Understanding the Impacts of Healing Agents on the Properties of Fresh and Hardened Self-Healing Concrete: A Review

Abstract

Self-healing concrete has emerged as one of the prospective materials to be used in future constructions, substituting conventional concrete with the view of extending the service life of the structures. As a proof of concept, over the last several years, many studies have been executed on the effectiveness of the addition of self-healing agents on crack sealing and healing in mortar, while studies on the concrete level are still rather limited. In most cases, mix designs were not optimized regarding the properties of the fresh concrete mixture, properties of the hardened concrete and self-healing efficiency, meaning that the healing agent was just added on top of the normal mix (no adaptations of the concrete mix design for the introduction of healing agents). A comprehensive review has been conducted on the concrete mix design and the impact of healing agents (e.g., crystalline admixtures, bacteria, polymers and minerals, of which some are encapsulated in microcapsules or macrocapsules) on the properties of fresh and hardened concrete. Eventually, the remaining research gaps in knowledge are identified.

A review of the efficiency of self-healing concrete technologies for durable and sustainable concrete under realistic conditions

“…Over the past years, several state-of-the-art papers have been published, focusing on the different autogenous and autonomous technologies and their effectiveness [17], the test methods to assess them [18], the mix design of self-healing concrete [19] and the models to predict, also from a design perspective, the outcomes of the phenomenon, including data-driven models derived through Artificial Intelligence (AI) algorithms [17,18,20,21]. Literature surveys provide ample confirmation of autonomous healing of cracks triggered by the crack formation or external stimuli.…”

Relationship between Bacterial Contribution and Self-Healing Effect of Cement-Based Materials

“…Some ubiquitous bacteria with BICP potential have the ability to biocalcify in a wide range of environmental conditions. This phenomenon has been used as a sustainable engineered alternative to conventional techniques in consolidation of soil, sand, stone, and cement, in the improvement of soil characteristics, and in remediation of pollutants in soil, water, and wastewater [ 10 , 11 , 12 ]. Considering that BICP can lead to effective CaCO 3 formation, the SH effect of concrete can be accelerated or bio-stimulated using bacteria whose presence and activity may affect crack repairing.…”

“…Therefore, many investigators and research groups are directed to the creation and application of bacteria-based concrete, with the capacity for self-repairing of cracks on a microscale [ 5 , 6 , 7 , 8 , 9 ]. Although self-healing concrete has been developed for two decades, it is very common that the desired activity of used bacteria does not occur in due time, which represents a problem for further industrialization and commercialization of this type of material [ 10 ]. The importance of bacteria contribution during the self-healing (SH) effect has been neglected in many scientific-relevant studies, without explanations of the obtained results in a view of maintaining viability and activity of bacteria in extreme conditions (high alkalinity, limited water availability, minimal nutrient concentration, etc.).…”

Research on the production of cement composites with autonomous self-healing performance

“…The self-healing mechanism is produced because of chemical reactions of a self-healing agent embedded directly, embedded in capsules or introduced through vascular networks when designing and making the concrete mixture. Among the most used systems are superabsorbent polymers [9], [10], crystalline mixtures [11], [12], microencapsulated sodium silicate [13], tubes with adhesives [14][15][16] and bacteria [17][18][19][20].…”