Temperature effects on the bond behavior between deformed steel reinforcing bars and hybrid fiber-reinforced strain-hardening cementitious composite

The authors have recently developed a hybrid fiber-reinforced strain-hardening cementitious composite (HFR-SHCC) using steel and polyvinyl alcohol (PVA) fibers. When subjected to high temperatures (up to 800 °C), this HFR-SHCC retains a higher proportion of its tensile strength compared to SHCCs containing only PVA fibers. The objective of the current study is to experimentally investigate whether the improved material properties of HFR-SHCC at high temperatures lead to better bond with conventional deformed steel reinforcing bars (rebar) compared to other SHCCs and conventional concretes. Rebar pullout specimens with a deformed rebar centrally embedded inside a SHCC/concrete cylinder were used in this study to determine the rebar-matrix bond. The bond behavior of HFR-SHCC with deformed steel rebar was compared with two concretes of different compressive strengths, a commonly used PVA-SHCC containing only PVA fibers, and a PVA-SHCC with very high content of fly ash. The rebar pullout specimens were subjected to temperatures of 100 °C, 200 °C, 400 °C, 600 °C and 800 °C and were tested after cooling down to room temperature to determine the residual bond strength. Results show that while the specimens made with the conventional concretes exhibit the largest bond strength at room temperature, the specimens made with HFR-SHCC retain the largest proportion of their room temperature bond strengths after exposure to high temperatures and show a more ductile pullout behavior instead of the abrupt splitting failure exhibited by the other materials.