By eliminating the need for further compaction from the outside, High strength self-compacting concrete (HSSCC) is a unique kind of concrete with improved Workability. The incorporation of Supplementary Cementitious Materials (SCMs) into HSSCC manufacturing is widely regarded as crucial for economic, technological, and ecological reasons. For this reason, GGBS and Fly-ash is an innovative, potentially useful mineral admixture based on slag that may be used as an SCM. Reinforcing concrete buildings in harsher settings may benefit from using Glass Fibre Reinforced Polymers (GFRP) rebars as an alternative to steel rebars. The purpose of this research is to conduct the first investigation of its kind into the flexural behaviour of steel and GFRP-reinforced GGBS and Fly-ash based SCC beams. The effects of reinforcement and HSSCC mix proportions on concrete and reinforcement's bearing capacity, ultimate deflection, cracking, and energy absorption were investigated. Notable results showed that steel-reinforced beams broke under flexure, whereas GFRP beams broke brittlely.