Recent advances in cementless ultra-high-performance concrete using alkali-activated materials and industrial byproducts: A review

This paper offers a comprehensive review of recent advancements in cementless ultra-high-performance concrete (UHPC) that employs alkali-activated materials and industrial byproducts. Initially, the raw materials used in fabricating cementless UHPC, focusing on their physical and chemical attributes, are summarized and analyzed. Subsequently, the impact of various ingredients, their combinations, the water-to-binder (W/B) ratio, alkali activators, and fiber reinforcement on the properties of both fresh and hardened cementless UHPC are investigated. The durability of cementless UHPC is also compared with its conventional counterpart based on ordinary Portland cement. The environmental benefits, like reductions in CO2 emissions and energy use due to the absence of cement, are highlighted. With the adoption of alkali-activated materials instead of regular cement, CO2 emissions from UHPC production can be curtailed by roughly 70–75 %. Newly introduced strain-hardening cementless UHPC based on alkali-activated materials is discussed, with a focus on its tensile characteristics influenced by several factors such as fiber type and the sand-to-binder ratio. Lastly, the innovative approach of using hydrated lime and calcium oxide in cementless UHPC is examined, bypassing traditional alkali activating solutions.