Bacterial Self-Healing Concrete and the Role of Nano-Additives: A Systematic Review of Healing Performance, Reporting Quality and Synergy Evidence

Abstract

This review quantifies the reported performance of bacterial self-healing concrete and examines whether combining bacteria with nano-additives, chiefly nano-silica, produces a demonstrable synergistic benefit. Following the PRISMA 2020 framework, 106 reports were sought for full-text assessment and 87 were included: 59 primary experimental studies (48 bacterial, 6 bacterial with a nano-additive and 5 nano-additive only) and 28 contextual records. Pre-defined rules selected one value per study and outcome; values were pooled as medians with interquartile ranges, and subgroups were compared exploratorily. Across 54 bacterial studies, the median crack closure was 86.4%, the compressive-strength gain 21.2%, the reduction in water absorption 48.0% and the healed crack width 0.50 mm. Only one study reported all four core outcomes, 9.3% reported permeability or chloride transport, 77.8% tested healing under continuous immersion, and pooled closure showed no clear dependence on crack width (R² = 0.061), a pattern consistent with selective reporting. No advantage of encapsulation was detected in small subgroups, and no bacteria–nano study included the nano-only control needed to test synergy. Future work should adopt a minimum reporting protocol, wet–dry and saline exposure, long-term testing and a four-arm factorial design.