Rheological properties of cementitious composites with nano/fiber fillers

In this paper, rheology of cement pastes with various types of nano- and micro-fillers are tested by rheometer and the rheological behaviors are described by modified Bingham model. The fillers include nano-SiO2, nano-TiO2, carbon nanotubes (CNTs), carbon nanofibers and carbon fibers. Yield stress and plastic viscosity of cement pastes are calculated and compared. Experimental results indicate that the rheological properties are strongly correlated with the types and content of fillers, the w/c ratio, the superplasticizer (SP) content, the ultrasonic time and mix rates. High specific surface area of fillers is the main reason affecting the rheology of cement paste. The yield stress of cement paste with fiber fillers is much higher than that with particle fillers due to the intertwining effect of fiber fillers. The rheological properties can be effectively regulated by w/c ratio with extremely small change, especially for cement paste with CNTs. The SP dosage exists a saturation point that above this dosage the fluidity of paste rises slowly. Ultrasonic treatment can overcome the problem of filler aggregation and significantly decrease the yield stress of cement paste. Both yield stress and the plastic viscosity of cement paste decrease with the increasing mixing rate in a certain range. However, the effect of the mixing rate is inferior to ultrasonication.