Effects of Elevated Temperatures on the Properties of High Strength Cement Paste Containing Silica Fume

High strength concrete (HSC) production is worldwide increased and gradually replacing the normal strength concrete (NSC). The cement matrix of concrete is the essential part that governs the behavior and strength of concrete. Several researchers have focused on the performance of hardened cement paste (HCP) at ambient temperature such as using different types of supplementary cementitious materials (SCM). However, the performance of HCP after exposure to elevated temperatures requires further evaluation. The present study investigates the influence of different replacements of silica fume (SF) to cement and different water/binder ratios (w/b) on the compressive strength of HCP before and after exposure to elevated temperatures. Eighteen mixes have been prepared and tested. Results of compressive strength tests at ambient temperature were ranged from 58 to 102 MPa depending on the difference of w/b. Furthermore, a new method has been adopted for comparing the responses of HCP at elevated temperatures "heat endurance". Results showed that using SF enhances the residual compressive strength of HCP after exposure to elevated temperatures due to the pozzolanic reaction and the filler contribution. Mixes containing 6%, 12%, and 15% of SF have shown the highest relative residual compressive strength values for 0.30, 0.35, and 0.40 w/b, respectively. Consequently, the results were significantly affected by changing the w/b ratio. Finally, different measurement techniques were provided to support the work, including Thermo-Gravimetric (TG), Computed Tomography (CT), and Scanning Electron Microscope (SEM) analysis to characterize the loss of mass, porosity, and microstructure alteration of HCP.