STUDY OF SPALLING BEHAVIOR AND MECHANISM IN FIRE OF ACRYLIC POLYMER CEMENT MORTAR USING RING RESTRAINED SPECIMEN

Abstract

 The authors evaluated the spalling of polymer cement mortar (PCM) restrained by a steel ring in high temperature. The polymer cement mass ratio (P/C) was 20%. In addition, a specimen of ordinary cement mortar was used for comparison. The spalling test by the ring restrained specimen measured the internal temperature, restrained stress and water vapor pressure. The spalling scale after heating was graded based on the spalling depth distribution on the heated surface of the ring restrained specimens. The heating conditions were the RABT30 heating curve. The tensile fracture strain was calculated from the restrained stress at the time of spalling of PCM and NCM specimens. Furthermore, P/C and tensile fracture strain are shown by relational expressions. From this equation, the time which tensile strain fracture of PCM with P/C=5 to 20% occurred was estimated. As a result, it almost same the time when the spalling occurred. When PCM spalling occurred, the restrained stress caused tensile strain fracture of the mortar and a sharp decrease in water vapor pressure. On the other hand, the specimens made of polymer cement mortar mixed with nylon fibers stopped spalling during heating. In PCM mixed with fibers, gaps were created at the interface between fibers and PCM and by melting of fibers at high temperature. Water vapor moved into these gaps, and the vapor pressure was relaxed, causing the spalling to stop.