| Self-compacting concrete(SCC)is highly flowable,homogeneous,non-segregating concrete that can pour the framework and reinforcement easily without any manual and mechanical consolidation,and exhibiting great hardened mechanical and durable properties as well.However,SCC usually contains high proportional content of cementitious material,which leads to high hydration heat,shrinkage and creep.And the CO2 emission produced by concrete production will increase the environmental pollution as well.In order to realize the green ecology of SCC,the green SCC with low cementitious material in this study was designed based on compressible packing model of particle packing theory,which can balance the workability and mechanical performance.On the basis of the above problems and purposes,this study includes the following aspects:According to compressible packing model of particle packing theory,the research on the paste and mortar systems was carried out.Firstly both paste and mortar level systems consisting of different materials parameters on the variation laws of packing density were analyzed,and meanwhile based on compressible packing model,the variation of different material composition parameters on the rheological properties of paste and mortar was studied by the orthogonal design method.Thus the relationship model of the mortar packing density and rheological properties was established based on theory of solid particle concentration,providing a theoretical basis for the design of green SCC with low cementitious material content.Based on the study of paste and mortar packing density effects on rheological properties,the influence of different material parameters including the amount of cementitious materials,sand ratio,the mixed volume of superfine sand powder and fly ash on the packing density of concrete was studied by the orthogonal design method.And in the meantime,the effect tendency of the mixture packing density on SCC workability performance was revealed by the variation of aggregate and powder volume ratio.On this basis,the analysis and comparison of three kinds of particle distribution curve model of concrete performance were conducted.The results proved that the SCC optimized by CPM model can balance workability and mechanical performance,and the green SCC performance of low cementitious material mixed with fly ash and nano Ti O2 was further studied as well.The mixture density of the reasonable range of 0.8150~0.8350 was concluded based on the relationship between packing density and SCC properties.And the flow performance of the corresponding SCC met the requirements of workability,exhibiting great passing capacity and anti-segregation.The 28 d compressive strength of the hardened concrete was above 35 MPa,and the minimum amount of 340 kg/m3 was achieved of cementitious materials.On this basis,mixed with 5% nm Ti O2,low cementitious material dosage SCC was produced for more than C40.According to the study on compressible packing model and SCC,the design method that can balance workability and the mechanical performance of the low cementitious materials green SCC was recommended,and the feasibility and practicability of this method was verified. |
