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

Tube shape alterations for improved concrete pouring survivability in vascular self-healing concrete

The upscaling of self-healing mechanisms for concrete from simple laboratory experiments to full-size industrial applications remains a huge challenge. In the present work, the potential for upscaling of vascular self-healing is investigated. The vanes of the vascular system, should on one hand be strong enough to survive the rather aggressive concrete production conditions, i.e. casting and pouring, while on the other hand they should be brittle in order to break when a crack in the hardened concrete surpasses them in the hardened concrete. Until now, the search for suitable materials received most attention and often the influence of the geometry was neglected. This work the shape is altered in order to investigate its influence on the survivability of the system under real production conditions. For vascular systems, the vanes should be able to resist the high forces when concrete is poured onto it. A comparison between different shapes is made, i.e. circular, square, droplet and ellipsoidal (i.e. rugby-ball) shaped cross section. From this study it can be seen that the shape is a parameter that could help to survive the pouring process

A Probabilistic Methodology to Determine Acceptance Criteria and Failure Probabilities for the KBS-3 Ductile Cast Iron Inserts

The paper summarizes the main findings of the joint project between JRC and Swedis partners to determine failure probabilities for copper cast iron inserts for disposal of spent nuclear fuel. The paper describes the statistical test programme and it key results, how these data are used in a probabilistic analysis for canister failure. It is shown that failure probabilities are extremely low. The results of the paper can be used to derive acceptance criteria for defects, material properties and geometrical design parameters.JRC.F.4-Nuclear design safet

A Probabilistic Methodology to Determine Failure Probabilities and Acceptance Criteria for the KBS-3 Inserts under Ice-Age Load Conditions

The Swedish KBS-3 copper-cast iron canister for geological disposal is in an advanced stage. This reports deals with the cast iron insert that provides the mechanical strength of the canister and outlines an approach to assess the failure probabilities at large isostatic pressure (44 MPa) for manufactured canisters and how to derive acceptance criteria. The work includes a statistical test programme using three inserts for the tensile, compression and fracture properties. Specimens used for material characterization were also investigated by micro-structural analysis to determine the microstructure and to classify and size defects. It was found that the material scatter and low ductility was caused by many defect types, but with slag defects in the form of oxidation films as the most important one. These data were then used to compute defect distributions and as direct input to FE-calculations of KBS-3 canisters. A large number of FE-analyses were performed at the maximum design load (44 MPa) covering distributions of material parameters and geometrical features of the canisters. The computed probabilities for fracture and plastic collapse were very low even for material data with poor ductility. Two large scale isostatic compression tests of KBS-3 mock-ups to assess safety margins are also described. The failure occurred at loads above 130 MPa in both cases, indicating a safety margin of at least a factor three against the maximum design load.JRC.F.4-Nuclear design safet

Probabilistic Analysis and Material Characterisation of Canister Insert for Spent Nuclear Fuel. Summary Report

The report summarizes the results from a three-year research programme to determine material properties for ductile cast iron using a statistical test programme and the associated analyses to identify and quantify defects. This data are subsequently used in a probabilistic failure analysis of a canister loaded in isostatic pressure. The large variation in ductility was due to slag defects. The computed failure probabilities for fracture and plastic collapse are extremely low even when the material ductility is lower than the basic material requirements.JRC.F.4-Nuclear design safet

Research Progress on Numerical Models for Self-Healing Cementitious Materials

In this paper, research progress on numerical models for self-healing cementitious materials (SHCMs) is discussed. Models developed specifically for SHCMs, as well as other relevant work, are considered. A summary of current self-healing (SH) techniques is provided along with descriptions of the processes that govern their behavior. Models for mechanical self-healing, transport processes in materials with embedded healing systems, fully coupled models, and other modeling techniques used to simulate SH behavior are discussed. The mechanics models discussed include those based on continuum–damage–healing mechanics (CDHM), micromechanics, as well as models that use discrete elements and particle methods. A considerable section is devoted to the simulation of carbonation in concrete since the essential mechanisms that govern this process are applicable to SH systems that employ calcite as a healing material. A number of transport models for simulating early-age self-healing are also considered. This highlights the fact that there are currently very few papers that describe fully coupled models, although a number of approaches that couple some aspects of transport and mechanical healing behavior are discussed. This article closes with a discussion that highlights the fact that many models are presented with limited or no experimental validation