The partial replacement of cement by mineral additions such as metakaolin has been widely applied in the production of high-strength and durable concretes due to the pozzolanic action, allowing a reduction in the consumption of cement. Tests are performed to determine the mechanical properties of these materials, such as compressive strength, for which there are different levelling techniques of specimens, such as sulphur and neoprene, indicated for different resistance classes. The present study aimed to characterize the behaviour, in the hardened state, of concrete produced with high initial strength Portland cement (CPV-ARI) and metakaolin and evaluate the different levelling methods. Three groups of samples dosed by the IPT-EPUSP method, with mix designs of 1:3, 1:5, and 1:6, and replacements of 8 and 10% of cement by metakaolin, were subjected to compressive strength test, at the ages of 28 days, with levelling by neoprene, and 90 days, with levelling by sulphur. It was observed an increase in strength with addition of metakaolin at both ages. Comparing the results in the two ages, it was verified an increase in strength for the mix designs 1:5 and 1:6 and a reduction for the mix design 1:3. Such fact can be explained by the high strengths achieved by this mix design. As the levelling method used was sulphur, it is confirmed the imprecision of results for strengths above 50 MPa with this technique.
O presente estudo teve como objetivo desenvolver um modelo para prever a vida útil de revestimentos de paredes externas em argamassa com acabamento em pintura, com base no estado de degradação de 28 edificações na cidade de Recife, Brasil. A área de revestimento afetada por diferentes manifestações patológicas foi medida e um índice numérico para descrever a gravidade da degradação do revestimento (Sw) foi calculado. A partir deste índice, foram construídas curvas de degradação em função de fatores intrínsecos (orientação cardeal, textura, cor e presença de detalhes construtivos) e extrínsecos (distância do mar e proximidade de fontes poluentes). Nas amostras analisadas houve o predomínio de manchas, e em menor número, fissuras e descolamentos. Dos fatores estudados, a orientação cardeal das fachadas foi o que apresentou maior influência no processo de degradação. Os resultados obtidos demonstram claramente a aplicabilidade do modelo no estudo da degradação de revestimentos, contribuindo para o desenvolvimento de ações de manutenção focadas nos fatores mais importantes na degradação de revestimentos.
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