显示，当土料替代率为10%时表现最优，各评测指标存在小幅波动。尽管如此，为优化适用于当代的应用配方，仍需开展进一步研究以深入了解这类曾被广泛应用的石灰土砂浆的各项性能。