M&S highlight: Schlangen and van Mier (1992), Simple lattice model for numerical simulation of fracture of concrete materials and structures

This commentary is part of our celebration of 75 years of RILEM, highlighting Materials and Structures most highly influential and cited publications.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen

Advanced tensile testing as a new tool to quantify properties of food

Mechanical properties of food products are regularly analysed by tensile tests. The aim of this study was to demonstrate the potential of using advanced tensile testing techniques to better understand the mechanical properties of anisotropic food products, such as meat analogues and certain dairy products. The effects of various tensile testing parameters, including tensile gauge length and deformation rate, on the interpretation of mechanical properties of meat analogues was studied. Additionally, digital image correlation, an image analysis technique, was used for true distance recording and analysis of fracturing behaviour of the products. An isotropic product was prepared from solely soy protein isolate, and an anisotropic product was prepared from soy protein isolate and pectin using the shear cell technology. The tensile properties of the products were studied with four different moulds with varying gauge lengths of 17.5, 15, 11.5, and 8.5 mm, and at three deformation rates of 46.2, 23.1, and 11.6 mm/min. A smaller gauge length and slower deformation rate improved visualization and interpretation of the multi-stage descending branch in force – distance curves of anisotropic products. Additionally, tensile parameters, specifically toughness, proved to be more accurate at small gauge length and slow deformation rate, because overestimation due to rapid crack propagation was prevented. True distance data obtained with digital image correlation further improved the interpretation of the fracturing behaviour of the products. Inhomogeneous strain distribution in anisotropic products was shown with digital image correlation, in contrast to the homogeneous strain distribution observed in isotropic products. Furthermore, the Poisson's ratio, obtained through digital image correlation, explained inherent differences in structure and plasticity between isotropic and anisotropic meat analogues. This study shows the importance of careful selection of testing parameters and techniques. Moreover, it advises the use of digital image correlation for better measurement of fracture mechanics and strain distribution.Materials and Environmen

Novel approach to make concrete structures self-healing using porous network concrete

Many researchers proposed self healing mechanism using hollow fibres and or microcapsule containing a modifying agent dispersed in the concrete to prolong its service life and make it more durable. A novel self healing concrete concept is proposed in this paper by using porous network concrete components. They are placed at the surface or internally in the concrete structure. The porous network is considered as media to transport healing agent to a crack or cracks in the concrete structures. In order to test the concepts, we designed two concrete specimens. The proposed self healing mechanism was tested by applying a uniaxial direct tension load in a cylinder and a three points bending load for a beam. After the crack was formed, manual injection through the porous network was carried out until healing agent reached the fracture surface. Experimental results showed that the crack was healed and mechanical recovery took place.Structural EngineeringCivil Engineering and Geoscience

A three-dimensional numerical research on probability characteristics of a crack hitting capsules for self-healing concrete

In self-healing concrete, healing agents (including the bacteria and nutrients for the bacteria) are often sealed in capsules to survive the mixing of concrete. When the crack occurs, these capsules can be damaged, the healing agents can be released and the chemical actions can be activated. This research mainly focuses on the probability characteristics of a crack hitting the capsules. To conduct the research, the meso-scale models for two kinds of capsules, i.e., spherical and tubular capsules, are established. Statistical analysis is conducted to estimate the hitting probability and the number of capsules damaged by a crack based on the meso-scale models. With the numerical method proposed in this research, it is possible to estimate the efficiency of the self-healing system, as well as optimize the proper usage of the capsules. An application of this numerical method in a bacterial self-healing concrete based on Liapor (a light weight aggregate) is also included.Structural EngineeringCivil Engineering and Geoscience

Autogeneous healing and chloride ingress in cracked concrete

An experimental study of the influence of autogeneous healing on chloride ingress in cracked concrete is presented. In the study, two concrete mixtures (a Portland cement mix and a blast furnace slag mix), two healing regimes (submerged and fog room regime), two cracking ages (14 and 28 days), and multiple crack widths are used as parameters. An adapted Rapid Chloride Migration testing procedure is used after the healing period to assess the effectiveness of healing. It was found that small bending-type (i.e. tapered) cracks can heal fully, and larger cracks partially under tested conditions. The obtained results provide a good starting point for further study of the influence of autogeneous or self-healing on concrete durabilityStructural EngineeringCivil Engineering and Geoscience

Self-healing asphalt for road pavements

This paper presents a unique self-healing system for asphalt pavement which employs compartmented calcium-alginate fibres encapsulating an asphalt binder healing agent (rejuvenator). This system presents a novel method of incorporating rejuvenators into asphalt pavement mixtures. The compartmented fibres are used to distribute the rejuvenator throughout the pavement mixture, thereby overcoming some of the problems associated with alternate asphalt pavement healing methods, i.e., spherical capsules and hollow fibres. The healing system performance, when embedded in Porous Asphalt (PA) mix was tested by employing: (i) Indirect Tensile Stiffness and Strength test (ii) 4 Point Bending Fatigue test. The Semi Circular Bend (SCB) test was adopted to study crack propagation and its closure (healing) in an asphalt mix. The findings demonstrate that compartmented alginate fibres have capacity to survive asphalt mixing and compaction process. The fibres can efficiently repair damage (close the cracks), increase asphalt mix stiffness and strength. However, when the asphalt mix is subjected to fatigue loading the system does not significantly improve healing properties of the asphalt mix. Nevertheless, the findings indicate that, with further enhancement, compartmented calcium alginate fibres may present a promising new approach for the development of self-healing asphalt pavement systems.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Materials and Environmen

Self-healing technology for asphalt pavements

Materials and EnvironmentMicrola

Self Healing of Concrete Structures: Novel Approach Using Porous Network Concrete

Structural EngineeringCivil Engineering and Geoscience

Use of phase change materials (PCMs) to mitigate early age thermal cracking in concrete: Theoretical considerations

Phase change materials (PCMs) have found their use in concrete technology for increasing energy efficiency of building envelopes. In recent years, however, new potential applications for PCMs in concrete have been suggested, for example for reducing freeze-thaw damage and melting of ice forming on top of concrete pavements. A recent application of PCMs in concrete technology is their use for mitigating earlyage cracking in hydrating concrete. The focus on this paper is therefore on theoretical considerations related to this particular application of phase change materials. In particular, the focus is on simulating microencapsulated PCMs, which show very promising experimental results. Numerical models are developed for 2 scales: the meso-scale, in which the PCM microcapsules are simulated as discrete inclusions in the cementitious matrix; and the macro-scale, where the effect of PCM microcapsule addition is considered in a smeared way. On the meso-scale, the effect of PCM volume percentage, their phase change temperature, and latent heat of fusion on simulated adiabatic heat evolution are assessed. On the macro-scale, influence of these parameters on the temperature evolution in semi-adiabatic (field) conditions and tensile stress development are simulated. The outcomes of this study provide valuable insights related to the influence of PCM microcapsule parameters on the behaviour of cementitious materials, enabling tailoring composites for different environmental conditions.Materials and Environmen

Modelling the influence of cracking and healing on modal properties of concrete beams

Concrete structures are commonly cracked when in service. To overcome issues arising from cracking, self-healing concrete is being developed. Together with the development of the material, techniques to verify and quantify self-healing are being developed. A number of destructive techniques have been used in the past. It would be beneficial to use non-destructive testing for continuous monitoring of self-healing. It is well known that cracking causes changes in natural frequencies of structural elements. A change in natural frequencies can be, therefore, used as an indication of damage. Consequently, the recovery of natural frequencies can be used as an indication of healing. In this work, a model which enables calculation of mode shapes and natural frequencies is presented. First, it is shown that the proposed 2D model can reasonably mimic modal behavior of thin structures under different boundary conditions [6]. It is then used to assess the influence of cracking and healing on the change of modal properties of concrete beams. Finally, based on the modelling results, conclusions are drawn.Structural EngineeringCivil Engineering and Geoscience