The Mix Design Optimization And Its Effect On The Fracture Properties Of Fiber Reinforced Self-Compacting Concrete

The self-compacting concrete is a heterogeneous compound material, when some single material is mixed;Some performances of self-compacting concrete are improved. But such enhancement of the performance is based on a specific level, and the multi-phase and multi-level performance of concrete is not improved comprehensively. This is the reason of its limitation. If the overall performance of the self-compacting concrete wants to be enhanced with greater degree, the added fiber is also multi-level, so hybrid fiber self-compacting concrete is formed. If a single fiber is adopted to strengthen the self-compacting concrete, its effect is limited, while the application of hybrid fiber can make up for one’s deficiency by learning from other strong points. But at present researches and engineering applications about the hybrid fiber self-compacting concrete are not sufficient, particularly about the hybrid effects of different fibers are not clear and the interpretation model of strengthening mechanism has not formed its system.This thesis centers on the goal of enhancing crack resistance performance of self-compacting concrete, aiming at the plain SCC, polypropylene fiber reinforced SCC, steel fiber reinforced SCC and hybrid fiber reinforced SCC; studies on adding different type of fiber to enhance the crack resistance performance and explores hybrid effect of different fiber. We have completed the work of the following aspects:(1)The effects of each component on the workability of SCFRC are analyzed in theory, and the methodology of desiralbe mix proportion with good filling ability and segregation resistance are founded. The methodology is that the correlations of steel fibres and the sand to total aggregate ratio, additional dosage of admixtures and fibre content can be established with the adjustment of the sand to aggregate ratio, cementitious materials content, water content and dosage and type of chemical.admixtures.(2) Cracking tests of polypropylene fibers in three sizes,sing-doped and mix-doped with SCC by same mixing technique and in same dose ratio,were completed.The results show that,Polypropylene fiber obvious reduced the cracking area of the self-compacting concrete, under the same dosage,the more the polypropylene fibers is,the smaller the cracking area is; The mixed blend of fine polypropylene fibers with different resistance performance is better than that of a single size.so as to effectively reduce cracks and rearch the crack-resist purposes in different phases and levels. And polypropylene fibers mixed with the size of 6 mm and 12 mm at lower dosage, have good resistance crack-resist.(3) Three point beam test and induced cracking experiment were applied, to discuss the effects of polypropylene fiber with different content and size on the self-compacting concrete fracture toughness and fracture energy. The test results indicate that the addition of fiber has extensively improved the fracture properties of SCC. The addition of polypropylene fiber has no impacts on the KIC, but increases the GF. With the increase dosage of polypropylene, GF increase respectively,and the varying of KIC has no disciplinarian;Different geometry size fiber hybrid can improve self-compacting concrete fracture energy, but the effect is limited.(4)Three point beam test and induced cracking experiment were applied, to discuss the effect of steel fiber with different content and types on the self-compacting concrete fracture toughness and fracture energy. The test results indicate that the addition of steel fiber can significantly improve the fracture properties of SCC.As the increase of steel fiber volume ratio, the fracture parameters of steel fiber reinforced SCC increase differently. In comparison with the dumbbell steel fiber and waved steel fiber, the addition of bowed steel fiber to SCC improves its fractural properties more.(5)Three point beam test and induced cracking experiment were applied, the fracture properties of hybrid fiber reinforced SCC and the synergy effect on SCC have been investigated. The test results indicate that a positive synergy effete between steel fiber and polypropylene has been observed at low fiber dosage and the synergy effect disappears with the increase of fiber dosage. Steel fiber plays a key role on the improvement of fracture properties of hybrid fiber reinforced SCC. The improvement effete of polypropylene on the fracture properties of hybrid reinforced SCC is small. Bowed steel fiber is more effective on the improvement of fracture properties of hybrid fiber reinforced SCC.