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Ca(OH) 2 nanoparticles dispersed in isopropyl alcohol were exposed under different relative humidities (RH) during 7, 14, 21 and 28 days. Higher RH (75%-90% RH) gives rise to a faster carbonation (amorphous CaCO 3 , CaCO 3 •H 2 O, calcite, aragonite and vaterite) and larger particles sizes compared to lower RH (33%-54% RH) that gives rise only to portlandite (Ca(OH) 2) and vaterite with smaller particle sizes.

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A study was conducted on the effect of a polycarboxylate (PC) admixture on the mechanical, mineralogical, microstructural and rheological behaviour of Portland cement pastes. It was observed that the presence of PC admixture retards the initial cement hydration reactions, although this effect may be offset by possible increased diffusion in later stages. Additionally, the PC admixtures produce a few alterations in the structure and composition of the formed C-S-H gel. The addition of 1% PC admixture in the pastes generates a higher percentage of silicate bridge (Si Q 2 units) mainly at 2 days. The admixture used in this study induced microstructural modifications in the pastes which slightly reduced the porosity; however the admixture did not affect the mechanical strength of the pastes at either 2 or 28 days of hydration. Finally, from the results of the rheological studies it was concluded that a low dosage of PC led to a substantial reduction (over 70%) in the yield stress.

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Recent investigations have revealed the great potential of Raman spectroscopy for the characterization of clinker minerals and commercial Portland cements. The usefulness of this technique for the identification of anhydrous, hydrated, and carbonated phases in cement-based materials has been demonstrated. In the present work, the application of micro-Raman spectroscopy for the characterization of the main clinker phases of calcium aluminate cements and calcium sulfoaluminate cement is explored. The main stable hydrated phases as well as several important carbonated phases are investigated. Raman measurements on the following phases are reported: (i) pure, unhydrated phases: CA, C12A7, CA2, C2AS, cubic-C3A, C4AF, and C4A3inline image; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet (C3AH6); (iii) carboaluminate phases: hemicarboaluminate and monocarboaluminate. The present results, which are discussed in terms of the internal vibrational modes of the aluminate, carbonate, and sulfate molecular groups as well as stretching O–H vibrations, show the ability of Raman spectroscopy to identify the main hydrated and unhydrated phases in the aluminate and sulfoaluminate cements. The Raman spectra obtained in this work provide an extended database to the existing data published in the literature.Peer ReviewedPostprint (published version

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