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 33 g/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.
Highlights
IntroductionSelf-healing concretes and self-healing technologies have nowadays reached quite a remarkable scientific maturity and technological readiness level and can surely represent a breakthrough innovation in the concrete construction industry and market to design and build more durable and longer-lasting structures and infrastructures
Self-healing concretes and self-healing technologies have nowadays reached quite a remarkable scientific maturity and technological readiness level and can surely represent a breakthrough innovation in the concrete construction industry and market to design and build more durable and longer-lasting structures and infrastructures.Though their application is somewhat scattered, most often driven, meritoriously, by university–industry partnerships owners and/or investigators of each single technology, an agreed upon framework is so far lacking, mainly with reference to standardized test methodologies which should enable designers, contractors, and end-users to quantitatively assess the efficiency of a particular technology with reference to the performance demand of the intended application
After one-month exposure, in the UHPC without crystalline admixture, an immediate quite strong penetration of the chlorides throughout the crack depth is evident, with chloride content holding almost constant at 0.1% from 10 mm inward
Summary
Self-healing concretes and self-healing technologies have nowadays reached quite a remarkable scientific maturity and technological readiness level and can surely represent a breakthrough innovation in the concrete construction industry and market to design and build more durable and longer-lasting structures and infrastructures. Though their application is somewhat scattered, most often driven, meritoriously, by university–industry partnerships owners and/or investigators of each single technology, an agreed upon framework is so far lacking, mainly with reference to standardized test methodologies which should enable designers, contractors, and end-users to quantitatively assess the efficiency of a particular technology with reference to the performance demand of the intended application. The same happens, e.g., for the durability of ultra-high-performance (fiber-reinforced) concrete (UHPC/UHPFRC) which, having been in most cases inferred, from an “educated guess”, as an obvious consequence of the high compactness and extremely low porosity of the material, has more rarely been demonstrated in wider real structural service scenarios, which, as a matter of fact, do include cracked state of the material [6]
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