Álcalis incorporados ao aluminato tricálcico: efeitos na hidratação

Abstract

Resumoaluminato tricálcico (C 3 A) é a fase que reage mais rápido na hidratação do cimento quando em contato com a água. Geralmente, a forma cristalina sintetizada durante o processo de clinquerização é cúbica. No entanto, o íon Na + pode ser incorporado na estrutura cristalina do C 3 A, em substituição ao Ca 2+ , levando à modificação da forma cristalina cúbica, para a ortorrômbica (Na-C 3 A). Embora alguns estudos tenham investigado a interferência desta fase modificada na hidratação do cimento, algumas lacunas de conhecimento ainda existem. O presente estudo utiliza fases puras sintetizadas em laboratório, para, desta forma, examinar as reações isoladamente. A hidratação destes aluminatos na presença de gipsita foi estudada utilizando calorimetria isotérmica, microscopia eletrônica de varredura (MEV), difração de raios X (DRX) e ensaio de reologia de modo dinâmico, para comprovar e observar o comportamento diferenciado de cada aluminato. Os resultados mostraram que existem grandes diferenças na hidratação de cada aluminato, sendo o C 3 A ortorrômbico mais reativo nas primeiras idades quando em presença de gipsita, consumindo-a totalmente em poucos minutos. As pastas com C 3 A ortorrômbico na presença de gipsita apresentaram um calor total liberado no mínimo 10 vezes maior quando comparado às pastas com C 3 A cúbico. As imagens de MEV e os difratogramas demonstraram que as pastas contendo C 3 A ortorrômbico reagiram mais rápidas formando cristais maiores de etringita. Palavras-chave:Aluminato tricálcico cúbico e ortorrômbico. Etringita. Hidratação. Abstract Tricalcium aluminate (C 3 A) is the phase that reacts more quickly in the cement

Copper Slag Mortar Properties

“…Studies where grinded original copper slag was incorporated in mortar and concrete as partial substitute of cement in small proportions, less than 20%, show that compressive strength and other characteristics such as porosity and durability were increased, when compared to reference mixtures [1][2][3][4][5], although some studies [6] does not revealed increments in strength. When grinded copper slag is used in cement mixtures as partial cement substitute, after its use as abrasive, the compressive strength decrease when compared to the reference mixtures [7].…”

The influence of low temperature on the evolution of concrete strength

“…In order to prevent this, gypsum (CaSO.2H 2 O) is added to the clinker manufacturing process of Portland cement. According to Kirchheim et al (2010) [8], an example of the action of the C 3 A can be seen in the execution of Iberê Camargo museum in Porto Alegre, where it was used white Portland cement with C 3 A contents above 9%. The calcium silicates (C 3 S e βC 2 S) are responsible for about 75% of the constitution of ordinary Portland cement, exerting a dominating role in determining the characteristics of hardness, also known as the rate of development of resistance.…”

“…Cements with high hydration heat, hydrate faster compared to cements that generate less heat of hydration (Taylor, 1967) [9]. Kirchheim et al (2010) [8] add that in certain works use large amounts of concrete, its thermal conductivity can be low and with a high heat release due to the hydration reaction, which can generate cracks through thermal retraction. According to Mehta and Monteiro (2008) [4] the heat of hydration can sometimes be unfavorable, for example, in the mass-concrete structures.…”

Accelerated cementitious matrices : hydration, microstructure and mechanical strength

“…Due to the higher alkali content, orthorhombic C3A has a very complex crystal structure, characterized by large structural voids, making it more soluble and reactive than cubic C3A. Therefore, orthorhombic C3A content must be limited in cements for special applications, such as in sulfate-resistant cements [35].…”

“…Influence of spraying on hydration __________________________________________________________________________________________________________________________________________________________________________________________________________________________________ __________________________________________________________________________________________________________________________________________________________________________________________________________________________________ Renan Pícolo Salvador 133 the increase in temperature [35], the spraying process may lead to the formation of AFm phases at the moment of accelerator addition. Larger amounts of gypsum in cement may be required to suppress the formation of AFm phases due to the increase in temperature caused by spraying.…”