Effect of fly ash replacement level on the shear strength of high-volume fly ash concrete beams

An experimental investigation was conducted to study the shear strength of full-scale beams constructed with high-volume fly ash concrete (HVFAC) - concrete with at least 50% of the cement replaced with fly ash - and conventional concrete (CC). This study includes two HVFAC mixes and one CC mix. The two HVFAC mixes are identical except for the amount of Class C fly ash replacement of cement, with one mix replacing 50% of the cement with fly ash and the other replacing 70%. This experimental program consisted of 18 beams without stirrups with three different longitudinal reinforcement ratios. The beams were tested under a simply supported four-point loading condition. The experimental shear strengths of the beams were compared with the shear provisions of both U.S. and international design codes (U.S. [ACI-318 and AASHTO LRFD], Australia, Canada, Europe, and Japan). Furthermore, the shear strengths of the beams were evaluated based on fracture mechanics approaches, modified compression field theory (MCFT), and a shear database of CC specimens. In addition, statistical data analyses (parametric and non-parametric) were performed to evaluate whether or not there is any statistically significant difference between the shear strength of the HVFAC and CC beams. Results of this study show that the HVFAC mix with 70% Class C fly ash has higher shear strength compared with the HVFAC mix with 50% Class C fly ash and the CC.