Developing ultra-high performance concrete with different strength grade based on mix proportion sensitivity factor analysis

Abstract Owing to the excellent strength and durability, ultra-high-performance concrete (UHPC) has been used for fabricating large-scale and important infrastructures. However, mix proportion of UHPC is still the core factor influencing its workability, strength, cost and energy resource consumption. Based on this, the amount of cementitious materials, water-binder ratio, and the content of steel fibers were matched to obtain UHPC with required workability and strength according to three-factor five-level orthogonal range analysis considering the interaction of these three parameters. Experimental results show that the water-binder ratio and steel fiber content is the primary factor to guarantee the fluidity/compressive and flexural strength of UHPC, respectively. For developing UHPC with compressive strength grade of 150 MPa and flexural strength higher than 50 MPa, the amount of cementitious materials (including cement, silica fume, cenosphere, and fly ash) and the content of steel fibers should be higher than 1000 kg m −3 and 2.5 vol.%, and the corresponding water-binder ratio is equal to 0.16. When the aim is to fabricate UHPC with compressive strength grade of 120 MPa and flexural strength higher than 40 MPa, the water-binder ratio can be increased but should be lower than 0.20 with the increasing amount of cementitious material, and the volume fraction of steel fibers should be higher than 1.5 vol.%. High steel fiber content and water-binder ratio all easily coarsens the microstructure and pore structure of UHPC, and this phenomenon cannot be compensated by using high amount of cementitious materials. It should be adjusting the matching degree of amount of cementitious materials and water-binder ratio to obtain a slurry with appropriate fluidity and cohesiveness, and then content of steel fibers can be selected to perform without adverse effects.