Propriedades nanomecânicas de pastas de cimento

Abstract

O entendimento da influência de cada fase do concreto, dentre as quais merece destaque a pasta de cimento, é importante para o desenvolvimento de um concreto mais eficiente, com maior velocidade de hidratação e resistência à propagação de fissuras. O módulo de elasticidade do concreto é um dos principais parâmetros de projeto de estruturas e têm grande influência na velocidade do processo de construção e na durabilidade das estruturas. A capacidade de deformação do concreto depende das características intrínsecas dos produtos de hidratação do cimento, agregados, zona de transição e poros, além de variáveis inerentes ao processo, como velocidade de hidratação e condições climáticas. O objetivo deste estudo foi avaliar as propriedades mecânicas de módulo de elasticidade e resistência superficial (dureza) para uma pasta de cimento, através da técnica da nanoindentação instrumentada e, complementarmente, comparar este valor do módulo de elasticidade, utilizando o método normatizado para concreto. Os resultados obtidos pela nanoindentação foram de 17,2 GPa para o módulo de elasticidade e de 0,90 GPa para a dureza. A determinação do módulo de elasticidade tangente inicial calculado pela NBR 6118 1 foi de 9,6 GPa. A nanoindentação mostrou-se uma ferramenta válida para avaliar modificações nanoestruturais de pastas de cimento.

Effect of the Ca/Si Molar Ratio on the Micro/nanomechanical Properties of Synthetic C-S-H Measured by Nanoindentation

“…The results presented here cannot be directly transferred to C-S-H formed from the hydration of Portland cement, but as mentioned previously, similarities exists between the nanostructure of C-S-H in Portland cement and synthesized C-S-H; these similarities are evident between their micro/nanomechanical properties, determined by the same method and apparatus described herein. Studies characterizing the nanostructure of the cement paste resulted in mean values of indentation modulus 17.2 ± 2.9 GPa and 16.8 ± 2.3 GPa (in two samples of Portland cement paste with w/c = 0.5), 33 indicating the formation of low-density C-S-H, as mentioned in the literature. 15,18 Results obtained from TEM micrographs for the two types of C-S-H (Ca/Si = 2.1 in Figure 9 and Ca/Si = 0.7 in Figure 10) reveal the characteristics of C-S-H and the similarities of its disordered particulate arrangement to that of C-S-H from Portland cement.…”

“…Table shows the values of the indentations shown in Figures and . It is important to consider that in the indentation tests performed on cement pastes, as reported in the literature, ,, C-S-H synthesis shows a lower roughness.…”

Effect of the water/binder ratio on the hydration process of Portland cement pastes with silica fume and metakaolin

“…Understanding the influence of each phase of cementitious pastes is important for the development of a transition zone more efficient, with greater hydration speed, and better performance of the mechanical properties and durability. The deformation capacity of concrete is connected to intrinsic characteristics of cement hydration products, aggregates, transition zone, and pores, besides other particular variables to process, such as hydration speed and climatic conditions [1]. The Portland cement, when hydrated, has as main phases the hydrated calcium silicate (C-S-H) and the calcium hydroxide (CH), which are directly connected to the physical and mechanical properties of construction materials [1], [2].…”

“…The deformation capacity of concrete is connected to intrinsic characteristics of cement hydration products, aggregates, transition zone, and pores, besides other particular variables to process, such as hydration speed and climatic conditions [1]. The Portland cement, when hydrated, has as main phases the hydrated calcium silicate (C-S-H) and the calcium hydroxide (CH), which are directly connected to the physical and mechanical properties of construction materials [1], [2]. Also, the water/cement (w/c) ratio is one of the parameters to control the micro and nanostructure of these phases [1].…”

“…The Portland cement, when hydrated, has as main phases the hydrated calcium silicate (C-S-H) and the calcium hydroxide (CH), which are directly connected to the physical and mechanical properties of construction materials [1], [2]. Also, the water/cement (w/c) ratio is one of the parameters to control the micro and nanostructure of these phases [1].…”