- Parte de libroAcceso AbiertoMechanical Response of High Strength Fibre Reinforced Concrete Under Extreme Loads(Springer, Cham, 2021)High Strength Fibre Reinforced Concrete (HSFRC) presents great advantages when compared with conventional concrete under static loads and thus, it constitutes a promising material to withstand extreme loads. An experimental and numerical research carried out with the objective of developing design criteria for HSFRC use in protective structures construction is presented. The mechanical behaviour of HSFRC elements under extreme loads is experimentally and numerically analysed. Numerical models represent useful tools for the design of this type of HSFRC applications but they should be carefully calibrated and validated with experimental results. HSFRC prisms and slabs including different types of hooked-end steel fibres are tested under static, blast and impact loads. Material models at the meso and the macro scale are developed, they are calibrated with characterization tests and validated with experimental results. Experimental results are analysed with the aid of numerical models showing the effect of fibre type and content under extreme load. Numerical models are able to reproduce the blast and impact tests results and give additionally information about the local and structural response under impulsive loads that could be valuable for the design of protective structures.
- Parte de libroAcceso AbiertoEffects of Fibres on the Flexural Behaviour of Sound and Damaged RC Beams(Springer, Cham, 2021)The incorporation of fibres in Reinforced Concrete (RC) beams controls the width and evolution of cracks leading to positive effects on the durability of the element. The study of damage processes in concrete and their effects on the residual properties represents a key point related to the service life of RC structures. The contribution of fibres on the bending behaviour of sound and damaged RC beams was investigated. In order to use alkali silica reaction as a damaging tool, RC beams with and without fibres and reactive aggregates were subjected to service loading conditions during eight months in an environment with high humidity. The evolution of deformations and the distribution and propagation of cracks were recorded. As reference, similar RC beams without reactive aggregates were also evaluated. After the treatment, all RC beams were loaded up to failure. The free expansion, the compressive strength and the bending residual capacity of plain and fibre concrete were measured on companion specimens for material characterization. The effect of both fibres and alkali silica reaction on bearing capacity and ductility of RC beams were analysed. Results showed that alkali silica reaction damage provokes a significant reduction of RC beam ductility, while the flexural strength is preserved.
- Parte de libroAcceso AbiertoVolumetric deformations at early age on portland cement pastes with the addition of illitic calcined clay(Springer, Singapore, 2020)With the aim of reducing the environmental impact associated with cement production, during the last decade, different percentages of clinkers have been replaced in cement by supplementary cementitious materials (SCMs). When new SCMs are incorporated in concrete, it is necessary to evaluate, not only the mechanical properties (as strength and stiffness) and the durability but also the deformations that can generate cracking and decrease the service life of the structures. This paper is focused on the study of volumetric changes at the early ages of pastes made with blended cements with the addition of illitic calcined clays from the Buenos Aires province, Argentina. The objective of this work is to present preliminary studies on the effect of illitic calcined clays on the autogenous and chemical shrinkage of pastes. The studies were made on pastes (water/cementitious material ratio equal to 0.275) using a Portland cement type II/A-L, with the incorporation of different percentages (10%, 20% and 30%) of illitic calcined clays. A device for direct deformation measurement was used to register linear dimensional changes; the general guidelines of ASTM C 1608 were applied for the determination of chemical and autogenous shrinkage. The volumetric changes measured with direct device are the sum of the chemical and autogenous shrinkage accompanied with the expansion due to the heat released during hydration. It was found that pastes incorporating calcined clays had early deformations similar to or lower than reference paste without clay.
- Parte de libroEmbargadoImpact Response of Different Classes of Fibre Reinforced Concrete(2021)The use of fibre reinforced concrete in structural elements exposed to impacts or different types of extreme loading represents one of the main fields of application of this high-performance material. Nevertheless, there is not a general consensus about a test for impact characterization of fibre concretes and, specifically a procedure to evaluate the contribution of fibres after cracking. It is well known that fibres control the evolution of cracks, improving the durability of concrete elements. Nowadays there are many structural fibres available; one of the greatest advantages to enhance the use of different fibres is the introduction of FRC classes in the fib Model Code 2010. However, there are not references about the relationship between the residual capacity measured in static tests (i.e. EN 14651) and the impact response. A drop weight impact test method is proposed to evaluate the contribution of different fibres considering both the cracking resistance and the behaviour in cracked state. Results of FRC belonging to different classes, incorporating different contents of steel, glass and polymer macrofibres are presented and compared. The effect of the residual capacity measured on standard bending tests on the impact resistance is discussed.
- Parte de libroAcceso AbiertoUso de macrofibras sintéticas en hormigón(2020)El hormigón representa uno de los materiales más utilizados por el ser humano en todo el mundo. Entre los materiales que emplea la ingeniería civil se destaca por varias cualidades, es capaz de resistir la acción del agua sin un serio deterioro y permite moldear elementos estructurales con gran variedad de formas y tamaños; no menos importante es que representa el material más económico y rápidamente disponible en las obras y que comparado con otros materiales requiere menores insumos de energía, y finalmente puede incorporar grandes cantidades de desperdicios o subproductos, lo que considerando aspectos ecológicos, lo hará cada vez más atractivo en el futuro. Sin embargo, el hormigón que es un material frágil, o si se quiere cuasifrágil, se caracteriza por contener microfisuras y en ocasiones fisuras en su interior, lo que constituye un aspecto determinante de la respuesta de los elementos estructurales. Las fisuras se producen no sólo por acción de las cargas, sino que el mismo desarrollo del proceso de hidratación del cemento genera cambios de volumen que se intensifican con el secado (contracción) o los saltos térmicos pueden dar lugar a la aparición de micro o macrofisuras ante las restricciones externas. A la vez la exposición a altas temperaturas o el desarrollo de reacciones deletéreas pueden generar niveles de fisuración aún mayores. Las micro y macrofisuras preexistentes poseen una incidencia directa en el mecanismo de rotura del material. No menos importante es que tales fisuras adquieren un rol determinante sobre la durabilidad de las estructuras de hormigón, tanto en elementos simples como armados.