Properties Of Aggregate Interlocking Concrete And Its Formation Mechanism

The conventional concrete overemphasizes workability,although high-flowability concrete facilitates the construction of concrete structure and saves labor costs,the increasing amount of cementitious materials increases the hydration heat,decreases the volume stability,and increases the risk of aggregate segregation,which is conducive to the stability and service performance of concrete structures.Distributing-filling aggregate process(DFCA)overcomes the contradiction between the workability of the fresh concrete and the volume fraction of aggregate and can produce aggregate interlocking concrete with good performance.In this paper,the coarse aggregate interlocking concrete prepared with the distributing-filling coarse aggregate process is used as the main research object,and in order to interpret the effect of coarse aggregate on the concrete performance,the following jobs were carried out.(1)The relationship between the mechanical properties of mortar and concrete and the volume fraction of aggregate and the influence of different factors on the DFCA concrete were investigated.The image analysis method was combined with existing mathematical models to propose a more accurate quantitative model of the mesoscopic structure in concrete,then the quantitative relationship between mechanical properties and mesoscopic structure was analyzed.The results indicate that coarse aggregate has stronger interlocking effect than fine aggregate.The compressive strength and elastic modulus present a increase trend with the increase of coarse aggregate volume fraction,but high volume fraction of coarse aggregate would lead to the decrease of flexural strength.DFCA process effectively improves the compressive strength,elastic modulus and splitting tensile strength,and the suitable surface modification of DFCA could further improve the compressive strength of DFCA concrete.In addition,the quantitative relationship between the mesoscopic structure and the coarse aggregate volume fraction was improved,and the quantitative interlocking effect of coarse aggregate was obtained.(2)The experimental study of the influence of coarse aggregate on the permeability,drying shrinkage and frost resistance of concrete was conducted to clarify the mechanism of the effect of coarse aggregate on these properties.The dilution effect of coarse aggregate is the direct factor to improve the penetration resistance and volume stability of concrete.the percolation effect of interfacial transition zone increases with the increase of coarse aggregate volume fraction,and it is more significant in the higher strength grade concrete.The restraint effect becomes more and more significant with the increase of concrete strength grade.High volume fraction coarse aggregate could worsen the frost resistance of concrete,while the frost resistance of aggregate interlocking concrete could be significantly improved by prolonging the curing age and using air entraining agent,a hypothesis model was proposed for interpreting the effect of coarse aggregate on the frost resistance of concrete.(3)In order to verify the applicability of the concept of aggregate interlocking concrete,DFCA process was applied in the preparation of the recycled aggregate concrete.Compared with the ordinary concrete,recycled aggregate concrete prepared with DFCA process has better compressive strength,elastic modulus,permeability resistance and volume stability,and they have comparative frost resistance.The analysis of meso-and micro-structure in DFCA concrete shows that DFCA process is beneficial to improve the homogeneity of concrete and the bond between coarse aggregate and paste.(4)To interpret the improvement mechanism of aggregate interlocking concrete,finite element simulation study based on random aggregate model was conducted.The positive and negative effects of aggregate and the evolution model of concrete homogeneity as the volume fraction of aggregate increases are proposed.The improvement effect of DFCA process on the compressive strength of concrete is verified,but it needs to be based on the good bond of aggregate and paste.In conclusion,a series of research work is carried out on the mechanical properties,durability and performance improvement mechanism of aggregate interlocking concrete in this paper,which provides theoretical support for the popularization and application of aggregate interlocking concrete and lays the foundation for the further researches.