Abstract
Recently, the use of lime mortars in the restoration of historic buildings has found a renewed interest because they can guarantee the required mechanical, chemical and physical compatibility with the existing substrate. Spontaneous occurrence of self-healing phenomena in lime-based mortars is well known; the possibility of engineering the self-healing capacity, through tailored additions, is therefore of the utmost interest with the aim of enhancing the durability of the building masonry restoration works. This work proposes a system for the evaluation of the self-healing capacity with reference to traditional and advanced lime mortars. The autogenous healing capacity of a reference lime mortar has been first of all evaluated. Then, the possibility of engineering the aforementioned capacity has also assessed, through both commercial crystalline admixtures and tailored encapsulated additives. These should work according to a twofold mechanism: first, the coated granules envelope a core of lime mortar with purpose of making it inert during the hardening phase. Secondly, once the coated granules rupture upon cracking and damage of the mortar, the reactive binder is released and undergoes a delayed hardening, which is responsible of the healing phenomena. The results show that the mortar is able to heal micro-cracks; moreover, the addition of the crystalline admixture enhances this capacity. The different kinds of employed coated granules were also able to induce a sensible self-healing, but they decrease the instantaneous compressive strength.
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Abbreviations
- NHL5:
-
Natural hydraulic lime
- CEM:
-
Portland cement 32.5 R
- NaF:
-
Sodium fluoride
- AM:
-
Maleic anhydride
- AF:
-
Phthalic anhydride
- \(f_{c(\Delta t)}\) :
-
Initial compressive strength
- \(f_{c(28)}^{*}\) :
-
Compressive strength re-tested up to failure right after pre-cracked phase (70% \(f_{c(28)}^{{}}\))
- \(f_{{c(28 + \Delta t\text{c.p.a})}}^{*}\) :
-
Compressive strength after pre-cracked phase (70% \(f_{c(28)}^{{}}\)) and after a conditioning period in lab environment
- \(f_{{c(28 + \Delta t\text{c.p.w})}}^{*}\) :
-
Compressive strength after pre-cracked phase (70% \(f_{c(28)}^{{}}\)) and after a conditioning period in water immersion
- \({\text{ILRair}} = \frac{{f_{{c(28 + \Delta t\text{c.p.a})}}^{*} - 0.7f_{c(28)} }}{{f_{c(28)} }}\) :
-
Index of load recovery under lab environmental conditions
- \({\text{ILRwater}} = \frac{{f_{{c(28 + \Delta t\text{c.p.w})}}^{*} - 0.7f_{c(28)} }}{{f_{c(28)} }}\) :
-
Index of load recovery under water immersion
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Acknowledgements
The authors acknowledge the support of Penetron Italia and the kind availability of its CEA, MArch. Enrico Maria Gastaldo Brac, for providing the crystalline admixtures employed in this investigation. The authors also thank the technicians of the Construction/Materials Science Laboratory (Labsco) University Iuav, for the support in performing experimental tests, and Mrs Beatrice Bordin, Ca’ Foscari University, for the support in chemical experimental tests. A special thanks to prof. Antonella Cecchi, IUAV University of Venice, for her insightful review of the manuscript and for her valuable comments in the concept of the investigation.
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C. De Nardi, S. Bullo, L. Ferrara, L. Ronchin and A. Vavasori declares that they have no conflict of interest.
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De Nardi, C., Bullo, S., Ferrara, L. et al. Effectiveness of crystalline admixtures and lime/cement coated granules in engineered self-healing capacity of lime mortars. Mater Struct 50, 191 (2017). https://doi.org/10.1617/s11527-017-1053-3
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DOI: https://doi.org/10.1617/s11527-017-1053-3