Investigation of the durability and self-healing properties of ultra-high performance concrete based on crystalline admixtures and nano-additives, exposed to a chloride-rich aggressive environment

Abstract

The objective of the study is to assess the durability performance of self-healing ultra-high performance concrete based on crystalline admixtures and three different types of nano-additives when exposed to different environmental conditions. The durability performance of UHPC is enhanced through the exploitation of crystalline admixtures which promote self-healing and nano-additives. UHPC is exploited in aggressive costal environment in XS exposure conditions in order to enhance to service life of structures throughout their life cycle. UHDC with self healing properties, was produced with different constituents including crystalline admixture and three different types of nano additives: Nano Alumina, Nano Cellulose and Nano Cellulose Fibres. The different UHDC mixes developed were exposed to different environments namely water and a chloride-rich environment in order to assess the performance of the material over time. Cracked and un-cracked UHDC samples were assessed to determine the self-healing capabilities of the concrete. The fresh properties of the self-healing fibre-reinforced UHDC were determined with respect to empirical tests. The mechanical properties including the compressive and flexural strength and the UPV were defined over the curing period. Durability properties of the UHDC were determined over time, with respect to direct and indirect durability tests, including chloride penetration, chloride migration, sorption, water permeability, Vacuum saturation porosity and resistivity. The crack-healing capability of cracked UHPC was assessed through microscopy. Results confirmed that all the nano-additives used in the production of UHDC, led to an enhancement of the mechanical and durability performance over time. All the mixes also maintained good results in aggressive environment, with an improvement in durability performance for mixes exposed to a chloride-rich environment. The research confirmed the improved performance of UHDC based on crystalline admixture and nano-additives, mechanical and durability properties as well as their ability to self-heal in a chloride rich environment.