Mechanisms of carbon black in multifunctional cement matrix: Hydration and microstructure perspectives

•The comprehensive effects of carbon black on workability, strength, hydration, and microstructure on cement properties were evaluated.•Carbon black obviously decreases flexural strength in the early period.•Carbon black mainly shows a filler effect in the cement matrix.•2% carbon black contributes to optimizing matrix microstructure. Carbon black (CB) possesses a good prospect for producing multifunctional building materials. The existing literature, however, mainly reported the electrical properties. Systematic reports on the influence of CB on hydration and microstructure are still lacking. Thus, the variations in fluidity, strength, hydration, porosity, and microstructure of CB-cement materials were thoroughly examined. It revealed that CB shows a clear negative effect on fluidity and early flexural strength, but proper CB increases compressive strength. The pore structure and the interfacial transition zone are optimized manifestly by 2% CB (by mass of cement).