Influence of Elevated Temperature on Performance of Ultra High Strength Fibre Reinforced Self Compacting Concrete (UHSFRSCC) Produced from Local Materials

: Exposure of concrete structures to elevated temperatures extremely affects its durability and service life. Therefore, evaluating the concrete performance after being exposed to high temperatures is very essential. This study investigates the effect of elevated temperatures (25 ℃ , 200 ℃ , and 300 ℃ ) in the furnace with a heating time of 1 h on residual mechanical, transport and microstructure properties of different UHSFRSCC concrete. This study presents a systematic experimental investigation to evaluate the effect of Silica fume (SF) (partially replaced by 20% cement), blended 5% Metakaolin (MK) with 15%SF (partially replaced by cement)and, Limestone (LS) Powder (partially replaced by 20% cement), and Quartz Powder (QP) (partially replaced by 34% sand) on fresh characteristics, the mechanical (compressive and splitting tensile strength), transport properties (sorptivity) and microstructure (SEM-EDS) properties of UHSFRSCC. The results reveal that, incorporating QP to UHSFRSCChas not significant effect on its rheological classes (flowability, viscosity and passing ability) while MK significantly decrease it.The mix containing 20%SF has a compressive, splitting tensile strength of 120.7 MPa and 13.6 MPa respectively after 28 days water curing .Moreover, incorporating 20%LS as cement replacement and replacing 5% MK by SF to mixture contained 34% QP as sand replacement improves compressive, splitting tensile strength and sorptivity by 9.6, 16.9 and 40.7% respectively under normal ambient temperature. Although relative residual compressive, splitting tensile strengths, transport and microstructure properties were gradually degraded by exposure to elevated temperature up to 300 ℃ , relative residualstrengths, transport and microstructure properties of UHSFRSCC were significantly increased with incorporating compound LS and/or MK powders as a cement replacement material.Incorporating compound 20%LS and 5%MK increases residual compressive strength by 10% and 19%while, residual splitting tensile strength significantly increases by 21% and 28% after exposure to elevated temperatures 200 ℃ and 300 ℃ respectively. Furthermore, residual sorptivity decreases by 39% after exposure to elevated temperatures. Microstructure results explain and consistent with compressive, splitting tensile strengths and transport properties.