This study presents the influences of talc as an additive in intumescent coating formulations on the thermal insulation, degradation and water resistance. The fire test was performed according to ASTM-E119 standard to study the heat shielding properties of the coated substrates. The results showed that the 20% of the talc enhanced the heat shielding and recorded substrate temperature 75 °C after 100 min of fire test. The morphology of the char was analyzed by Scanning Electron Microscopy (SEM). X-ray fluorescence (XRF), X-ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) results showed the presence of P2O5, MgO, TiO2, and SiO2 respectively. The functional groups analysis of char confirmed the presence of high temperature compounds and enhanced thermal performance of coatings. Thermogravimetric analysis (TGA) showed that addition of 20% talc increased residual mass of the char by 55.55%. The lap shear test result showed that the talc also improved the adhesion of the intumescent coating with steel substrate and the highest shear strength observed was 7 MPa for a formulation, F5 containing 20% talc. Water immersion test was performed according to ASTM D870-15 and the results showed the higher water-resistance was recorded for a formulation containing 10% talc in the control formulation.

Microstructure of the talc used in this work.

The ingredients of intumescent coating are listed in Table 1. A freshly grounded mixture of all the ingredients was mixed with epoxy and hardener. The coating mixture was stirred at 40 rpm for 30 min for the homogeneous mixture. Steel substrate was sandblasted and the surface roughness was determined by profilometer and the surface roughness average was Ra 2.5. The dimensions of steel cross-section 10 xx 10 cm2 were used. Epoxy zinc phosphate primer was used as interlayer in this work to provide corrosion protection and improve the adhesion of the coating with steel substrate. The intumescent coating was applied using a brush on the steel substrate and an average thickness of the coating was maintained at 1.5 mm and it was measured by digital vernier caliper. The coated substrates were cured in the oven at 70 °C for overnight.

Expansion of coating with different talc content.

Enhanced Fire Safety: The study demonstrates that talc additives significantly improve the fire protection performance of intumescent coatings. This enhancement is critical for the safety of buildings, particularly in preventing structural collapse and ensuring safe evacuation during fire incidents.

Advancement in Fire Protection Technology: By identifying and validating the effectiveness of talc as an additive, this research contributes to the advancement of fire protection technologies. This could lead to the development of more effective fire retardant materials in the construction industry.

Regulatory Compliance: The findings support the creation of coatings that meet stringent building regulations and fire safety codes. This can have a significant impact on construction practices and the materials used in buildings worldwide.

Enhanced Adhesion Properties: The improved adhesion properties of the coatings, demonstrated by a shear strength of 7 MPa for a formulation with 20% talc, ensure that the coating remains intact under fire conditions, maintaining its protective function.

Enhanced Material Performance: The incorporation of fillers such as metal oxides (e.g., Al2O3, TiO2) and hexagonal boron nitride improves the overall fire resistance characteristics of coatings. These enhancements include better char formation, reduced flammability, and improved adhesion to substrates.

Expansion of char before and after water immersion test.

Physical properties of intumescent coating and char were determined by observing the expansion of char and the quality of char yield after burning at 800 °C. Table 2 shows the physical properties of coating and char after burning at 800 degC. For F1, F2 and F3, the coatings were less viscous and had a sticky surface compared to F4 and F5. The coating of F5 was highly viscous due to the increased talc content (15-20%) and the decreased epoxy content. After fire test, the results of char expansion were measured based on the thickness of the coating (in X times with considering error + 0.05) were: 3.80 (F1), 4.65 (F2), 6.00 (F3), 6.75(F4) and 6.85 times (F5). This expansion is measured with reference to the original coating thickness on the substrate are given in Fig. 2.

Regulatory Compliance and Safety Needs: The construction industry is increasingly focused on meeting stringent building regulations that mandate fire protection to ensure the safety and integrity of structures during fires. This is driven by regulations aimed at preventing structural collapse to allow safe evacuation (Purkiss and Li, 2013). The enhanced fire performance of intumescent coatings with talc additives makes them highly attractive for compliance with these regulations.

Superior Fire Protection Performance: The study demonstrates that intumescent coatings with talc additives significantly improve fire protection performance. Specifically, a formulation containing 20% talc reduced the substrate temperature to 75 °C for a fireproofing time of 100 minutes, indicating excellent insulation properties. The presence of talc enhances the formation of a silicate layer 'foam' on the char, acting as a barrier to protect the substrate.

Improved Char Expansion and Thermal Stability:The addition of talc improves char expansion and thermal stability. The study shows that talc enhances the thermal degradation and increases the residual mass of the coatings, with a formulation containing 20% talc showing a 55.55% higher residual mass compared to other formulations. This improved char structure and thermal stability provide better protection to the substrate during fire exposure.

Micrograph of char after 358 h of water immersion test of (a) SEM image of F1char, (b) SEM image of F2 char (c) SEM image of F3 char, (d) SEM image of F4 char (e, f) SEM image of F5 char.