Self-healing concrete: efficiency evaluation and enhancement with crystalline admixtures

Los materiales autosanables son materiales con la capacidad de reparar sus daños de forma autónoma o con ayuda mínima de estímulos externos. En el campo de la construcción, el desarrollo de elementos autosanables aumentará la durabilidad de las estructuras y reducirá las acciones de mantenimiento y reparación. Los elementos de hormigón armado presentan frecuentemente pequeñas fisuras (< 0.3 mm), no relevantes mecánicamente, pero que pueden suponer un punto de entrada para agentes agresivos. El hormigón tiene una cierta capacidad de autosanación, capaz de cerrar pequeñas fisuras, producida principalmente por la hidratación continuada y la carbonatación. Estudios recientes han intentado mejorar dicha capacidad y diseñar productos específicos para conseguirla. Estos productos incluyen, entre otros, aditivos cristalinos, agentes micro o macroencapsulados, e incluso el uso de bacterias. Los aditivos cristalinos (CA) son un tipo de aditivo para hormigón que se considera que aporta propiedades de autosanación. No obstante, la falta de conocimiento sobre su comportamiento limita su uso. Además, los métodos para evaluar la autosanación en hormigones no están estandarizados todavía. Esto complica la realización de un análisis crítico de los diferentes productos y métodos de evaluación propuestos en la literatura. Para responder a esta falta de conocimiento, los objetivos de esta tesis son: 1) estudiar y proponer procedimientos experimentales para evaluar los fenómenos de autosanación en hormigón y, 2) evaluar experimentalmente las mejoras producidas al introducir aditivos cristalinos. Esta tesis incluye como ensayos para la determinación de la autosanación: la evaluación del cierre de fisuras, la permeabilidad al agua, flexión a tres puntos y absorción capilar. Además, se han realizado varias campañas experimentales para validar los ensayos propuestos. Posteriormente, estos ensayos se han utilizado para analizar la influencia de varios parámetros, incluyendo entre otros: presencia de aditivos cristalinos, nivel de daño, tiempo necesario para el sanado, composición del hormigón y condiciones de sanado. Finalmente, se analizan los efectos producidos al añadir aditivos cristalinos en hormigón en la fluidez, resistencia e hidratación. Los resultados muestran que el cierre de fisuras es un ensayo eficaz y sencillo para evaluar la autosanación. Sin embargo, la orientación de la fisura durante el sanado ha resultado ser de gran importancia, y no considerar este aspecto puede llevar a conclusiones engañosas. El ensayo de permeabilidad al agua propuesto en este trabajo presenta una buena estabilidad y es fácil de implementar en laboratorios. Además, las relaciones obtenidas entre los parámetros de fisura y la permeabilidad del agua han confirmado la relación cúbica indicada en la literatura. Este trabajo muestra que analizar la eficiencia de autosanado mediante el cierre de fisuras puede llevar a una sobreestimación de la capacidad de sanación, comparada con los resultados obtenidos mediante permeabilidad. Los ensayos de sorptividad resultaron fáciles de implementar, sin embargo, los resultados obtenidos mostraron una alta dispersión y sensibilidad a las variaciones en las fisuras producidas durante el proceso de prefisuración. En cuanto a la evaluación de la recuperación mecánica, los resultados muestran que la evolución de las propiedades del hormigón con el tiempo es un parámetro que debe considerarse, especialmente en fisuras de edades tempranas. En este trabajo se ha obtenido que los aditivos cristalinos potencian las reacciones de autosanación, pero tienen una capacidad limitada. La proximidad de los CA a la industria es un punto positivo para su inclusión como un nuevo tipo de aditivo de hormigón. Sin embargo, los resultados obtenidos en esta tesis indican que se necesitan más análisis para determinar sus efectos completos en hormigón, especialmente con respectSelf-healing materials are materials with the capability to repair their damage autonomously or with minimal help from an external stimulus. In the construction field, the development of self-healing elements will increase the durability of structures and reduce their maintenance and repair actions. Reinforced concrete elements frequently suffer small cracks (< 0.3 mm), not relevant mechanically, but they can be an entrance point for aggressive agents. Concrete has a natural self-healing capability able to seal small cracks, produced by the continuing hydration and carbonation processes. Recent studies have attempted to improve that healing capability and to design specific products to achieve it. These products include, among others: crystalline admixtures, micro- or macro-encapsulated agents, and even the use of bacteria. Crystalline admixtures (CA) are a concrete admixture that is claimed to provide self-healing properties. However, the lack of knowledge on their behavior and self-healing properties limits their usage. In addition, the methods to evaluate the self-healing capability of mortar and concrete are not standardized yet. This complicates the performance of a critical analysis of the different self-healing products and evaluation methods found in the literature. In order to answer to this lack of knowledge, the objectives of this thesis are: 1) to study and propose experimental procedures in order to evaluate self-healing in concrete and, 2) to evaluate experimentally the self-healing enhancements produced when introducing crystalline admixtures. This thesis includes the following tests for the determination of the self-healing: the evaluation of crack closing, water permeability, three point bending tests and capillary absorption test. In addition, several experimental campaigns have been performed with the objective of validating the proposed tests. Afterwards, these methods have been used to analyze the influence of several parameters, including among others: the presence of crystalline admixtures, the damage extent, healing time needed, concrete composition and healing conditions. Finally, the effects that crystalline admixtures produce in concrete are analyzed in terms of slump, strength and hydration. The results show that crack closing is an effective and simple method to evaluate self-healing. However, the orientation of the crack during healing is of great importance, and disregarding this aspect may lead to misleading conclusions. The water permeability method proposed in this work has good stability and it is easy to implement in concrete laboratories. Moreover, the relations obtained between crack parameters and water permeability confirmed the cubic relation, as reported in the literature. This work shows that analyzing healing efficiency by means of crack closing tends to overestimate self-healing if compared with the results obtained by means of water permeability. Sorptivity analysis tests were easy to implement, however, the results obtained in this work showed high dispersion and sensitivity to the variations of the cracks introduced during the precracking process. Regarding the evaluation of mechanical recoveries, the results show that the evolution of concrete properties with time is a parameter of importance that, therefore, should be considered, especially for early age cracks. In this work, crystalline admixtures have been reported as an enhancer of self-healing reactions, but with a limited capacity of enhancement. The proximity of CA to the industry is a positive point to their inclusion as a new type of admixture for concrete. However, the results obtained in this thesis indicate further analyses are needed to determine their full effects on concrete, especially regarding self-healing.Els materials autosanables són materials amb la capacitat de reparar els seus danys de forma autònoma o amb ajuda mínima d'estímuls externs. En el camp de la construcció, el desenvolupament d'elements autosanables augmentarà la durabilitat de les estructures i reduirà les accions de manteniment i reparació. Els elements de formigó armat presenten freqüentment fissures menudes (< 0.3 mm), no rellevants des del punt de vista mecànic, però poden suposar un punt d'entrada per a agents agressius. El formigó té una capacitat de autosanació capaç de tancar fissures menudes, produïda principalment per la hidratació continuada i la carbonatació. Estudis recents han intentat millorar eixa capacitat i dissenyar productes específics per aconseguir-la. Aquests productes inclouen, entre d'altres, additius cristal·lins, agents micro- o macroencapsulats, i fins i tot l'ús de bacteris. Els additius cristal·lins (CA) són un tipus d'additiu reductor per formigó que es considera que proporciona propietats de autosanació. No obstant, la manca de coneixement sobre el seu comportament limita el seu ús. A més, els mètodes per avaluar la autosanació de formigons encara no estan estandarditzats. Açò complica la realització d'una anàlisi crítica dels diferents productes i mètodes d'avaluació proposats a la literatura. Per respondre a aquesta manca de coneixement, els objectius d'aquesta tesi són: 1) estudiar i proposar procediments experimentals per avaluar els fenòmens d'autosanació en formigó i, 2) avaluar experimentalment les millores produïdes en introduir additius cristal·lins. Aquesta tesi inclou com assajos per a la determinació de l'autosanació: l'avaluació del tancament de fissures, la permeabilitat a l'aigua, flexió a tres punts i absorció capil·lar. A més, s'han realitzat diverses campanyes experimentals per validar els assajos proposats. Posteriorment, aquests assajos s'han utilitzat per analitzar la influència de diversos paràmetres: presència d'additius cristal·lins, nivell de dany, temps necessari per a la sanació, composició del formigó i condicions de sanació. Finalment, s'analitzen els efectes produïts en afegir additius cristal·lins en formigó en fluïdesa, resistència i hidratació. Els resultats mostren que el tancament de fissures és un assaig eficaç i senzill per avaluar l'autosanació. No obstant això, l'orientació de la fissura durant la sanació ha resultat ser de gran importància, i no considerar aquest aspecte pot portar a conclusions enganyoses. L'assaig de permeabilitat a l'aigua proposat presenta una bona estabilitat i és fàcil d'implementar en laboratoris. A més, les relacions obtingudes entre els paràmetres de fissura i la permeabilitat a l'aigua han confirmat la relació cúbica de la literatura. Aquest treball mostra que analitzar l'eficiència de l'autosanació amb el tancament de fissures pot sobreestimar la capacitat de sanació, comparada amb els resultats obtinguts-dues mitjançant permeabilitat a l'aigua. Els assajos de sorptivitat van resultar fàcils d'implementar, però, els resultats obtinguts en aquest treball van mostrar una alta dispersió i sensibilitat a les variacions en les fissures produïdes durant el procés de prefissuració. Pel que fa a l'avaluació de la recuperació mecànica, els resultats mostren que l'evolució de les propietats del formigó amb el temps és un paràmetre d'importància que, per tant, s'ha de considerar, especialment per fissures primerenques. En aquest treball s'ha obtingut que els additius cristal·lins potencien les reaccions d'autosanació, però tenen una capacitat limitada. La proximitat dels CA a la indústria és un punt positiu per a la seva inclusió com un nou tipus d'additiu de formigó. Tanmateix, els resultats obtinguts en aquesta tesi indiquen que calen més anàlisis per determinar els seus efectes complets en formigó, especialment pel que fa a l'autosanació.Roig Flores, M. (2018). Self-healing concrete: efficiency evaluation and enhancement with crystalline admixtures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/100082TESI

Characterization of Glass Powder from Glass Recycling Process Waste and Preliminary Testing

This work studies the possibility of incorporating different proportions of glass powder from the waste glass (rejected material called fine cullet) produced during the glass recycling process into the manufacturing of mortar and concrete. For this purpose, the material is characterized by its chemical composition and pozzolanic activity, and the shape and size of its particles are studied. It is then incorporated as a substitute for cement into the manufacturing of mortar and concrete at 25% and 40% of cement weight, and its effect on setting times, consistency, and mechanical strength is analyzed. Its behavior as a slow pozzolan is verified, and the possibility of incorporating it into concrete is ratified by reducing its cement content and making it a more sustainable material

Concrete Early-Age Crack Closing by Autogenous Healing

[EN] Autogenous healing is mainly produced by continuing hydration or carbonation. The aim of this research is to quantify the crack closing produced by autogenous healing for early-age concrete. This healing was evaluated for two crack size levels, 0.1 mm and 0.4 mm, under three healing conditions: water immersion, a humidity chamber, and wet/dry cycles. Crack closing was evaluated after 7, 14, 28 and 42 days under healing conditions. The internal status of the cracks was verified visually and using phenolphthalein. The results show that specimens stored in the humidity chamber did not experience healing, while specimens under wet/dry cycles and water immersion achieved the complete closing of small-sized cracks (under 0.15 mm). Autogenous healing showed higher speed under wet/dry cycles but higher final efficiency under water immersion. However, the inspection of the interior of the specimens showed that self-closing occurred mostly on the surface, and carbonation in the crack faces was only noticed very near the specimen's surface. Additionally, this study proposes a preliminary strategy to model autogenous healing in concrete in terms of crack closing.Roig-Flores, M.; Serna Ros, P. (2020). Concrete Early-Age Crack Closing by Autogenous Healing. Sustainability. 12(11):1-16. https://doi.org/10.3390/su12114476S1161211De Belie, N., Gruyaert, E., Al-Tabbaa, A., Antonaci, P., Baera, C., Bajare, D., … Jonkers, H. M. (2018). A Review of Self-Healing Concrete for Damage Management of Structures. Advanced Materials Interfaces, 5(17), 1800074. doi:10.1002/admi.201800074Van Tittelboom, K., & De Belie, N. (2013). Self-Healing in Cementitious Materials—A Review. Materials, 6(6), 2182-2217. doi:10.3390/ma6062182Yuan, L., Chen, S., Wang, S., Huang, Y., Yang, Q., Liu, S., … Zhou, Z. (2019). Research on the Improvement of Concrete Autogenous Self-healing Based on the Regulation of Cement Particle Size Distribution (PSD). Materials, 12(17), 2818. doi:10.3390/ma12172818Gagné, R., & Argouges, M. (2012). A study of the natural self-healing of mortars using air-flow measurements. Materials and Structures, 45(11), 1625-1638. doi:10.1617/s11527-012-9861-ySuleiman, A. R., & Nehdi, M. L. (2018). Effect of environmental exposure on autogenous self-healing of cracked cement-based materials. Cement and Concrete Research, 111, 197-208. doi:10.1016/j.cemconres.2018.05.009Qian, S., Zhou, J., de Rooij, M. R., Schlangen, E., Ye, G., & van Breugel, K. (2009). Self-healing behavior of strain hardening cementitious composites incorporating local waste materials. Cement and Concrete Composites, 31(9), 613-621. doi:10.1016/j.cemconcomp.2009.03.003Yıldırım, G., Khiavi, A. H., Yeşilmen, S., & Şahmaran, M. (2018). Self-healing performance of aged cementitious composites. Cement and Concrete Composites, 87, 172-186. doi:10.1016/j.cemconcomp.2018.01.004Rajczakowska, M., Habermehl-Cwirzen, K., Hedlund, H., & Cwirzen, A. (2019). The Effect of Exposure on the Autogenous Self-Healing of Ordinary Portland Cement Mortars. Materials, 12(23), 3926. doi:10.3390/ma12233926Roig-Flores, M., Pirritano, F., Serna, P., & Ferrara, L. (2016). Effect of crystalline admixtures on the self-healing capability of early-age concrete studied by means of permeability and crack closing tests. Construction and Building Materials, 114, 447-457. doi:10.1016/j.conbuildmat.2016.03.196Yang, Y., Lepech, M. D., Yang, E.-H., & Li, V. C. (2009). Autogenous healing of engineered cementitious composites under wet–dry cycles. Cement and Concrete Research, 39(5), 382-390. doi:10.1016/j.cemconres.2009.01.013Yang, Y., Yang, E.-H., & Li, V. C. (2011). Autogenous healing of engineered cementitious composites at early age. Cement and Concrete Research, 41(2), 176-183. doi:10.1016/j.cemconres.2010.11.002Liu, H., Huang, H., Wu, X., Peng, H., Li, Z., Hu, J., & Yu, Q. (2019). Effects of external multi-ions and wet-dry cycles in a marine environment on autogenous self-healing of cracks in cement paste. Cement and Concrete Research, 120, 198-206. doi:10.1016/j.cemconres.2019.03.014Van Tittelboom, K., Gruyaert, E., Rahier, H., & De Belie, N. (2012). Influence of mix composition on the extent of autogenous crack healing by continued hydration or calcium carbonate formation. Construction and Building Materials, 37, 349-359. doi:10.1016/j.conbuildmat.2012.07.026Huang, H., Ye, G., & Damidot, D. (2014). Effect of blast furnace slag on self-healing of microcracks in cementitious materials. Cement and Concrete Research, 60, 68-82. doi:10.1016/j.cemconres.2014.03.010Wiktor, V., & Jonkers, H. M. (2011). Quantification of crack-healing in novel bacteria-based self-healing concrete. Cement and Concrete Composites, 33(7), 763-770. doi:10.1016/j.cemconcomp.2011.03.012Snoeck, D., & De Belie, N. (2012). Mechanical and self-healing properties of cementitious composites reinforced with flax and cottonised flax, and compared with polyvinyl alcohol fibres. Biosystems Engineering, 111(4), 325-335. doi:10.1016/j.biosystemseng.2011.12.005Ferrara, L., Van Mullem, T., Alonso, M. C., Antonaci, P., Borg, R. P., Cuenca, E., … De Belie, N. (2018). Experimental characterization of the self-healing capacity of cement based materials and its effects on the material performance: A state of the art report by COST Action SARCOS WG2. Construction and Building Materials, 167, 115-142. doi:10.1016/j.conbuildmat.2018.01.143Zhong, W., & Yao, W. (2008). Influence of damage degree on self-healing of concrete. Construction and Building Materials, 22(6), 1137-1142. doi:10.1016/j.conbuildmat.2007.02.006Sisomphon, K., Copuroglu, O., & Koenders, E. A. B. (2013). Effect of exposure conditions on self healing behavior of strain hardening cementitious composites incorporating various cementitious materials. Construction and Building Materials, 42, 217-224. doi:10.1016/j.conbuildmat.2013.01.012Argiz, C., Menéndez, E., Moragues, A., & Sanjuán, M. Á. (2014). Recent Advances in Coal Bottom Ash Use as a New Common Portland Cement Constituent. Structural Engineering International, 24(4), 503-508. doi:10.2749/101686613x1376834840051

Study of the feasibility of self-healing Concrete with and without crystalline admixtures

[EN] Self-healing concrete is able to recover completely or partially its properties after being damaged (usually by cracking). This work studies the effect on self-healing of introducing a crystalline admixture into concrete. The focus has been made in analyzing cracks of different sizes (up to 0.4 mm) produced at early ages of concrete and the effectiveness of the healing process under several exposures. The properties that have been analyzed, before and after the healing process, are permeability of cracked specimens and visual closure of the crack.[ES] El hormigón autosanable es aquél capaz de recuperar total o parcialmente sus propiedades tras sufrir un daño (generalmente en forma de fisuras). En este trabajo se ha estudiado el efecto de la introducción de un aditivo cristalino en el potencial de autosanación de un hormigón. En concreto, se han analizado fisuras producidas a edades tempranas del hormigón de distintos tamaños (hasta 0.4 mm) y la efectividad del proceso de sanación bajo diferentes ambientes de exposición. Las propiedades analizadas antes y después del proceso de sanación han sido la permeabilidad de probetas fisuradas y el cierre visual de la fisura.Roig Flores, M. (2015). Study of the feasibility of self-healing Concrete with and without crystalline admixtures. http://hdl.handle.net/10251/7515

A Study of the Flexural Behavior of Fiber-Reinforced Concretes Exposed to Moderate Temperatures

[EN] The use of synthetic fibers in fiber-reinforced concretes (FRCs) is often avoided due to the mistrust of lower performance at changing temperatures. This work examines the effect of moderate temperatures on the flexural strengths of FRCs. Two types of polypropylene fibers were tested, and one steel fiber was employed as a reference. Three-point bending tests were carried out following an adapted methodology based on the standard EN 14651. This adapted procedure included an insulation system that allowed the assessment of FRC flexural behavior after being exposed for two months at temperatures of 5, 20, 35 and 50 °C. In addition, the interaction of temperature with a precracked state was also analyzed. To do this, several specimens were pre-cracked to 0.5 mm after 28days and conditioned in their respective temperature until testing. The findings suggest that this range of moderate temperatures did not degrade the behavior of FRCs to a great extent since the analysis of variances showed that temperature is not always a significant factor; however, it did have an influence on the pre-cracked specimens at 35 and 50 °C.This research was funded by Spanish Ministry of Science, Innovation and Universities, grant number FPU18/06145.Caballero-Jorna, M.; Roig-Flores, M.; Serna Ros, P. (2021). A Study of the Flexural Behavior of Fiber-Reinforced Concretes Exposed to Moderate Temperatures. Materials. 14(13):1-18. https://doi.org/10.3390/ma14133522S118141

Self-healing efficiency of Ultra High-Performance Fiber-Reinforced Concrete through permeability to chlorides

This study presents a novel methodology to evaluate the self-healing capability of Ultra High-Performance Fiber-Reinforced Concrete (UHPFRC) designed to compare conventional concrete types. The procedure used combines loading reinforced concrete elements until a fixed strain level to have a comparable total crack opening. Afterwards, water penetration to chlorides is used as an indicator of permeability. This work compares autogenous healing efficiency of a conventional concrete, a high-performance concrete, and two types of UHPFRCs with and without 0.8% of a crystalline admixture (CA) by the binder weight. The results show that all UHPFRC specimens exhibited excellent autogenous healing, higher than conventional concretes for an equivalent total crack. The self-healing results depended greatly on the crack size and the fiber content. Additionally, UHPFRCs with CA obtained the lowest water permeability after promoting self-healing for one month in water immersion and presented almost complete healing against chloride penetration.The activity described in this paper has been performed in the framework of the project “Rethinking coastal defence and Green-energy Service infrastructures through enHancEd-durAbiLity high-performance cement-based materials-ReSHEALience”, funded by the European Union Horizon 2020 research and innovation programme under GA No 760824. The authors would also like to thank Sika and Penetron for providing materials for the tests and E.J. Mezquida-Alcaraz for the characterization of UHPFRC mixes with Inverse Analysis

Characterization of Glass Powder from Glass Recycling Process Waste and Preliminary Testing

[EN] This work studies the possibility of incorporating different proportions of glass powder from the waste glass (rejected material called fine cullet) produced during the glass recycling process into the manufacturing of mortar and concrete. For this purpose, the material is characterized by its chemical composition and pozzolanic activity, and the shape and size of its particles are studied. It is then incorporated as a substitute for cement into the manufacturing of mortar and concrete at 25% and 40% of cement weight, and its effect on setting times, consistency, and mechanical strength is analyzed. Its behavior as a slow pozzolan is verified, and the possibility of incorporating it into concrete is ratified by reducing its cement content and making it a more sustainable material.This research was funded by Agencia Valenciana de la Innovacio (AVI) grant number INNEST/2020/85.Gimenez-Carbo, E.; Soriano Martinez, L.; Roig-Flores, M.; Serna Ros, P. (2021). Characterization of Glass Powder from Glass Recycling Process Waste and Preliminary Testing. Materials. 14(11):1-15. https://doi.org/10.3390/ma14112971S115141

Influencia de aditivos orgánicos en las propiedades reológicas de pastas de cemento de aluminato de calcio

[ES] El cemento de aluminato de calcio (CAC) es un tipo de cemento utilizado en elementos constructivos que necesitan propiedades refractarias, debido a su resistencia a elevadas temperaturas. Sin embargo, este tipo de cemento presenta diversas dificultades para su puesta en obra debido a su fraguado rápido y la dificultad para obtener trabajabilidades elevadas con relaciones agua/cemento bajas. Este trabajo realiza un análisis de la reología obtenida al utilizar distintas familias de aditivos con CAC, incluyendo superplastificantes basados en policarboxilato, vinílicos, naftalenos o lignosulfonatos, así como aditivos retardadores como ácido cítrico y gluconato. Además, se estudia la influencia de la presencia de cenizas volantes y escorias de alto horno como adiciones minerales. Para ello se ha calculado el esfuerzo de cizalla umbral de pastas con aditivos a partir de los valores de escurrimiento a lo largo del tiempo. Los resultados muestran la elevada compatibilidad de los aditivos tipo lignosulfonato y de los retardadores manteniéndose la fluidez hasta 90 minutos tras el inicio de la hidratación. Finalmente, la adición conjunta de aditivos basados en lignosulfonato y policarboxilato ha permitido obtener una fluidez óptima de los sistemas de CAC.Los autores agradecen al proyecto NewSOL H2020-IA-NMBP-17-2016 (project ID: 720985) la financiación recibida, así como a las empresas Cementos Molins S.A., Cementos Tudela Veguín y Secil Companhia Geral de Cal e Cimento, por el suministro de material y las discusiones técnicas.Roig-Flores, M.; Palacios, M.; Martínez-Urbanos, M.; Alonso, M. (2018). Influencia de aditivos orgánicos en las propiedades reológicas de pastas de cemento de aluminato de calcio. En HAC 2018. V Congreso Iberoamericano de hormigón autocompactable y hormigones especiales. Editorial Universitat Politècnica de València. 75-84. https://doi.org/10.4995/HAC2018.2018.7226OCS758

Utilisation of Ceramic Stoneware Tile Waste as Recycled Aggregate in Concrete

The construction industry has a significant environmental impact and concrete production is responsible for a large part of CO2 emissions and energy consumption. This study focused on the reutilisation of a specific type of tiles ceramic waste (TCW), composed only of stoneware and porcelain stoneware tiles, hereafter referred to as ceramic stoneware (CS), as recycled aggregate in concrete. Natural limestone and CS aggregates (sand and gravel) were characterised (particle size distribution, water absorption, resistance to wear, density and X-ray diffraction analyses) and recycled aggregate concrete (RAC) was prepared by replacing 20, 50 and 100 vol.% of sand and gravel, separately. Concrete workability generally improved with CW addition, especially when replacing natural gravel. Although the compressive strengths of the concrete specimens prepared with recycled sand were slightly lower than those of the reference specimens, similar or better results were recorded with the recycled CS gravel. In consonance, the RAC developed with recycled gravel obtained lower water penetration depths than the reference concrete. No significant variation in tensile strength was observed when varying CS content (values within the 2.33–2.65 MPa range). The study contributes to sustainable construction practices and circular economy by promoting the valorisation and reutilisation of industrial waste and reducing the consumption of natural resources.This research was funded by Generalitat Valenciana, the regional government of Valencia, through Project INVEST/2022/243, and by Universitat Jaume I (UJI) through Project UJI-B2021-34

Influencia de aditivos orgánicos en las propiedades reológicas de pastas de cemento de aluminato de calcio

El cemento de aluminato de calcio (CAC) es un tipo de cemento utilizado en elementos constructivos que necesitan propiedades refractarias, debido a su resistencia a elevadas temperaturas. Sin embargo, este tipo de cemento presenta diversas dificultades para su puesta en obra debido a su fraguado rápido y la dificultad para obtener trabajabilidades elevadas con relaciones agua/cemento bajas. Este trabajo realiza un análisis de la reología obtenida al utilizar distintas familias de aditivos con CAC, incluyendo superplastificantes basados en policarboxilato, vinílicos, naftalenos o lignosulfonatos, así como aditivos retardadores como ácido cítrico y gluconato. Además, se estudia la influencia de la presencia de cenizas volantes y escorias de alto horno como adiciones minerales. Para ello se ha calculado el esfuerzo de cizalla umbral de pastas con aditivos a partir de los valores de escurrimiento a lo largo del tiempo. Los resultados muestran la elevada compatibilidad de los aditivos tipo lignosulfonato y de los retardadores manteniéndose la fluidez hasta 90 minutos tras el inicio de la hidratación. Finalmente, la adición conjunta de aditivos basados en lignosulfonato y policarboxilato ha permitido obtener una fluidez óptima de los sistemas de CAC