Sustainable bacteria-based self-healing steel fiber reinforced concrete

Self -healing concrete presents an innovative and eco-friendly solution with the potential to reduce maintenance costs through self -activated crack repair. This study examined the effect of varying bacterial content across different environmental conditions. Additionally, the coupling effect between bacteria and steel fiber to enhance the mechanical and physical properties at different ages has been investigated. Bacillus Sphaericus ( B. Sphaericus ) was incorporated into the concrete at concentrations of 2 x 10 9 (CFU/ml), and different bacterial percentages selected utilizing calcium lactate as a nutrient source. Bacterial content of 0.0 %, 0.25 %, 1.0 %, and 2.5 %, cured in both fresh water and magnesium sulfate water solution, were tested to examine concrete behavior in harsh environments. Additionally, steel fibers at volume fraction percentages (Vf%) of 1.0 % and 1.5 %, along with 1.0 % bacterial content, were tested to highlight their combined effect. Tests were conducted at different ages to measure compressive, tensile, and flexural strengths. In addition, SEM and EDS analyses for cracked and uncracked specimens were performed. The results showed a significant increase in the long-term compressive, tensile, and flexural strengths at 180 days by 47 %, 80 %, and 50 %, respectively, with a bacterial content of 2.5 %. Moreover, the incorporation of steel fibers, 1.0 % and 1.5 % content, in the bacterial concrete resulted in a longterm compressive strength increase at 180 days by 45 % and 55 %, respectively with 1.0 % bacterial content, compared to 15 % and 27 % for 0 % bacteria. Curing in sulfate -rich water, concrete specimens exhibited increasing compressive strength at 180 days from 47 MPa for 0 % bacteria to 77 MPa with 2.5 % bacteria content. Despite lower initial strength of 29 MPa at 7 days, bacterial incorporation led to significant strength improvements, highlighting effective selfhealing even in aggressive curing environments.