Research, Development, and Performance of Lightweight, Heat-Insulating, and Spalling-Resistant Cement Mortar

Abstract Because most existing fireproof coatings have low strength and durability levels, they cannot effectively meet the long-term fire resistance requirements of tunnel structures. Therefore, a lightweight, heat-insulating, and spalling-resistant cement mortar was designed in this study using expanded perlite (EP), silica aerogel (SA), and basalt fiber (BF) materials to address these issues. For perlite–aerogel–basalt–cement (PABC) mortars with different admixtures, the thermal conductivities were tested with a thermal conductivity meter, the explosive spalling resistance values were evaluated with high-temperature testing, and the mechanisms of heat insulation and high-temperature resistance were determined using scanning electron microscopy. The results show that the optimal mix (A12) achieved a dry density of 1,647 kg / m 3 , a thermal conductivity of 0.3499 W / ( m · K ) , and a compressive strength of 47 MPa. After exposure to 800°C with 50% moisture content, no explosive spalling occurred, and a residual strength of 4.4 MPa was retained. Increasing EP and SA contents effectively reduced density and thermal conductivity, and EP had a greater influence than SA. Notably, when the EP replacement ratio exceeded 80%, explosive spalling was completely prevented, whereas SA mainly alleviated spalling severity. Microstructural analysis indicated that the synergistic effect of EP-induced microcracks and SA-generated pores facilitated vapor-pressure dissipation, thereby enhancing spalling resistance. The PABC mortar combines adequate strength with superior fire resistance, offering a promising solution for long-term fire protection of tunnel linings. The results showed that the experimental PABC mortar has good heat insulation and explosive-spalling resistance, and it can maintain a specific compressive strength. Thus, this mortar meets the fire-resistance requirements of tunnel structures. The thermal conductivity and density of PABC mortar are closely related to increases in the amounts of EP and SA. Reducing the density of PABC mortar can reduce its thermal conductivity. The contents of EP, SA, and BF can affect the explosive-spalling resistance of PABC mortar. When the replacement rate of EP exceeded 80%, PABC mortar did not undergo spalling at high temperatures. Conversely, SA and BF improved only the explosive-spalling resistance. When the porosity of SA resulting from high-temperature shrinkage and the microcracks of EP resulting from thermal stress reach certain proportions, high-temperature vapor pressure is dissipated via a synergistic effect, thereby improving the explosive-spalling resistance of the material.