David Torrens Martín

The cement industry is a major contributor to global CO₂ emissions, which has led to the development of low-carbon cements. A critical factor in ensuring the durability of these materials is their resistance to freeze-thaw (F-T) cycles, especially as climate change expands the relevance of these tests beyond traditionally cold regions to areas with increasingly variable climates. This review analyzes current testing standards for low-CO₂ cements exposed to F-T cycles, highlighting gaps in performance research in this field. The study proposes a novel testing framework tailored to the specific temperature and humidity fluctuations found in the Mediterranean corridor, with a focus on north-eastern Spain. A thermal curve model was developed based on regional climate data, offering a more realistic assessment of cement durability in the Mediterranean corridor. The findings emphasize the lack of global data in some countries, as well as the fact that most research has been conducted by countries in cold regions, overlooking the rest of the world where freeze-thaw cycles also occur. This underscores the need for future research to address these gaps and to combine durability and sustainability not only in freeze-thaw testing but also in broader construction and cement research.

This study examines how calcium aluminate cement (CAC) and calcium sulfate influence the hydration and gel structure of Portland cement (PC). A binary PC/CAC (85/15) mix was compared with ternary systems containing 3% and 5% calcium sulfate under two curing conditions. FTIR and 29Si NMR analyses showed that CAC promotes aluminum incorporation into the C-S-H gel, leading to a more homogeneous C-A-S-H structure. Water curing further enhanced this integration, with increased Q² and reduced Q¹ signals. Calcium sulfate addition mitigated the silicate hydration delay caused by CAC and promoted longer silicate chains and higher Al(IV)/Si ratios. Overall, CAC enhances aluminum incorporation, while calcium sulfate improves silicate polymerization, resulting in a more uniform and well-structured C-A-S-H gel.

Volcanic ashes (VA) ejected by the Tajogaite Volcano were studied to determine their potential as pozzolanic materials for construction applications. A representative number of VA samples (15 in total) were collected from different geolocations and altitudes during and immediately after the volcanic eruption, in order to assess their reactivity as a function of position and environmental exposure. Various analytical techniques—XRD, FTIR, and SEM/EDX—were used to determine the initial microstructural composition of the VA samples. Additionally, saturated lime testing and the Frattini test were performed to evaluate their pozzolanic reactivity for use in historical mortars. The microstructural analyses revealed that the dominant mineral phases are aluminosilicates. The reactivity tests confirmed a good pozzolanic response, with the formation of C-A-S-H gels identified as the main hydration products at the studied curing times.

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 , C ₁₂ A ₇ , CA ₂ , C ₂ AS , cubic‐ C ₃ A , C ₄ AF , and C ₄ A ₃ ; (ii) hydrated phases: ettringite, monosulfoaluminate, and hydrogarnet ( C ₃ AH ₆ ); (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.