Study On The Shear Performance Of High-Strength Concrete Beams Including Steel Fibers And Large-Particle Recycled Coarse Aggregates

China produces more than 41 million tons of construction waste in building construction every year,the traditional landfill method not only consumes a lot of manpower,financial resources,and easy to cause environmental pollution.After 1980,the United States and some European countries took the lead in the research,development and recycling of construction waste.Application of these construction wastes to actual projects such as roadbeds,pavements and non-load-bearing elements.The problem of wasted land resources is solved and environmental pollution is avoided.Nowadays,natural resources are seriously depleted,and this approach can realize the rational allocation of resources and improve the economic efficiency of the construction industry.The construction waste is made into recycled aggregate after a series of operations such as crushing and cleaning,and the concrete made after replacing or partially replacing natural sand and gravel is called recycled concrete.The study of the workability and mechanical properties of recycled concrete and its components is of great importance for its application in structural engineering.However,recycled aggregates have large porosity,high crushing value index,low compactness,strong water absorption,weak bonding ability,low aggregate strength and other shortcomings,which constrain the widespread use of recycled concrete and its components in building construction.Therefore,in this thesis,the recycled concrete mix ratio was improved and high-strength concrete with steel fibers and large particle size recycled coarse aggregates was obtained through mix ratio optimization.Meanwhile,four high-strength concrete beams with steel fibers and large particle size recycled coarse aggregates were designed and fabricated.The shear performance of the recycled concrete beams was analyzed by monotonic loading tests with recycled coarse aggregate replacement rate as the main variable.Shear reinforcement of pre-damaged recycled concrete beams was carried out by applying CFRP sheets.The differences in the shear performance of the diagonal sections before and after reinforcement of the specimens were compared.Based on the current code,a simplified calculation method for the shear bearing capacity of the diagonal section of high-strength concrete beams with steel fibers and large particle size recycled coarse aggregates with different recycled coarse aggregate replacement rates was proposed.And compared with the experimental results to verify the applicability of the formula.Numerical simulation of the test specimen was carried out using ABAQUS finite element analysis software.Finite element simulation results and experimental results were compared and analyzed.The validity of the model was proven.The main conclusions of this thesis are as follows.(1)The compressive failure mode of the specimens of high-strength concrete with steel fibers and large particle size recycled coarse aggregates was similar to that of ordinary concrete.When the water-cement ratio was 0.36,the replacement rate of fly ash and silica fume was 10%,and the amount of steel fiber was 1%,the compressive strength of regenerated high-strength fiber concrete with coarse aggregate of large grain size is higher and the working performance was better.(2)The high-strength concrete beams with steel fibers and large particle size recycled coarse aggregates all suffered shear compression failure under monotonic loading.With the increase of the replacement rate of recycled coarse aggregate,the shear load capacity of the The high-strength concrete beams with steel fibers and large particle size recycled coarse aggregates increased and the overall resistance to deformation was similar to that of ordinary concrete beams.For the specimens reinforced with CFRP sheets,the structural stiffness was significantly improved and the overall resistance to deformation was enhanced at the late loading stage.(3)The finite element model of the specimen established by ABAQUS was used to verify the validity of the model by selecting suitable material intrinsic relationships and relevant parameters to obtain simulation results that were more consistent with the test.(4)The calculation method of shear bearing capacity of recycled high-strength fiber concrete beams with large-size coarse aggregate under different recycled coarse aggregate substitution rates proposed based on the specification has good correctness,and the calculated values of the fitting formula are in good conformity with the measured values,which is a certain reference for practical projects.