Experimental investigation of thermal pore pressure in reinforced C80 high performance concrete slabs at elevated temperatures

Abstract

Based on the pore pressure test of the cylindrical specimens at high temperatures, the pore pressure in the reinforced slabs (390 (L) × 390 (W) × 120 (H) mm) made of high strength concrete and high performance concrete (HSC/HPC) exposed to elevated temperatures was studied, and the effects of elevated temperatures and heating duration on the pore pressure in heated HSC/HPC were presented. Four types of slabs made of C80 HPC including plain HPC slabs (HPCS), plain rebar-reinforced HPC slabs (RHPCS), PP fiber-reinforced HPC slabs (PPHPCS), rebar-PP fiber-reinforced HPC slabs (RPPHPCS) were tested. The pore pressure results indicate that the heating rate of the concrete slabs gradually decreases with increase of the depth from the heated surface. The 50 mm depth in slabs may be a “moisture clog”, which is consistent with the relevant numerical results. Comparison with tensile strength shows that the pore pressure is not the only cause of spalling. According to few related reports, studies on the effects of the rebar mesh on the pore pressure and spalling of slabs have showed that spalling in RHPCS is not as severe as that in HPCS at high temperatures, but the pore pressure of rebar-reinforced concrete slabs is greater compared to the plain concrete slabs. Adding PP fibers can effectively prevent the occurrence of spalling and reduce the pore pressure in the heated slabs. It was determined that the rebar mesh and PP fibers reduce the occurrence of spalling, which provides ideas and test data for improving the fire resistance (anti-spalling) of HSC/HPC.