Çiflikli M.Sarıdemir M.Soysat F.2019-08-012019-08-0120180950-0618https://dx.doi.org/10.1016/j.conbuildmat.2018.04.150https://hdl.handle.net/11480/1638Adverse effects of high temperatures (HTs) and freeze-thaw (F-T) cycles on the properties of hybrid fibers reinforced high strength concretes (HFRHSCs) containing silica fume (SF) and silica fume + metakaolin (SF + MK) were investigated in this study. Concrete mixtures without and with hybrid fibers (HFs) up to 20% replacement by the weight of Portland cement (PC) with SF and SF + MK were made with the water-binder ratio of 0.25. Experimental studies were conducted on the specimens prepared from these mixtures to determine the ultrasound pulse velocity (Upv), compressive strength (fc), flexural strength (fct,fl) and splitting tensile strength (fct,sp) values of concretes without and with HFs exposed to ambient temperature (AT) and HTs. Moreover, the experimental studies were performed to determine the Upv and fc values of concretes exposed to F-T cycles. Microstructure analyses were also conducted on the specimens to examine the changes in the matrix, interface zone and aggregate of concretes without HFs exposed to AT, HTs and F-T cycles. Experimental results have revealed that replacement ratios of SF and SF + MK have important effects on the properties of concretes without and with HFs. The experimental results have also shown that the fc, fct,fl and fct,sp values of the concretes with HFs are higher than the concretes without HFs. The Upv, fc, fct,fl and fct,sp values of the concretes with HFs have been affected more than that of the concretes without HFs due to the adverse effects of HTs. © 2018 Elsevier Ltdeninfo:eu-repo/semantics/closedAccessFreeze-thaw cyclesHigh strength concretesHigh temperatureHybrid fibersMicrostructure analysesArticle17450751910.1016/j.conbuildmat.2018.04.1502-s2.0-85046363000Q1WOS:000433656300048Q1