Evaluation of PVA and PBI-based engineered-cementitious composites under different environments

• The effect of firing temperature of 400 °C on PVA and PBI fibers is described.
• The effect of firing temperature was critical in the PVA monofiber system.
• A synergistic hybrid combination of PVA and PBI (1:1) showed encouraging results.
• At 400 °C, the tensile capacity of PBI reached about 9 times than that of PVA.
• SHCC possible with a potential firing resistance with limited spalling explosion.

Strain-hardening cement-based composites (SHCCs) as engineered cementitious composites are well-known for their ultra-ductility. The unique strain-hardening property of SHCCs is mainly attributed to the mix composition; however, the advanced research behind this type of construction technology must be extended to evaluate such properties in different environments. The fire-resistivity of SHCCs is questionable and a matter of concern, specifically when non-fire resistant fibers are used. The most well-known utilized non-fire resistant fibers, such as poly vinyl alcohol (PVA) fibers, are unable to withstand a critical high temperature of 400 °C, despite their unique properties under normal conditions. At this critical temperature, PVA fibers thermally decompose into gases, create voids and thus lead to a disappearance of the strain-hardening behavior and decrease other hardened properties. On one hand, the developed voids due to melting of PVA fibers might prevent explosive spalling from occurring under the effect of pressurized pore water vapor. On the other hand, polybenzimidazole (Poly-[2,2′-(m-phenylen)-5,5′-bisbenzimidazole]) short fibers (PBI) are non-metallic and fire resistant fibers that have a higher melting point beyond the critical temperature of PVA and have an effective chemical resistance. In the current study, the effect of the hybridized combination of PVA and PBI on the strain-hardening and microstructural properties of SHCC was investigated under normal conditions and at a critical fire temperature of 400 °C.