Preparation and Performance Study of Flame-Retardant Composite Filling Materials for Tunnel Surrounding Rock

Rigid polyurethane foam (RPUF) is a common filling material for tunnels surrounding rock in China. The Chinese national standard explicitly stipulates that RPUF, utilized as a tunnel filling material, must adhere to the following criteria: a thermal conductivity of ≤0.1 W/(m·K), a compressive strength of ≥150 kPa, a limiting oxygen index of ≥26%, and a flame-retardant grade of B2. However, the flame-retardant grade B2 is still possible to burn in the special environment of the tunnel. In view of the strict requirements of national standards for thermal conductivity, compressive strength, and flame-retardant performance of RPUF, this study focuses on optimizing the comprehensive performance of RPUF through scientific matching of flame retardants. The aim is to prepare RPUF that not only meets the national standard but also can reach B1 level. Three flame retardants, melamine polyphosphate (MPP), expandable graphite (EG), and low melting point glass powder (LGP), were selected for the ratio test. Measurement correlation coefficient. A comprehensive analysis of these test results was conducted. The results show that: When the overall proportion of EG-MPP-LGP is 41% and EG:MPP:LGP = 26:13:2. Its thermal conductivity is 0.0555 W/(m·K), compressive strength is 216.72 kPa, and the limiting oxygen index is 32.2%, which increases by 74% compared with pure RPUF. The flame-retardant grade achieved is B1, categorizing it as a flame-retardant material. Additionally, all other properties measured align with national standards. This innovative preparation method provides material support for tunnel safety engineering and has practical value.

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