Influence of Crystalline Admixtures and Bacteria on the Fresh Properties of Self-healing Concrete

Abstract

Concrete is undeniably susceptible to cracking due to its low tensile strength in spite of its ability to withstand high compressive stresses. Cracks may jeopardize the concrete core and reinforcements due to the ingress of water and aggressive substances. A promising technique to effectively seal cracks in hardened concrete is using a self-healing technology by introducing healing agents to the fresh concrete mixes. Crystalline admixtures and bacteria emerge as promising self-healing agents to promote stimulated autogenous healing and autonomous healing mechanisms, respectively, improving simultaneously the durability of the concrete. Healing agents are mostly added on top of the normal mix without changing the mix design of the concrete, while in fact, it may induce considerable effects on the fresh and hardened properties of concrete. In this study, two types of cement (CEM I 52.5N and CEM III/A 42.5N) as well as crystalline admixtures and bacterial spores, both in powder form, and PCE-based superplasticizer are utilized to evaluate the changes in consistency and setting time. The dosage of healing agents is taken between 0 − 5% by weight of powders. To start, tests on paste level were executed. The results show that the addition of healing agents affects the water demand, the consistency and setting time of the pastes. The inclusion of crystalline admixtures increases the water demand, while a declined trend of setting time is observed. The gradual addition of bacteria up to 5% slightly changes the water demand, but a significant delay on the initial and final setting times was detected.