Durability Analysis of Ultra High-Performance Fiber Reinforced Concrete Structures in Cracked Serviceability Limit State

Ultra High Performance (Fibre Reinforced) Concrete and Cementitious Composites (UHPFRCCs) have not only the potential to control the crack width but, even better, the potential ability to spread a damage state into a set of multiple tiny and tightly spaced cracks in the strain hardening regime, which would otherwise localize into a single crack. This is extremely advantageous for durability since the governing parameter is the opening of the single crack. Within the framework of the H2020 ReSHEALience project, one of the main objectives is to upgrade the concept of Ultra High Performance Concrete (UHPC) structures to Ultra High Durability Concrete (UHDC) structures, by implementing micro- and nano-scale constituents, which stimulate the autogenous self-healing capacity of concrete. From 4-point bending tests on UHDC 30 mm thick beams, it was observed a sequential cracking behaviour with evenly distributed spacing, which also resulted into a deflection and strain-hardening behaviour. In this paper, based on material identification test data, a sectional analysis of UHDC structural elements has been performed taking into account the sequential cracking behaviour and, from the sectional analysis, the member displacement behaviour was evaluated. Degradation mechanism governing laws, referring to penetration of chlorides and sulphates, have then been incorporated into the aforementioned structural design algorithms, in order to predict the long-term serviceability flexural behaviour of UHDC structures under structural service scenarios characterized by extremely aggressive conditions. The results are being validated against experimental monitoring of a real scale basin for collecting water from a geothermal power plant made with selected UHDC mixes.