Experimental Investigation And Analysis On Drying-Shrinkage And Freeze-thaw Durability Of LHFRC

Our researchers have accomplished lots of test since 1997, it is indicated that Layered Steel Fiber Reinforced Concrete (LSFRC) and Layered Hybrid Fiber Reinforced Concrete (LHFRC) have excellent properties of flexural strength, fatigue resistance, crack resistance and durability. Compared with steel fiber concrete pavement, LHFRC has realized "using resources where they are needed mostly ". At the same time, the layered steel fiber and synthetic fiber combined in the LHFRC have realized "positive intermixing effect", which will open new vision for the LHFRC pavement.On the basis of the test in the previous stage, this paper presents experimental investigation on the dry-shrinkage and freeze-thaw resistance which are two of most important properties of the LHFRC pavement. By the standard test methods for 24 test specimens, the dry-shrinkage and freeze-thaw durability have been analyzed on ordinary concrete (OC), LSFRC, LHFRC and LHFRC with grinding slag and fly ash. The dry-shrinkage test indicates that at the age of 180 days, the dry-shrinkage ratio of LHFRC is 0.021% smaller than those of OC and LSFRC, namely relatively 26.9%, and the dry-shrinkage ratio of LHFRC with grinding slag and fly ash decreases 40.2%. However, there is minute difference between the dry-shrinkage ratio of the LSFRC and the OC. The freeze-thaw durability test indicates that relative dynamic modulus of elasticity of LHFRC and OC have nearly identical falling trend in the initial freeze-thaw phase, while the falling trend of LHFRC is slower than that of OC in the freeze-thaw damage propagation phase. Obviously, dry-shrinkage and resistance freeze-thaw properties of LHFRC are better than those of OC and LSFRC. At the same time, the mechanism of the dry-shrinkage and resistance freeze-thaw of the LHFRC has been investigated. In the end, a damage model has been formulated for the freeze-thaw resistance degradation of LHFRC. The damage model is based on the least squares theory and a damage variable D . Degradation equations for the LHFRC and OC have been regressed with the experimental data. They are identical in the initial phase, but different in the damage propagation phase. Furthermore, Steel fibers and polypropylene fibers are major factors that greatly increase the freeze-thaw resistance of concrete. The freeze-thaw resistance of LHFRC is better than that of the OC because steel fibers and polypropylene fibers have depressed deterioration of concrete.