Assessing the self-healing capacity of concrete in aggressive environments using crystalline admixtures and nanoadditives

Abstract

The aim of this study is to assess the self-healing capacity of concrete using crystalline admixtures and three different nanoadditives in two different environmental conditions. Self-healing is an inherent property of concrete that is experiencing moist conditions. This is called autogenous healing. This characteristic can be enhanced by several additives, one of which is crystalline admixtures. Crystalline admixtures form crystals when hydration is present, that fill cracks in cementitious materials, and reduce their permeability. Environmental conditions are some of the largest contributing factors to the degradation of materials. Concrete, like other materials is susceptible to these exposures. Some of the most aggressive environments are chloride environments (marine). Hence, if concrete is able to withstand such conditions, degradation can be controlled, and its lifespan increased. Hence, durability is increased. Ultra High Durability Concrete is a product of this objective. It is a concrete that is able to withstand higher loads and stronger environments. The addition of nanoadditives to this concrete, could be a further enhancement. Alumina nanofibers have the ability of controlling the initial crack width of the concrete, which in turn makes it easier for self-healing to take place. Also, nanocellulose reduces shrinkage and increases density. These materials combined with crystalline admixtures can create highly durable concrete with a high capacity for self-healing. UHDC was produced with different constituents including crystalline admixture and 3 types of nano additives: Nano Alumina, Nano Cellulose and Nano cellulose fibres. The UHDC was exposed to different environments namely water and a chloride rich environment. The mechanical (compressive and flexural strength, UPV) and durability (porosity, chloride penetration and chloride migration, sorption) properties of the UHDC were assessed over time. Results confirmed how nano-additives used in the production of UHDC, improve the mechanical and durability performance over time. All the mixes also maintained good results in aggressive environments, with self-healing being enhanced in such conditions. This dissertation confirmed the improved performance of UHDC based on these relatively new materials in combination with a cementitious mortar, on mechanical and durability properties as well as their ability to self-heal in a chloride rich environment.