Study Of Mechanical Properties And Load Carrying Capacity Calculation Methods Before And After C-FRCM Strengthening Of Heavily Deteriorated RC Beams

Reinforced concrete(RC)structures in the harsh environment of coal mines are prone to premature deterioration.In the context of the "double carbon" objective and the requirement to ensure secondary use and safe production,it is important to accurately evaluate and predict the reliability and durability of RC structures,and to make life predictions and rehabilitation and reinforcement accordingly to ensure the reliability of RC structures.Based on the existing research results of the group,this thesis addresses the problem of severe degradation of the mechanical properties of heavily deteriorated RC beams,and analyses and studies both microscopically and macroscopically through both experimental and theoretical research.Finally,carbon fibre fabric reinforced cementitious(C-FRCM)reinforcement with woven carbon fibre mesh is used,and carbon fibre fabric reinforcement is used as a control group to investigate the effect of the same mesh rate but different number of reinforcement layers on the mechanical performance enhancement and the advantages of woven carbon fibre mesh reinforcement.The results include the evolution of mechanical properties of materials in deteriorated RC beams,the degradation of mechanical properties of RC beams,the enhancement of mechanical properties of deteriorated RC beams after reinforcement and the calculation of load capacity before and after reinforcement.The main conclusions are as follows:(1)The evolution laws of material properties of deteriorated concrete and mechanical properties of reinforcement were revealed,and the microscopic mechanism of the evolution of material mechanical properties of deteriorated RC beams was discovered.Compared with the non-deteriorated beams,the damage degree and neutrality depth of the environmentally deteriorated beams increased by 390%-490% and 530%-591%,respectively,and the compressive strength decreased by 43.5%-55.9% in the time period of 616-728 days of deterioration.The coupled deteriorated beams show an increase in damage and depth of neutralisation of 390%-520% and 520%-665% respectively,and a reduction in compressive strength of 43.4%-65.1%;the corrosion rate of the reinforcement continues to increase and the mechanical properties continue to deteriorate.The maximum corrosion rates of hoop,longitudinal and erector bars were 26.89%,21.34% and 18.24% respectively,which were consistent with the characteristics of heavily deteriorated RC beams;the theoretical models of neutralisation depth,compressive strength,corrosion rate and damage degree of reinforcement and the nominal strength and corrosion rate of rusted reinforcement were established respectively.(2)The mechanical property degradation laws of heavily deteriorated RC beams were obtained.The corrosion damage of the heavily deteriorated RC beams was serious,with some of the protective layer peeling off and the reinforcement leaking out;the damage form of the RC beams in the heavy deterioration stage was moderate reinforcement damage,and the coupled deteriorated beams at 728 days of deterioration,with a small number of cracks at the time of damage,produced similar brittle damage;the load carrying capacity decreased as the degree of deterioration increased,and the corresponding deflection decreased under the same level of load.The overall load carrying capacity index of the RC beams deteriorated for616-728 days is in the range of 0.52-0.65,which is in line with the defined range for heavily deteriorated RC beams.The ambient deteriorated beam at 728 days of deterioration was 9.3%lower than at 672 days,and the coupled deteriorated beam at 728 days of deterioration was10.4% and 19.3% lower than at 672 and 616 days respectively.The ultimate load capacity of the coupled deteriorated beam was significantly lower than that of the environmentally deteriorated beam within the same deterioration time.(3)The mechanical properties of the heavily deteriorated RC beams were enhanced by C-FRCM reinforcement,which restrained the development of cracks better,and the development of cracks was more uniform with C-FRCM reinforced with woven carbon fibre mesh than with carbon fibre cloth reinforced with C-FRCM.The ultimate load capacity and ductility of the reinforcement were improved with increasing deterioration time by 39%,32%and 27% for 2 layers of 5 mm mesh and 30% and 22% for 4 layers of 10 mm mesh respectively.Although the increase in load capacity with carbon fibre reinforcement is better than that with woven carbon fibre mesh,the increase in ductility is weaker and more prone to brittle damage.When reinforced with carbon fibre woven fabric of the same distribution rate and different number of plies,the reinforcement with a smaller number of plies and smaller mesh has a greater improvement.As the degree of deterioration increases,the effect of reinforcement on the load-bearing capacity decreases.(4)The mechanical properties of light-medium-severe deteriorated RC beams were obtained,and the calculation method of the load capacity of deteriorated RC beams before and after C-FRCM strengthening was modified.The load carrying capacity of the deteriorated RC beams decreases with the increase of the deterioration degree,and the overall trend is "fast-slow-fast-faster",with the fastest decrease rate in the severe deterioration stage.Compared with the non-deteriorated beams,the load carrying capacity of heavily degraded beams decreases by 37.6%-43.1%,and that of coupled degraded beams decreases by35.2%-47.7%;with the increase of degradation time,the yield deflection and ultimate deflection of the degraded beams continue to decrease,and the yield load and ultimate load yield decrease accordingly.The load carrying capacity calculation method for deteriorated RC beams was modified to take into account the effects of concrete strength degradation,concrete section damage,strength utilisation of rusted reinforcement and reinforcement index.Based on the above factors and taking into account the effective utilisation rate of the VRCM and the strength utilisation rate of the fibres,the method of calculating the load carrying capacity of heavily deteriorated RC beams strengthened by C-FRCM is modified and its applicability is verified by combining the test data.The thesis has 52 figures,27 tables and 110 references.