This study investigates the potential use of pulverized water hyacinth (PWH) as a concrete admixture and water hyacinth extract (WHE) as a natural superplasticizer to develop a more economical and environmentally sustainable concrete mix. PWH, derived from dried and pulverized water hyacinth, is explored for its potential to reduce material costs and promote the reuse of green waste; however, its high water absorption is known to reduce concrete workability. To address this limitation, WHE was incorporated as a workability-enhancing agent to counteract the adverse effects of PWH. The study focused on optimizing the proportions of PWH and WHE to achieve acceptable workability and compressive strength without compromising structural performance. Slump and compressive strength tests were conducted to evaluate the fresh and hardened properties of the proposed mixes. Results indicate that increasing PWH content reduced slump but did not adversely affect compressive strength at low dosages, while WHE consistently improved workability but caused significant reductions in compressive strength. Optimization analysis identified an optimal mixture of approximately 0.48% PWH with no WHE, yielding a predicted compressive strength of 26.75 MPa. The findings demonstrate that PWH can function as an effective bio-based micro-admixture in concrete, whereas WHE acts primarily as a workability modifier whose dosage must be strictly limited, underscoring the importance of dosage optimization in sustainable bio-admixture applications.

Abstract. Replacing and repairing cracked concrete can be a costly and time-consuming process that can also be disruptive, with adverse environmental impacts. Taking these challenges into consideration, the current study explores Bacillus subtilis as a bio-admixture to activate an intrinsic self-healing mechanism that allows concrete to heal its cracks by itself. More specifically, the use of Bacillus subtilis ATCC 6633, incorporated into the concrete at a dosage of 2.36 x 109 CFU to heal cracks in the size range of 1-2 mm were tested. Each of the bacteria was assessed at four concentrations—1%, 3%, 5%, and 10% were evaluated for their ability to enhance the self-healing property of the concrete. The self-healing performance and internal structure recovery were assessed using two different methods: the Sorptivity Test (ASTM C 1585) and the Ultrasonic Pulse Velocity (UPV) equipment PUNDIT PL200. The findings revealed that Bacillus subtilis significantly enhanced the self-healing process in 3-7 days, effectively repairing cracks within a 10-day period, as demonstrated by improvements in material recovery, absorption rates, and ultrasonic pulse velocity. The results suggest that 5% Bacillus subtilis concentration has considerable potential to improve the durability and sustainability of concrete, offering a more environmentally friendly and cost-effective solution for autonomous crack repair using the two distinct methods.