The use of different technologies have contributed to the increase in durability facing the aggressive agents that damage the concrete structures. Therefore, it is possible to reduce the capillary porosity in concrete lowering the ratio water/binder; using pozzolan, hydrophobic or waterproofing products in the mixture; applying hydrophobic products or waterproofing in the concrete surface; replacing pure cements for compounds cements, pozzolanic cements or cements with blast furnace slag; among other actions. The waterproofing has the function to prevent the water or fluid passage in liquid or steam state, thereby protecting structures. The waterproofing creates a barrier when coating is applied to close surface pores with the aim of preventing the water pervasion by any transport mechanism. This paper has evaluated the use of crystalline waterproofing as admixtures, as well as a coating, sanding and no-sanding, in order to know the benefits it can bring to the concrete water absorption, comparing their performance with other concretes with or without silica fume admixture. Developed tests were: total absorption, under pressure water penetration (30 kPa) and compressive strength test. The results have showed that the silica fume admixture is more efficient than the analyzed crystalline waterproofing, as it has contributed to the compressive strength increase and decrease of water absorption and penetration. The crystalline waterproofing admixture has contributed to compressive strength increase; however, there was also an increase in the absorption and penetration. On the other hand, the coating waterproofing has not influenced the compressive strength, but reduced absorption and penetration when sanded.
RESUMO Essa pesquisa teve por finalidade avaliar um resíduo de lodo de efluentes de indústrias de papel quanto à potencialidade de emprego em matrizes cimentícias. Verificou-se a composição química do resíduo e realizaram-se misturas com adições de 0, 5 e 10%, em relação à massa de cimento. As matrizes cimentícias foram analisadas por meio de calorimetria isotérmica, resistência à compressão, resistência à tração na compressão diametral, absorção de água por capilaridade, densidade de massa aparente e módulo de elasticidade dinâmico. Os resultados obtidos não foram satisfatórios, visto que a adição do resíduo à matriz apresentou aumento no consumo de cimento para atingir a resistência requerida e aumento no consumo de água para manutenção da consistência.
Self-healing is recognized as a promising technique for increasing the durability of concrete structures by healing cracks, thereby reducing the need for maintenance activities over the service life and decreasing the environmental impact. Various self-healing technologies have been applied to a wide range of cementitious materials, and the performance has generally been assessed under 'ideal' laboratory conditions. Performance tests under ideal conditions, tailored to the self-healing mechanism, can demonstrate the self-healing potential. However, there is an urgent need to prove the robustness and reliability of self-healing under realistic simulated conditions and in real applications before entering the market. This review focuses on the influence of cracks on degradation phenomena in reinforced concrete structures, the efficiency of different healing agents in various realistic (aggressive) scenarios, test methods for evaluating self-healing efficiency, and provides a pathway for integrating self-healing performance into a life-cycle encompassing durability-based design.
Several factors, such as chemical shrinkage or environmental attack can produce concrete cracks. Calcium hydroxide content from the environment or cement hydration can promote the self-healing phenomenon (SHP). This study evaluates the calcium hydroxide concentration influence on the self-healing phenomenon of cement-based materials. Cracked mortars with different types of cement, such as a filler, pozzolanic, and high initial strength, were exposed to four environmental conditions. Titration was the method proposed to determine the amount of calcium hydroxide content leached in the water, and the cracks closure were analyzed by optical microscopy. CPII F (Portland Cement, type II, compound with limestone) samples showed no trend to Ca(OH)2 leached, and to superficial cracking closure. Regarding CPV (Portland cement, type V, high initial strength cement) samples, their behavior showed the highest Ca(OH)2 content to all environmental exposure, and cracking closure to samples in submerged condition. Thus, a significant influence in the cracks´ closure regarding the presence of Ca2+ leached to the exposure environments, and a water source related to this behavior seems to be a primary factor to improve the SHP.
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