Study On Long-term Deflection Of Recycled Concrete Beams Based On Creep And Shrinkage Prediction Model

The wide promotion and application of recycled aggregate concrete and recycledaggregate concrete structures in the constructional engineering can make full use ofenormous quantity of construction waste which leads to the occupation of land andsecondary pollution caused by the traditional landfill treatment of the waste on the onehand，also it makes the waste to be useful and solves the grim problem that thebuilding materials are becoming rare gradually and then makes the building materialsdevelop circularly on the other hand. The immeasurable benefits of economy，societyand environment brought by the widespread use of recycled aggregate concrete provethat it is a true environmentally friendly material and an important component of greenbuilding. At present，large number of researches on recycled aggregate concrete arefocused on the material properties and the design method of limit state of bearingcapacity，thus the achievements are rich relatively. However，studies on the deformationproperties about checking of serviceability limit states are rare，especially on thelong-term deformations. So，this serious problem has disadvantage on the legislation ofrelated code and the design of recycled aggregate concrete structures. Thus this papermakes studies on the bending stiffness and long-term deflections of recycled aggregateconcrete beams made with different replacement rate of recycled aggregate based on themethod which combines the experiment and theoretical calculation at first，and then thecalculation formula of bending stiffness is provided and the calculation formula oftime-dependent deformation is proposed based on the creep and shrinkage predictionmodel. At last，the practical calculation method of long-term deformation of recycledaggregate concrete beams is proposed. The main works and achievements including six aspects are as follows：（1）The experimental study on the bending stiffness of recycled aggregateconcrete beams is conducted，the destruction process and destruction model is clarified，the applicability of plane cross-section assumption is proved，the similarities anddifferences between recycled aggregate concrete beams and ordinary concrete beamsabout the rhythmicity of initial deformation are analysed and the main reasons causedthe differences are proposed.（2）The calculation formulas of key parameters used to calculate the stiffness arefitted again based on the experimental dates and stiffness analytic method，then thecalculation formula of bending stiffness is given. The formula is proved proper and canbe widely used to the related calculation based on checking of nationwide123datepoints (62experimental beams).（3）The experimental study on long-term deformation of three recycled aggregateconcrete beams is conducted and the duration of the applied constant load is39months(nearly1190days). A new long-term experimental device，called simply supportedloading beam with large-scale cantilever, is adopted in the experiment.The developmentlaw of total long-term deflection and additional deflection is summarized.The influenceof humidity of the surroundings and different replacement rate of recycled aggregate onthe long-term deflection is investigated.The similarities and differences betweenrecycled aggregate concrete beams and ordinary concrete beams about the long-termdeformation are analysed by contrast. At last，the“hysteresis effect”of the long-termdeflection in recycled aggregate concrete beams is proposed.（4）The adhere mortar adjusted coefficient about creep and adhere mortaradjusted coefficient about shrinkage，namedC AMandS AMrespectively，are proposedbased on the theoretical simulation and introduced to the three widely used creep andshrinkage prediction models which adopted by the ordinary concrete. And thus thecalculation formula of creep and shrinkage of recycled aggregate concrete is proposed.（5）The calculation formula of long-term time-dependent deflection of recycledaggregate concrete beams is derived based on the Aging Adjusted Effective ModulusMethod（AAEMM）and the proposed creep and shrinkage prediction model by themeans of the analysis of the mechanic property and deformation fixture. The calculated value fits well with the experimental value and the proposed formula can be used tocalculate the deflection at any time point.（6）The practical method to calculate the long-term deflection of recycledaggregate concrete beams is proposed and the calculation pattern is similar to the《Code for design of concrete structures》GB50010. The calculated value fits well withthe existing researches and the calculation precision meets the requirements well, thus itcan be used to calculate the long-term deflection under the serviceability limit states.The paper makes a study on the stiffness and long-term deflection of recycledaggregate concrete beams, the related calculation formula is proposed and the precisionmeets the requirements well. Thus, it lays a foundation for the design of recycledaggregate concrete structures.