Overview of recent work on self-healing in cementitious materials

Smart Bio-Agents-Activated Sustainable Self-Healing Cementitious Materials: An All-Inclusive Overview on Progress, Benefits and Challenges

Cementitious materials deteriorate progressively with the formation of cracks that occur due to diverse physical, chemical, thermal, and biological processes. Numerous strategies have been adopted to obtain cement-based self-healing materials and determine the novel self-healing mechanisms. The uses of microbes have been established to improve the thickness of the healed crack and mechanical properties of the concrete, a phenomenon seldom addressed in the literature. Based on these factors, this article comprehensively appraises the smart bio-agents-based autonomous healing performance of concrete to demonstrate the recent progress, expected benefits, and ongoing challenges. The fundamentals, design strategies, and efficacy of the smart bio-agents-activated self-healing cementitious materials are the recurring themes of this overview. Furthermore, the effects of various processing parameters on the performance of cementitious self-healing smart bio-agents are discussed in-depth. The achievements, knowledge gaps, and needs for future research in this ever-evolving area for the sustainability and resilience of the built environment are highlighted.

Numerical Simulation of the Response of Concrete Structural Elements Containing a Self-Healing Agent

Self-healing of a crack is a relatively novel technique allowing for the partial recovery of the initial mechanical characteristics of a structural element after some period of exploitation. By a widely accepted convention, self-healing is either autogenous or autonomous. The former is a mechanism inherent for cementitious composites (in particular—concrete), while the latter is an engineered process. Both autogenous and engineered healing have recently been the object of numerous studies. Despite the large amount of research work being carried out, the potential of this technique has not yet been fully realized. The article focuses on the modeling and the finite element simulation of the recovery of the initial material properties resulting from the sealing of cracks. The employed numerical procedure uses a constitutive relation for concrete based on the continuum damage mechanics. It captures both the strain-softening and the inverse process—the crack healing. Finite element simulations of benchmark cases illustrate the effect of self-healing. The numerically obtained constitutive relations for specimens with and without a healing agent are compared.

Bio-mineralized self-healing recycled aggregate concrete for sustainable infrastructure

Various carriers have been investigated by researchers to introduce bacteria inside the concrete however, factors such as local availability, cost and long-term protection of bacterial cells have barred the application of this contemporary technology in the construction industry. In the present study, bacteria were immobilized via recycled coarse aggregate (RCA) and virgin fine aggregate (FA) besides direct induction to preserve natural resources and emulate sustainability. The application of RCA in substitution of virgin coarse aggregate is dropping anthropogenic emissions, minimizing energy consumption and managing construction waste effectively. Vegetative cells of Bacillus subtilis bacterium were incorporated in RCA through vacuum impregnation to boost crack healing efficiency. Crack healing efficiency was studied by quantifying the crack healing widths and percentage of strength regained after pre-cracking at 3,7 and 28 days. Similarly, mechanical properties were gauged via compressive and split tensile strengths at specified intervals while healing precipitate was characterized using analytical means. Results of experimental work revealed that specimens having RCA and 50% virgin FA as bacteria immobilizers exhibited the most efficient crack healing remedy by healing crack widths up to 1.1 mm and recovering 85% of compressive strength. Specimens containing RCA exclusively displayed a maximum of 0.7 mm crack healing widths and 76% strength recovery while direct incorporation of bacteria lagged behind with 0.6 mm crack healing width having 69% strength recovery. Likewise, synergetic formulation and direct induction depicted increase in compressive strength of 4% and 6% respectively while exclusive RCA formulation decreased the compressive strength up to 3% Moreover, field-emission scanning electron microscopy (FE-SEM), thermo-gravimetric analysis (TGA), X-ray diffraction (XRD) and X-ray fluorescent (XRF) characterized the crack healing precipitate as bio-mineralized calcite crystals.

Admixtures in Cement-Matrix Composites for Mechanical Reinforcement, Sustainability, and Smart Features

For more than a century, several inclusions have been mixed with Portland cement-nowadays the most-consumed construction material worldwide-to improve both the strength and durability required for construction. The present paper describes the different families of inclusions that can be combined with cement matrix and reviews the achievements reported to date regarding mechanical performance, as well as two other innovative functionalities of growing importance: reducing the high carbon footprint of Portland cement, and obtaining new smart features. Nanomaterials stand out in the production of such advanced features, allowing the construction of smart or multi-functional structures by means of thermal- and strain-sensing, and photocatalytic properties. The first self-cleaning concretes (photocatalytic) have reached the markets. In this sense, it is expected that smart concretes will be commercialized to address specialized needs in construction and architecture. Conversely, other inclusions that enhance strength or reduce the environmental impact remain in the research stage, in spite of the promising results reported in these issues. Despite the fact that such functionalities are especially profitable in the case of massive cement consumption, the shift from the deeply established Portland cement to green cements still has to overcome economic, institutional, and technical barriers.