Processing and characterisation of standard and doped alite-belite-ye'elimite ecocement pastes and mortars

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cemconres.2019.105911.Cement and Concrete Research 127 (2020) 105911Here, we report the processing optimisation of two laboratory-prepared alite-belite-ye'elimite ecocements (standard and doped) that release to the atmosphere ~13% less CO2 than Portland Cement during fabrication. The processing was optimised through rheological measurements, where homogeneous pastes and mortars were finally prepared through the study and optimisation of both the superplasticiser content and the water-to-cement ratio. Both parameters were correlated with the phase assembly of selected pastes and compressive strength of the corresponding mortars. After optimisation, mortars with high compressive strengths (~72 and ~77 MPa for the standard mortar, and ~41 and ~75 MPa for the doped one, at 7 and 28 days, respectively) were prepared. Furthermore, the important increase in compressive strength from 7 to 28 days of the optimised mortar prepared from the doped ecocement is due to its composition (the higher content of belite jointly with the reaction of its active polymorph (α'H-belite)).This work is part of the PhD of Mr. Jesus D. Zea-Garcia. This research has been supported by Spanish MINECO and FEDER [BIA2017- 82391-R research project and I3 (IEDI-2016-0079) program]

In-situ early-age hydration study of sulfobelite cements by synchrotron powder diffraction

Eco-friendly belite calcium sulfoaluminate (BCSA) cement hydration behavior is not yet well understood. Here,we report an in-situ synchrotron X-ray powder diffraction study for the first hours of hydration of BCSA cements. Rietveld quantitative phase analysis has been used to establish the degree of reaction (α). The hydration of a mixture of ye'elimite and gypsum revealed that ettringite formation (α ~70% at 50 h) is limited by ye'elimite dissolution. Two laboratory-prepared BCSA cements were also studied: non-active-BCSA and active-BCSA cements, with β- and α′H-belite as main phases, respectively. Ye'elimite, in the non-active-BCSA system, dissolves at higher pace (α ~25% at 1 h) than in the active-BCSA one (α ~10% at 1 h),with differences in the crystallization of ettringite (α ~30% and α ~5%, respectively). This behavior has strongly affected subsequent belite and ferrite reactivities, yielding stratlingite and other layered phases in non-active-BCSA. The dissolution and crystallization processes are reported and discussed in detail.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Influence of fly ash blending on hydration and physical behavior of Belite-Alite-Ye'elimite cements

A cement powder, composed of belite, alite and ye’elimite, was blended with 0, 15 and 30 wt% of fly ash and the resulting lended cements were further characterized. During hydration, the presence of fly ash caused the partial inhibition of both AFt degradation and belite reactivity, even after 180 days. The compressive strength of the corresponding mortars increased by increasing the fly ash content (68, 73 and 82 MPa for mortars with 0, 15 and 30 wt% of fly ash, respectively, at 180 curing days), mainly due to the diminishing porosity and pore size values. Although pozzolanic reaction has not been directly proved there are indirect evidences.This work is part of the Ph.D. of D. Londono-Zuluaga funded by Beca Colciencias 646—Doctorado en el exterior and Enlaza Mundos 2013 program grant. Cement and Building materials group (CEMATCO) from National University of Colombia is acknowledged for providing the calorimetric measurements. Funding from Spanish MINECO BIA2017-82391-R and I3 (IEDI-2016-0079) grants, co-funded by FEDER, are acknowledged

Enthalpy of formation of ye’elimite and ternesite

Calcium sulfoaluminate clinkers containing ye’elimite (Ca4Al6O12(SO4)) and ternesite (Ca5(SiO4)2SO4) are being widely investigated as components of calcium sulfoaluminate cement clinkers. These may become low energy replacements for Portland cement. Conditional thermodynamic data for ye’elimite and ternesite (enthalpy of formation) have been determined experimentally using a combination of techniques: isothermal conduction calorimetry, X-ray powder diffraction and thermogravimetric analysis. The enthalpies of formation of ye’elimite and ternesite at 25 °C were determined to be − 8523 and − 5993 kJ mol−1, respectively

Aluminum-rich belite sulfoaluminate cements: clinkering and early age hydration

Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO2 into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C2S (50-60%), C4A3$(20- 30$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt% of C4A3$, had 19.6, 27.1 and 27.7 wt$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the b-C2S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C4A3$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution

Hydration of Belite-Ye’elimite-Ferrite(BYF) cements with different calcium sulfate sources

Belite-Ye’elimite-Ferrite cements, BYF, are a sustainable alternative to OPC to reduce CO2 emissions. The aim of this research is to understand the influence of the sulfate source on the hydration of two laboratory-prepared BYF-cements. One studied clinker contained β-belite and orthorhombic-ye'elimite (non-active), and the other one α'H-belite and pseudo-cubic-ye'elimite (activated with borax during clinkering). Pastes were mainly characterized through Rietveld-quantitative-phase-analysis of powder patterns, thermal analysis and scanning-electron-microscopy. Active-mortars developed higher compressive strengths than non-active-mortars, independently of the sulfate source. The highest values for active-mortars (w/c=0.55) were 40±1MPa (28d) with anhydrite, and 68±1MPa (120d) with gypsum.This work is part of the PhD work of G. Álvarez-Pinazo funded by MINECO BES-2011-044690 grant. Funding from Junta de Andalucía (P11-FQM-7517), Spanish MINECO (BIA2014-57658-C2-2-R, which is co-funded by FEDER, and BIA2014-57658-C2-1-R research grant

Hydration Reactions and Mechanical Strength Developments of Iron- Rich Sulfobelite Eco-cements

Belite calcium sulfoaluminate (BCSA) cements are low-CO2 building materials. However, their hydration behavior and its effect on mechanical properties have still to be clarified. Here, we report a full multitechnique study of the hydration behavior up to 120 days of nonactivated and activated BCSA laboratory-prepared clinkers, with β- or αH-belite as main phase, respectively. The effects of the amount of gypsum added were also studied. The hydration and crystallization processes are reported and discussed in detail. Finally, shrinkage/expansion data are also given. The optimum amount of gypsum was close to 10 wt %. Our study has demonstrated that β-belite reacts at a higher pace than α′H-belite, irrespective of the gypsum content. The hydration mechanism of belite determines the development of the mechanical strengths. These are much higher for activated BCSA cement, ∼65 MPa at 120 days, against ∼20 MPa for nonactivated BCSA cement, with the latter having larger amounts of stratlingite.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

X-ray powder diffraction applied to cement related phases: in-situ and high resolution applications

XRPD is a powerful tool for material characterization in general, and for in-situ studies of chemical processes in particular. The use of an intense X-ray source, .i.e. synchrotron X-rays, coupled with fast X-ray detection permits time-resolved diffraction experiments allowing in-situ quantitative phase analysis during the early ages of cement hydration. CSA cements may have variable compositions, but all of them contain ye’elimite (Ca4Al6O12SO4). This phase is also included, ~25 wt%, in sulfobelite cements. Also, another important phase in these cements is tetracalcium aluminoferrite (Ca2AlFeO5). The aim of this work is to better understand the early age hydration of stoichiometric (orthorhombic) and doped (pseudo-cubic) ye’elimite and tetracalcium aluminoferrite phases at early ages in order to understand “eco-cement” performances. Chiefly, we want to determine the hydration kinetic and mechanisms of these phases with different water/cement ratio, with different calcium sulfate sources. This work has allowed establishing kinetics and mechanisms for hydration of ye’elimite samples by in-situ SXRPD with internal standard methodology. Moreover, some pastes were studied by ex-situ LXRPD with the external standard method, G-factor, at 2 and 7 days. Both strategies were able to quantify the amorphous contents, including free water. It is important to highlight that the results obtained by the internal standard method are in agreement with those obtained at later ages showing the consistence of both methodologies to follow hydration reactions with time by diffraction methods. Moreover, the hydration of tetracalcium aluminoferrite and some combinations of this phase with ye’elimite have been studied by in-situ SXRPD in order to understand the dissolution/crystallization processes that take place during those hydration processes. Furthermore, we have measured some hydrated phases by high resolution SXRPD in order to perform a structural study with the objective of revising or obtaining the crystal structure descriptions.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

In-situ hydration studies of ye’elemite at early ages for understanding eco-cement performances'

Póster; ALBA User Meeting and VI AUSE Conferenc

Hydration mechanisms of two polymorphs of synthetic ye'elimite

Ye'elimite is the main phase in calcium sulfoaluminate cements and also a key phase in sulfobelite cements. However, its hydrationmechanismis not well understood. Here we reported newdata on the hydration behavior of ye'elimite using synchrotron and laboratory powder diffraction coupled to the Rietveld methodology. Both internal and external standard methodologies have been used to determine the overall amorphous contents. We have addressed the standard variables: water-to-ye'elimite ratio and additional sulfate sources of different solubilities. Moreover, we report a deep study of the role of the polymorphism of pure ye'elimites. The hydration behavior of orthorhombic stoichiometric and pseudo-cubic solid-solution ye'elimites is discussed. In the absence of additional sulfate sources, stoichiometric-ye'elimite reacts slower than solid-solution-ye'elimite, and AFm-type phases are the main hydrated crystalline phases, as expected. Moreover, solid-solution-ye'elimite produces higher amounts of ettringite than stoichiometric-ye'elimite. However, in the presence of additional sulfates, stoichiometric-ye'elimite reacts faster than solid-solution-ye'elimite.This work has been supported by Junta de Andalucía through P11-FQM-7517 research grant and by Spanish MINECO through MAT2010-16213 research grant, which is co-funded by FEDER. ALBA synchrotron is thanked for providing synchrotron beamtime at BL04-MSPD beamline