Properties of magnesium potassium phosphate cement-expanded perlite composites applied as fire resistance coating

Abstract

Cement-based composites have been a commonly used fire resistance material. As a new cement, magnesium potassium phosphate cement (MKPC) has been a popular and important research object due to its various excellent properties including heat resistant. However, only limited studies have been conducted on its application as fire-resistant coating. In this paper, the thermal properties of MKPC blended with/without expanded perlite (EP) under fire exposure were investigated. Two types of EP with open-pore and closed-pore structures were used, and each type of EP contained two different sized particles including 212–270 μm and 270–550 μm. The fluidity and setting time of MKPC-EP composites and adhesive strength between MKPC-EP composites coating and plywood were measured. The fire resistance properties of MKPC-EP composites were studied, including loss of weight (LOW), generated cracks, phase changes, thermal analysis, residual adhesive strength, and microstructure changes. The obtained results were intended to reveal the feasibility of MKPC-EP composites applied as coating to protect the substrate against exposure to fire. The addition of EP decreased the fluidity, extended the setting time, and enhanced the adhesive strength before and after fire test. LOW and accumulative lengths of visible cracks after fire exposure reduced for certain formula and are dependent on the pore structures, sizes and dosage of EP. X-ray diffraction (XRD) investigation and thermal analysis-infrared spectroscopy reveal MgKPO4⋅6H2O decomposed to MgKPO4⋅H2O by losing crystal water stage by stage during elevating temperature. Scanning electron microscopic (SEM) observations show that EP refined the MgKPO4⋅6H2O, and, after exposure to flame, the MKPC-EP exhibited a much denser microstructure with interconnecting MgKPO4·H2O of radiative flakes, when compared to the MKPC paste.