Development and preliminary mix design of ultra-high-performance concrete based on geopolymer

Abstract This study reports a preliminary mix design of the geopolymer-based ultra-high-performance concrete (G-UHPC) developed using the alkaline activated alumino-silicate source materials. A combination of the sodium silicate (Na2SiO3) solution and sodium hydroxide (NaOH) was used as the alkaline activator, and the alumino-silicate source materials included the granulated blast furnace slag (GGBFS), fly ash and silica fume. The effect of the sodium silicate modulus, fly ash, GGBFS, Si/Al ratio, Ca/(Si + Al) ratio and steel fiber on the flowability of the fresh mixture and mechanical behavior of G-UHPC was comprehensively investigated via a series of flowability, compression and flexure tests. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses were conducted to reveal the performance enhancement mechanism based on the reaction products and micromorphology. It was observed that an increase in the sodium silicate modulus, GGBFS and Si/Al ratio negatively impacted the flowability of the fresh G-UHPC mixture, whereas a significantly positive effect on the flowability was observed on incorporating the fly ash. Overall, the compressive and flexural strength of G-UHPC exhibited an increasing trend, followed by a decline, on increasing the sodium silicate modulus, fly ash, GGBFS and Ca/(Si + Al) fractions. The compressive and flexural strength demonstrated an identical trend on increasing the Si/Al fraction at a CaO fraction of 0.1 or 0.2. On the other hand, an increment in the Si/Al fraction exhibited a negative impact on the compressive and flexural strength as the CaO fraction increased to 0.3. The steel fiber dosage negatively affected the flowability, whereas an increase in the steel fiber dosage enhanced the compressive and flexural strength. Further, the flowability and flexural strength could be effectively estimated from the length (Lf) -to-dimeter (Df) ratio (Lf / Df), whereas 1/(LfDf)could be used to estimate the compressive strength. The XRD and SEM analyses revealed the fundamental contribution of the mentioned factors on the reaction products and micromorphology of G-UHPCs. Eventually, suggestions have been made for the effective preliminary mix design of G-UHPC for the civil engineers.