International Concrete Abstracts Portal

This study evaluated the effect of class F fly ash (5, 10, 15, and 20%) and silica fume (20%) as partial cement replacements on bacterial crack healing. Concrete cylinders were prepared, cracked into one-inch disks, and submerged in fresh water. Healing progress was monitored over 18 weeks using microscopy and quantified through a healing index. Results showed that bacterial activity substantially improved healing compared to natural hydration in control specimens. Fly ash replacement did not prevent healing, and several disks across all percentages achieved complete crack closure. However, higher fly ash levels shortened the duration of bacterial activity, indicating sensitivity to calcium availability. At 20% fly ash, healing progressed more slowly but remained active at 18 weeks. In contrast, specimens containing 20% silica exhibited significantly lower healing efficiency, with few disks achieving full closure and overall lower healing indices. These results confirm that bacteria-based self-healing concrete remains effective with fly ash but is constrained by high silica fume content due to very low to zero calcium content in silica fume. The findings indicated that lower calcium content in supplementary cementitious material (SCM) replacement, either due to higher fly ash content with lower calcium compared to OPC or with silica fume with almost zero calcium content, with bacteria, may have a significant effect on the healing progress.

This study presents a comprehensive review of eco-friendly materials and advanced repair techniques for rehabilitating reinforced-concrete (RC) structures, emphasizing their role in promoting sustainability and enhancing performance. By evaluating fifty-five research programs conducted between 2001 and 2024, the study focuses on emerging materials such as geopolymers, natural fibers, and fiber-reinforced composites, highlighting their mechanical properties, environmental benefits, and potential for integration into traditional RC systems. The review is thematically organized into four areas: (1) Sustainability and Environmental Impacts, (2) Material Innovation and Properties, (3) Repair Techniques and Efficiency, and (4) Structural Performance. Key findings reveal that these materials not only reduce the carbon footprint of construction but also significantly improve structural durability, corrosion resistance, and long-term performance under varying environmental conditions. Specifically, geopolymer concretes exhibit low CO₂ emissions and superior bond strength; bamboo and flax fibers offer strong tensile capacity with renewable sourcing; and MICP techniques deliver self-healing functionality that reduces dependency on chemical-based crack sealants. Additionally, the use of recycled and bio-based materials further contributes to cost-efficiency and environmental resilience, fostering circular economy principles. By synthesizing findings across these domains, this study provides practical insights into how eco-friendly materials can simultaneously address environmental, structural, and economic challenges in RC repair. The study underscores the importance of adopting innovative repair methods that incorporate these sustainable materials to address modern civil engineering challenges, balancing infrastructure longevity, sustainability, and reduced environmental impact.

This laboratory study employed synthesized urea-formaldehyde (UF) microcapsules and polyvinyl alcohol (PVA) microfibers as a self-healing system to improve the durability of concrete in cold climates. The resistance of concrete specimens to rapid freezingand- thawing (F/T) cycles was evaluated by measuring the change of relative dynamic modulus of elasticity (RDM) with respect to the number of F/T cycles. The control specimens (either with or without PVA microfibers) approached the failure state with a reduction of 38% in RDM after being subjected to 54 F/T cycles, whereas the self-healing specimens (either with or without PVA microfibers) remained in a good state with a reduction of approximately 10 to 15% in RDM after 732 F/T cycles. A polynomial regression model was developed to establish the relationship between the RDM and number of F/T cycles, and a three-parameter Weibull distribution model was employed to conduct the probabilistic damage analysis and characterize the relationship between the number of F/T cycles (N) and the damage level (D) with various reliabilities. The results revealed that the benefits of UF microcapsules and PVA microfibers to the frost durability of concrete diminish once the damage level exceeds a certain high level. Based on the Weibull distribution model, the relationships were established and validated between N and D by comparing the experimental data, the predicted data based on the nonlinear polynomial regression model, and the predicted data based on N-D relationships. The field service life of the self-healing concrete was then predictable at any given reliability.

Self-healing is a process by which concrete is able to recover its properties after the appearance of cracks, which can improve mechanical properties and durability and reduce the permeability of concrete. Self-healing materials can be incorporated into concrete to contribute to crack closure. This study aims to evaluate the influence of crystalline admixtures and silica fume on the self-healing of concrete cracks. The rapid chloride penetration test was performed on cracked and uncracked samples, from which it was possible to estimate the service life of concretes. The concretes were characterized by tests of compressive strength and water absorption by capillarity. The use of crystalline admixtures did not have a negative influence on concrete properties, but did not favor the chloride penetration resistance. The concrete with silica fume showed the lowest charge passed and highest values of estimated service life.

The built environment is facing an increasing challenge of reducing emissions regarding both embodied and operational carbon. As an ultra-durable concrete, engineered cementitious composites (ECC) reduce the need for repair, thus resulting in a prominent reduction of life-cycle footprints. Herein, a new version of low-carbon ECC was developed for cast-in-place applications by sequestering CO2 through mineralization. Two waste streams were pre-carbonated and incorporated into ECC as fine aggregate and supplementary cementitious material, respectively. At 28 days, the CO2-sequestered ECC exhibited a compressive strength of 32.2 MPa (4670 psi), tensile strength of 3.5 MPa (508 psi), and strain capacity of 2.9%. Multiple fine cracks were distinctly identified, with a residual crack width of 38 μm (0.0015 in.) and a selfhealing behavior comparable to that of conventional ECC. The new ECC sequestered 97.7 kg/m3 (164.7 lb/yd3) CO2 (equivalent to 4.7 wt% of final mixture) and demonstrated a 42% reduction in cradle-to-gate emissions compared to conventional concrete at the same strength level. This study demonstrates the viability of turning waste CO2 gas into durable construction materials and proposes a potential path towards carbon neutrality.