Impact of micromechanics on dynamic compressive behavior of ultra-high performance concrete containing limestone powder

To improve sustainability and reduce costs, interest in using limestone powder (LP) in ultra-high performance concrete (UHPC) has been increasing in recent years. Incorporating LP changes packing, characteristics of C–S–H and pore structure of interfacial transition zone (ITZ) and matrix by physical and chemical effects. However, the influences of LP replacement on the mechanical properties of UHPC, from micromechanics to macroscopic impact behaviors, have not been well understood. Herein, mercury intrusion porosimetry (MIP), thermal gravimetric (TG), nanoindentation test and Split Hopkinson pressure bar (SHPB) test are performed to reveal the relationships between the micromechanical properties and the dynamic performances of UHPC. Results show that appropriate amount of LP incorporation optimizes the packing, leading to a narrower space and more densely compacted C–S–H that improves the percentages of high-density C–S–H and ultra-high density C–S–H in ITZ. The higher density of C–S–H results in a higher steel fiber-matrix bond strength, which benefits a higher dynamic compressive strength and energy absorption while a lower dynamic increase factor. More low-density C–S–H are generated due to the dilution effect of excessive LP, leading to a weak steel fiber-matrix bond strength that deteriorates the impact resistance. Additionally, the mechanism of LP enhancing the quality of C–S–H in ITZ is proposed, which favors understanding the relation between macro dynamic performance and interfacial behavior at the micro and nanoscale