Rheological Properties Of Cementitious Composites With Nano/Fiber Fillers

Mechanical properties and durability of cementitious materials can be improved by adding nano/fiber fillers, and functional and intelligent properties can also be genereted. By this way, the sustainable development of cementitious composites can be achieved. However, nano/fiber fillers are characterized by small size, large specific surface area, and high aspect ratio for fiber fillers. As a result, the high water absorption capacity and poor dispersion of nano/fiber fillers may have great influence on the rheological properties of fresh cementitious materials. Not only the homogeneity and workability of fresh mixture are determined by the rheological properties, but also the hardened properties of cementitious materials have relevant with it. Considering these issues, rheological methods were employed in this paper to study the effect of different types and dosages of nano/fiber on the rheological behavior of fresh cement paste mixtures. Additionally, the relevance of rheology in fresh state and mechanical and/or electrical properties in hardened state of cementitious paste with nano/fiber fillers are discussed. Main contents and results are as follows:1 Rheological behaviors of cement paste with different contents of nano-silica (NS) and nano-titanium (NT) were compared. The effect of water to cement ratio, super-plasticizer, ultrasonic time and stirring speeds on the rheological properties of NS cement paste were also studied. The results indicated that both yield stress and plastic viscosity were increased with the increasing dosage of NT and NS. Rheological parameters were significantly affected by the variation of water to cement ratio and super-plasticizer concertration. In addition, the ultrasonic time and stirring speeds have influence on the rheology of fresh NS cement paste. Rheological properties of cement paste with NT and NS coincided to the Flatt and Liu model, and rheological parameters can be calculated accurately by these two models.2 Rheological behaviors of cement paste with carbon nanotube (CNT) and carbon nanofiber (CNF) were studied and made comparison with that of cement paste with nano-particles. The influences of water to cement ratio, super-plasticizer concertration on the rheology of the CNT cement paste were discussed and compared with the results of NS cement paste. The relationships between mechanical and electrical properties in hardened state and rheology in fresh state of CNT cement paste were also analyzed. The results showed that beyond the contents of 0.1 wt.% nano-fiber had prominent effect on the rheological properties of fresh cement paste than nano-particle. With the same dosages, CNT showed larger effect than CNF on the rheology of cement paste. Rheological property of CNT cement paste was more sensitive to water to cement ratio than that of NS cement paste. Additionally, the super-plasticizer absorption of CNT cement paste became saturated as the concertration of super-plasticizer is higher than 1.0 wt%. And then, the yield stress of CNT cement paste remained unchanged while the plastic viscosity decreased continuously. The decreased compressive strength and electrical resistivity of cement matrix in hardened state with CNT contents higher than 0.1 wt% can be explained by the poor rheology of CNT cement paste in fresh state.3 Rheological behaviors of cement paste with 3mm carbon fiber (CF) and 6mm CF were investigated and made comparison with the results of cement paste with nanofibers. The effect of water to cement ratio and super-plasticizer on on the rheology of the 3mm CF cement paste were studied and compared with the rheology of CNT cement paste. The results illustrated that the rheological parameters of cement paste with nanofiber were always higher than that of cement paste with micron fiber. There was a negative correlation between rheological parameter values and aspect ratio of fiber.