Abstract
abstract: The microstructure of cement pastes is important to understand the effect of some parameters in the hydration process. In this context, this study had as objective to evaluate the effect of different water/binder (w/b) ratios in the hydration process of cementitious pastes produced with and without incorporation of silica fume and metakaolin. The pastes were obtained with water/binder ratios of 0.3, 0.4 e 0.5, with replacement, by weight, of Portland cement for silica fume and metakaolin, in the contents of 10% and 20%, respectively. It was performed the X-ray diffraction test of the pastes in the ages of 1, 3, 7, and 28 days, to evaluate the hydration evolution of the cementitious materials. According to the results obtained, it was observed that the cementitious pastes presented similar mineralogical phases, except for the pastes containing metakaolin due to the formation of new aluminate phases. With the increase of the water/binder ratio, the pozzolanic reactions and hydration occurred in greater proportion, standing out the metakaolin with greater reactivity.
Highlights
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 results found are consistent with the results of some researchers who presented a similar behavior in the hydration process for the mineralogical phases identified in this study, mainly for the portlandite peaks (P), which in the cementitious pastes containing metakaolin and silica fume, decreased at 28 days due to the progress of hydration of the alite and belite phases and of the pozzolanic reactions [9]–[11], [14], [19]
All the cementitious pastes presented similar mineralogical phases, except for pastes containing metakaolin, which during the hydration process presented the formation of aluminate phases, due to the presence of alumina in this material, denominated in this study as hydrated calcium aluminum silicate (CS) and hydrated calcium aluminum oxide (CO)
Summary
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. Due to the environmental impact caused by the extraction of raw materials and CO2 emission in cement production has been sought a reduction of the consumption of this constituent of concrete, together with the need to increase the durability [3], [4] In this context, it arises as an alternative the using supplementary cementitious materials (SCMs) in partial replacement to Portland cement [4]–[8]. The hydration reactions of the cement and the release of heat are directly related to several parameters: the composition of the binder, type and content of the supplementary cementitious materials used in replacement to clinker, chemical admixture added, water/cement ratio and curing temperature. Taking into consideration the importance of the presence of water in the hydration process and the lack of more comprehensive studies to understand the effect of the synergy between pozzolanic additions and the water/binder ratio, the present article aimed to evaluate the joint effect of different w/b ratios and supplementary cementitious materials in the hydration process of cementitious pastes through the microstructural analysis of Xray diffraction
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