Structural fibre-reinforced cement-based composite designed for particle bed 3D printing systems: case study Parque de Castilla Footbridge in Madrid

This paper presents the material and process-related research that underpinned the realisation of the Parque de Castilla Footbridge in Madrid in 2016, going from the laboratory to the industrial scale. The fibre-reinforced cement-based composite was first developed and tested in a small-scale particle bed printer focusing on evaluating the influence of the material and process on the mechanical response and density of the printed parts. The solution was then upscaled to a full-size particle bed printer that underwent technical modifications to ensure adequate control and production quality of the footbridge segments. The observations derived from the study provide valuable insights on relevant process-related differences induced by the technology upscaling that can inform future applications of the technology.The authors acknowledge ACCIONA, S.A., for the funds provided. The authors also acknowledge Mr. Enrico Dini for his seminal role in the popularisation and visibility of particle bed 3D printing, holding the Application Patents of this system. The experimental program carried out at the Laboratory of Structures and Materials (LATEM) of the Polytechnic University of Catalonia (UPC, BarcelonaTECH) allowed identifying the parameters that govern the mechanical performance of the fibre reinforced cement-based composite designed and oriented to the manufacturing of structural components with particle bed 3D-printing systems. Additionally, the first and third author want to express their gratitude to AGAUR-FEDER for the financial support through the project 2019PROD00066.Peer ReviewedPostprint (published version

Influence of size effect on the design parameters of fibre reinforced concrete

Debido a la reducción de la resistencia residual del hormigón reforzado con fibras (HRF) al incrementar el tamaño de un elemento, resulta de gran interés determinar el alcance del efecto escala para el cálculo de los parámetros del modelo constitutivo. Para ello, se han realizado ensayos de flexotracción en probetas de tres dimensiones planteando el uso de la rotación de la probeta como alternativa a la abertura de fisura para establecer los valores fR1 y fR3 del modelo constitutivo. Tras comparar los resultados experimentales con una simulación por análisis inverso, se observa que la utilización de la rotación de la probeta en lugar de la abertura de fisura lleva a resultados menos influenciados por el efecto escala.Los autores agradecen el apoyo económico del Ministerio de Economía, Industria y Competitividad a través del proyecto SAES (BIA2016-78742-C2-1-R). El primer autor agradece el apoyo económico del Ministerio de Ciencia, Innovación y Universidades a través de la beca FPU.Postprint (published version

Optimización del control de calidad para hormigón con fibras mediante el ensayo Barcelona y el método inductivo

El ensayo de flexotracción a tres puntos es uno de los métodos más empleados en la caracterización de la resistencia residual y el control de calidad del hormigón reforzado con fibras (HRF). Sin embargo, la elevada variabilidad de los resultados junto con la complejidad de dicho ensayo ha motivado la aparición de nuevos métodos para determinar resistencia post-fisuración del HRF. En este aspecto, el ensayo Barcelona surge como alternativa para la caracterización del HRF debido a la menor variabilidad de sus resultados, el menor consumo de material en la fabricación de probetas y la mayor simplicidad del ensayo. Asimismo, resulta de gran relevancia controlar el contenido de fibras en el HRF dada su influencia en la resistencia residual. Por este motivo, se propone el método inductivo como herramienta complementaria para determinar el contenido de fibras en el HRF. Así, el principal objetivo de este estudio es mostrar una metodología orientada a la utilización del ensayo Barcelona junto con el inductivo para el control de calidad del HRF especialmente en obras de grandes dimensiones.Los autores quieren agradecer el apoyo económico del Ministerio de Economía, Industria y Competitividad (MECIC) a través de la ayuda RTC-2016-5263-5 asociada al proyecto eFIB (optimización de procesos constructivos y de diseño de elementos estructurales empleando hormigones reforzados con fibras en sustitución de la armadura convencional), proyecto desarrollado conjuntamente con SACYR Ingeniería e Infraestructuras. Los autores también agradecen al MECIC la ayuda asociada al proyecto SAES (BIA2016-78742-C2-1-R). El primer autor agradece al Ministerio de Ciencia, Innovación y Universidades la ayuda económica recibida a través de la beca FPU13/04864.Postprint (published version

Statistical analysis of an experimental database on residual flexural strengths of fiber reinforced concretes: performance-based equations

The postcracking capacity of fiber reinforced concrete (FRC) mainly depends on the content, material, and geometry of the fibers considered. Even though the general influence of these factors on FRC behavior has been extensively addressed, the uncertainty of the FRC performance prediction along with the variability of the results still poses a challenging issue that needs to be solved to encourage the use of FRC for design and construction purposes. In this line, a database including the results of the flexural residual strength obtained from different experimental programs combined with the results of previous studies has been gathered and analyzed herein to obtain general correlations and trends providing additional information about the influence of the fibers in FRC behavior, these meant to serve for initial design stages (e.g., make decisions on the type and amount of fibers based on technical and economical requirements). The results are analyzed distinguishing between the fiber material, the fiber shape, the aspect ratio and tensile strength. The results presented herein may provide valuable information on the initial prediction of the residual strength of FRC to fully take advantage of the mechanical properties of the material.The authors from UPC wish to express their acknowledgment to the Ministry of Economy, Industry and Competitiveness of Spain for the financial support received under the scope of the projects BIA2016-78742-C2-1-R and PID2019-108978RB-C32.Peer ReviewedPostprint (published version

Novel compressive constitutive model for 3D printed concrete

3D concrete printing (3DCP) is emerging as a promising technology in the construction industry. From the engineering and architectural point of view, the use of 3DCP offers a great potential in terms of enhancing construction automation, more freedom of shapes and a substantial reduction of manufacturing costs associated with production and materials. Unlike traditional poured concrete, 3DCP is a layer-to-layer based manufacturing method. Such productive method makes concrete to present a layer-based structure than can lead to an anisotropic element because of the varying properties on the different spatial directions of the material. Consequently, and given the specific manufacturing method and the internal structure of 3DCP, a new approach in terms of constitutive models for design purposes is required. The objective of this is study is to develop a novel constitutive model for compression considering the influence of the anisotropy of the material. For this, an experimental program involving the characterization of 3D printed concrete specimens was conducted. The compressive strength and the modulus of elasticity was determined to obtain the stress-strain diagram on different loading directions, taking into account the influence of the layer-based structure of 3DPC. The results revealed no significant differences between spatial directions, given the great homogeneity of the 3D printed concrete in all directions. However, such approach becomes necessary so engineers and designers can fully take advantage of the material and remain on the safe side of the structural design.AGAUR-FEDER for the financial support through the project 2019PROD00066. Likewise, the authors want to acknowledge the economic and technical support provided by ACCIONA.Peer ReviewedPostprint (published version