Phase and microstructure evolutions in LC3 binders by multi-technique approach including synchrotron microtomography. (20th September 2021)

• Record Type: Journal Article
• Authors: Bernal, Isabel M.R.; Shirani, Shiva; Cuesta, Ana; Santacruz, Isabel; Aranda, Miguel A.G.
• Is Part Of: Construction & building materials. Volume 300(2021)
• Publication Date: 2021-09-20
• Subjects: CO2 footprint -- LC3 cements -- Rietveld analysis -- synchrotron X-ray microtomography -- Microstructure -- Porosity -- Pore connectivity; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2021.124054
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: Mechanical strength values for the studied limestone calcined clay cement with 50 wt% clinker replacement are slightly better than those derived from the neat cement after one week of hydration. Porosity evolution in this limestone calcined clay cement has been quantitatively measured by phase-contrast synchrotron X-ray microtomography. Porosity connectivities decreased from 92% at 7 hydration days to 9% at 60 days explaining the good durability properties of these binders. Limestone reactivity has been proved, in these aluminium-rich binders, by thermal analysis, X-ray powder diffraction coupled to the Rietveld method and synchrotron microtomography. Abstract: Limestone Calcined Clay Cements, LC 3, are attracting a lot of attention as it is possible to reduce the clinker factor by 50%, which means a cement CO2 footprint reduction of 40%. This is compatible with maintaining the mechanical strength performances after one week, if the kaolinite contents of the raw clays are above ~40 wt%. Durability properties are also maintained or even enhanced. Here, it is used a multi-technique approach to understand the phase and microstructure developments. From the thermal analysis, partial limestone reactivity is proven. Chiefly, high-resolution synchrotron microtomography has been employed, for the first time in these systems, to characterize their microstructures. The measured total porosities, within our 1 μm spatial resolution (voxel size 0.32 μm), were 16.6, 10.0 and 2.4 vol% at 7, 8 and 60 days of hydration, respectively. Pore connectivity strongly decreases with hydration time due to the chemical reactions producing new phases filling the pores. The 6-connected porosity fractions were 92, 78, and 9% at 7, 8 and 60 days. The reactions filling the pores were investigated by Rietveld quantitative phase analysis and 27 Al MAS-NMR.