Local structure and Ca/Si ratio in C-S-H gels from hydration of blends of tricalcium silicate and silica fume

X-ray Total Scattering Study of Phases Formed from Cement Phases Carbonation

“…This value is smaller than the expected value according to reaction (7), 1.5%. However, this difference could arise from: (i) The belite hydration degree being lower that 100% as measured by diffraction; (ii) the experimental errors; and (iii) because the calcium content of the C-S-H gel can be slightly higher than 1.80 as previously reported [23].…”

“…These PDF traces for C 3 S_hyd and C 2 S_hyd, Figure 8a,c, are consistent with the contribution of C-S-H gel and a few layer thick nanoportlandite. This has been extensively discussed very recently and the interested reader is addressed to the publication [23]. The changes in the differential PDF traces for the carbonate materials are readily evident.…”

“…Now, we turn our attention to the low r-ranges. Due to the lack of structural descriptions for nanocrystalline and amorphous components, we have employed the differential PDF approach [23,32,53]. This methodology consists on subtracting from the raw patterns, some known contributions, in this case the ones from the crystalline components.…”

“…Collecting a total scattering data with enough Q-resolution, Rietveld quantitative phase analyses could be carried out in the reciprocal-space and PDF analyses in the directspace. In fact, PDF analyses have been recently carried out for better understanding of the local structure of C-S-H gel which could be satisfactorily explained as a mixture of nanocrystalline defective clinotobermorite and an amorphous component with an atomic local order of few layer-thick calcium hydroxide [23,32,33]. PDF methodology has been recently used for improving our understanding in cement chemistry.…”

Caracterização do comportamento de pastas e argamassas de cimentos Portland durante o processo de lixiviação acelerada

“…A alteração da composição dos cimentos tem impacto em todas as características dos concretos produzidos, desde a cinética da hidratação até a composição dos produtos hidratados, sendo essa variação mais observada em cimentos pozolânicos (Lothenbach et al, 2011). Além do aumento das fases AFm e da Portlandita ser consumida em idades posteriores pela reação com os materiais silicosos ou sílico-aluminosos, os C-S-H formados a partir de cimentos pozolânicos possuem menores relações Ca/Si e um aumento no teor de aluminato incorporado, influenciando as propriedades mecânicas e de durabilidade dos concretos e argamassas produzidos devido a interação da matriz cimentícia com os agentes agressivos (Cuesta et al, 2021;Dai et al, 2014). Apesar da água ser um elemento fundamental na produção de concretos e argamassas, o contato com a mesma pode causar a degradação por meio de alguns fenômenos, como a lixiviação.…”