Despite, its environmental and historical significance, the use of lime-based mortars still presents some limitations, such as limited thermal isolation, prolonged hardening times and relatively low mechanical performance. Generally, these issues can be solved with additives, although the necessary methods to test the impact of these materials on air lime binders are still limited or not entirely suitable. These challenges have driven ongoing scientific research across many disciplines, such as material science, chemistry, geochemistry and engineering. The primary objective of this research project was to develop simple and sustainable strategies to enhance both the performance and testing methods of lime-based materials, thereby promoting their application in sustainable architecture and restoration of built heritage. Particularly, two types of additives were the principal focus of this thesis: PCM and nano- & micro-cellulose. In this context, testing the macro-scale mechanical properties of lime-based mortars and binders is a key focus in the field. Current testing methods for these materials are mainly based on cement materials, which are not fully appropriate for lime. This thesis introduces a novel methodology for assessing both the superficial and bulk macro-mechanical response of lime binders. The proposed method allowed to successfully determine the compressive and flexural strength of lime binders that aligned with those reported in the literature, underscoring its reliability. Additionally, the absence of aggregates and the consequent homogeneity of the specimens enabled to perform micro-scratch resistance measurements of air lime binder specimens. This micro-invasive technique is promising, as it correlates well with the compressive strength of the material, yielding reproducible results with a low noise-to-signal ratio. On the other hand, improving thermal efficiency in historical buildings remains a pressing issue. Heating and cooling systems are the main contributor to environmental emissions related to the use phase of buildings. However, installing conventional insulation systems in heritage buildings may cause damage to the original masonries, or might even be impossible to perform. Promising alternative solutions like Phase Change Materials (PCMs) additives provide an increment of the thermal response of air lime mortars. Nonetheless, this often compromises the mechanical properties of the material. This thesis specifically investigates the implementation of a specific PCM, Form Stable Phase Change Material (FS-PCM) aggregates, in air lime mortars. The performed investigation revealed that the lack of confinement of the PCM within the FS-PCM aggregates provokes its dispersion into the binder phase and consequent weakening. The PCM hinders the crystalline interlocking between calcite crystals and, under compressive stress, acts as a lubricant, facilitating the gliding between crystals. To counteract this effect, a practical and cost-effective solution was developed using a coating methodology with fine powders. Five different coating materials were tested—calcium hydroxide, milk of lime, NHL, cocciopesto, and pozzolana. The majority of these coatings successfully retained PCM within FS-PCM aggregates and decreased cracks and fissures within the mortar, possibly incrementing its cohesiveness. Finally, carbonation of air lime is a slow process and is affected by several factors. Often additives are used to accelerate this process. One example are biomimetic-inspired solutions where organic molecules, such as carbohydrates, accelerate carbonation and improve mechanical performance of lime. Despite their vast availability, nano- and micro-cellulose fibers have not yet been used with this aim. In consequence, the final section of this thesis focuses on the use of nano- and micro-cellulose as sustainable additives to increment the carbonation speed of air lime binders. The effect of these fibers was tested during the mineral formation of Ca(OH)2 and also during the carbonation process. The obtained results highlighted that the fiber crystallinity directly influences the obtained mineral morphology upon Ca(OH)2 formation. These modified morphologies are more reactive, thus carbonate faster. Furthermore, the inclusion of nano- and micro-cellulose accelerates the carbonation also when the fiber additives are included to a hydrated lime paste.
Nonostante la loro rilevanza storica e il minor impatto ambientale, l’impiego di malte a base di calce presenta ancora diverse limitazioni, tra cui una limitata capacità di isolamento termico, tempi di indurimento prolungati e ridotte prestazioni meccaniche. Generalmente, tali problematiche possono essere risolte mediante l'uso di additivi; tuttavia, i metodi attualmente disponibili per valutare l’impatto di questi materiali sui leganti a base di calce aerea risultano ancora limitati o non del tutto adeguati. Queste sfide hanno stimolato un'attività di ricerca scientifica continua in numerose discipline, tra cui la scienza dei materiali, la chimica, la geochimica e l'ingegneria. L'obiettivo principale del presente progetto di ricerca è stato quello di sviluppare strategie semplici e sostenibili per migliorare sia le prestazioni sia i metodi di analisi dei materiali a base di calce, promuovendone così l'applicazione in architettura e nel restauro del patrimonio edilizio. In particolare, la tesi si concentra sull’utilizzo di due tipologie di additivi: materiali a cambiamento di fase (PCM) e nano- & micro-cellulosa. In questo contesto, lo studio delle proprietà meccaniche macroscopiche delle malte e dei leganti a base di calce rappresenta un aspetto cruciale. I metodi di prova attualmente impiegati per questi materiali derivano principalmente da quelli utilizzati per i materiali cementizi, che tuttavia non risultano completamente adeguati per la calce. La presente tesi introduce una nuova metodologia per la valutazione sia della risposta macro-meccanica superficiale sia di quella in massa dei leganti a base di calce. Il metodo proposto ha permesso di determinare con successo la resistenza a compressione e a flessione dei leganti, ottenendo valori in linea con quelli riportati in letteratura e confermandone così l'affidabilità. Inoltre, l'assenza di aggregati e la conseguente omogeneità dei provini hanno reso possibile l’esecuzione di misurazioni di resistenza al micro-graffio sui campioni di legante a base di calce aerea. Questa tecnica micro-invasiva si è rivelata promettente, poiché ha mostrato una buona correlazione con la resistenza a compressione del materiale, fornendo risultati riproducibili e caratterizzati da un basso rapporto segnale/rumore. D'altro canto, il miglioramento dell’efficienza termica negli edifici storici rimane una questione di grande rilevanza. I sistemi di riscaldamento e raffreddamento rappresentano infatti i principali responsabili delle emissioni ambientali durante la fase di utilizzo degli edifici. Tuttavia, l’installazione di sistemi di isolamento convenzionali negli edifici storici può causare danni alle murature originali o risultare addirittura impraticabile. Soluzioni alternative promettenti, come l’aggiunta di materiali a cambiamento di fase (PCM), consentono di incrementare la risposta termica delle malte a base di calce aerea; tuttavia, ciò comporta spesso una riduzione delle prestazioni meccaniche del materiale. La presente tesi analizza nello specifico l’integrazione di un particolare PCM, ovvero aggregati di Form Stable Phase Change Materials (FS-PCM), nelle malte a base di calce aerea. L'indagine condotta ha rivelato che l'assenza di confinamento del PCM all'interno degli aggregati FS-PCM ne provoca la dispersione nella fase legante e il conseguente indebolimento del materiale. Il PCM ostacola l’interconnessione cristallina tra i cristalli di calcite e, a compressione, agisce come un lubrificante, facilitando lo scorrimento tra i cristalli. Per contrastare questo effetto, è stata sviluppata una soluzione pratica ed economicamente vantaggiosa basata su una metodologia di rivestimento con polveri fini. Sono stati testati cinque diversi materiali di rivestimento—idrossido di calcio, latte di calce, NHL, cocciopesto e pozzolana—e la maggior parte di essi ha dimostrato di trattenere efficacemente il PCM all'interno degli aggregati FS-PCM, riducendo la formazione di fessure e crepe nella malta e contribuendo così ad aumentarne la coesione. Infine, la carbonatazione della calce aerea è un processo lento, influenzato da molteplici fattori. Spesso si ricorre all'uso di additivi per accelerare tale processo. Un esempio è rappresentato da approcci biomimetici, in cui molecole organiche, come i carboidrati, favoriscono la carbonatazione e migliorano le prestazioni meccaniche della calce. Nonostante la loro ampia disponibilità, le fibre di nano- e micro-cellulosa non sono ancora state impiegate a tale scopo. Di conseguenza, l'ultima sezione della tesi è dedicata allo studio dell’impiego di nano- e micro-cellulosa come additivi sostenibili per incrementare la velocità di carbonatazione dei leganti a base di calce aerea. L'effetto di queste fibre è stato analizzato sia durante la formazione minerale di Ca(OH)₂ sia nel corso del processo di carbonatazione. I risultati ottenuti hanno evidenziato che la cristallinità delle fibre influenza direttamente la morfologia minerale che si forma durante la sintesi di Ca(OH)₂. Le morfologie così modificate risultano più reattive e, di conseguenza, carbonatano più rapidamente. Inoltre, l’inclusione di nano- e micro-cellulosa accelera ulteriormente la carbonatazione anche quando tali additivi vengono incorporati in una pasta di calce idrata.
Green lime-based mortars for the restoration and repair of buildings
GUZMÁN GARCÍA LASCURAIN, PAULINA
2024/2025
Abstract
Despite, its environmental and historical significance, the use of lime-based mortars still presents some limitations, such as limited thermal isolation, prolonged hardening times and relatively low mechanical performance. Generally, these issues can be solved with additives, although the necessary methods to test the impact of these materials on air lime binders are still limited or not entirely suitable. These challenges have driven ongoing scientific research across many disciplines, such as material science, chemistry, geochemistry and engineering. The primary objective of this research project was to develop simple and sustainable strategies to enhance both the performance and testing methods of lime-based materials, thereby promoting their application in sustainable architecture and restoration of built heritage. Particularly, two types of additives were the principal focus of this thesis: PCM and nano- & micro-cellulose. In this context, testing the macro-scale mechanical properties of lime-based mortars and binders is a key focus in the field. Current testing methods for these materials are mainly based on cement materials, which are not fully appropriate for lime. This thesis introduces a novel methodology for assessing both the superficial and bulk macro-mechanical response of lime binders. The proposed method allowed to successfully determine the compressive and flexural strength of lime binders that aligned with those reported in the literature, underscoring its reliability. Additionally, the absence of aggregates and the consequent homogeneity of the specimens enabled to perform micro-scratch resistance measurements of air lime binder specimens. This micro-invasive technique is promising, as it correlates well with the compressive strength of the material, yielding reproducible results with a low noise-to-signal ratio. On the other hand, improving thermal efficiency in historical buildings remains a pressing issue. Heating and cooling systems are the main contributor to environmental emissions related to the use phase of buildings. However, installing conventional insulation systems in heritage buildings may cause damage to the original masonries, or might even be impossible to perform. Promising alternative solutions like Phase Change Materials (PCMs) additives provide an increment of the thermal response of air lime mortars. Nonetheless, this often compromises the mechanical properties of the material. This thesis specifically investigates the implementation of a specific PCM, Form Stable Phase Change Material (FS-PCM) aggregates, in air lime mortars. The performed investigation revealed that the lack of confinement of the PCM within the FS-PCM aggregates provokes its dispersion into the binder phase and consequent weakening. The PCM hinders the crystalline interlocking between calcite crystals and, under compressive stress, acts as a lubricant, facilitating the gliding between crystals. To counteract this effect, a practical and cost-effective solution was developed using a coating methodology with fine powders. Five different coating materials were tested—calcium hydroxide, milk of lime, NHL, cocciopesto, and pozzolana. The majority of these coatings successfully retained PCM within FS-PCM aggregates and decreased cracks and fissures within the mortar, possibly incrementing its cohesiveness. Finally, carbonation of air lime is a slow process and is affected by several factors. Often additives are used to accelerate this process. One example are biomimetic-inspired solutions where organic molecules, such as carbohydrates, accelerate carbonation and improve mechanical performance of lime. Despite their vast availability, nano- and micro-cellulose fibers have not yet been used with this aim. In consequence, the final section of this thesis focuses on the use of nano- and micro-cellulose as sustainable additives to increment the carbonation speed of air lime binders. The effect of these fibers was tested during the mineral formation of Ca(OH)2 and also during the carbonation process. The obtained results highlighted that the fiber crystallinity directly influences the obtained mineral morphology upon Ca(OH)2 formation. These modified morphologies are more reactive, thus carbonate faster. Furthermore, the inclusion of nano- and micro-cellulose accelerates the carbonation also when the fiber additives are included to a hydrated lime paste.File | Dimensione | Formato | |
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Descrizione: PhD Thesis Paulina Guzman Garcia Lascurain
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https://hdl.handle.net/10589/237118