Creep Of Concrete And The Effect Of Creep On Mechanical Properties Of Concrete Components

Concrete creep is an important indirect action of concrete structural members.Creep causes redistribution of internal force and stress,and affects the behaviors of structural members.In order to accurately predict the creeo of concrete component and to clarify the influence of creep on the mechanical properties of concrete components,the following studies were carried out:(1)In order to investigate the creep of concrete with mineral admixture and the creep of reactive powder concrete,three strength grades concrete prisms with mineral admixture were tested for creep.The experimental results show that the creep of concrete with mineral admixture decreases with increase of compressive strength at loading age.Based on the results of creep of concrete prism with mineral admixture and reference,a creep model for concrete with mineral admixture was established considering the influence of compressive strength of concrete at loading age,contents of mineral admixture,and ratio between aggregate and cementitious material.(2)In order to investigate the strain recovery of concrete columns under axial compression after creep,22 prism concrete specimens with size 100 mm × 100 mm × 400 mm were tested for strain recovery of concrete columns after compression creep,with axial compressive strengths 53.6 MPa to 63.7 MPa at loading age.The loading age was 28 d,and the load duration time is 210 d.The compressive stress levels of concrete were 0.20 to 0.50.The experimental results showed that the initial strain recovery coefficient decrease with increase of stress level with the stress level under 0.5.Intial strain recovery coefficient is the ratio between initial recovery stain and initial strain at loading time.Creep recovery was proportional to creep with the stress level lower than 0.5.The creep recovery coefficient increased with the increase of concrete strength at loading age and loading age,however,decreased with load duration.The formula of initial strain recovery and the model of creep recovery considering the influence of some parameters were established.(3)In order to study the behavior of creep of reinforced concrete columns under axial compression and the influence of creep on the mechanical properties of reinforced concrete columns after creep,41 reinforced concrete short co lumns and 16 full-scale reinforced concrete columns were carried out for creep and axial compression after creep.The experimental results showed that the creep coefficient of reinforced columns decreased with increase of concrete strength at loading age and the ratio of reinforcement for the compressive stress levels of concrete under 0.4.The creep coefficient of reinforced column is the ratio between creep strain and initial strain at loading age.The creep model of reinforced concrete columns was established,which consider the influences of ratio of longitudinal compression reinforcement,axial compressive strength of concrete at loading age,loading age,and specimen size.The formula for the compressive strain corresponding the peak compressive stress of reinforced concrete columns under axial compression after creep was obtained.This formula took compressive strength of concrete at failure time,creep strain,and the size of specimens as independent variable.(4)In order to investigate the effect of strain gradient on the creep of concrete components and the mechanical properties of concrete components after creep,16 reinforced concrete beams were tested for creep and bending failure after creep.The strength grades of concrete in the beams were C30 to C80.The load levels of the beams were 0.3 to 0.7,which was the ratio between bending moment at stage of creep and flexural capacity.The relative pressure zone height of the beams were 0.15 to 0.45.The height of the beams were 150 mm to 600 mm.The experimental results show that the creep coefficient of curvature for reinforced concrete beams increaseed with increase of load level of reinforced concrete beams,decrease d with increase of reinforcement ratio of longitudinal tensile reinforcement,and d ecreased with increase the compressive strength of concrete at loading age.The creep coefficient of curvature for reinforced concrete beams is the ratio between the increased curvatures at stage of creep and initial curvatures of reinforced concrete beams.The curvature creep model for reinforced concrete beams was established,which based on the curvature creep model of Park.The proposed model introduced the influence coefficient of stress level of concrete at compression edge of beam on curvature creep,the influence coefficient of reinforcement ratio of longitudinal tensile reinforcement on curvature creep,the influence coefficient of compressive strength at loading age on curvature creep,and the influence coefficient of height for beams on curvature creep into Park curvature creep model.The formula for ultimate compressive strain of concrete at compression edge of reinforced concrete beams was obtained,which took initial strain of concrete at compression edge at loading time,creep strain,and standard cube compressive strength of concrete at loading age as independent variable.The ultimate compressive strain is the sum of initial strain of concrete at compression edge of beams at loading age,creep strain,and the increased strain of concrete after creep at the moment of bending failure.