Effect of Elevated Temperature on Microstructural and Durability Properties of High-Strength Concrete-Containing Eggshell

Researchers have recently discovered that eggshell contains a significant amount of calcium carbonate through the characteristics of both fresh and hardened concrete by partially substituting cement with eggshell powder (ESP) at room temperature. The objective of this experimental investigation was to examine the microstructural and durability characteristics of high-strength concrete exposed to elevated temperatures using ESP as partial cement replacement. The impact of elevated temperature intensity (200, 400, 600, and 800°C) for one hour of exposure on the specimens and natural air-cooling method was studied. Various ESP cement blending percentages (0%, 5%, 10%, and 15%) were examined through different microstructural and durability tests such as workability, fire resistance, scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy, and 3D optical surface profiler, air content tests, ultrasonic pulse velocity, weight loss, spalling and color changes, water absorption, and acid attack experimental tests. According to the findings, the amount of ESP exceed 5% replacement reduces the workability of fresh concrete mixtures. The best performance was reached by a mixture comprising 5%ESP specimens, with values of 63.41 and 64.07 MPa at ambient and 200°C, respectively. SEM results of 5%ESP at 200°C illustrate a decrease in the occurrence of pores and act as a bridge to form crystals between CH and C─S─H. The XRD result also indicates a high amount of jennite (C─S─H gel) was formed at 200°C due to the melting of ESP, which densifies the crystal of C─S─H. Regression analysis provided a more reliable expression for the relationship between the residual compressive strength and UPV with R² values of 0.9833 and 0.9966 for control and 5%ESP mixes, respectively. As a result, it was determined that concrete with 5%ESP as a partial cement replacement performs better over time than control concrete and has the potential to be used in construction.