Polyolefin Fibres for the Reinforcement of Concrete

Given that concrete has limited tensile strength, it has been necessary to combine its properties with the use of steel bars. This resulted in the arrival of reinforced concrete which was the main solution used in structures in the last century. Partial or even full substitution of steel bars for fibres would not only allow the cost of a structure to be reduced but also provide certain improved properties. Modern fibre‐reinforced concrete (FRC) now permits reduction or substitution of steel bars that has given rise to the commonly named structural FRC. Advances in the plastic industry during the last three decades have allowed the production of macro‐polymer fibres as an alternative to steel fibres due to their chemical stability and lower weights for analogous residual strengths. After 30 years of research and practice, polyolefin‐based macro‐fibres have offered additional advantages such as safe handling, low pump wear and reduction in weight when transported and stored. This chapter provides an overview of the properties and structural capacities of polyolefin fibre‐reinforced concrete (PFRC). Furthermore, the respective codes and test methods are examined. Moreover, the results obtained for structural design and the mechanical properties, found both in the literature and in practice, are supplied and discussed

Sustainability evaluation of the concrete structures

Sustainability is a new and settled concept in advanced societies, even though the term is sometimes inappropriately used, which may represents a threat. For this reason it is suitable to supply methods of measuring sustainability. Given that the sustainability concept involves distinct requirements and criteria, it seems reasonable to use multi-criteria methods in the decision making process. This work shows a brief review of such methods applied to concrete structures. The MIVES method is applied in this work for assessing the sustainability of the concrete structures. Three examples are proposed to show the capacity of the method. One of them is based on the general application of the Spanish Structural Code for Concrete Structures (EHE-08), and the other two assess the sustainability of reinforced concrete columns by adopting distinct type of concrete and building procedures.Postprint (published version

Importancia de las clases de laboratorio en la motivación de los alumnos de la asignatura Materiales Construcción

Durante el curso 2020/2021 se han retomado las clases de laboratorio de la asignatura de Materiales de Construcción I del grado de Ingeniería Civil y Territorial de la ETSI de Caminos, Canales y Puertos de la Universidad Politécnica de Madrid. Estas clases, de carácter voluntario, se han impartido en los tres grupos de la asignatura. Los resultados de la experiencia han sido contrastados con los datos del curso 2018/2019, debido a la excepcionalidad del curso 2019/2020, afectado por la pandemia del COVID 19. Además, se ha realizado una encuesta voluntaria a los participantes de las clases de laboratorio para conocer su motivación para asistir a estas clases y sus impresiones sobre ellas. El 70 % de los estudiantes matriculados en la asignatura durante el curso 2020/2021 han asistido voluntariamente a las clases de laboratorio y realizado los trabajos exigidos con la intención de mejorar la nota de la asignatura. Sin embargo, durante el desarrollo de las clases, su interés aumentó, lo que se ha traducido en el aumento de la participación de los estudiantes en la modalidad de evaluación continua de la asignatura, disminuyendo, igualmente, el abandono de esta modalidad durante este curso con relación al curso 2018/2019

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

Modelling of corrosion-induced cover cracking in reinforced concrete by an embedded cohesive crack finite element

Corrosion of a reinforcement bar leads to expansive pressure on the surrounding concrete that provokes internal cracking and, eventually, spalling and delamination. Here, an embedded cohesive crack 2D finite element is applied for simulating the cracking process. In addition, four simplified analytical models are introduced for comparative purposes. Under some assumptions about rust properties, corrosion rate, and particularly, the accommodation of oxide products within the open cracks generated in the process, the proposed FE model is able to estimate time to surface cracking quite accurately. Moreover, emerging cracking patterns are in reasonably good agreement with expectations. As a practical case, a prototype application of the model to an actual bridge deck is reported

Implementación de Laboratorios Virtuales aplicados a los Materiales de Construcción para la resolución de cuestionarios en Moodle

Durante el curso 2022/23 se ha implementado un Laboratorio Virtual, utilizando la plataforma Moodle, para la resolución de un cuestionario asociado a las clases de laboratorio de la asignatura Materiales de Construcción de grado de Ingeniería Civil. Dicho recurso, reproduce los experimentos realizados, de tal forma que los estudiantes tienen que volver a manipular virtualmente los equipos empleados en el laboratorio para obtener los datos necesarios para resolver el cuestionario propuesto. Los resultados obtenidos de esta experiencia han sido muy positivos. El 100 % de los estudiantes superaron el cuestionario, siendo la nota media de 9,23. Además, se realizó una encuesta de satisfacción donde más del 90 % de participantes opina que el Laboratorio Virtual es un recurso muy didáctico y recomienda su implementación en futuros cursos

Ballistic performance of nanocrystalline and nanotwinned ultrafine crystal steel

Because of their remarkable mechanical properties, nanocrystalline metals have been the focus of much research in recent years. Refining their grain size to the nanometer range (<100 nm) effectively reduces their dislocation mobility, thus achieving very high yield strength and surface hardness—as predicted by the Hall–Petch relation—as well as higher strain-rate sensitivity. Recent works have additionally suggested that nanocrystalline metals exhibit an even higher compressive strength under shock loading. However, the increase in strength of these materials is generally accompanied by an important reduction in ductility. As an alternative, efforts have been focused on ultrafine crystals, i.e. polycrystals with a grain size in the range of 500 nm to 1 μm, in which “growth twins” (twins introduced inside the grain before deformation) act as barriers against dislocation movement, thus increasing the strength in a similar way as nanocrystals but without significant loss of ductility. Due to their outstanding mechanical properties, both nanocrystalline and nanotwinned ultrafine crystalline steels appear to be relevant candidates for ballistic protection. The aim of the present work is to compare their ballistic performance against coarse-grained steel, as well as to identify the effect of the hybridization with a carbon fiber–epoxy composite layer. Hybridization is proposed as a way to improve the nanocrystalline brittle properties in a similar way as is done with ceramics in other protection systems. The experimental campaign is finally complemented by numerical simulations to help identify some of the intrinsic deformation mechanisms not observable experimentally. As a conclusion, nanocrystalline and nanotwinned ultrafine crystals show a lower energy absorption than coarse-grained steel under ballistic loading, but under equal impact conditions with no penetration, deformation in the impact direction is smaller by nearly 40%. This a priori surprising difference in the energy absorption is rationalized by the more important local contribution of the deviatoric stress vs. volumetric stress under impact than under uniaxial deformation. Ultimately, the deformation advantage could be exploited in the future for personal protection systems where a small deformation under impact is of key importance

High overlap between traditional ecological knowledge and forest conservation found in the Bolivian Amazon

Unidad de excelencia María de Maeztu MdM-2015-0552Altres ajuts: FBBVA research grant (BIOCON_06_106-07)It has been suggested that traditional ecological knowledge (TEK) may play a key role in forest conservation. However, empirical studies assessing to what extent TEK is associated with forest conservation compared with other variables are rare. Furthermore, to our knowledge, the spatial overlap of TEK and forest conservation has not been evaluated at fine scales. In this paper, we address both issues through a case study with Tsimane' Amerindians in the Bolivian Amazon. We sampled 624 households across 59 villages to estimate TEK and used remote sensing data to assess forest conservation. We ran statistical and spatial analyses to evaluate whether TEK was associated and spatially overlapped with forest conservation at the village level. We find that Tsimane' TEK is significantly and positively associated with forest conservation although acculturation variables bear stronger and negative associations with forest conservation. We also find a very significant spatial overlap between levels of Tsimane' TEK and forest conservation. We discuss the potential reasons underpinning our results, which provide insights that may be useful for informing policies in the realms of development, conservation, and climate. We posit that the protection of indigenous cultural systems is vital and urgent to create more effective policies in such realms

Simulación de la fractura del hormigón en modo mixto

Este trabajo presenta un procedimiento de cálculo numérico para simular la fractura de materiales cuasifrágiles bajo tensiones de tracción y tensiones tangenciales (modo mixto I y II). Predice la trayectoria de la grieta o grietas. El modelo de rotura se basa en las hipótesis del modelo de la fisura cohesiva discreta,desarrollado para la rotura bajo solicitaciones de tracción (modo I). Establece el crecimiento de la grieta mediante la definición de una superficie de rotura similar a la superficie de plastificacón en plasticidad clásica y emplea la formulación de la plasticidad computacional no asociada. El modelo se ha incorporado a un código de elementos finitos comercial y se ha contrastado experimentalmente. Se presentan las predicciones de los ensayos de fractura en modo mixto de vigas de hormigón de varios tamaños desarrollados por los autores y de los ensayos desarrollados por Arrea e Ingraffea. Además se han simulado los resultados experimentales de una nueva geometría de ensayos de fractura en modo mixto: probetas compactas entalladas solicitadas a compresión asimétrica. En todos los casos se ha obtenido un buen ajuste y una adecuada convergencia numérica.Peer Reviewe