Experimental Research On Adherence Property Of Fresh Fiber Reinforced Concrete To Old Concrete

Bonding Fresh concrete to old concrete is a discussible question that often related to actual project of concrete engineering. The study on behavior of adherence interface has important value in terms of theory and engineering application. Referenced to the subject "Research on mechanism of adherence and measure method of young on old concrete", which is sub-subject of national momentous foundational research subject(Climbing Project B)—《The foundational study on safety and durability of huge civil and water conservancy engineering》, a systemic study of bonding fresh fiber reinforced concrete on old concrete is carried out in the thesis. A series of experiments and research on the mechanical properties of the bonding interface between fresh fiber concrete and old concrete, such as shearing and splitting tensile strength, has been conducted. And the durability of freezing-thaw resistance and impermeability on bonding interface has also been studied. The theory of fracture mechanics are adopted in the analysis, and some analysis have been carried out in shrinkage difference between fresh concrete and old concrete through restriction shrinkage test.The main contents of research are as follows:1. Using Z-shape specimens, the bonding shear property of fresh fiber reinforced concrete to old concrete was explored. 93 bonding specimens were experimented and the main influence factors were researched, such as the type of fiber, the content of fiber, roughness of interface and adhesive agent. The test results indicated that the bonding shear behavior of fresh to old concrete is improved with the using of fiber in fresh concrete. In some range of fiber content, with the increase of fiber content, the bonding shear strength of fresh to old concrete continuously increase, the shear deformation property of bonding interface is improved and the utmost deformation is increscent when the shear failure of bonding specimens occurred. Based on experiments, the relation curve of shear stress-deformation on bonding interface of fresh fiber concrete to old concrete and the calculating formulae of shear strength of fresh fiber concrete to old concrete were put forward.2.111 composite cubic specimens of fresh fiber concrete to old concrete were test for behavior researching of bonding splitting tensile and the main influence factors were analyzed. In some range of steel fiber volume fraction, with the increase of steel fiber content, the test results indicated that the bonding splitting tensile strength continuously increase and for steel fiber volume fraction being 1.5%, bonding splitting tensile strength of fresh steel fiber concrete to old concrete increase 14.1% compared with ordinary concrete to old concrete. On the other hand, the using of steel fiber in fresh concrete can improve behavior of deformation on splitting tensile testing. Polypropylene fiber in fresh concrete can increase bonding splitting tensile strength similar to steel fiber but for polypropylene fiber content being 1.5Kg/m~3, bonding splitting tensile strength of fresh polypropylene fiber concrete to old concrete increase 18.1% compared with ordinary concrete to old concrete. The orientation of adhesive interface has some influence on bonding strength that the bonding splitting tensile strength of level adhesive interface is higher than vertical adhesive interface. Based on experiments, the calculating formulae of splitting tensile strength of fresh fiber concrete to old concrete were put forward.3. Subjected to freeze-thaw cycle, splitting tensile test of 219 composite cubic specimens of fresh fiber concrete to old concrete were carried out. The freeze-thaw damage mechanism and main influence factors were analyzed. It was found that the damage of fiber concrete were continue cumulate under freeze-thaw cycle and the relative dynamic modulus and strength were reduced, but the mass losing of specimens were increase. The freeze-thaw cycle have important influence on bonding splitting tensile property of fresh fiber concrete to old concrete. With the increase of freeze-thaw cycle, the bonding splitting tensile decrease rapidly. The using of fiber in fresh concrete can increase bonding splitting tensile strength of bonding specimens subjected to freeze-thaw cycle. For certain freeze-thaw cycle, in some range, with the increase of fiber content in fresh concrete, the bonding splitting tensile strength continually increase and when the times of freeze-thaw cycle is higher, the influence of fiber is more prominent. Based on experiments, the calculating formulae of splitting tensile strength of new fiber concrete to old concrete subjected to freeze-thaw cycle were put forward.4. The composite impervious specimen was designed and 114 bonding specimens were presented. The main influence factors on bonding seepage properties of fresh fiber concrete to old concrete were discussed. Also the seepage properties and mechanical parameter, such as equivalent hydraulic fracture width, permeability coefficient and seepage law were explored. The test results indicated that the using of fiber in fresh concrete can improve the impermeability of fresh to old concrete. In some range, with the fiber content increase, the impermeability of bonding interface was enhanced. For steel fiber volume fraction being 1.5%, the increment ratio of steel fiber on bonding impermeability reached to 27% and for polypropylene fiber content being 1.5Kg/m~3, the increment ratio of polypropylene fiber on bonding impermeability reached to 60%. Based on experiments, the calculating formulae of average permeability coefficient of fresh fiber concrete to old concrete were put forward.5. The double direct shear specimen with notch was designed for the mode II fracture. 57 specimens of fresh fiber concrete to old concrete and 144 fiber concrete specimens subjected to freeze-thaw cycle were carried out mode II fracture test. The main influence factors on mode II fracture properties of fresh fiber concrete to old concrete were discussed. The test results indicated that the interfacial treatment method had some influence on mode II fracture properties of fresh fiber concrete to old concrete. With the interfacial roughness increase, the mode II fracture toughness of adhesive interface. The using of adhesive agent can improve the mode II fracture toughness of fresh fiber concrete to old concrete. Adding fiber to fresh concrete, the mode II fracture properties of fresh fiber concrete to old concrete were obviously improved. For steel fiber volume fraction being 2.0%, the mode II fracture toughness of fresh fiber concrete to old concrete increase 25% compared with ordinary concrete to old concrete, and for polypropylene fiber content being 1.5Kg/m~3, the increment was16.3%. Using of the fiber in concrete, the mode II fracture properties of concrete can be improved great. With the increase of fiber content, the mode II fracture toughness of concrete was continuously increased and this increment influence was more obvious under freeze-thaw cycle. The cycle of freeze-thaw has great influence on the mode II fracture toughness of fiber concrete and with the increase of cycle, the mode II fracture toughness was decrease. Based on experiments, the calculating formulae of the mode II fracture toughness of fiber concrete subjected to freeze-thaw cycle and adhesive interface of fresh fiber concrete to old concrete were put forward.6. Tests of free shrinkage of 162 specimens of fiber concrete and restriction shrinkage of 162 specimens of fresh fiber concrete to old concrete were carried out. The influence of shrinkage difference between fresh concrete and old concrete on adhesive property of fresh fiber concrete to old concrete was explored, and the influences of main factors on adhesive interface restriction shrinkage were discussed, such as the type of fiber and the content of fiber in fresh concrete. The experiment result indicated that the shrinkage difference between fresh concrete and old concrete can been effectively reduced by adding steel or polypropylene fiber to fresh concrete. These decreases of shrinkage difference can reduce shrinkage force on adhesive interface, as a result, the adhesive property of fresh fiber concrete to old concrete can been improved and these influence was more obviously with the increase of fiber content. The test results indicated that the free shrinkage strain of fiber concrete has a mode of hyperbola function and the unification calculating formulae of free shrinkage strain of fiber concrete were put forward. Based on experiments, a mechanics model about restriction shrinkage of fresh fiber concrete to old concrete has been found.