Vascular self-healing of a reinforced concrete beams under 4-point bending

Self-healing materials are inspired on self-healing capabilities of living organisms. For plants, animals and people, the vascular system that distributes nutrients to all parts of the organism is also key for the self-healing capability. In a concrete element, a self-healing approach with an incorporated vascular system possess advantages towards repeatable self-healing and controlled placement of the self-healing system in the areas of interest. This study presents such a vascular system, which is designed to be accessible from outside of the concrete beam. Both clay and inorganic phosphate cement are compared as materials for the vanes of this system. The specimen contain steel reinforcement and are tested by means of 4-point bending, in order to obtain realistic conditions. Ease of construction and placement are discussed. From the experiments it can be seen that repeatable selfhealing is possible, that the system is able to heal multiple cracks at the same time and that cracks can be sealed and mechanical properties restored

Ideal material properties for capsules or vascular sustem used in cementitious self-healing materials

Self-healing in cementitious materials, i.e. concrete, has a huge potential towards reducing maintenance and repair costs and increasing the service life of concrete structures. The biggest advantage of self-healing concrete is that small cracks, who provide access to hazardous gasses and liquids, are healed and structural degradation is prevented. Several techniques are trending in the field of self-healing concrete, self-healing using bacteria, self-healing using a vascular system and self-healing using capsules. Focusing on the two latter, an encapsulation material is needed. This paper describes the ideal properties of such an encapsulation material, taking into account as many steps of the life-cycle of the self-healing concrete, i.e. from production until the end of the structure. Such an ideal encapsulation material should be resistant through time to the healing-agent as well as to the cementitious environment. The ideal material should be brittle enough to rupture upon cracking of the (aged) concrete on one hand, and on the other it should be strong enough to survive the concrete mixing and casting process. The properties are not always to be combined by one and the same material, combinations of materials who take up different requirements are possible. In current research glass is most often used as encapsulation material. It’s a brittle material which is able to contain the healing agent, but it also suffers from a slow chemical interaction with the alkali-environment, and a very low survival rate when implemented in realistic industrial concrete casting processes. The goal of this study is to investigate the wanted versus the needed properties in order to select other materials than glass or to select other materials to combine with glass

Experimental and numerical study of the energy absorption capacity of pultruded composite tubes

A numerical and experimental investigation was carried out in order to evaluate the response of composite tubes, made of poly-vinylester or polyester matrix reinforced unidirectionally with glass fibers, under quasistatic loading. The influence of triggering in failure and energy absorption was investigated. Also a series of finite element models was created using LS-DYNA3D and compared with experimental results. The correlation between simulations and experiments was relatively satisfactory and from the results of the study the energy absorbing suitability of each tube was evaluated. Results would provide more data that are needed for designing effective energy absorption mechanisms subjected under high speed loads

Determination of strength and debonding energy of a glass-concrete interface for encapsulation-based self-healing concrete

This paper presents a combined experimental-numerical analysis to assess the strength and fracture toughness of a glass-concrete interface. This interface is present in encapsulation-based self-healing concrete. There is absence of published results of these two properties, despite their important role in the correct working of this self-healing strategy. Two setups are used: uniaxial tensile tests to assess the bonding strength and four point bending tests to get the interfacial energy. The complementary numerical models for each setup are conducted using the finite element method. Two approaches are used: cohesive zone model to study the interface strength and the virtual crack closure technique to analyze the interfacial toughness. The models are validated and used to verify the experimental interpretations. It is found that a glass-concrete interface can develop a maximum strength of approximately 1 N/mm^2 with fracture energy of 0.011 J/m^2

Comparison of the crushing performance of hollow and foam-filled small-scale composite tubes with different geometrical shapes for use in sacrificial cladding structures

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