Effect of Fly Ashes with High Total Alkali Content on the Alkalinity of the Pore Solution of Hydrated Portland Cement Paste

Durability is one of the focal points of recent research on the behavior of new blended cement matrices in aggressive environments. The material selected for this study was ceramic waste (CW) rejected by Spanish manufacturers, primarily for reasons such as unsuitable kiln temperature or dimensional or mechanical failure. The resistance of CW-containing cement pastes to three aggressive environments (SO 4 2 -, Cl -, and substitute seawater) was tested using the Koch-Steinegger method in this in-depth analysis of the effect of CW on the chemical resistance of new blended matrices. The samples were also tested for performance in freeze-thaw cycles. The reaction mechanism was analyzed using X-ray diffraction (XRD), pore-size distribution, scanning electron microscopy (SEM), and backscattered electron images (BSE) with energy-dispersive X-ray (EDX) techniques. The results showed that CW contributed to cement resistance to such media; this enhancement of its mechanical properties was the result of the pozzolanic reaction induced by the addition of CW.

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“…Sulfates and chlorides activated the pozzolanic reaction when added during mixing . Lorenzo et al . and Guerrero et al .…”

Section: Resultsmentioning

confidence: 99%

Durability of Blended Cement Pastes Containing Ceramic Waste as a Pozzolanic Addition

et al. 2014

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“…25, bottom. In hydration studies, generally a decrease of the Ca/Si ratio of the C-S-H Potassium and sodium concentrations in the pore solution after 7 and 365 days of hydration depending on the total content of K 2 O and Na 2 O, respectively [3,10,11,15,19,26,27,31,32,39,40,42] and lowering of the portlandite content is observed but not a complete depletion of portlandite [10,39,74] even after 12 years of hydration. The resilience of portlandite in hydrating FA-PC blends has been explained by the inhomogeneity of the microstructure and the lack of water.…”

Section: Fly Ashmentioning

confidence: 99%

The pore solution of blended cements: a review

et al. 2015

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This paper is the work of working group 3 of the RILEM Technical Committee on Hydration and Microstructure of Concrete with SCM (TC 238-SCM). The pore solution is an essential but often overlooked part of hydrated cements. The composition of the cement pore solution reflects the ongoing hydration processes and determines which solid phases are stable and may precipitate, and which phases are unstable and may dissolve. The study of the cement pore solution therefore contributes to the understanding of the mechanisms as well as of the kinetics of cement hydration. This paper reviews the impact of supplementary cementitious materials (SCMs) on the pore solution composition of blended cements. In a first part, the extraction and analysis methods of cement pore solutions are reviewed, leading to a set of practical guidelines and recommendations. In a second part, an extensive literature survey is used to document the effect of the addition of SCMs (blast furnace slag, fly ash and silica fume) on the pore solution. Finally, in a third part the collected literature data are compared to thermodynamic simulations. The performance and current limitations of thermodynamic modelling of blended cement hydration are demonstrated and discussed in view of future progress.

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“…The blending of OPC with supplementary cementitious materials rich in silicon and poor in alkalis leads to a reduction of the pH and the alkali concentrations in the pore solutions as (i) the Portland cement is diluted and (ii) as C-S-H with a lower C/S ratio leads to an increase in alkali uptake by C-S-H [75,76]. The blending of Portland cement with low calcium fly ash lowers the alkali and hydroxide concentrations in the pore solution significantly [121,124,[130][131][132][133]. The same effect can also be observed for Portland systems blended with silica fume [133][134][135].…”

Section: Other Systemsmentioning

confidence: 99%