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

Abstract

Abstract: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.

A Review on Cementitious Self-Healing and the Potential of Phase-Field Methods for Modeling Crack-Closing and Fracture Recovery

“…However, when the chemical kinetics is slow enough, the precipitation process becomes chemically determined [ 218 ]. A review of existing models for self-healing that are based on chemical reactions show that these models are employing a reaction-diffusion process to describe the self-healing evolution [ 12 , 31 , 32 , 33 , 34 ]. These models focus on two processes: (1) the diffusion mechanism where dissolved ions (e.g., calcium ions) are transferred from the concrete interior toward the surface of the crack, and (2) the precipitation of mineral ions reacting with, for example, carbon dioxide or carbonate ions to form calcium carbonate.…”

“…These models focus on two processes: (1) the diffusion mechanism where dissolved ions (e.g., calcium ions) are transferred from the concrete interior toward the surface of the crack, and (2) the precipitation of mineral ions reacting with, for example, carbon dioxide or carbonate ions to form calcium carbonate. They mostly consider how the chemical environment affects the formation of self-healing products and how to achieve agreement with experimental results [ 12 , 32 , 33 , 34 , 35 , 36 , 41 , 45 , 219 ].…”

“…From a modeling point of view, the presently existing numerical approaches can be grouped according to the nature of their particular self-healing mechanism into (1) chemical reaction-based models [12,[31][32][33][34], for predicting carbonation, hydration, polymerization and precipitation phenomena;…”

“…From a modeling point of view, the presently existing numerical approaches can be grouped according to the nature of their particular self-healing mechanism into (1) chemical reaction-based models [ 12 , 31 , 32 , 33 , 34 ], for predicting carbonation, hydration, polymerization and precipitation phenomena; (2) transport phenomena-based models [ 35 , 36 ], in which the phases affecting the healing processes are transported through the concrete pore-structure network; and (3) fracture-based models, smeared [ 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 ] and discrete [ 47 , 48 , 49 , 50 , 51 , 52 , 53 ] crack approaches for predicting strength recoveries of self-healing systems.…”

Enhancement in the Performance of Concrete using Crystalline

“…Crystalline materials consist of proprietary active chemicals that increase the density of calcium silicate hydrate (CHS) and/or generate pore-blocking deposits that reduce permeability up to 70% and enhance durability characteristics, which is why it is most suitable than others [7][8][9][10][11][12]. It penetrates deep inside the concrete, sealing/fixing the pores, capillary/fine tracts and shrinkage cracks [13][14][15][16][17][18]. The Fluid and chemical resistance of crystalline systems settles on it an ideal choice in areas subject to extreme/ outrageous chemical conditions [10,12].…”