Effects of Autogenous and Stimulated Self-Healing on Durability and Mechanical Performance of UHPFRC: Validation of Tailored Test Method through Multi-Performance Healing-Induced Recovery Indices

Abstract

Chloride diffusion and penetration, and consequently chloride-induced corrosion of reinforcement, are among the most common mechanisms of deterioration of concrete structures, and, as such, the most widely and deeply investigated as well. The benefits of using Ultra-High Performance (Fiber-Reinforced) Concrete—UHP(FR)C to extend the service life of concrete structures in “chloride attack” scenarios have been addressed, mainly focusing on higher “intrinsic” durability of the aforementioned category of materials due to their compact microstructure. Scant, if nil, information exists on the chloride diffusion and penetration resistance of UHPC in the cracked state, which would be of the utmost importance, also considering the peculiar (tensile) behavior of the material and its high inborn autogenous healing capacity. On the other hand, studies aimed at quantifying the delay in chloride penetration promoted by self-healing, both autogenous and autonomous, of cracked (ordinary) concrete have started being promoted, further highlighting the need to investigate the multidirectional features of the phenomenon, in the direction both parallel and orthogonal to cracks. In this paper, a tailored experimental methodology is presented and validated to measure, with reference to its multidirectional features, the chloride penetration in cracked UHPC and the effects on it of self-healing, both autogenous and stimulated via crystalline admixtures. The methodology is based on micro-core drilling in different positions and at different depths of UHPC disks cracked in splitting and submitted to different exposure/healing times in a 33g/L NaCl aqueous solution. Its validation is completed through comparison with visual image analysis of crack sealing on the same specimens as well as with the assessment of crack sealing and of mechanical and permeability healing-induced recovery performed, as previously validated by the authors, on companion specimens.

A review of the efficiency of self-healing concrete technologies for durable and sustainable concrete under realistic conditions

“…The higher the chloride content, the faster and better the crack healing with CA occurred. More recently, Cuenca et al [219] studied the effect of autogenous healing and CA as a healing agent on the chloride ingress of cracked ultra-high performance fibre-reinforced concrete (UHPFRC). Cracks with a width of 100 ± 50 μm were generated, and the cracked samples were immersed in 3% NaCl solution for 1, 3, 6 and 12 months.…”

A holistic life cycle design approach to enhance the sustainability of concrete structures

“…56 This is a quite severe assumption and, however, it should be noted that in the case of UHPC, as an advantage in comparison to other materials, the tendency to have narrower crack widths can potentially delay the corrosion process. Furthermore, it is worth remarking that recent studies 21,57,58 have demonstrated the delay in terms of chlorides penetration due to the autogenous self-healing properties, also favored by the presence of crystalline admixture even for quite high values of initial crack openings (up to 0.5 mm). The same self-healing capacity is able to compensate for early age cracking, for example, due to restrained shrinkage.…”

Performance evolution and tensile behaviour of long-term exposed UHPC under sustained load, aggressive environments and autogenous healing

“…A similar phenomenon was observed for chloride solution at two months. The chloride binding capacity of the cement might have fostered the sealing process [22]. Upon longer exposure periods, the differences among the environments are negligible, and only at twelve months a more pronounced recovery was observed for specimens in tap water.…”