The durability and self-healing performance of ultra-high performance concrete in aggressive chloride-rich environments

Abstract

Ultra-High performance concrete (UHPC) with improved functional performance characteristics is developed for structures in extremely aggressive exposure conditions to improve their durability performance in extreme environments. UHPC can be used and exploited in aggressive costal environment in XS exposure conditions in order to enhance to service life of structures throughout their life cycle. In this study, the durability performance of self-healing ultra-high performance concrete based on crystalline admixtures and three different types of nano-additives was assessed with respect to different environmental exposure conditions. The UHPC durability performance was enhanced through the exploitation of crystalline admixtures which promote self-healing and nano-additives. Three different types of nano-additives were assessed in the research: Nano Alumina, Nano Cellulose and Nano Cellulose Fibres. The different UHDC mixes developed were exposed to different environmental conditions including water and a chloride-rich environment in order to assess the performance of the material over time. Furthermore, both cracked and un-cracked UHPC samples were assessed to determine the self-healing capabilities of the concrete. The fresh properties of the self-healing fibre-reinforced UHPC were determined with respect to empirical tests for self-compacting concrete. The mechanical properties including the compressive and flexural strength and the Ultrasonic Pulse Velocity were defined over the curing period. Durability properties of the UHPC were determined over time, with respect to direct and indirect durability tests, including chloride-ion penetration, chloride migration, water sorptivity, water permeability, Vacuum saturation porosity and concrete resistivity. The crack-healing capability of cracked UHPC was assessed through microscopy. Results confirmed that all the nano-additives used in the production of UHPC, led to an enhancement of both the mechanical and durability performance over time. All the UHPC samples indicated a very good performance when cured in aggressive environment, with even an improvement in durability performance for UHPC mixes exposed to a chloride-rich environment. The research confirmed the improved performance of UHPC based on crystalline admixture and nano-additives, mechanical and durability properties as well as their ability to self-heal in a chloride rich environment.