Effects of Fire on Concrete – two seminars by professors from Gunma University, Japan.

Seminar

Friday, May 22 at 2-3 p.m. GB217, Galbraith Building

There will be two presentations on effects of fire on concrete buildings presented by:

Professor Mitsuo Ozawa, and Dr. Taku Koyama, Assistant Professor

Civil and Environmental Engineering at Gunma University, Japan.

Presentation 1. Behavior of Ring-Restrained High-Performance Concrete under Extreme Heating and Development of a Screening Test

Abstract

Fire represents one of the most critical hazards for concrete buildings and infrastructure, as it can lead to explosive spalling of concrete. Two primary mechanisms are known to govern fire-induced damage in concrete. The first is restrained thermal dilation, which generates biaxial compressive stresses parallel to the heated surface and induces tensile strain in the perpendicular direction. The second is the build-up of pore pressure caused by the vaporization of physically and chemically bound water, which imposes tensile loading on the microstructure of the heated concrete.

This study investigates the behavior of restrained high-performance concrete subjected to the extreme heating conditions associated with fire. Thermal stress was estimated from the strain induced in a restraining steel ring, while vapor pressure within the concrete was measured under heating conditions corresponding to the RABT 30 rapid heating curve. The thermal stress was calculated using the thin-walled cylinder model.

Based on these evaluations, a spalling failure model grounded in a tensile strain failure criterion was proposed. The results demonstrate that the model effectively predicts both the initiation of spalling and the resulting spalling depth.

Presentation 2: Estimation of chloride diffusion coefficients of high-strength concrete with synthetic fibers after fire exposure

Abstract

In this study, the durability of concrete exposed to fire was investigated based on tracer analysis after the specimens had been soaked in salt water. Two types of concrete specimens: high-strength concrete (HSC) and HSC with polypropylene (PP) fibers were subjected to heating tests at temperatures of 100, 200, 300 and 500°C before being soaked for 30 days in a 10% sodium chloride (NaCl) solution. After the soaking period, chloride penetration depth was measured using electron-probe microanalysis (EPMA), and the relevant chloride diffusion coefficients were estimated. Relative chloride penetration was found to be deeper in specimens exposed to higher temperatures. HSC with PP fibers also exhibited greater penetration due to the melting of its fiber content. The chloride diffusion coefficient also increased with higher exposure temperatures.