Document Type : Original Article
Authors
1
Civil Engineering Department, Faculty of Engineering, Port Said University, Port Said, Egypt,
2
Department of civil engineering, Faculty of engineering, Port Said University
3
Microbiology and immunology department faculty of pharmacy Port Said University, Port Said x University
4
Civil Engineering Department, Faculty of Engineering, Port Said University, Port Said, Egypt
Abstract
The inherent susceptibility of Ground Granulated Blast-Furnace Slag (GGBS) geopolymers to shrinkage-induced cracking compromises their durability. This study addresses this challenge by investigating the efficacy of Microbially Induced Calcite Precipitation (MICP) as a self-healing mechanism, utilizing the bacterium Bacillus subtilis. A comprehensive experimental program was designed to systematically optimize the key system parameters: sodium hydroxide activator molarity (10 M and 12 M), bacterial concentration (10⁵ and 10⁷ CFU/mL), and bacterial dosage (0%, 1%, 2%, and 3%). The mechanical performance was evaluated through compressive and splitting tensile strength tests, while durability was assessed via acid (HCl) and sulfate (MgSO₄) resistance tests. Microstructural and mineralogical analyses using SEM and XRD were performed to validate the macroscopic findings. The results revealed a strong synergy at a moderate alkalinity, with the optimal formulation being a 10 M activator solution combined with a 10⁷ CFU/mL bacterial concentration at a 2% dosage (M10C7D2). This mix achieved a compressive strength of 43.2 MPa, a 32% increase over its corresponding control. Conversely, the highly alkaline 12 M activator produced a stronger baseline geopolymer matrix but significantly inhibited bacterial activity, negating the benefits of MICP. The optimized bacterially-modified specimens demonstrated superior durability, attributed to the formation of a protective biogenic calcite barrier. These findings confirm that MICP is a highly effective strategy for enhancing the performance of GGBS geopolymer composites, provided the system's alkalinity is carefully controlled to support bacterial viability.
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