Phase and Microstructural Characterization of Lime-MK Blended Mixes

Abstract:

Metakaolin (MK) is nowadays a well-known pozzolanic material used in cement-based materials. Its benefits are related to its great pozzolanic reactivity when compared with some others pozzolanic materials, like fly ash or ground-granulated blast furnace slag. When MK reacts with calcium hydroxide, cementitious products are formed. It is known that the main phases produced during its pozzolanic reaction at ambient temperature are calcium silicate hydrates (CSH), stratlingite (C₂ASH₈) and calcium aluminate hydrate (C₄AH₁₃). However, in literature there are several discrepancies regarding these phases stability, namely the transformation of stratlingite and C₄AH₁₃ into hydrogarnet (C₃AH₆) at long term. The consequences of that instability are a reduction in the porosity and a loss of microstructural strength that can induce a complete material degradation. The MK is a material with great potential in Portugal, since there is a large abundance of kaolinitic clays, however its development is not yet achieved. In order to answer this demand a research project was initiated with the aim of optimizing the production of MK in Portugal and enhancing the durability of aerial calcitic lime mortars, to be mainly used in conservation and restoration of historical buildings. With the objective of studying the compounds formed in lime/MK and their stability during time, we have prepared different lime/MK ratio pastes (molar ratios). These lime/MK pastes were stored at saturated conditions (RH > 95%) and 23 ± 2 °C temperature being analysed at several ages by TGA-DTA, XRD and SEM-EDS. In this paper the results obtained are presented and discussed.

• Periodical: Materials Science Forum (Volumes 730-732)
• Pages: 135-140
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.730-732.135
• Online since: November 2012
• Authors: André Gameiro, António Santos Silva, R. Veiga, Ana Velosa
• Keywords: Lime, Metakaolin (MK), Pozzolan, SEM, TGA, X-Ray Diffraction (XRD)

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