The thermal degradation of concrete is a result of the coupled heat penetration, temperature-dependent degradation of materials and thermally induced deformation. This paper presents an experimentally validated three-dimensional finite element study of normal strength concrete cylinders coated with different thicknesses of intumescent coatings. The temperature-displacement ABAQUS model with Concrete Damage Plasticity (CDP) and temperature-dependent material properties was validated with the experimental data of unprotected and 2 mm-coated concrete cylinders, which were exposed to 500 °C for 5400 s. The intumescent coating was represented by an equivalent-layer approach with temperature dependent thermal conductivity; its physical volumetric expansion was not explicitly modelled. A parametric study was then performed on uncoated and 1, 2 and 4mm coated cylinders at 100, 300, 500 and 700 °C. The coating thickness was found to significantly affect transient heat penetration and the subsequent mechanical response. The 4-mm coating retained 84.89% of the compressive strength at 700 °C versus 36.75% for the uncoated concrete, reducing the strength loss from 63.25% to 15.11%. Thicker coatings also reduced the heat penetration into the core, thermal induced tensile damage and displacement, proving that coating thickness is a crucial parameter to control the thermal protection and residual concrete performance.
