Experimental study on color change and compression strength of concrete tunnel lining in a fire

- Concrete color turns from dark gray to whitish gray as temperature increasing.
- After spraying phenolphthalein, the concrete turn red, the degree of red declines with the temperature increases.
- Intensity strength decreases with the increasing of EFET.
- Color change of concrete is helpful to evaluate the damage caused by fire.

In order to investigate the characteristics of tunnel concrete lining after a fire, a 1/10 scale tunnel fire model was constructed to study the color change and strength reduction of the concrete tunnel lining. The compression strength of concrete specimens was measured to quantify the damages and it is observed that the compressive strength of the concrete varied inversely with the EFET (equivalent flame exposure time) values. The surface and inside temperatures of the concrete lining were measured during the fire test, and the color change from applied phenolphthalein was observed and correlated to concrete damages. A tricolor image processing method is used to analyze the concrete color changes, the results indicate that a light red color on the concrete surface demonstrates a deeper neutralization of the concrete material, which can be correlated to the temperature effect during fire test and that the intensity of the red color decreases as the temperature increases. Thus, a low cost and nondestructive evaluation technique based on the tunnel lining color change can be developed.