Effect of Shrinkage Reducing Agent and Steel Fiber on the Fluidity and Cracking Performance of Ultra-High Performance Concrete.

Due to the low water-cement ratio of ultra-high-performance concrete (UHPC), fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete. In this study, the effects of different types of cementitious materials, chemical shrinkage-reducing agents (SRA) and steel fiber (SF) were assessed. Compared with M2-UHPC and M3-UHPC, M1-UHPC was found to have better fluidity and shrinkage cracking performance. Moreover, different SRA incorporation methods, dosage and different SF types and aspect ratios were implemented. The incorporation of SRA and SF led to a decrease in the fluidity of UHPC. SRA internal content of 1% (NSRA-1%), SRA external content of 1% (WSRA-1%), STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%, 8.3%, 9.2% and 25%, respectively. However, SRA and SF improved the UHPC shrinkage cracking performance. NSRA-1% and STE-0.7 reduced the shrinkage value of UHPC by 40% and 60%, respectively, and increased the crack resistance by 338% and 175%, respectively. In addition, the addition of SF was observed to make the microstructure of UHPC more compact, and the compressive strength and flexural strength of 28 d were increased by 26.9% and 19.9%, respectively. [ABSTRACT FROM AUTHOR]