Hormigones con áridos reciclados procedentes de demoliciones : dosificaciones, propiedades mecánicas y comportamiento estructural a cortante

[Resumen] La evolución que se ha alcanzado en este siglo ha dado lugar a cambios sociales muy importantes que han obligado a grandes demoliciones. La última mitad de siglo ha permitido la construcción de numerosas estructuras que poco a poco irán envejeciendo y se irán demoliendo. En España se recicla una cantidad muy limitada, muy diferente es la situación de otros países de la Comunidad Europea, en los que tras años de Ilevar a cabo actividades recicladoras, gracias a la formulación de objetivos políticos, a una legislación y control apropiados y a unas normativas y control de calidad, se están consiguiendo unos niveles de reciclado aceptables y en todo caso siempre crecientes. Con tal motivo este trabajo trata de avanzar en este campo, intentando establecer conclusiones que afecten tanto al área de las propiedades básicas, como a la del comportamiento estructural. De esta forma se han Ilevado a cabo ensayos experimentales de tres tipos: • Ensayos sobre el material: se realizan ensayos de caracterización de áridos procedentes de desconstrucción (correspondientes a la fracción 6-12mm y 12-25mm) con el fin de establecer procedimientos que permitan establecer conclusiones sobre la adecuación o no de los áridos reciclados existentes en el mercado español al campo de los hormigones. Para ello se Ilevan a cabo ensayos normativos de densidad, absorción, granulometría, coeficiente de forma, índice de lajas y dureza. Los resultados obtenidos ponen de manifiesto que, a pesar de que existen diferencias notables (sobre todo en cuanto a densidad y absorción) con lo áridos convencionales, las características de estos áridos son tales que permiten su uso para la fabricación de hormigones. • Ensayos sobre propiedades básicas de los hormigones: se establecieron parámetros de dosificación correspondientes a hormigones de prestaciones no comprometidas desde el punto de vista de propiedades mecánicas, trabajabilidad y durabilidad. Con dichos parámetros de fabricó un hormigón convencional y un hormigón convencional con humo de sílice (ambos de control) y a continuación se ajustó la dosificación para la fabricación de un hormigón con áridos reciclados y un hormigón con áridos reciclados y humo de sílice (que sustituían el 50% de las fracciones gruesas convencionales). Se Ilevaron a cabo ensayos de caracterización de sus características, densidad en fresco y en estado endurecido, absorción y sus propiedades mecánicas, resistencia a compresión, resistencia a tracción, módulo de deformación y roturas bajo cargas lentas. Los resultados indicaron que las substitución del 50 % de las fracciones gruesas de áridos convencionales por áridos reciclados proporciona hormigones de características físicas similares (menores densidades y absorción mayor en los hormigones que incorporan áridos reciclados) y características mecánicas también similares • Ensayos sobre propiedades estructurales: con los hormigones diseñados se fabricaron vigas de hormigón armado de sección rectangular. Para cada tipo de hormigón, se fabricaron cuatro vigas con distintas cuantías de armadura transversal que se ensayaron hasta rotura. EI diseño del ensayo se realizó de forma que la rotura se debiese principalmente a esfuerzos de cortante, de forma que se pudiese estudiar el comportamiento de los nuevos hormigones frente a este esfuerzo y la influencia de las diferentes cuantías en dicho comportamiento. Los resultados obtenidos mediante instrumentación (del acero, del hormigón y de las flechas en cada escalón de carga) indican pequeñas diferencias de comportamiento entre los diferentes hormigones, sobre todo en cuanto a cargas últimas, diferencias que aumentan cuando se trata la fisuración. • Los resultados de la instrumentación se contrastaron con el programa Response que aplica la teoría de cortante del MCFT (Modified Compression Field Theory), basada en el comportamiento real de los materiales frente a este esfuerzo, encontrándose que esta teoría caracteriza adecuadamente el comportamiento de todos los hormigones. También se realizó un contraste de los resultados con diferentes normativas (que aplican en general formulaciones empíricas), corroborando el carácter conservador de todas ellas, y en especial de la EHE. Finalmente se extraen conclusiones relativas al uso de hormigón con áridos reciclados en elementos estructurales y se dan recomendaciones y perspectivas de futuros trabajos.[Abstract] The developments carried out within this century have produced very important social changes that have been the cause of big demolitions. Many structures have been constructed during the last half of the century and sooner or latter they will get older and some day they will be demolished. In Spain the recycling culture is not as developed as it is in many other countries of the European Union, and the recycling activity is very limited. In those countries, acceptable recycling levels have been reached after years of increasing recycling activity, thanks to the formulation of politics aims, an appropriate legislation and control processes, and the existence of quality control regulations. For that reason, this work's aim is to move forward in this field, trying to find out conclusions that affect not only the area of the basic properties, but also those of the structural behaviour. In this sense, some experimental testing of three different types has been carried out, i.e.: • Tests on materials: characterizing tests have been carried out on aggregates from demolishing (corresponding to the interval 6-12 mm and 12-25 mm) with the aim of establishing procedures which allow us to find out conclusions about the adaptation to the field of concrete of the Spanish market existing recycled aggregates. For that purpose, regulation tests have been carried out on density, absorption, grading, shape coefficient, slab index and hardness. The results so obtained have shown that in spite of the outstanding differences (specially about density and absorption) that show up in comparison with the traditional aggregates, the features of these aggregates are such that they are allowed for their use in the production of concrete. • Tests on the basic properties of concretes: some proportioning parameters were established for concretes with not very tough requirements from the mechanic properties, workability and durability point of view. With those parameters, control conventional concrete and control conventional silicon-smoke concrete were produced and following, the proportioning was adjusted for the producing of concrete with recycled aggregates and silicon smoke (which constituted by 50% of the coarse conventional fractions). Characterization tests of those concretes were also carried out to determine their features: raw density and hardness state, absorption and mechanical properties, compression resistance, traction resistance, strain module and breakability under slow loads. The results showed that the substitution of the 50% of the conventional coarse fraction by recycled aggregates provides concretes with similar physical features (with smaller densities and greater absorptions for the recycled aggregates concretes) and similar mechanical features. • Tests on structural properties: with the so-designed concretes, some reinforced beams with a circular cross-section were cast. For each type of concrete, four beams were cast with different distribution reinforcement that were tested to collapse. The design of the test was carried out so as to achieve a shear force collapse, in that way, the behaviour related to that kind of forces of the new released concretes can be regarded, and so can be the influence of the different quantities in that behaviour. The results obtained with the gauging (of steel, concrete and strains in each load step) show some small differences in the behaviour of the different concretes, especially in relation to the limit state loads. These differences grow bigger as the cracking increases. • The results of gauging is compared with the programme Response, that makes use of the shear theory of the MCFT (Modified Compression Field Theory), based upon the real behaviour of the materials against this force. This theory results in an adequate characterization of the behaviour of all the concretes. The contrast of the results obtained by using some different regulations (that make use of experimental formulations) was also carried out, and as a result they all seem to be conservative in their analysis, especially the EHE regulation. Finally, some conclusions are obtained in relation with the use of recycled aggregate concretes in structural elements and some recommendations and prospects are given for future works

Influence of the Mixing Procedure on the Fresh State Behaviour of Recycled Mortars

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] The effect of two different mixing protocols on the fresh-state behaviour of self-compacting mortars with and without recycled sand was compared. For this purpose, the mortar mixes were designed considering three solid volume fractions, while maintaining the water to cement ratio and superplasticiser dosage constant. The results conclude that the inclusion of recycled sand harmfully affects the rheological behaviour of the mortars and this effect can be mitigated using mixing protocols with longer mixing times and delayed admixture addition times. Finally, a rheograph was developed to explain the expectable changes in a conventional mix when recycled sand is incorporated, the solid volume fraction is varied and changes are applied to the mixing procedure

Rheology, Durability, and Mechanical Performance of Sustainable Self-Compacting Concrete With Metakaolin and Limestone Filler

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] This study analyzed the performance of self-compacting concrete with a paste composition that includes limestone filler and metakaolin replacing cement to design binary (75% cement and 25% limestone filler) and ternary binders (60% cement, 25% limestone filler and 15% metakaolin). Furthermore, to analyze the effect of the solid volume fraction (volume of sand and coarse aggregate) on concrete rheology, the concretes were designed using four volumes of paste (350 l, 400 l, 450 l and 500 l). Rheological tests were performed at three resting times to measure the viscosity and yield stress over time. The results indicated that the viscosity decreased by 43.3% when the cement was replaced by limestone filler and increased by 73.1% when the cement was replaced by 15% metakaolin while maintaining the limestone filler. These values were obtained as 27.6% and 62.2%, respectively, when the yield stress was analyzed. In addition, the hardened properties (mechanical behavior and durability) were studied by measuring the strengths at 28 days, as well as the electrical resistivity and ultrasonic pulse velocity over time. In this case, at 28 days the use of binary binder reduces the strength and resistivity (about 20%) and the employment of ternary binder reduces strength (15%) while increases the resistivity up to the double (when compared to the 100 C concrete). Moreover, to measure the efficiency of the concrete, a material index was designed that considers the fresh behavior, mechanical performance, durability, cost, and environmental impact. Self-compacting concretes with ternary binders provided the highest indices. The use of alternative materials, particularly metakaolin has been proven to be a good option to enhance concrete sustainable performance.The study is part of two projects entitled: “Robust self-compacting recycled concretes: rheology in fresh state and mechanical properties (Ref: BIA2014-58063-R)” and “Sustainable High Performance Self-Compacting Concrete using low clinker cement, and integral curing and self-healing agents (HACCURACEM) (BIA2017-85657-R)” funded by MINECO. Moreover, this work was also made possible by the financial support of a pre-doctoral grant of MINECO (FPI 2015- ref BES-2015-071919) and two grants for international pre-doctoral stays: (a) FPI 2015 and (b) IACOBUS program for “Galicia–North of Portugal Euroregion

Assessment of the Durability Dynamics of High-Performance Concrete Blended With a Fibrous Rice Husk Ash

[Abstract] The present study examines the durability properties of Class 1 (50–75 MPa) high-performance concrete (HPC) blended with rice husk ash (RHA) as a partial replacement of CEM II B-L, 42.5 N. Six HPC mixes were prepared with RHA and used as 5%, 10%, 15%, 20%, 25%, and 30% of CEM II alone and properties are compared with control mix having only CEM II. The binders (CEM II and RHA) were investigated for particle size distribution (PSD), specific surface area (SSA), oxide compositions, mineralogical phases, morphology, and functional groups using advanced techniques of laser PSD, Brunauer–Emmett–Teller (BET), X-ray fluorescence (XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared/attenuated total reflection (FTIR/ATR), respectively, to understand their import on HPC. Durability properties, including water absorption, sorptivity, and chemical attack of the HPC samples, were investigated to realise the effect of RHA on the HPC matrix. The findings revealed that the durability properties of RHA-based HPCs exhibited an acceptable range of values consistent with relevant standards. The findings established that self-produced RHA would be beneficial as a cement replacement in HPC. As the RHA is a cost-effective agro-waste, a scalable product of RHA would be a resource for sustainable technology

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

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-

Mussel shell mortars durability: Study of aggregate replacement limit

[Abstract]: The knowledge acquired through previous experimental phases with coating mortars with mussel shell aggregates led to conclude that irregular, flaky and hydrophobic particles of the mussel shell and the organic matter content introduce entrapped air and entrained air in the mixes. This phenomenon causes different and opposite effects on the main properties of mortars, which are in some way positive and negative (for durability), consequently, their durability cannot be easily predicted. The present work pretends to analyse the results of different durability tests, such as water vapour permeability, adhesive strength, and weathering cycles to recommend the maximum percentage of mussel shell sand used in coating mortars that guarantee the required lifespan. After an in-depth literature review, it can be said that it is not easy to predict the durability of mortars using mussel shell aggregates. This question has been hardly analysed in the existing literature and the maximum substitution percentage of conventional aggregate that can be replaced is not clear. This work aims to answer this issue by analysing different properties: water vapour permeability, adhesive strength, and weathering cycles. Mussel shell content improves the water vapour permeability of both air lime and cement mortars but worsens the adhesive strength and weathering cycle behaviour. For most applications, 25 % of mussel shell aggregate can be employed, but for some applications, 50 % or even 75 % of mussel shell aggregate is feasible and will avoid the undesirable landfilling of this waste.This work has been developed within the framework of the project "Valorización de las conchas de bivalvos gallegos en el ámbito de la construcción" (Valorisation of Galician bivalve shell in the construction sector; Code 00064742/ITC-20133094), funded by CDTI (Centro para el Desarrollo Tecnológico e Industrial) under the FEDER-Innterconecta Program, and co-financed with European Union ERDF funds

Wood Ash Versus Expanded Clay Aggregate as Internal Curing Water Reservoirs in High Performance Concrete

Financiado para publicación en acceso aberto: Universidade da Coruña/CISUG[Abstract] The performances of expanded clay aggregate and wood ash as internal curing water reservoirs were studied in the mortar phase of a hypothetical high performance concrete with a low water-to-binder ratio. The two materials substituted the 15 and 30% of the sand volume. Two different binders, Portland cement and high-volume fly ash blended cement, were used. The compressive strength and the volume stability of the mortars in sealed and air-drying conditions were studied. Furthermore, the desorption capacity of the internal curing water reservoirs and the internal humidity inside the mortars during the first days after casting were analysed. The results shown that the reduction in the self-desiccation shrinkage was higher when the expanded clay aggregate was used, even in air-drying curing conditions, due to its higher desorption capacity in low-relative-humidity environments in comparison to that of the wood ash. However, wood ash had a stronger beneficial effect on early age autogenous shrinkage without significantly increasing the drying shrinkage. The two alternative aggregates influenced the strength moderately. Considering the technical, economic, and environmental implications of using the two lightweight aggregates, wood ash is recommended.Funding for open access charge: Universidade da Coruña/CISUG. 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 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-

Wood ash versus expanded clay aggregate as internal curing water reservoirs in high performance concrete

The performances of expanded clay aggregate and wood ash as internal curing water reservoirs were studied in the mortar phase of a hypothetical high performance concrete with a low water-to-binder ratio. The two materials substituted the 15 and 30% of the sand volume. Two different binders, Portland cement and high-volume fly ash blended cement, were used. The compressive strength and the volume stability of the mortars in sealed and air-drying conditions were studied. Furthermore, the desorption capacity of the internal curing water reservoirs and the internal humidity inside the mortars during the first days after casting were analysed. The results shown that the reduction in the self-desiccation shrinkage was higher when the expanded clay aggregate was used, even in air-drying curing conditions, due to its higher desorption capacity in low-relative-humidity environments in comparison to that of the wood ash. However, wood ash had a stronger beneficial effect on early age autogenous shrinkage without significantly increasing the drying shrinkage. The two alternative aggregates influenced the strength moderately. Considering the technical, economic, and environmental implications of using the two lightweight aggregates, wood ash is recommended.Funding for open access charge: Universidade da Coruña/CISUG. 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