Characterization of C-S-H gels by pair distribution function analysis

Portland cement (PC) is the most manufactured world product. However, cement industry is one of the major contributors for greenhouse gas emissions. On average, for every ton of grey PC clinker, around 0.87 CO2 tons are released into the atmosphere. Alternative cements showing similar performances to ordinary PC are needed. A recent work [1] commissioned by the United Nations Environment Program Sustainable Building and Climate Initiative has identified the use of supplementary cementitious materials (SCMs) as the most favourable approach for lowering CO2 emissions in the cement industry. In order to develop more sustainable cements, the hydration products must be well understood which is far from straightforward. The hydration reactions of tricalcium silicate, Ca3SiO5 (main phase of PC) consist of its dissolution, the formation of the nanocrystalline calcium-silicate-hydrate (C-S-H) gel, jointly with the crystallization of portlandite, Ca(OH)2 according to equation (1). C-S-H gel seems to be composed by defective nanocrystalline clinotobermorite, amorphous (a few layers thick) Ca(OH)2 and gel pore water [2].Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

High pressure and temperature spinning capillary cell for in-situ synchrotron X-ray powder diffraction

In situ research of materials under moderate pressures (hundreds of bar) is essential in many scientific fields. These range from gas sorption to chemical and biological processes. One industrially important discipline is the hydration of oil well cements. Existing capillary cells in this pressure range are static as they are easy to design and operate. This is convenient for the study of single-phase materials; however, powder diffraction quantitative analyses for multiphase systems cannot be performed accurately as a good powder average cannot be attained. Here, the design, construction and commissioning of a cost-effective spinning capillary cell for in situ powder X-ray diffraction is reported, for pressures currently up to 200 bar. The design addresses the importance of reducing the stress on the capillary by mechanically synchronizing the applied rotation power and alignment on both sides of the capillary while allowing the displacement of the supports needed to accommodate different capillaries sizes and to insert the sample within the tube. This cell can be utilized for multiple purposes allowing the introduction of gas or liquid from both ends of the capillary. The commissioning is reported for the hydration of a commercial oil well cement at 150 bar and 150°C. The quality of the resulting powder diffraction data has allowed in situ Rietveld quantitative phase analyses for a hydrating cement containing seven crystalline phases.The design, production and commissioning of this cell was carried out at the ALBA synchrotron as part of Edmundo Fraga’s PhD project. This work was financially supported by the Spanish Ministry of Economy and Competitiveness through Grants BIA2014-57658-C2-1-R and BIA2017-82391-R which are co-funded by FEDER. We are grateful to Prof. Angus Wilkinson, Georgia Institute of Technology Atlanta, for sharing his knowledge and details on the high pressure cell developed by his team. We also thank Dr. Marcus Paul, Dyckerhoff-Lengerich, Germany, for fruitful discussion on Oil Well Cements. The cell was commissioned at BL11-NCD-SWEET beamline

Synthesis of active Belite-Alite-Ye'elimite clinker (BAY)

Póster en congreso científicoOrdinary Portland cement (OPC) is an environmentally contentious material, as for every ton of OPC produced, on average, 0.97 tons of CO2 are released. Ye'elimite-rich cements are considered as eco-cements because their manufacturing process releases less CO2 into the atmosphere than OPC; this is due to the low calcite demand. Belite-Alite-Ye’elimite (BAY) cements are promising eco-friendly building materials as OPC substitutes at a large scale. The reaction of alite and ye´elimite with water should develop cements with high mechanical strengths at early ages, while belite will contribute to later curing times. However, they develop lower mechanical strengths at early-medium ages than OPC. It is known that the presence of different polymorphs of ye'elimite and belite affects the hydration due to the different reactivity of those phases. Thus, a solution to this problem may be well the activation of BAY clinkers by preparing them with 'H-belite and pseudo-cubic-ye'elimite, jointly with alite. The aim of this work is the preparation and characterization of active-BAY clinkers which contain high percentages of coexisting 'H-belite and pseudo-cubic-ye'elimite, jointly with alite to develop, in a future step, comparable mechanical strengths to OPC. The parameters evolved in the preparation of the clinker have been optimized, including the selection of raw materials (mineralizers and activators) and clinkering conditions. Finally, the clinker was characterized through laboratory X-ray powder diffraction, in combination with the Rietveld methodology, and scanning electron microscopy.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R, the latter co-funded by FEDER

Synthesis and behavior of Belite-Alite-Ye’elimite (BAY) cement

Póster en congreso científicoYe’elimite based cements have been studied since 70’s years in China, due to the irrelevant characteristics from a hydraulic and environmental point of view. One of them is the reduced fuel consumption, related to the lower temperature reaction required for this kind of cement production as compared to Ordinary Portland Cement (OPC), another characteristic is the reduced requirement of carbonates as a typical raw material, compared to OPC, with the consequent reduction in CO2 releases (~22%)from combustion. Thus, Belite-Ye’elimite-Ferrite (BYF) cements have been developed as potential OPC substitutes. BYF cements contain belite as main phase (>50 wt%) and ye´elimite as the second content phase (~30 wt%). However, an important technological problem is associated to them, related to the low mechanical strengths developed at intermediate hydration ages (3, 7 and 28 days). One of the proposed solutions to this problem is the activation of BYF clinkers by preparing clinkers with high percentage of coexisting alite and ye'elimite. These clinkers are known Belite-Alite-Ye’elimite (BAY) cements. Their manufacture would produce ~15% less CO2 than OPC. Alite is the main component of OPC and is responsible for early mechanical strengths. The reaction of alite and ye´elimite with water will develop cements with high mechanical strengths at early ages, while belite will contribute to later curing times. Moreover, the high alkalinity of BAY cement pastes/mortars/concretes may facilitate the use of supplementary cementitious materials with pozzolanic activity which also contributes to decrease the CO2 footprint of these ecocements. The main objective of this work was the design and optimization of all the parameters evolved in the preparation of a BAY eco-cement that develop higher mechanical strengths than BYF cements. These parameters include the selection of the raw materials (lime, gypsum, kaolin and sand), milling, clinkering conditions (temperature, and holding time), and clinker characterization The addition of fly ash has also been studied. All BAY clinker and pastes (at different hydration ages) were mineralogically characterized through laboratory X-ray powder diffraction (LXRPD) in combination with the Rietveld methodology to obtain the full phase assemblage including Amorphous and Crystalline non-quantified, ACn, contents. The pastes were also characterized through rheological measurements, thermal analyses (TA), scanning electronic microscopy (SEM) and nuclear magnetic resonance (NMR). The compressive strengths were also measured at different hydration times and compared to BYF.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. MINECO (BIA2014-57658-C2-1-R and BIA2014-57658-C2-2-R, the latter co-funded by FEDER

Processing and characterisation of Calcium SulfoAluminate (CSA) eco-cements coated with a hybrid organo-inorganic material for photocatalytic applications

On the one hand, Calcium SulfoAluminate (CSA) eco-cements are receiving increasing attention since their manufacture produces up to 40% less CO2 than ordinary Portland cement (OPC). In addition, they show interesting properties such as high early-age strengths, short setting times, impermeability, sulfate and chloride corrosion resistance and low alkalinity. On the other hand, water treatment is a key issue and it will become much more important in the decades ahead. We have developed a photocatalytic material capable to degrade contaminants in water, under both UVA and visible radiations. In both cases, it works more effectively than nano-TiO2 (Evonik P25). The environmental benefits of the use of CSA eco-cements with a photocatalyst are two folds: the photocatalytic treatment of contaminated water, and lower CO2 emissions because of the use of eco-cements rather than OPC. However, before preparing the coating, different parameters need to be under control. This includes the effect of the photocatalyst onto the eco-cement (setting time, phase assemblage, and so on), and the effect of the eco-cement on the photocatalyst. This work deals with the processing and characterisation of coatings onto CSA eco-cement pastes, including rheological behaviour, setting time, adhesion, and so on.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech. This work has been supported by Junta de Andalucía (Spain) through P11-FQM-7517 and P12-FQM-1656 research grants and FEDER/University of Málaga (FC14-MAT-23). Dr. I. Santacruz thanks a Ramón y Cajal fellowship, RYC-2008-03523