Experimental Research On Freeze-Thaw Resistence Property And Impermeability For Adherence Of New-Old Concrete

The thesis is a part of 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 great civil and water conservancy engineering》 , and national nature science found(59778045) 《Study on mechanism of adherence of new-old concrete》 .Freeze-thaw resistance and impermeability usually are used as a key index to measure the durability of concrete, which are also as an important basis to evaluate the durability of new-old concrete adherence. In cold areas, seasonal and daily temperature variations have caused numerous freezing-and-thawing cycles, especially for those repaired hydraulic concrete structure, resulting in differential thermal expansion between the new and the old concrete. Differential expansion could contribute to bond damage, premature bond separation, or both, resulting in failure of the bond of new-old concrete. And the adherence of new-old concrete may produce seepage under water pressure. The author had conducted experimental research on the mechanical properties of the interfacial bond of new-old concrete exposed to freeze-and-thaw cycles and the impermeability under water pressure, and hoped that the research could be used to evaluate the safety and durability of bond performance after having been repaired and retrofitted.The main contents of research are as follows:1.Using composite cubic specimens of new-old concrete, the bond splitting tensile strength for the interface of new-old concrete in saturating state were explored when exposed to freeze-thaw cycling. 162 old concrete cubic Specimens were experienced zero, 25, 50, 75 and 100 and 125 freezing cycles for old concrete before bonded with new concrete to, and zero, 5, 10, 15, 20, 25 and 30 for 162 composite specimens were bonded prior to freezing-and-thawing. The freezing deteriorate mechanism of concrete itself and adherence of new-old concrete were discussed. The freezing cycles, roughness and types of adhesion agent were also investigated. The test results indicated that the bond splitting tensile strength decreased with increasing numbers of freezing-and-thawing cycles, and that the rate of decrease was greater for specimens that were bonded prior to freezing-and-thawing. The roughness and adhesion agent had different effect on the bonding strength.2. The bond splitting tensile strength of 216 composite cubic specimens with air-entraining agent were tested when subjected to zero 10, 20, 30, 40, 50 and 60 and 70 freezing cycles. The effect of air-entraining agent for the frost resistance of new-old concrete was studied. The test results indicated that the frost resistance of specimens for new-old concrete with air-entraining agent exposed to freezing cycles was two times that of those specimens without air-entraining agent.3. Using Z-shape specimens of new-old concrete, the bond shear strength for the interface of new-oldconcrete in saturating state were explored when subjected to freeze-thaw cycling. 162 Specimens were experienced zero, 25, 50, 75 and 100 and 125 freezing cycles for old concrete was frosted before bonded, and 5, 10, 15, 20, 25 and 30 for 135 composite specimens were bonded prior to freezing-and-thawing. The freezing cycles, roughness and types of adhesion agent were also investigated. The test results indicated that the bond shear strength decreased with increasing numbers of freezing-and-thawing cycles. The shear strength of new-old concrete, for those specimens were bonded before exposed to freezing-and-thawing, declined slowly with increased numbers of freezing-and-thawing cycles at the beginning of freezing cycles and abruptly decreased after a certain numbers of freezing-and-thawing cycles. And the rate of decrease was abrupt at the beginning of freezing for those specimens were bonded prior to subjecting to freezing.4. According to impervious testing machine, the composite impervious specimen was designed and 168 specimens we...