Phase and microstructure evolutions in LC3 binders by multi-technique approach including synchrotron microtomography

Limestone Calcined Clay Cements, LC3, are attracting a lot of attention as it is possible to reduce the clinker factor by 50%, which means a cement CO2 footprint reduction of 40%. This is compatible with maintaining the mechanical strength performances after one week, if the kaolinite contents of the raw clays are above ~40 wt%. Durability properties are also maintained or even enhanced. Here, it is used a multi-technique approach to understand the phase and microstructure developments. From the thermal analysis, partial limestone reactivity is proven. Chiefly, high-resolution synchrotron microtomography has been employed, for the first time in these systems, to characterize their microstructures. The measured total porosities, within our 1 lm spatial resolution (voxel size 0.32 lm), were 16.6, 10.0 and 2.4 vol% at 7, 8 and 60 days of hydration, respectively. Pore connectivity strongly decreases with hydration time due to the chemical reactions producing new phases filling the pores. The 6-connected porosity fractions were 92, 78, and 9% at 7, 8 and 60 days. The reactions filling the pores were investigated by Rietveld quantitative phase analysis and 27Al MAS-NMR.Financial support from research grant No. PID2019-104378RJI00 (Spanish Ministry) and No. UMA18-FEDERJA-095 (Junta de Andalucía and Universidad de Málaga), are gratefully acknowledged. SLS is thanked for granting beamtime at TOMCAT beamline. We also thank Dr. Olbinado (SLS) for her support during synchrotron data collection. Funding for open access charge: Universidad de Málaga/CBUA

Hydration characteristics and mechanical performances of LC3 binders with spanish kaolinitic calcined clays

Limestone Calcined Clay Cements (LC3) are binders with complex phase development and microstructures. Although the hydration chemistry of these cements are being widely researched [1], due to the clay mineralogy variability, more studies are needed to build full knowledge. The use of calcined kaolinitic clays as SCMs in Portland cement is one of the best approaches, as metakaolin shows exceptional pozzolanic properties. Here, we report a summary of our ongoing research dealing with LC3 binders based on Spanish calcined clays with different kaolinite content. The kaolinite contents [2], jointly with the particle size of the calcined clays [3] will determine the reactivity, and consequently, the mechanical performances. Initially, a selection of three commercially available Spanish kaolinitic clays was carried out. Mineralogical and elemental analyses were obtained by Xray powder diffraction (XRPD) and X-ray fluorescence (XRF), respectively, are elsewhere [3]. The clay provenance and estimated average kaolinite contents are given in Table 1; the latter was obtained through the combination of three methodologies (LXRPD, thermal analysis and XRF) [3].Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Hidratación y prestaciones mecánicas de cementos LC3 con arcillas caoliníticas calcinadas españolas

La búsqueda de alternativas que reduzcan esas emisiones es prioritario. Dentro de esas estrategias se encuentra la sustitución parcial de cemento por material cementicio suplementario (SCM, de sus siglas en inglés, Supplementary Cementitious Materials), como es el caso de arcillas calcinadas. En este grupo, se encuentran los denominados cementos LC3, de sus siglas en inglés Limestone Calcined Clay Cement, cuyas emisiones CO2 se reducen hasta un 40% respecto del PC sin adiciones. Según la UNE-EN 197-5 (versión española, julio-2021) para cemento Portland compuesto CEM II/C-M, el clínker podría sustituirse hasta en un 50%p. Este trabajo se centra en cementos LC3 con 52%p de PC 42.5 R, 30%p de arcilla calcinada, 15%p de caliza y 3%p de yeso adicional, y la utilización de 3 arcillas caoliníticas españolas con diferente porcentaje en caolinita (70-83%p), activadas térmicamente a 860ºC y molidas a dos tamaños de partícula relevantes (Dv,50 10 y 5 m). Se abordará el estudio de las pastas de cemento LC3 preparadas en una relación agua/binder (w/b) de 0.40 con superplastificante basado en policarboxilato, a través de su comportamiento reológico, ensamblaje de fases de pastas (RQPA, del inglés Rietveld Quantitative Phase Analysis) a diferentes edades (2, 7, 28 y 120 días) y calorimetrías (20ºC/7d). A modo de ejemplo, LC3 con la arcilla calcinada CVPM3B desprende 50.6 y 135.5 J/g a 2 y 7d, respectivamente, pero con SY1 el calor liberado era 12.9 J/g y 63.0 J/g, respectivamente. Estos valores están justificados principalmente por el mayor área superficial (y menor tamaño de partícula) de CVPM3V (y su estructura local altamente tensionada), a pesar de su menor contenido en caolinita. Finalmente, los resultados se relacionarán con las resistencias mecánicas de los morteros correspondientes.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

In situ synchrotron powder diffraction study of LC3 cement activation at very early ages by C-S-H nucleation seeding.

Limestone Calcined Clay Cements, LC3, are being widely researched as low-carbon binders. However, the hydration reactions during the first day are key for their performances and they were not well known. Here, we employ in situ synchrotron X-ray powder diffraction to understand the hydration reactions that take place during the first day. The influence of two superplasticisers and three strength-enhancing admixtures have been investigated. The diffraction data were analysed by the Rietveld method and the results compared to mass balance calculations. For LC3 binders and in the absence of strength-enhancing admixtures, the hydration rates of the clinker phases, i.e. C3S, C3A and C4AF, are accelerated because of the filler effect. The C-S-H based-admixtures further accelerate the hydration of tricalcium aluminate and ferrite. Chiefly, it is firmly proved that the pozzolanic reaction takes place from 7 h onwards in the studied experimental conditions. The estimated degree of hydration of metakaolin at 22 h, in the studied binders, was ∼10 %.This research was partly supported by the research grant PID2020-114650RB-I00 which is co-funded by ERDF. ALBA synchrotron is thanked for providing beamtime at the BL04-MSPD beamline. We thank thorough discussions with Peter Schwesig and Sebastien Dhers from Master Builders Solutions. Funding for open access charge: Universidad de Malaga/CBU

Cementos de arcillas calcinadas y caliza preparados en la Universidad de Málaga

Adjuto documentoproyectos del MICINN (cofinanciados FEDER) PID2019-104378RJ-I00 y PID2020-114650RB-I00. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Early-age reactivity of calcined kaolinitic clays in LC3 cements: a multitechnique investigation including pair distribution function analysis

https://www.tandfonline.com/doi/full/10.1080/21650373.2022.2117248Limestone Calcined Clay Cements, LC3, allows CO2 emissions savings up to 40%. The resulting binders have competitive mechanical performances after a week. However, the reactivity of LC3 at early ages is slow and should be improved. Here, we use a multitechnique approach to help in the understanding of early age reactivities which were measured by calorimetry, Frattini assay, and mechanical strengths. The disorder in the kaolinites was quantified by powder diffraction. Some footprints of the local disorder in the resulting metakaolin have been investigated by synchrotron pair distribution function (sPDF). It is concluded that Al-O interatomic correlation position and intensity in the sPDF of the calcined kaolinitic clays could be an additional good descriptor to follow early age reactivity. The results were complemented by 27Al MAS-NMR studies. The rate of the pozzolanic reaction at early ages is governed by the particle size, surface area, and local disorder of metakaolin.PID2019-104378RJ-I00 from the Spanish government and P18-RT-720 from Junta de Andalucía are acknowledged by the financial support

Data for: In situ synchrotron powder diffraction study of LC3 cement activation at very early ages by C-S-H nucleation seeding

<p>Data for: In situ synchrotron powder diffraction study of LC3 cement activation at very early ages by C-S-H nucleation seeding</p&gt

Human immunodeficiency virus continuum of care in 11 european union countries at the end of 2016 overall and by key population: Have we made progress?

Background. High uptake of antiretroviral treatment (ART) is essential to reduce human immunodeficiency virus (HIV) transmission and related mortality; however, gaps in care exist. We aimed to construct the continuum of HIV care (CoC) in 2016 in 11 European Union (EU) countries, overall and by key population and sex. To estimate progress toward the Joint United Nations Programme on HIV/AIDS (UNAIDS) 90-90-90 target, we compared 2016 to 2013 estimates for the same countries, representing 73% of the population in the region. Methods. A CoC with the following 4 stages was constructed: number of people living with HIV (PLHIV); proportion of PLHIV diagnosed; proportion of those diagnosed who ever initiated ART; and proportion of those ever treated who achieved viral suppression at their last visit. Results. We estimated that 87% of PLHIV were diagnosed; 92% of those diagnosed had ever initiated ART; and 91% of those ever on ART, or 73% of all PLHIV, were virally suppressed. Corresponding figures for men having sex with men were: 86%, 93%, 93%, 74%; for people who inject drugs: 94%, 88%, 85%, 70%; and for heterosexuals: 86%, 92%, 91%, 72%. The proportion suppressed of all PLHIV ranged from 59% to 86% across countries. Conclusions. The EU is close to the 90-90-90 target and achieved the UNAIDS target of 73% of all PLHIV virally suppressed, significant progress since 2013 when 60% of all PLHIV were virally suppressed. Strengthening of testing programs and treatment support, along with prevention interventions, are needed to achieve HIV epidemic control