An overview on the research on self-healing concrete at Politecnico di Milano

Self-healing cement based materials, by controlling and repairing cracks, could prevent “permeation of driving factors for deterioration”, thus extending the structure service life, and even provide partial recovery of engineering properties relevant to the application. The author’s group has undertaken a comprehensive investigation focusing on both experimental characterization and numerical modelling of the self-healing capacity of a broad category of cementitious composites, including high performance cementitious composites reinforced with different kinds of fibres. Both autogenous healing has been considered and self-healing engineered techniques, including the use of pre-saturated natural fibres and of crystalline admixtures. Tailored methodologies have been employed to characterize the healing capacity under different exposure conditions and for different time spans, ranging up to two years. The healing capacity has been quantified by means of suitably defined “healing indices”, based on the recovery of mechanical properties correlated to the amount of crack closure, measured by means of optical microscopy. A predictive modelling approach, based on modified micro-plane model, has been formulated. The whole investigation represents a step towards the reliable and consistent incorporation of self-healing concepts and effects into a durability-based design framework for engineering applications made of or retrofitted with self- healing concrete and cementitious composites

DEPOLYMERIZABLE AND DISSIPATIVE CHEMICAL SYSTEMS: ROLE IN MATERIAL SYNTHESIS AND APPLICATIONS

Biomimetic systems which can show a functional response when treated with external stimuli are advantageous in applications such as self-healing, drug delivery, diagnostic and sensing. Depolymerizable and dissipative chemical systems are ideal tools to synthesize biomimetic systems that mimic nature. While there is abundance of synthetic chemistry tools to design depolymerizable systems, there is a lack of synthetic and formulation methodologies for developing useful materials from them. Majority of this thesis is directed towards narrowing that gap in knowledge, by utilizing depolymerizable systems to synthesize useful materials such as hydrogel and polyelectrolyte complexes for applications including self-healing, drug delivery and sensing. Minor part of this thesis involves dissipative chemical systems and it is directed towards achieving artificial systems that mimic several dynamic pathways predominant in nature which are regulated in presence of energy input

Experimental Assessment and Numerical Modeling of Self Healing Capacity of Cement Based Materials via Fracture Mechanics Concepts

The authors’ research group has undertaken for about a lustrum a comprehensive research project, focusing on both experimental characterization and numerical predictive modelling of the self-healing capacity of a broad category of cementitious composites, ranging from normal strength concrete to high performance cementitious composites reinforced with different kinds of industrial (steel) and natural fibers. In this paper reference will be made to normal strength concrete: both autogenous healing capacity has been considered and self-healing engineered through the use of crystalline admixtures. A tailored methodology has been employed to characterize the healing capacity of the investigated concrete, based on comparative evaluation of the mechanical performance measured through 3-point bending tests. Tests have been performed to pre-crack the specimens to target values of crack opening, and after scheduled conditioning times to selected exposure conditions, including water immersion and exposure to open air. The healing capacity has been quantified by means of the definition and calculation of suitable “healing indices”, based on the recovery of the mechanical properties, including load bearing capacity, stiffness, ductility, toughness etc. and correlated to the amount of crack closure also “estimated” through suitable indirect methodologies. Chemical characterization of the healing products by means of SEM has been performed to understand the different mechanisms governing the observed phenomena and also discriminate among the different amounts of recovery of the different mechanical properties. As a further step a predictive modelling approach, based on modified microplane model, has been formulated. This incorporates the self-healing effects, in particular, the delayed cement hydration, as well as the effects of cracking on the diffusivity and the opposite repairing effect of the self-healing on the micro-plane model constitutive laws. The whole experimental and numerical investigation represents a comprehensive and solid step towards the reliable and consistent incorporation of self-healing concepts and effects into a durability-based design framework for engineering applications made of or retrofitted with self-healing concrete and cementitious composites

Increasing Stretchability of Conjugated Polymers Using Metal-Ligand Coordination

Stretchable and mechanically robust materials are now becoming crucial for the development of wearable electronics. In particular, semiconducting conjugated polymers have been shown to be remarkable candidates when preparing new electronic devices as the exhibit good charge transport properties, synthetic versatility and easy tunability. In recent years, the development of these types of materials have been utilized the use of dynamic crosslinking, especially metal-ligand interactions, is a promising avenue to prepare and design stretchable materials while also enabling novel properties such as self-healing. However, in their synthesis and application, there are many challenges overcome to achieve stretchable conjugated polymers, due to the intrinsic competition between electronic and mechanical properties. The objective of the project is to develop a novel strategy towards developing intrinsically stretchable and self-healing conjugated polymers for application in stretchable electronics. This main objective will be achieved by incorporating metal coordinating moieties, namely imine side-chains, to the polymer in order to chelate to Iron(II). This dynamic coordination will allow for the polymer network to dissipate strain, thus enhancing the mechanical properties of the materials. Moreover, this will also allow for regeneration of the polymer network after being damaged through a process known as self-healing. This presentation will discuss our recent progress toward new metal-coordinating conjugated polymers, especially focusing on their design and preparation

Self-healing concepts involving fine-grained redundancy for electronic systems

The start of the digital revolution came through the metal-oxide-semiconductor field-effect transistor (MOSFET) in 1959 followed by massive integration onto a silicon die by means of constant down scaling of individual components. Digital systems for certain applications require fault-tolerance against faults caused by temporary or permanent influence. The most widely used technique is triple module redundancy (TMR) in conjunction with a majority voter, which is regarded as a passive fault mitigation strategy. Design by functional resilience has been applied to circuit structures for increased fault-tolerance and towards self-diagnostic triggered self-healing. The focus of this thesis is therefore to develop new design strategies for fault detection and mitigation within transistor, gate and cell design levels. The research described in this thesis makes three contributions. The first contribution is based on adding fine-grained transistor level redundancy to logic gates in order to accomplish stuck-at fault-tolerance. The objective is to realise maximum fault-masking for a logic gate with minimal added redundant transistors. In the case of non-maskable stuck-at faults, the gate structure generates an intrinsic indication signal that is suitable for autonomous self-healing functions. As a result, logic circuitry utilising this design is now able to differentiate between gate faults and faults occurring in inter-gate connections. This distinction between fault-types can then be used for triggering selective self-healing responses. The second contribution is a logic matrix element which applies the three core redundancy concepts of spatial- temporal- and data-redundancy. This logic structure is composed of quad-modular redundant structures and is capable of selective fault-masking and localisation depending of fault-type at the cell level, which is referred to as a spatiotemporal quadded logic cell (QLC) structure. This QLC structure has the capability of cellular self-healing. Through the combination of fault-tolerant and masking logic features the QLC is designed with a fault-behaviour that is equal to existing quadded logic designs using only 33.3% of the equivalent transistor resources. The inherent self-diagnosing feature of QLC is capable of identifying individual faulty cells and can trigger self-healing features. The final contribution is focused on the conversion of finite state machines (FSM) into memory to achieve better state transition timing, minimal memory utilisation and fault protection compared to common FSM designs. A novel implementation based on content-addressable type memory (CAM) is used to achieve this. The FSM is further enhanced by creating the design out of logic gates of the first contribution by achieving stuck-at fault resilience. Applying cross-data parity checking, the FSM becomes equipped with single bit fault detection and correction

Self-healing cement-based materials: an asset for sustainable construction industry

Worldwide increasing consciousness for sustainable use of natural resources has made “overcoming the apparent contradictory requirements of cost and performance effectiveness a challenging task” as well as a major concern. Self-healing cement-based materials, by controlling and repairing cracks, could prevent “permeation of driving factors for deterioration”, thus extending the structure service life, and even provide partial recovery of the engineering properties relevant to the application. This paper will outline the current state of art on self-healing cement-based materials and experimental methods for the assessment of the self-healing capacity. Moreover, it will also critically analyse the current hindrances which challenge the engineering community in paving the way towards the reliable and consistent incorporation of self-healing concepts and effects into a durability-based design framework for buildings and structures made of or retrofitted with self- healing concrete and cementitious composites

Autonomous self-healing structural composites with bio-inspired design

Strong and tough natural composites such as bone, silk or nacre are often built from stiff blocks bound together using thin interfacial soft layers that can also provide sacrificial bonds for self-repair. Here we show that it is possible exploit this design in order to create self-healing structural composites by using thin supramolecular polymer interfaces between ceramic blocks. We have built model brick-and-mortar structures with ceramic contents above 95 vol% that exhibit strengths of the order of MPa (three orders of magnitude higher than the interfacial polymer) and fracture energies that are two orders of magnitude higher than those of the glass bricks. More importantly, these properties can be fully recovered after fracture without using external stimuli or delivering healing agents. This approach demonstrates a very promising route towards the design of strong, ideal self-healing materials able to self-repair repeatedly without degradation or external stimuli

Designing dynamic mechanics in self-healing nanocomposite hydrogels

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2018.Cataloged from PDF version of thesis.Includes bibliographical references (pages 127-136).The functional versatility and endurable self-healing capacity of soft materials in nature is found to originate from the dynamic supramolecular scaffolds assembled via reversible interactions. To mimic this strategy, extensive efforts have been made to design polymer networks with transient crosslinks, which lays the foundation for synthetic self-healing hydrogels. Towards the development of stronger and faster self-healing hydrogels, understanding and controlling the gel network dynamics is of critical importance, since it provides design principles for key properties such as dynamic mechanics and self-healing performance. For this purpose, a universal strategy independent of exact crosslinking chemistry would be regulating the polymer material's dynamic behavior by optimal network design, yet current understanding of the relationship between network structure and macroscopic dynamic mechanics is still limited, and implementation of complex network structure has always been challenging. In this thesis, we show how the dynamic mechanical properties in a hydrogel can be controlled by rational design of polymer network structures. Using mussel-inspired reversible catechol coordination chemistry, we developed a nanocomposite hydrogel network (NP gel) with hierarchical assembly of polymer chains on iron oxide (Fe3O4) nanoparticles as network crosslinks. With NP gel as a model system, we first investigated its unique dynamic mechanics in comparison with traditional permanent and dynamic gels, and discovered a general approach to manipulate the network dynamics by controlling the crosslink structural functionality. Then we further explored the underlying relationship between polymer network structure and two key parameters in relaxation mechanics, which elucidated universal approaches for designing relaxation patterns in supramolecular transient gel network. Finally, by utilizing these design principles, we designed a hybrid gel network using two crosslinking structures with distinct relaxation timescales. By simply adjusting the ratio of two crosslinks, we can precisely tune the material's dynamic mechanics from a viscoelastic fluid to a rigid solid. Such controllability in dynamic mechanics enabled performance optimization towards mechanically rigid and fast self-healing hydrogel materials.by Qiaochu Li.Ph. D

\u27Workshops in healing\u27 for senior medical students: 5 year overview and appraisal

We report upon the design, content and feedback from an interactive, experiential series of Workshops in Healing for senior medical students. Fifty-six final year medical students enrolled in 2×3 h workshops designed around the core themes of ‘physician know thyself’ (Workshop 1) and ‘confronting suffering’ (Workshop 2). Of the 56 students who initially enrolled, 48 students completed both workshops and provided a written openended reflection of their learning experience. The study, undertaken over a consecutive 5-year period (2008–2012), employed an emergent, qualitative design using thematic analysis of the reflective comments. We found that the design and content of both workshops promoted transformative learning for these final year medical students. Students identified the following benefits: (1) the opportunity to reaffirm their commitment to their chosen career path; (2) the value of listening to other students share their stories; (3) the importance of the timing of the workshops to occur after exams; (4) the use of various mediums such as art, poetry, music and contemporary/classic literature to present concepts of suffering and healing; and (5) the creation of a safe and confidential space. Students reported that these innovative workshops gave them a renewed sense of drive and enthusiasm for their chosen career. They highlighted the importance of addressing an aspect of medicine (healing) not covered in the traditional medical curriculum. Workshops in Healing helped them to rediscover a deeper meaning to medicine and their roles as future healthcare professionals