Studying the Mechanical Properties and Microstructure of Concrete Containing Steel Slang exposed to High Temperature

Heat, both in transient and steady state, changes the physical and chemical properties of concrete. In addition, the use of slag with Portland cement is very effective on development of concrete microstructure. The main products of hydration process are cement paste and slag, which plays important role in increasing concrete strength, C-S-H and C-A-Fe-H microstructures. Based on this, this paper has focused on the concrete containing varying degrees of steel slag in order to get a deeper perception of the changing behavior of C-S-H and C-A-Fe-H due to being exposed to high temperature. In this regard, 150 cubic samples of concrete with zero, 5%, 10%, 15% and 20% replacement of steel slag to Portland cement were treated for 28 days in a moisture bath. Then, all samples were exposed for 1 hour to 25 to 800 ºC. The percentage of weight change, compressive strength and cracking behavior of samples were investigated. Furthermore, in order to evaluate the microstructural behavior of test samples in different temperatures, SEM photos and EDS were used. Based on the results, the behavior of concrete samples depends on the variations of C-S-H and C-A-Fe-H microstructures under high temperature. The compressive strength of samples containing 5 to 15% steel slag increased as compared to conventional concrete sample. Based on SEM photos, the reason for this increase is higher density of C-S-H and C-A-Fe-H microstructures and FeO(OH).