The role of crystalline admixtures in the long-term healing process of fiber-reinforced cementitious composites (FRCC)

Crystalline admixtures (CAs), categorized as permeability-reducing admixtures according to ACI-212, are additives serving in the construction industry for decades and have recently been used as self-healing promoters. Although substantive research has been done on concretes' durability properties and healing efficiency at the macroscopic level, limited information was available regarding its microstructural features and chemical properties. Therefore, this paper aimed to analyze fiber-reinforced cementitious composites (FRCC) with polypropylene fibers (PP) in the long-term healing process. Initially, an analysis of the CAs raw materials was carried out. Then, the concrete compositions' physicomechanical properties were tested. For the healing analysis, specimens were pre-cracked after 28-days with an estimated crack width between 50 and 500 mu m. The specimens were cured in three healing conditions: seawater immersion at 20 C, immersed in tap water at 20 C, and wet/dry cycles. The healing rate was evaluated based on the crack closure, recovery of compressive strength, and sealing efficiency through water absorption. An almost perfect surface healing was observed for specimens immersed in seawater and tap water. At the same time, the wet/dry condition proved to be insufficient for both CAs types. The analysis of the healing material highlighted significant differences in the agent's structure at the surface and inside the crack. Also, the influence of other compounds, such as Mg, during the hydration of C3S to the healing agents has been analyzed, indicating M-S-H compounds, magnesium calcite, and brucite according to SEM and XRD analysis.

Automated summary

This paper analyzes the long-term healing process of fiber-reinforced cementitious composites (FRCC) with polypropylene fibers (PP). The results show that immersion in seawater and tap water can achieve almost perfect surface healing, while the wet/dry condition is insufficient for healing. Additionally, the study highlights the differences in agent's structure between the crack surface and interior, and analyzes the influence of other compounds, such as magnesium, on the healing agents.