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

Reducing the Porosity and Sealing Cracks by Using Crystalline Admixture in Conventional Concrete

There is a continuous increase of quality on civil engineering materials in developed countries and parallel increase of need for new constructions in developing countries. Professional community should propose solutions for the durability that can resist in different severe environments. The most important factor that can affect concrete durability is represented by the pore distribution. Transport properties can take place through the porous network inside the cementitious composites and the aggregates interface, permitting the ingress of aggressive agents damaging concrete function intrinsically as a material and the well-functioning of the entire structure. The use of a crystalline admixture during the mixing procedure can fill the pores and capillarity of the cement composites, while in case of the appearance of the cracks, can perform as sealing agent, representing a secondary innovative benefit. Concrete structure, in this case will be more durable and there will be no need for un-planned intervention

Reducing the Porosity and Sealing Cracks by Using Crystalline Admixture in Conventional Concrete

There is a continuous increase of quality on civil engineering materials in developed countries and parallel increase of need for new constructions in developing countries. Professional community should propose solutions for the durability that can resist in different severe environments. The most important factor that can affect concrete durability is represented by the pore distribution. Transport properties can take place through the porous network inside the cementitious composites and the aggregates interface, permitting the ingress of aggressive agents damaging concrete function intrinsically as a material and the wellfunctioning of the entire structure. The use of a crystalline admixture during the mixing procedure can fill the pores and capillarity of the cement composites, while in case of the appearance of the cracks, can perform as sealing agent, representing a secondary innovative benefit. Concrete structure, in this case will be more durable and there will be no need for unplanned intervention

Reducing the Porosity and Sealing Cracks by Using Crystalline Admixture in Conventional Concrete

There is a continuous increase of quality on civil engineering materials in developed countries and parallel increase of need for new constructions in developing countries. Professional community should propose solutions for the durability that can resist in different severe environments. The most important factor that can affect concrete durability is represented by the pore distribution. Transport properties can take place through the porous network inside the cementitious composites and the aggregates interface, permitting the ingress of aggressive agents damaging concrete function intrinsically as a material and the well-functioning of the entire structure. The use of a crystalline admixture during the mixing procedure can fill the pores and capillarity of the cement composites, while in case of the appearance of the cracks, can perform as sealing agent, representing a secondary innovative benefit. Concrete structure, in this case will be more durable and there will be no need for un-planned intervention

Reducing the Porosity and Sealing Cracks by Using Crystalline Admixture in Conventional Concrete

There is a continuous increase of quality on civil engineering materials in developed countries and parallel increase of need for new constructions in developing countries. Professional community should propose solutions for the durability that can resist in different severe environments. The most important factor that can affect concrete durability is represented by the pore distribution. Transport properties can take place through the porous network inside the cementitious composites and the aggregates interface, permitting the ingress of aggressive agents damaging concrete function intrinsically as a material and the wellfunctioning of the entire structure. The use of a crystalline admixture during the mixing procedure can fill the pores and capillarity of the cement composites, while in case of the appearance of the cracks, can perform as sealing agent, representing a secondary innovative benefit. Concrete structure, in this case will be more durable and there will be no need for unplanned intervention

Influence of self-healing property of Ultra-High Performance Concrete under aggressive environment

This paper investigates the evolution of self-healing properties of ultra-high performance concrete exposed to aggressive environments. Double edge wedge splitting UHPC specimens with 0.8% crystalline admixture and 1.5% steel fibre by volume have been first pre-cracked up to a average 0.30 mm crack opening displacement (COD) obtained by two linear variable differential transformers attached to both sides of the sample surface. Then, the pre-cracked samples have been exposed to three different environments: tap water, salt water (a NaCl aqueous solution at 3.3% concentration) and geothermal water obtained from a geothermal power plant. After one month exposure, samples were carried out re-crack to know the self-healing properties. The results from ultrasonic pulse velocity tests (UPV) reveal that the samples exposed to tap water exhibit the highest rate of recovery along the exposure time, while those exposed to geothermal water show the lowest. The calculated indexes of cracking self-healing (ICS) show a 73.8% closure in tap water, 58.4% in salt water 43.9% in geothermal water. Additionally, the index of damage recovery, evaluated from UPV frequencies as well as from the stress vs. COD curves of pre-cracking and post-healing re-cracking tests on specimens, and the equivalent tensile stress also indicate a higher level of healing capable of inducing a significant recovery of mechanical properties

High performance fibre reinforced cementitious composites: Six memos for the XXI century societal and economical challenges of civil engineering

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. High Performance Fibre Reinforced Cementitious Composites, by providing tailored and multiple functionalized performance can represent an asset for the construction industry to face the challenges imposed by the needs of our continuously and fast evolving society. The paper, moving from a parallel with “Six memos from the next millennium” by Italo Calvino, the author will provide his own perspective on the current state on the topic, trying to highlight the benefits achievable through a reliable and consistent incorporation into a design and construction practice for both new and existing buildings and structures

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

Early age performance and mechanical characteristics of recycled PET fibre reinforced concrete

In this study the performance of concrete reinforced with fibres produced from waste non-biodegradable plastic, polyethylene terephthalate (PET), has been thoroughly investigated. The novelty of the study, to the authors’ knowledge, consists in the fact that fibres have been employed as directly shredded from collected waste plastic bottles, with no processing through, e.g., plastic melting and fibre spinning. Moreover, a comprehensive investigation has been herein undertaken, which ranges from the identification of the mechanical behaviour of the fibres to the assessment of their bond with the matrix and of the early age and hardened state properties of the recycled PET fibre reinforced concrete. Different types of shredded recycled PET fibres, straight and deformed, together with different fibre lengths, 30 mm and 50 mm, have been assessed, for varying percentage addition in concrete. The tensile properties and pull out characteristics of the fibres have been determined. The effects of fibres in mitigating plastic and restrained drying shrinkage cracking were then assessed and, finally, the compressive strength and the flexural performance of the fibre concrete were determined. The cracking potential of fibre-reinforced mortar thin slabs was also assessed. The use of shredded recycled PET fibres in concrete has been shown to lead to interesting improvements in performance for various fibre concrete characteristics and offers a potential alternative for this material