The main objective of RILEM TC LHS-277 “Specifications for testing and evaluation of lime-based repair materials for historic Structures” is the revision, adaption and, when necessary proposal, of the test methods to accurately study lime-based binding systems and mixtures, such as mortars and grouts. The empiric use of the lime-based composites and the predominant employ of cement in the field of Civil Engineering have led to the widespread application of test methods developed for cement-based composites to test the former. However, the clear differences in composition and performance between modern cement binders and lime-based materials would advise to explore specific test methods for the latter. To undertake this task the previous knowledge on the mechanisms of setting and hardening of these binders must be revised, arranged and synthesized. Processes such as drying, carbonation, hydration and pozzolanic reaction may occur during the setting and hardening of lime-based mortars and competition between them cannot be underestimated. With the aim of underpinning the revision and proposal of test methods for lime-based systems, this review paper reports a comprehensive study of the mechanisms of setting and hardening of these binders, considering the variability of the composition, which includes pure air lime as well as lime with hydraulic properties, lime-cement and lime-pozzolan systems.

Lime-cement mortars are often used in restoration of existing buildings (especially twentieth century onward) as well as new constructions, in order to combine the individual strengths of either type of binder. Despite the knowledge that mortars have a significant impact on the non-linear mechanical behaviour of masonry from the earliest moments of construction, literature that systematically quantifies the impact of adding lime to cement mortars, or vice versa is scarce and scattered. This work is therefore focussed on bridging the research gap that exists in lime-cement masonry mortars with regard to their mechanical properties in the early ages (up to 7 days of curing). Five different mix compositions have been studied with 1:3 binder-aggregate ratio and 10% to 75% lime content in the binder, both by volume. Changes in properties like mechanical strength and stiffness along with ultrasound pulse velocity have been quantified, correlated and associated with change in quantity of lime in the binder (by volume) of the mortar. It was found that every 10% increase in the quantity of lime in the binder led to a 14% decrease in mechanical strength and a corresponding 12% decrease in stiffness, at 7 days of curing age. Emodulus was found to evolve faster than flexural strength, which in turn was found to evolve faster than compressive strength. Impact of curing temperature and the concept of activation energy has been addressed for the mix 1:1:6 (Cement: Lime: Sand).

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This paper focuses on the mechanical characterization of the early age behavior of three NHL mortars with different water/lime ratios. A vibration-based technique with continuous data recording (Elastic Modulus Measurement through Ambient Response Method -EMM-ARM) was used to measure stiffness of the different mortars that were found to range between 2.5 and 4.1 GPa on day 7. Other physical and mechanical properties such as strength and density were measured as a function of sample preparation protocols -vibrated, compacted, sealed and unsealed. After 7 days, sealed specimens led to 50% lower compressive strength and 25% lower flexural strength compared to unsealed specimens.

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