Abstract
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.
Highlights
Despite the wide research on cement-based systems, the knowledge about the lime-bearing mixtures has been rather empiric
Carbonation is responsible for the setting and hardening of lime-based mortars, and it consists in a series of chemical reactions between calcium hydroxide and atmospheric carbon dioxide, to form calcium carbonate [91,92]
This is controlled by diffusion-related factors and by the atmospheric CO2 concentration, so lime mortar carbonation generally proceeds gradually, according to an interfacial process and only after an initial dormant phase during which a partial drying occurs until reaching relative humidity (RH) between 40% and 80%, necessary to start CO2 diffusion and dissolution within the partially-filled pore network of the material [93]
Summary
Despite the wide research on cement-based systems, the knowledge about the lime-bearing mixtures has been rather empiric. To ascertain the most suitable test methods for these lime-based binders, it is of utmost importance to bear in mind the different mechanisms of setting and hardening involved in these systems These mechanisms differ from those taking place in cement materials and must be revised considering the diverse composition of the raw materials (consisting of aerial and hydraulic components) and their possible blends. This TC report is one of the expected outputs of the activities of the RILEM TC LHS-277 and deals with the analysis of the mechanisms of setting and hardening of composites produced with lime-based binders. The paper includes discussions on the main aforementioned mechanisms (drying, carbonation, hydration and pozzolanic reaction) prevailing in the main types of binders: pure air lime (both calcitic and dolomitic lime), natural hydraulic lime, pozzolan-lime and lime-cement binders
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