| Name: | Description: | Size: | Format: | |
|---|---|---|---|---|
| 5.13 MB | Adobe PDF |
Authors
Advisor(s)
Abstract(s)
Os rebocos são argamassas aplicadas como camada de finalização em paredes de diferentes materiais tanto para proteção contra os agentes atmosféricos como para fins estéticos. No caso em particular de intervenções de conservação de paredes antigas, a escolha do reboco a aplicar se torna diferenciada em termos dos materiais constituintes. Comumente, estes são à base de cal e com a utilização opcional de cor através da incorporação de pigmentos na mistura ou através de pintura como camada final (caiação). Estes revestimentos coloridos aparecem com grande destaque em culturas regionais do centro, sul e ilhas de Portugal, tendo um resultado esplendoroso.
Este estudo desenvolveu três composições diferentes de argamassas à base de cal, sendo a primeira livre de aditivos, a segunda adicionada de metacaulim, um material de alta reatividade pozolânica constituído basicamente de sílica e alumina, e à terceira cimento. As três composições foram ensaiadas no estado fresco, com objetivo de se obter consistências parecidas em nível de trabalhabilidade, e no estado endurecido, com caracterização mecânica através de ensaios de resistência a flexão e compressão nas idades de 28, 60, 90, 135 e 180 dias, além de ensaio de aderência em superfícies de blocos cerâmicos nas idades de 28 e 60 dias.
Argamassas à base de cal (ligante obtido através da decomposição térmica do calcário) são constantemente utilizadas, visto que este material apresenta propriedades compatíveis com estruturas antigas. Já o cimento é um material muito recorrente, sendo relevante seu comportamento nesta utilização. De qualquer forma, todas as argamassas de reboco devem apresentar uma durabilidade considerável quando exposta às intempéries. Portanto, este estudo tem como objetivo a caracterização da durabilidade destes materiais submetidos ao envelhecimento natural e artificial. Provetes foram sujeitos à toda a estação da primavera em Bragança, uma estação com altas amplitudes térmicas e de humidade, e simultaneamente à QUV Accelerated Weathering Testers, com ciclos alternados de luz UV, humidade controlada e temperaturas elevadas, simulando, respectivamente: luz solar com lâmpadas UV específicas, orvalho, brisa e chuva com humidade de condensação e spray de água, e variação de temperatura assim como ocorre durante os dias e estações. Os resultados obtidos mostram que 1008 horas de envelhecimento artificial podem gerar danos dobrados ao envelhecimento natural em uma única estação, assim como também pode potencializar o processo de carbonatação das argamassas estudadas, que obtiveram resultados mais expressivos de resistência mecânica quando envelhecidos artificialmente. Evidenciou-se os problemas de pigmentos artificial que se comportaram de forma heterogenia nas três composições, apresentando melhor comportamento quando em contato com metacaulim.
Rendering mortars are applied as finishing layers in walls of different materials to provide weather and aesthetic protection. In the case of historic masonry preservation interventions, the choice of the appropriate rendering mortar is differentiated in terms of its constituent materials, commonly lime-based, where colour may be achieved by incorporating pigments into the mixture or by using limewash as a finishing layer. Such colourful coverings appear prominently in the regional cultures of the central, southern and Portuguese islands, offering a splendid result. In this context, lime-based mortars (binder obtained by thermal decomposition of limestone) are constantly used, which particularly properties are compatible with historic structures. Furthermore, as cement is a very recurrent material, its behaviour in mortars is relevant. Regardless of the binder type, rendering mortars should have considerable durability when exposed to weathering. Therefore, the aim of this study was to characterize the durability of lime and cement-based mortars when subjected to natural and artificial ageing. Three different compositions of lime-based mortars were tried. The first was manufactured without additives, the second used metakaolin, a high-reactive pozzolanic material consisting primarily of silica and alumina, and in the third, cement was employed. All compositions were tested in the fresh state to obtain similar workability consistency, and in the hardened state, with mechanical characterization through flexural and compression strength tests at the ages of 28, 60, 90, 135 and 180 days. Moreover, the bond strength capacity to ceramic blocks at the ages of 28 and 60 days, was also evaluated. The test specimens were subjected to the entire spring in Bragança, a season with high thermal and humidity amplitude, and simultaneously to the QUV Accelerated Weathering Testers, with alternating cycles of UV light, controlled humidity and elevated temperatures, simulating, respectively: sunlight with specific UV lamps, dew, breeze and rain with condensation and water spray and temperature variation as it occurs during the days and seasons. The results showed that 1008 hours of artificial ageing can produce twice as more damage when compared to natural ageing in a single season. Also, when artificially aged, the mortars studied presented increased carbonation process and enhanced mechanical resistance. Furthermore, the common issues related to artificial pigments were noticed in the three compositions, where the pigment behaved heterogeneously and presented a better performance when in contact with metakaolin.
Rendering mortars are applied as finishing layers in walls of different materials to provide weather and aesthetic protection. In the case of historic masonry preservation interventions, the choice of the appropriate rendering mortar is differentiated in terms of its constituent materials, commonly lime-based, where colour may be achieved by incorporating pigments into the mixture or by using limewash as a finishing layer. Such colourful coverings appear prominently in the regional cultures of the central, southern and Portuguese islands, offering a splendid result. In this context, lime-based mortars (binder obtained by thermal decomposition of limestone) are constantly used, which particularly properties are compatible with historic structures. Furthermore, as cement is a very recurrent material, its behaviour in mortars is relevant. Regardless of the binder type, rendering mortars should have considerable durability when exposed to weathering. Therefore, the aim of this study was to characterize the durability of lime and cement-based mortars when subjected to natural and artificial ageing. Three different compositions of lime-based mortars were tried. The first was manufactured without additives, the second used metakaolin, a high-reactive pozzolanic material consisting primarily of silica and alumina, and in the third, cement was employed. All compositions were tested in the fresh state to obtain similar workability consistency, and in the hardened state, with mechanical characterization through flexural and compression strength tests at the ages of 28, 60, 90, 135 and 180 days. Moreover, the bond strength capacity to ceramic blocks at the ages of 28 and 60 days, was also evaluated. The test specimens were subjected to the entire spring in Bragança, a season with high thermal and humidity amplitude, and simultaneously to the QUV Accelerated Weathering Testers, with alternating cycles of UV light, controlled humidity and elevated temperatures, simulating, respectively: sunlight with specific UV lamps, dew, breeze and rain with condensation and water spray and temperature variation as it occurs during the days and seasons. The results showed that 1008 hours of artificial ageing can produce twice as more damage when compared to natural ageing in a single season. Also, when artificially aged, the mortars studied presented increased carbonation process and enhanced mechanical resistance. Furthermore, the common issues related to artificial pigments were noticed in the three compositions, where the pigment behaved heterogeneously and presented a better performance when in contact with metakaolin.
Description
Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do Paraná
Keywords
Argamassas Reboco Manutenção Reabilitação Cal Cimento Metacaulim Pigmento Caracterização experimental Envelhecimento