Effects of Replacing Cement with GGBS and Fly Ash on the Flexural and Shear Performance of Reinforced Concrete Beams

Cement has historically been a major contributor to carbon dioxide emissions, and substituting cement in concrete with alternative cementitious materials will lead to a decrease in carbon footprints. A vast amount of literature focuses on the mechanical properties and performance of concrete partially replaced with different cementitious materials. However, the literature on the structural performance of concrete with different cementitious materials is very limited. Therefore, the main aim of the current experimental study is to evaluate the flexural and shear performance of reinforced concrete (RC) beams cast with various replacement percentages of ordinary Portland cement (OPC) with supplementary cementitious materials (SCM) such as ground granulated blast furnace slag (GGBS) and fly ash. A total of 33 RC beams were cast with 50% and 70% replacement of cement with GGBS and fly ash. In addition, the tensile and compressive strengths of the different mixes with GGBS and fly ash were also compared with the 100% OPC mix at 28 and 56 days. All beams were subjected to monotonic four-point bending tests and load-deflection response curves along with failure modes were presented. The experimental results showed that the average compressive and tensile strength of mixes with GGBS and fly ash replacement were comparable with OPC. The mixes with 50% replacement and higher usage of GGBS showed higher compressive strengths compared to mixes with 70% replacement. In addition, the flexural performance of beams with GGBS and fly ash were comparable to the specimen with 100% OPC. Even GGBS and fly ash replacement increased the stiffness and yield strength of the beam specimens by 36 and 16% compared to the control specimen. The specimens tested at 56 days with higher usage of fly ash and 50% replacement showed the highest flexural load as compared with other specimens. In the case of the shear specimens, the normalized ultimate shear capacity of RC beams is not significantly affected when OPC is replaced with 50% and 70% of GGBS and fly ash, respectively. Therefore, it can be concluded that the overall behavior of SCM beams was comparable to that of the control OPC beams. The ACI 318-19 design guidelines were also used to predict the flexural and shear capacity of RC beams cast with GGBS and fly ash. The aforementioned experiments indicate the viability and effectiveness of cement replacements in concrete with SCM, which in return, contribute to lower carbon footprints.