Study On Long-term Deflection Of RAC Beams Based On Creep And Shrinkage Test

Promotion and application of recycled concrete materials and structure,not only solves the problem of construction waste pollution to the environment,but also reduces the pressure of demand for natural resources,satisfies China’s ecological civilization construction and the requirement of the sustainable development strategy.At present shrinkage and creep behavior of recycled aggregate concrete and bearing capacity of recycled coarse aggregate beams are mainly studied in domestic and abroad.However,deflection research of recycled concrete beams under long-term load is rarely less,cycles of the existing study is short,quantity of recycled concrete specimens is relatively less,failing to form a mature theory and method.Based on creep and shrinkage prediction model of normal concrete,long-term deflection calculation method of normal concrete beams is put forward.Creep and shrinkage tests of recycled aggregate concrete of different water-cement ratios in 180 days are conducted,the influence of water-cement ratios and replacement ratios on creep and shrinkage of recycled aggregate concrete are analysed.Taking attached mortar as main research object,attached mortar contents of recycled aggregate are determined.amplified coefficient about creep and shrinkage of attached mortar are proposed.Shrinkage and creep prediction model of recycled concrete is established later,and the applicability of prediction model is verified.The main works and achievements including five aspects as follows:(1)Deflection of recycled concrete beams with three different recycled coarse aggregate replacement ratios are tested and the duration of the applied constant load is up to 6 years(nearly 2290 days).The development law of long-term deflection of recycled aggregate concrete is explored based on the experiment results of research group.The influence of recycled coarse aggregate replacement ratios and environment humidity on the long-term deflection is investigated in great importance."Hysteresis effect" is proposed with the long-term deflection development over time.(2)Long-term time-dependent deflection calculation formula of normal concrete beams is derived on the basis of the principle of virtual work.The calculation formula is simplified by using the age-adjusted effective modulus method.Based on the prediction model of normal concrete,long-term deflection calculation formula of recycled concrete is established.(3)Shrinkage and creep behavior tests of different replacement ratios of recycled concrete are conducted,the influence of replacement ratio and water-cement ratio on shrinkage and creep behavior of recycled concrete is investgated.Adhesive mortar content of recycled coarse aggregate is measured,adhesive mortar content on shrinkage and creep behavior of recycled concrete is preliminarily analyzed,the fact that adhesive mortar is the key factor of long-term deformation of recycled concrete is clearly confirmed.(4)Taking adhesive mortar content of recycled coarse aggregate as research object,creep and shrinkage amplified coefficient of the adhesive mortar is put forward based on theoretical analysis.And then shrinkage and creep prediction model of recycled concrete is established,calculation precision is gained for selecting suitable model.(5)Based on shrinkage and creep prediction model of recycled concrete,long-term deflection of recycled concrete beams under long-term load is calculated and analysed,and the applicability of long-term deflection formula is also verified.Learned from the long-term deflection practical method of Code for Design of Concrete Structures,the practical calculation method is put forward for recycled concrete beams.