Shape and size effect on the compressive strength of ultra-high performance geopolymer concrete: Effects of steel fiber and binder material composition

Ultrahigh performance geopolymer concrete (UHPGC) is a novel engineering material that can significantly reduce the environmental impact of concrete production, while utilizing industrial by-products. The compressive strength of concrete is highly dependent on the shape and size of tested specimen. Disregarding the specimen shape and size effects may result in incomplete understanding of the compressive performance of UHPGC. However, very few studies have documented these effects, to date. In this study, the influence of steel fiber content and binder material composition on the shape and size effects of the compressive strength of UHPGC are investigated. The results indicate that UHPGC exhibits more pronounced shape and size effects than Portland-cement–based concrete and ultra-high performance concrete. The size effect of the compressive strength of UHPGC is more noticeable with increased steel fiber and silica fume contents and reduced fly ash content. Moreover, the size effect is more prominent in prismatic specimens than in cubic ones. Both the steel fiber and binder material composition affect the shape conversion factor of UHPGC. Formulas for the size effect of the compressive strength of UHPGC are proposed, based on the obtained experimental data.