Research On Compressive Constitutive Curve Of Recycled Concrete And Bond Behavior Between Steel Bar And Recycled Concrete After Exposure To High Temperatures

In recent years, fire accidents occurred frequently that brought heavy losses to people's lives and property due to the high concentration of the population and building. On the other hand, there are large number of construction waste to be treated worldwide while the building materials are greatly shortage, so it becomes a trend of development that recycled concrete is used in the construction of building structure..Therefore, a detail study is necessary about the mechanical properties of recycled concrete and reinforced recycled concrete after high temperature before the recycled concrete is widely used in structural engineering. Using the experimented studies and theoretical analysis methods, the compression constitutive relation of recycled concrete subjected after high temperature and the bond-slip performance of reinforced recycled concrete subjected after high temperature were studied. Completed works are as follows:Firstly, using super depth compared 3-D microscopic system after different temperature effect of concrete natural and recycled concrete compression destruction after the development of micro cracks to understand the interface bonding,through analysis it is concluded that after different temperature effect.Secondly, through uni-axial compression test of recycled concrete under high temperature, studied the stress-strain curve of recycled concrete with different recycled coarse aggregates replacement rate under different temperature conditions, established the stress-strain curves equation according to the curve characteristics of recycled concrete to high temperature.Thirdly, after passing the Center pullout test research of high temperature steel and bond-slip between recycled concrete performance, revealed in different temperatures, different recycled coarse aggregates replacement rate, the relative thickness of c/d stirrup and no transverse constraint conditions, such as under the influence of bond-slip characteristics, access to the corresponding bond-slip curve.Finally, assumption of equivalent strain based on damage mechanics theory analysis of a high temperature steel bars with bond-slip performance between recycled concrete, defined bond damage variable D, calculated damage evolution equation of D-S curve is established based on interface damage of bond-slip constitutive equation.Research main conclusions were as follows:(1) By observation and analysis using three dimensional imaging system showed that in after effects to different temperatures, when the weak side of internal damage to natural concrete aggregate-mortar interface;Recycled concrete compression damage when the internal order of the interface and relatively weak severity is:old aggregate-new mortar interface, old aggregate-old mortar interface, new-old mortar interface.(2) Under the same replacement rate, peak test of recycled concrete after high temperature stress decreased peak strain showed an increasing trend, and experience higher temperatures, peak stress, peak strain of larger peak stress maximum loss:53.8%, maximum peak strain as compared with 270.1%.(3) When the temperature of the specimen after less than or equal to 400?, with the increase of coarse aggregates replacement rate, peak stress decrease of recycled concrete, peak strain tend to increase;When the temperature of the specimen reaches 500?, appears contrary to the law, at the same temperature as the replacement rate increases and peak stress of recycled concrete as a whole tend to increase, and peak strain decreased.(4) In the same high temperature conditioning, replace the rate of 100% of recycled aggregate concrete peak stress is greater than other replacement rate results of peak strain is less than other replacement rate of peak strain.(5) Specimens without stirrups main failure modes of the specimens for fracturing, with stirrups main failure modes of the specimens for a split-pull damage.(6) Under the same replacement rate, experienced higher temperature of the specimen, specimen bond stress peaks, peaks greater slippage, bond stress peak maximum losses to 66.2%, peak maximum slip by 126.4%.Meanwhile, average peak with Stirrup specimen bond stress peak and average slip value must be greater than results of specimens without Stirrups; c/d relatively protected side thickness greater peak bond stress greater peak slip more.(7) When the temperature is less than or equal to 400?, each temperature has an optimal coarse aggregates replacement rate most advantageous to bond-slippage resistant specimens, and when the temperature reaches 500?, it is recycled coarse aggregates replacement rate, the greater, the better bond slippage resistance.