Effect of Ca/Si ratio on the characteristics of alkali-activated ultra-high performance concrete (A-UHPC): From hydration kinetics to microscopic structure development

Ultra-high performance concrete (UHPC) produces higher carbon emissions than ordinary concrete. To achieve sustainable development of UHPC, this article explores the use of alkali-activated technology to create a lowcarbon UHPC, in which the effect of different Ca/Si ratios (from 0.7 to 1.5) on the performance of alkaliactivated UHPC (A-UHPC) is detailed analyzed. The obtained results show that with an increase of Ca/Si ratio, the properties of A-UHPC firstly increases and then gradually decreases. When the Ca/Si ratio is 1.2, the performance of the developed A-UHPC can be optimized, such as the 28-day compressive strength is 121.3 MPa, the relative content of C-(A)-S-H gel is 99.38%, the main chain length is 14.27, and the porosity is 4.28%. In general, this study can provide guidance for the formulation design and production of a new low carbon construction material in the future.