Effect And Mechanism Of Emulsified Asphalt Modification Of The Paste-aggregate Interface On Concretes Properties

Brittleness is the essential attribute of cement and concrete.Interface transition zone plays an important role in the brittle failure process of concrete.Based on the previous researches of the emulsified asphalt modified cement mortar,in this work,the emulsified asphalt pretreated coarse aggregates were used with the purpose of gathering of asphalt film in the ITZ.Thus,with the help of the high ductility of the asphalt film,the toughness of the concrete was expected to be improved in the brittle failure process of the concrete.The main works and achievements are as follows:The influence of emulsified asphalt content on the mechanical properties of concrete was studied.With the increase of emulsified asphalt content,the cube compressive strength of C30 and C60 concrete decreased,and the decline of C60concrete was more obvious.The stress-strain curves of C30 and C60 concrete were analyzed,and the constitutive relations of the two kinds of concrete were analyzed by Dr.Guo's model.According to the load-displacement curves of the concrete,the yield energy consumption and the ductility coefficient of C30 concrete gradually increased with the increase of the emulsified asphalt content,while the yield energy consumption of C60 concrete increased in the initial stage and then decreased,and the ductility coefficient increased gradually.The theoretical asphalt film thickness of different emulsified asphalt dosages was calculated,and the thickness of the asphalt film increased gradually while the microhardness value decreased,indicating that the deterioration of ITZ in the concrete was increased.The methods of changing the proportion and particle size of the modified aggregate and the secondary modification technology were put forward.The results showed that the mechanical properties of concrete were well improved by changing the proportion of modified aggregate,and the energy consumption of C30 and C60concrete increased 30%⁵0%with the replacement of 10%and 30%modified aggregates.The decrease of strength was less than 10%.The influence of four modification methods on the seepage,carbonization and freezing and thawing resistance properties of the concrete was studied.The results showed that with the increase of the content of the emulsified asphalt,the water absorption of C30 concrete increased initially and then decreased,while the water absorption of C60 concrete reduced.The deformable modulus of emulsified asphalt is much lower than that of cement,aggregate and ITZ.In the process of long-term carbonization,the emulsified asphalt is more easily deformed to provide a transmission channel for CO₂,and the carbonization resistance is deteriorated.The high temperature deformation characteristic of the emulsified asphalt relative to the concrete also determines its negative effect on the frost resistance of concrete.The freezing thawing cycle will make the volume of asphalt change and the temperature decreases,resulting in the shrinkage of the asphalt volume,which leads to the water easier to enter the ITZ and the freezing thawing damage.The influence of emulsified asphalt content on the porosity and element distribution in the ITZ of concrete was analyzed.The thickness of ITZ formed after emulsified asphalt modified aggregate is about 35⁴5?m,and the farther the location is away from the aggregate surface,the lower porosity there is.With the increase of the content of emulsified asphalt,the porosity of ITZ increases.The initial porosity reaches more than 55%under the addition of 0.7%and 1%.The EDS results show that the content of Ca at the aggregate is the highest and low around the aggregate.With the increase of the aggregate surface distance,the content of Ca increases and goes into a stable stage.The contents of Si and Al begin to increase after reaching the aggregate interface and tend to be stable.When the emulsified asphalt content is over0.7%,the 0⁵?m area around the aggregate is basically occupied by asphalt,and the contents of Ca,Si and Al decrease significantly.