Aggregate gradation design of asphalt mixture with stone-to-stone contact based on fuller's model

Based on Fuller＇s model, a gradation design is presented for the load-carrying capacity of an asphalt mixture with stone-to-stone contact. The coarse aggregate gradation, fine aggregate and filler gradation are respectively designed for their different effects on an asphalt mixture with stone-to-stone contact. The equation of coarse aggregate gradation is deduced from the Fuller＇s model. Fine aggregate gradation is calculated by using Fuller＇s equation. The asphalt mixture with the 16 mm maximum size of aggregate is verified. When the coefficient of coarse aggregate gradation is 0.35 and fine aggregate gradation is 0.25, the volume parameters of asphalt mixture meet the technical specifications. Moreover, the high temperature stability and crack resistance at low temperature are all well.

Enhanced comprehensive properties of stereolithography 3D printed alumina ceramic cores with high porosities by a powder gradation design

Ceramic cores with complex structures and optimized properties are critical for hollow turbine blades applied in aeroengines.Compared to traditional methods,additive manufacturing(AM)presents great advantages in forming complex ceramic cores,but how to balance the porosity and strength is an enormous challenge.In this work,alumina ceramic cores with high porosity,moderate strength,and low high-temperature deflection were prepared using stereolithography(SLA)3D printing by a novel powder gradation design strategy.The contradiction between porosity and flexural strength is well adjusted when the mass ratio of the coarse,medium,and fine particles is 2:1:1 and the sintering temperature is 1600℃.The fracture mode of coarse particles in sintered SLA 3D printing ceramic transforms from intergranular fracture to transgranular fracture with the increase of sintering temperature and the proportion of fine powders in powder system.The sintered porosity has a greater influence on the high-temperature deflection of SLA 3D printed ceramic cores than grain size.On this basis,a"non-skeleton"microstructure model of SLA 3D printed alumina ceramic cores is created to explain the relationship between the sintering process and properties.As a result,high porosity(36.4%),appropriate strength(50.1 MPa),and low high-temperature deflection(2.27 mm)were achieved by optimizing particle size gradation and sintering process,which provides an insight into the important enhancement of the comprehensive properties of SLA 3D printed ceramic cores.

Establishment of a three-dimensional particle library for graded crushed stone based on a new aggregate morphology characterization method

The morphology of graded crushed stone(GCS)particles has an essential influence on the performance of aggregate mixtures.The impact of particle shape is a comprehensive effect that cannot be considered separately,leading to difficulties in establishing the relationship between the mixture properties and the aggregate morphology by using laboratory methods.The discrete element method(DEM)is an effective way widely adopted to reconstruct the morphology of particles and simulate performance tests of granular materials.However,selecting limited particles characterizing a real particle-assembly for simulation is still a challenge in current research due to the inherent rich variability of particle shapes.In this study,based on the acquisition of three-dimensional(3D)aggregate shapes by using laser scanning,ellipsoid index(EDI)translating the particle shape as a function of surface area,volume,and contour length is proposed to comprehensively evaluate aggregate morphology.Further,a particle library capable of characterizing aggregate morphology distribution is established based on the statistics of the corresponding morphological characteristics of particle samples.The model reliability is validated by carrying out a series of experimental and numerical penetration tests with nine different gradations.The established particle library can be used to model aggregate mixtures and the proposed simulation framework is promising for optimizing the mixture gradation design numerically.