| Self-compacting concrete has a certain cohesiveness while maintaining a large fluidity to ensure that the mixture does not segregate and secrete water,and has good mechanical properties and durability after hardening.Compared with ordinary concrete of the same strength grade,the aggregate content of self-compacting concrete decreases,but still accounts for about 50%65%of the total volume of self-compacting concrete.It is an important component of self-compacting concrete,which has a significant impact on the fluidity of mixtures and the mechanical properties and durability after hardening.From the perspective of aggregate particle characteristics,this paper firstly studied the influence of sand ratio,aggregate gradation and coarse aggregate maximum particle size on the workability and compressive strength of self-compacting concrete based on the theory of surplus slurry,and the coarse aggregate gradation was optimized.Secondly,based on digital image processing technology,the Image-Pro Plus software was used to quantitatively characterize the shape characteristics of coarse aggregate.Under the premise of unchanged coarse aggregate gradation,the influence of particle shape characteristics on the void rate of coarse aggregate,the workability and compressive strength of self-compacting concrete was studied.Finally,considered the volume relationship between aggregate and slurry,the influence of aggregate volume content on the workability and compressive strength of self-compacting concrete under different water-binder ratios was studied,and an optimum design method of aggregate volume content based on the thickness of slurry coating layer was proposed.The conclusions obtained are as follows:（1）The sand ratio had the optimum value;when it increased from 0.43 to 0.49,the fluidity of self-compacting concrete mixtures increased obviously,the slump flow increased gradually from 570mm to 630mm,continued to increase sand ratio to 0.51,the filling capacity,passing ability and homogeneity of the mixtures decreased.The 7 d compressive strength of self-compacting concrete has no obvious regularity with the increased of sand ratio,the 28 d compressive strength was first increased and then decreased with the increased of sand ratio.Properly increase in the maximum particle size of coarse aggregate can improve the workability of concrete to a certain extent,but the maximum particle size should not exceed 19mm,otherwise it will increase the segregation tendency of the mixture,resulting in homogeneity and passing ability decreased;The 28 d compressive strength of self-compacting concrete decreased with the increased of the maximum particle size of coarse aggregate.（2）Based on the paste thickness on coated aggregates,the influence of gradation on the workability of self-compacting concrete is studied,the experiment showed that there was an optimal value of the paste thickness on coated aggregates.In a certain range,increasing the paste thickness on coated fine aggregates can improve the fluidity of mortar,and then improve the workability of concrete mixtures.Over a certain range,because the viscosity of mortar is too small,the segregation of mixtures occured,the workability was worse;increasing the paste thickness on coated coarse aggregates can improve the slump flow of concrete mixtures,but it has little effect on the time of T50000 and the passing ability was improved.However,when the paste thickness on coated coarse aggregates was too large,the mixtures were prone to segregation,resulting in poor workability.（3）With the increased of coarse aggregate sphere ratio from 0.524 to 0.5922,the accumulated void ratio decreased first and then increased;the slump flow of self-compacting concrete mixtures increased gradually from 585mm to 620mm,the time of T50000 decreased,the passing ability increased,and the stability of mixtures increased;the 7 d compressive strength of self-compacting concrete increased gradually from 35.9MPa to39.6MPa,the 28 d compressive strength increased from 45.7 MPa to 50.3 MPa.（4）There was an optimum aggregate volume content;within a certain range,with the decreased of aggregate volume content,the slump flow of self-compacting concrete increased gradually,the time of T50000 decreased gradually,the passing ability increased,and the fluidity of mixtures improved significantly;when aggregate volume content was too small,the mixtures appeared segregation and the workability was worse.The 7 d and 28 d compressive strength of self-compacting concrete increased first and then decreased with the decreased of aggregate volume content.（5）Based on the paste thickness on coated aggregates,the gradation and volume content of coarse aggregate can be optimized,and then the amount of cementitious materials in self-compacting concrete can be reduced,the volume stability of concrete can be improved,and the purpose of guiding mix proportion design of concrete can be achieved. |
