Efecto de las deformaciones diferidas sobre la respuesta estructural a flexión y análisis del comportamiento adherente del hormigón reciclado

[Resumen]Este trabajo se centra en el estudio de hormigones reciclados para uso estructural, con sustituciones de árido grueso natural por reciclado del 20%, 50% y 100%. Para ello se fabrican dos series de hormigón, una con relación a/c igual a 0.50, que conferirá a los hormigones resistencias elevadas, y otra igual a 0.65 con resistencias más bajas. Se distinguen dos líneas de ensayo diferentes. En la primera de ellas (Fase Vigas) se fabrican dos vigas gemelas para cada tipo de hormigón sobre las que se realizan los ensayos bajo cargas incrementales y bajo carga sostenida durante 1000 días. Estos permiten conocer la respuesta estructural a flexión, instantánea y diferida, de los hormigones reciclados. Previamente se llevan a cabo los ensayos de caracterización del hormigón para determinar resistencias a compresión y tracción, módulo de deformación longitudinal y transversal, diagrama tensión – deformación, retracción y fluencia. Por último, la Fase Adherencia aborda el estudio del comportamiento adherente de los hormigones reciclados mediante ensayos de arrancamiento tipo pull-out a diferentes edades comprendidas entre 7 y 365 días. Con los resultados obtenidos se comprueba la bondad de las expresiones normativas para los hormigones reciclados, proponiéndose coeficientes correctores dependientes del porcentaje de árido reciclado cuando resulta necesario.[Resumo]Este traballo centrase no estudio dos formigóns reciclados para uso estructural, con sustitucións de árido grueso natural por reciclado do 20%, 50% y 100%. Para eso, fabricanse dua series de formigón, unha con relación a/c igual a 0.50 que conferirá aos formigóns resistencias elevadas, e outra igual a 0.65 con resistencias máis baixas. Distinguense duas líneas de ensaio diferentes. Na primeira delas, Fase Vigas, fabricanse duas vigas xemelgas para cada tipo de formigón sobre as que se realizan os ensaios baixo cargas incrementales e baixo carga sostida durante 1000 días. Estos permiten coñecer a resposta estrutural a flexión, instantánea e diferida, dos formigóns reciclados. Previamente, lévanse a cabo os ensaios de caracterización do formigón para determinar as resistencias a compresión e tracción, o módulo de deformación lonxitudinal e transversal, o diagrama tensión – deformación, a retracción e a fluencia. Por último, a Fase Adherencia aborda o estudio do comportamiento adherente dos formigóns reciclados mediante ensaios de arrancamento tipo pull-out a diferentes edades, de 7 a 365 días. Cos resultados obtidos compróbase a bondade das expresions normativas para os formigóns reciclados, propóndose coeficientes correctores dependentes do árido reciclado cando sexa necesario.[Abstract]This work is focused on the study of structural flexural performance and bond behaviour analysis of recycled concrete with different recycled coarse replacements, 20%, 50% and 100%. Therefore, two concrete series were designed, one with a water to cement ratio (w/c) of 0.50 (which allows good performance concrete) and the other one with a w/c ratio of 0.65 (with lower strengths). The research was developed into two phases. In the first one, Beams Phase, two twin (series) reinforced beams were made with each kind of concrete. One of the series was tested under static loading and the other under sustained load for 1000 days. This shows the structural short and long-term flexural performance of recycled concretes beams. Previously, the concretes were characterized in both fresh and hardened state: consistency, compressive and splitting strength, longitudinal and transversal modulus of elasticity, stressstrain curve, shrinkage and creep were determined. Finally, the second phase was developed. It deals with the bond behaviour study of recycled concrete as a result of pull-out tests at different ages, from 7 to 365 days. The results allow you to check the suitability of including correcting coefficients into the standards design expressions of structural concrete when the recycled coarse aggregate is used

Effects of bacteria-based self-healing nutrients on hydration and rheology of cement pastes

[Abstract:] Crack openings in concrete lead to a reduction in its lifespan. Many authors have analysed different techniques that could repair cracks autonomously, being the use of bacteria one of the most promising approaches. Bacteria are often introduced with nutrients in the concrete mixes, and they may alter the cement hydration. In this study, the effects that calcium lactate, calcium nitrate, and yeast extract have on cement pastes during the early hours of hydration were analysed. To accomplish this, calorimetry, in situ X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Vicat and rheology techniques were employed. The results demonstrated that the addition of calcium lactate led to higher values of ettringite, which altered the rheological behaviour of the pastes. Moreover, when added at 4%, calcium lactate also delayed the setting time by inhibiting the reaction of silicates, a similar effect was observed when yeast extract was added. Lastly, the incorporation of nitrate accelerated the setting time.This work has been carried out within the framework of the following projects: “Design of sustainable concrete for 3D printing based on rheology and on the control of very early properties (Eco3DConcrete)- [PID2020-115433RB-I00]”, “Design of concrete precast elements incorporating sustainable strategies for self-healing to increase their service life (PREHEALING)- [PDC2021-121660-I00]” and “Exploiting the synergic effects between 3D printing and self-healing technologies to design sustainable and durable concrete (3DHealConcrete) [TED2021-129757B-I00]” all funded by MINECO (Ministry of Economy, Industry and Competitiveness). In addition, the authors would like to thank the Xunta de Galicia (Spain) for the financial support through its pre-doctoral contracts program

Study of Different Granular By-Products as Internal Curing Water Reservoirs in Concrete

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] The use of three different waste-based materials, i.e. ceramic recycled aggregate (CRA), mixed recycled aggregate (MRA), and coal bottom ash (CBA), as internal curing water reservoirs was investigated. Their effects as fine aggregates in the mortar phase of a hypothetical concrete with a low water-to-binder ratio were studied. The used binders were ordinary Portland cement and high-volume fly-ash-blended cement. The addition of MRA and CBA significantly decreased the autogenous shrinkage, whereas their negative effects on drying shrinkage and the compressive strength were minimal. However, the CRA had the worst effect on autogenous shrinkage but increased the strength of the specimens.This work has been carried out within the framework of the HACCURACEM project (BIA2017-85657-R), funded by the Ministry of Economy, Industry and Competitiveness, State Program for Research, Development and Innovation aimed at the challenges of Society, within the framework of the State Plan for Scientific and Technical Research and Innovation 2013–2016, Call 2017. We also thank the Xunta de Galicia (Spain) for the financial support through its pre-doctoral contracts program. Finally, we highlight the collaboration of the companies Votorantim Cimentos and Grupo BASF, for the contribution of some of the materials used in this researc

Masonry and render mortars with tyre rubber as aggregate: Fresh state rheology and hardened state performances

[Abstract:] This work shows how it is possible to tailor cement-rubber composites suitable as renders and masonry mortars with a reduced liquid water absorption. Recycled tyre rubber is used as aggregate in mixture with siliceous sand and its content is tuned in order to limit depletion of mechanical properties and, at the same time, ensure a sufficiently massive utilization of this secondary raw material. An extended investigation of the properties both at the fresh and hardened state is conducted. We show that presence of rubber sensitively reduces fluidity (hence workability) of the mortar. In particular, rubber modifies rheological properties such as thixotropy and dynamic torque, while does not affect viscosity. Overall, the fresh state properties are compatible with the casting and application of these mortar typologies, even for the highest rubber content (20–25% by volume). This rubber content is shown to be sufficient to ensure, just after few days of curing, an almost complete abatement of water drop absorption, specific functionality of these novel and more sustainable mortars

Masonry mortars, precast concrete and masonry units using coal bottom ash as a partial replacement for conventional aggregates

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract:] Granular coal combustion products are problematic waste materials whose use as aggregates in concrete has been extensively studied. However, its integration into other non-structural materials and elements has not been so widely documented. Masonry mortars, precast concrete and masonry units with different ratios of coal bottom ash replacing conventional aggregates have been studied. With the incorporation of coal bottom ash in the mortars, the workability, density and strength decrease whereas the porosity, the weight loss and the drying shrinkage increase. However, low replacement ratios have slight effects. The use of coal bottom ash as an internal curing water reservoir is proposed as the most promising future line of research.Ministerio de Economía, Industria y Competitividad; BIA2017-85657-

Comparing circulating fluidised bed fly ash and limestone as additions for cement

[Abstract:] Circulating fluidized bed combustion (CFBC) power plants produce as by-product large ash particles with elevated calcium content. They are not commonly accepted as addition for cement although presenting pozzolanic potential. To enhance the activity of this material, the CFBC ash was ground to fineness equal to that of the cement, simulating a joint milling with the clinker. This ground fly ash (GFA) was included in blended cements in ratios of 10%, 20% and 40%. These new cements with GFA surpassed 52.5 MPa at 28 days for even 40% of substitution. Contrasted with limestone addition, the most used in Europe, the cements with GFA presented higher compressive strength, better durability with the only drawback of a slight reduction in workability. This CFBC fly ash could be used as clinker replacement once ground to similar fineness than cement allowing high reductions in clinker consumption and its consequent carbon footprint reduction

Long-term flexural performance of reinforced concrete beams with recycled coarse aggregates

[Abstract:] The aim of this study is to investigate the behaviour of recycled aggregate concrete subjected to sustained loading. For the tests, eight reinforced concrete beams were manufactured with recycled coarse aggregate, using water-to-cement ratios of 0.50 and 0.65, and four replacement percentages: 0%, 20%, 50%, and 100%. First, the basic concrete properties, mechanical strength and modulus of elasticity, were determined after 28 d, and at the ageing load. The beam specimens were then loaded at 42 d, using a four-point bending test. Bending moments and deformations were obtained during the loading process, when cracking and serviceability conditions were reached, as well as the long-term deformations of recycled concrete beams up to 1000 d. Based on these results, it can be reported that long-term deformations are greater for recycled aggregate concrete than for conventional concrete, regarding both strain and deflection. Furthermore, a direct relationship was found between these deformations and the replacement percentage used. Lastly, code-based expressions were used to calculate the long-term deflections of RC beams subjected to sustained loading, which included the recycled coarse aggregate content and corrections previously proposed to predict the mechanical properties, creep, and shrinkage of recycled aggregate concrete.The study has been funded by: “CLEAM: Clean, efficient and nice construction along its life cycle” funded by the Centre for the Technology and Industrial Development (CDTI) and led by the Group of Economical Interest CLEAM-CENIT, AIE comprising by the country’s largest construction companies (Acciona, Dragados, Ferrovial, FCC, Isolux Corsán, OHL and Sacyr) and some PYME (Informática 68, Quilosa and Martínez Segovia y asociados). “HORREO: Robust self-compacting recycled concretes: rheology in fresh state and mechanical properties (BIA2014-58063-R)” funded by the Ministry of Economy and Competitiveness. The authors declare that they have no conflict of interest

Deformation recovery of reinforced concrete beams made with recycled coarse aggregates

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract:] The purpose of this research is to analyse the long-term deformations of reinforced concrete beams made of recycled coarse aggregates (RCA), using four different replacement ratios, 0%, 20%, 50% and 100%. For said purpose, three different loading stages were carried out: firstly, loading and sustained load for 1300 days, secondly, unloading and recovery where the deformations were registered over a one year period, and lastly, testing the concrete beams up to failure in order to analyse the effect of recycled aggregates on pre-cracked concrete members. The results led to the analysis of deformations under sustained load, as well as those produced after removing the load and the performance of pre-cracked members, while identifying the effect of recycled coarse aggregates on concrete performance in terms of plastic deformation, recoverability and concrete stiffness, and also on structural design.Ministerio de Industria, Economía y Competitividad; BIA2017-85657-

Effect of aggregate content and fibre type on the rheological behaviour and structural build-up of fibre reinforced self-compacting concrete using two binder compositions

[Abstract:] Many parameters influence the fresh behaviour of fibre reinforced self-compacting concrete (FRSCC), such as length, aspect ratio, fibre content, solid volume fraction, and particle interaction. Most studies did not analyse rheological behaviour (just workability) and they are focused on paste or mortar. However, the analysis at the concrete level is also required to confirm the behaviour when the coarse aggregates and fibres are employed. This kind of analysis is scarce in the literature. Hence, this work aims to increase the knowledge about the effect of aggregate content and fibre type on FRSCC. To do so, the behaviour of self-compacting mixes with three different aggregate contents (550, 500, and 650 l/m3), two cementitious systems (100 % cement, and 60 % cement, 25 % limestone filler and 15 % metakaolin), and three different types of rigid fibres (two metallic and one polypropylene) were analysed. To characterise the concrete rheological performance, the stress growth test (SGT) was selected to avoid any fibre orientation. SGT was repeated twice under undisturbed and disturbed conditions to assess the structural build-up of the concrete. The results indicate that there is a critical value of the relative packing fraction that, once overcome, severely affects the fresh behaviour of FRSSC. This critical value can be calculated as the ratio between random loose packing fraction and dense packing fraction. It can be used to design a FRSCC mix guaranteeing that the fresh state remains in a suitable range where the hydrodynamic interactions dominate the behaviour and therefore, changes in the mix composition will not sharply modify the rheological performance of the concrete.This research was funded by the Spanish Ministerio de Ciencia e innovación - Agencia Estatal de investigación through three projects entitled: “Design of sustainable concrete for 3D printing based on rheology and on the control of very early properties (Eco3DConcrete)- PID2020–115433RB-I00”, “Design of concrete precast elements incorporating sustainable strategies for self-healing to increase their service life (PREHEALING)- PDC2021–121660-I00” and "Exploiting the synergic effects between 3D printing and self-healing technologies to design sustainable and durable concrete (3DHealConcrete) - TED2021–129757B-I00

Study of different granular by-products as internal curing water reservoirs in concrete

The use of three different waste-based materials, i.e. ceramic recycled aggregate (CRA), mixed recycled aggregate (MRA), and coal bottom ash (CBA), as internal curing water reservoirs was investigated. Their effects as fine aggregates in the mortar phase of a hypothetical concrete with a low water-to-binder ratio were studied. The used binders were ordinary Portland cement and high-volume fly-ash-blended cement. The addition of MRA and CBA significantly decreased the autogenous shrinkage, whereas their negative effects on drying shrinkage and the compressive strength were minimal. However, the CRA had the worst effect on autogenous shrinkage but increased the strength of the specimens.This work has been carried out within the framework of the HACCURACEM project (BIA2017-85657-R), funded by the Ministry of Economy, Industry and Competitiveness, State Program for Research, Development and Innovation aimed at the challenges of Society, within the framework of the State Plan for Scientific and Technical Research and Innovation 2013–2016, Call 2017. We also thank the Xunta de Galicia (Spain) for the financial support through its pre-doctoral contracts program. Finally, we highlight the collaboration of the companies Votorantim Cimentos and Grupo BASF, for the contribution of some of the materials used in this research.Peer ReviewedObjectius de Desenvolupament Sostenible::12 - Producció i Consum ResponsablesObjectius de Desenvolupament Sostenible::13 - Acció per al ClimaObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraPostprint (published version