Modelización del mecanismo de pérdida de consistencia provocado por arcillas en pastas de cemento con superplastificantes base policarboxilato

[ES] Este trabajo investiga acerca del mecanismo de interferencia provocado por arcillas sobre la fluidez de sistemas cementosos con condiciones asimilables al HAC en cuanto a baja relación agua/cemento y alta dosis de aditivo basado en polímeros de éter policarboxílico. Se propone una sistemática para determinar cómo repercuten de forma aislada la absorción de agua y la inhibición del efecto dispersante del aditivo, a partir de la cual se describe el mecanismo de sobre-absorción de la arcilla provocado por la intercalación múltiple de cadenas laterales.Borralleras, P.; Segura, I.; Aguado, A. (2018). Modelización del mecanismo de pérdida de consistencia provocado por arcillas en pastas de cemento con superplastificantes base policarboxilato. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 279-289. https://doi.org/10.4995/HAC2018.2018.5634OCS27928

Absorption conformations in the intercalation process of polycarboxylate ether based superplasticizers into montmorillonite clay

The intercalation of polycarboxylate based superplasticizers (PCE) into montmorillonite clay (MNT) is arranged preferably by two types of absorption conformations: one-to-one conformation and bridging conformation. A third model named plugged conformation is described but it seems not appropriate to polymers having anionic charge and it would be possible only for very particular cases. The preferred conformation of absorption of the PCE polymer is determined by key properties of the polymer and the clay. For the polymer, the two main characteristics are the length of side chains and the side chain density. For the MNT clay, the mains properties are the layer charge and to a lesser extent the morphology of the clay particle. PCE anionic charge is not a determining factor for the absorption conformation but is a key factor for the earlier saturation of the interlaminar space by intercalation. Since many variables are interplaying simultaneously and complementarily, the interaction process between PCE polymers and MNT clays is very complex that deserves further studies.Peer ReviewedPostprint (author's final draft

Influence of the polymer structure of polycarboxylate-based superplasticizers on the intercalation behaviour in montmorillonite clays

The influence of polymeric structure of polycarboxylate-ether (PCE) based superplasticizers on the intercalation behavior in sodium montmorillonite clay (Na-MNT) is investigated by performing in-situ X-ray diffraction (XRPD) on fresh, unaltered clay pastes. The use of this technique reveals the real influence of the PCE structure and of the PCE/clay dosage ratio on the expansion profile of the clay. This is not observed with the traditional XRPD methodology performed on dried clay pastes, which shows the same values of d-spacing despite using polymers of diverse structures. It is observed that PCE polymers with long side chains and high side chain density result in larger expansion. Additionally, polymers with a high anionic charge saturate the interlaminar space of montmorillonite at a lower dosage. The experimental results also indicate that clay exfoliation is critical in the intercalation process and the exfoliation tendency of the clay is influenced by the structure of PCE polymers.Peer ReviewedPostprint (author's final draft

Aditivos superplastificantes de última generación basados en polímeros PAE para el control de la viscosidad plástica del hormigón

[ES] Con la introducción de los aditivos reductores de agua basados en policarboxilatos (PCE) se abrieron las puertas para el desarrollo del hormigón autocompactante (HAC). La evolución de estos aditivos ha derivado en la más reciente tecnología de polímeros para el diseño de aditivos superplastificantes: los polímeros PAE. La aportación más relevante de los polímeros PAE es la mejora del comportamiento reológico del hormigón y la reducción de la viscosidad plástica, incluso en condiciones adversas de relaciones volumétricas agua/finos (Rvol A/F) extremamente bajas. Con estas características, los aditivos superplastificantes basados en polímeros PAE encajan perfectamente con las propiedades requeridas y en las particularidades de diseñó del HAC, para permitir la producción de hormigones de fácil bombeo y vertido y con mejor calidad de acabado. La reducción de viscosidad plástica aportada por los polímeros PAE no solamente permite la optimización de los costes de ejecución. También es posible optimizar el coste de producción y la huella de CO2 asociada al hormigón gracias a permitir maximizar el uso de adiciones en detrimento del cemento.Borralleras, P.; Jurado, J.; Parra, S.; Caballero, J. (2018). Aditivos superplastificantes de última generación basados en polímeros PAE para el control de la viscosidad plástica del hormigón. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 157-166. https://doi.org/10.4995/HAC2018.2018.5633OCS15716

Influence of experimental procedure on d-spacing measurement by XRD of montmorillonite clay pastes containing PCE-based superplasticizer

This study investigates the influence of the experimental procedure on determining the d-space enlargement of montmorillonite clay (MNT) produced by the absorption of polycarboxylate (PCE) based superplasticizers. d-Spacing alterations registered by in situ X-ray Diffraction (XRD) analysis on fresh clay pastes have been compared against the results obtained when clay pastes are previously centrifuged and dried (reference methodology reported in bibliography). Data from experiments show relevant differences between the two methodologies. While MNT clay d-spacing present limited expansion when recorded on samples previously separated and dried, direct XRD for fresh clay pastes shows much larger expansion of inter-laminar space. Clay expansion evolves with the increase of PCE dosage up to 3 times larger than typical data recorded when samples previously dried. The results shown here indicates that information collected following the typical experimental procedure based on sample drying could not be representative of MNT clay interference on dispersion mechanism of PCE superplasticizers.Peer ReviewedPostprint (author's final draft

Portland and Belite Cement Hydration Acceleration by C-S-H Seeds with Variable w/c Ratios

The acceleration of very early age cement hydration by C-S-H seeding is getting attention from scholars and field applications because the enhanced early age features do not compromise later age performances. This acceleration could be beneficial for several low-CO2 cements as a general drawback is usually the low very early age mechanical strengths. However, the mechanistic understanding of this acceleration in commercial cements is not complete. Reported here is a contribution to this understanding from the study of the effects of C-S-H gel seeding in one Portland cement and two belite cements at two widely studied water–cement ratios, 0.50 and 0.40. Two commercially available C-S-H nano-seed-based admixtures, i.e., Master X-Seed 130 and Master X-Seed STE-53, were investigated. A multi-technique approach was adopted by employing calorimetry, thermal analysis, powder diffraction (data analysed by the Rietveld method), mercury intrusion porosimetry, and mechanical strength determination. For instance, the compressive strength at 1 day for the PC (w/c = 0.50) sample increased from 15 MPa for the unseeded mortar to 24 and 22 MPs for the mortars seeded with the XS130 and STE53, respectively. The evolution of the amorphous contents was determined by adding an internal standard before recording the powder patterns. In summary, alite and belite phase hydrations, from the crystalline phase content evolutions, are not significantly accelerated by C-S-H seedings at the studied ages of 1 and 28 d for these cements. Conversely, the hydration rates of tetracalcium alumino-ferrate and tricalcium aluminate were significantly enhanced. It is noted that the degrees of reaction of C4AF for the PC paste (w/c = 0.40) were 10, 30, and 40% at 1, 7, and 28 days. After C-S-H seeding, the values increased to 20, 45, and 60%, respectively. This resulted in larger ettringite contents at very early ages but not at 28 days. (...)This research has been partly supported by a P18-RT-720 research grant, co-funded by ERDF, from Junta de Andalucía, Spain. Partial funding for open access charge: Universidad de Málaga

Portland and belite cement hydration acceleration by C-S-H seeds with variable w/c ratios

The acceleration of very early age cement hydration by C-S-H seeding is getting attention from scholars and field applications because the enhanced early age features do not compromise later age performances. This acceleration could be beneficial for several low-CO2 cements as a general drawback is usually the low very early age mechanical strengths. However, the mechanistic understanding of this acceleration in commercial cements is not complete. Reported here is a contribution to this understanding from the study of the effects of C-S-H gel seeding in one Portland cement and two belite cements at two widely studied water–cement ratios, 0.50 and 0.40. Two commercially available C-S-H nano-seed-based admixtures, i.e., Master X-Seed 130 and Master X-Seed STE-53, were investigated. A multi-technique approach was adopted by employing calorimetry, thermal analysis, powder diffraction (data analysed by the Rietveld method), mercury intrusion porosimetry, and mechanical strength determination. For instance, the compressive strength at 1 day for the PC (w/c = 0.50) sample increased from 15 MPa for the unseeded mortar to 24 and 22 MPs for the mortars seeded with the XS130 and STE53, respectively. The evolution of the amorphous contents was determined by adding an internal standard before recording the powder patterns. In summary, alite and belite phase hydrations, from the crystalline phase content evolutions, are not significantly accelerated by C-S-H seedings at the studied ages of 1 and 28 d for these cements. Conversely, the hydration rates of tetracalcium alumino-ferrate and tricalcium aluminate were significantly enhanced. It is noted that the degrees of reaction of C4AF for the PC paste (w/c = 0.40) were 10, 30, and 40% at 1, 7, and 28 days. After C-S-H seeding, the values increased to 20, 45, and 60%, respectively...This research has been partly supported by a P18-RT-720 research grant, co-funded by ERDF, from Junta de Andalucía, Spain

C-S-H seeding activation of Portland and Belite cements: An enlightening in situ synchrotron powder diffraction study

C-S-H seeding in Portland cements is well known from basic scientific works and field applications. Moreover, this activation approach could be beneficial for low-CO2 cements under development where a general drawback is poor mechanical strengths during the first week of hydration. However, a mechanistic understanding of the different processes taking place when seeding is still not developed. Here, we contribute to this knowledge gap by studying one commercial Portland cement and two industrial-trial belite cements. Three different admixtures are employed, viz. two types of commercial C-S-H seeding and triisopropanolamine as a typical alkanolamine. A multitechnique approach is employed including calorimetry, ultrasonic pulse velocity, thermal analysis and Rietveld analysis of laboratory X-ray powder diffraction data. Chiefly, an in situ X-ray synchrotron diffraction study has allowed mapping out the evolution of every crystalline phase. Furthermore, the use of an internal standard permitted to measure the changes in the overall amorphous content. In a nutshell, alite and belite (phases) hydrations are not significantly accelerated by C-S-H seeding for the three studied cements. Conversely, sulphate and aluminate phase dissolutions are enhanced. Faster ettringite crystallisation contributes to the observed improved mechanical properties at early ages. Moreover, a synergistic effect between C-S-H seeding and alkanolamine addition is proved. The importance of these findings for the possible acceleration of low-CO2 cement hydration is discussed.This research has been partly supported by two research grants PID2020-114650RB-I00 (from Spanish Government) and P18-RT-720 (from Junta de Andalucía, Spain), which are co-funded by ERDF. ALBA synchrotron is thanked for granting beamtime at BL04-MSPD beamline. We also thank the assistance of Dr. Oriol Vallcorba during the synchrotron experiment and thorough discussion of this work with Peter Schwesig (Master Builders Solutions). Funding for open access charge: Universidad de Malaga/CBUA

Activation of LC3 binders by C-S-H nucleation seeding with a new tailored admixture for low-carbon cements.

The use of supplementary cementitious materials is currently the most favorable strategy for reducing CO2 emissions in cements. Limestone Calcined Clay Cements, LC3, are a type of cement that allows the reduction of CO2 emissions up to 40%. The proportions of the mixtures can vary, but the most investigated combination, LC3-50, contains about 50 wt% clinker, 30 wt% calcined kaolinitic clay, 15 wt% limestone and an optimised calcium sulphate content. However, the mechanical strengths of LC3 at early ages are not good enough and they should be improved. One way of doing this is by employing commercial strength-enhancing (accelerator) admixtures based on C-S-H nucleation seeding. For this work, LC3-50 cements were prepared with clays with varying kaolinite contents. Mortars and pastes were fabricated using a new PCE-based superplasticizer developed to avoid the loss of fluidity at early ages typical of LC3 binders. The selected accelerator for this study was Master X-Seed STE53. The results show that the loss of fluidity of LC3 mortars during the first hours could be solved by a recently developed PCE-based superplasticizer. The compressive strengths at 1 day for LC3 mortars strikingly improved by using the C-S-H seeding admixture and this behavior was maintained for up to 28 days.Partial funding from PID2020-114650RB-I00 research grant, which is co-funded by ERDF, is gratefully acknowledged. Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Activation of LC3 binders by C-S-H nucleation seeding with a new tailored admixture for low-carbon cements.

The use of supplementary cementitious materials is currently the most favorable strategy for reducing CO2 emissions in cements. Limestone Calcined Clay Cements, LC3, are a type of cement that allows the reduction of CO2 emissions up to 40%. The proportions of the mixtures can vary, but the most investigated combination, LC3-50, contains about 50 wt% clinker, 30 wt% calcined kaolinitic clay, 15 wt% limestone and an optimised calcium sulphate content. However, the mechanical strengths of LC3 at early ages are not good enough and they should be improved. One way of doing this is by employing commercial strength-enhancing (accelerator) admixtures based on C-S-H nucleation seeding. For this work, LC3-50 cements were prepared with clays with varying kaolinite contents. Mortars and pastes were fabricated using a new PCE-based superplasticizer developed to avoid the loss of fluidity at early ages typical of LC3 binders. The selected accelerator for this study was Master X-Seed STE53. The results show that the loss of fluidity of LC3 mortars during the first hours could be solved by a recently developed PCE-based superplasticizer. The compressive strengths at 1 day for LC3 mortars strikingly improved by using the C-S-H seeding admixture and this behavior was maintained for up to 28 days.Partial funding from PID2020-114650RB-I00 research grant, which is co-funded by ERDF, is gratefully acknowledged