Mesostructural Characteristics Of Concrete With Aggregate Shape And Application

In studying the physico-mechanical properties of concrete, it is usually modeled as a three-phase composite material, composed of aggregates, interfacial transition zone (ITZ) and cement paste. The current experiments and theoretical analysis show that the mesostructure of concrete, such as the aggregate size distribution, aggregate volume (area) fraction, size and distribution of micro-cracks, interfacial transition zone (ITZ) thickness, and pores, are the important factors that affect the macroscopic properties of concrete. With the increasing development of computer technology and numerical analysis, the study of the quantitative relationship between the characteristics of mesostructure and the mechanical properties of concrete has become one of the major directions in the field of concrete technology.The intention of this thesis is to study the mesostructural characteristics of concrete and to predict the chloride diffusivity of concrete. First, by introducing an auxiliary ellipse, the octagonal aggregate is constructed, which is closer to the practical aggregate. Based on the simulation technique of concrete mesostructure, a simulation algorithm is presented for the generation and distribution of octagonal aggregates with periodic boundary conditions. The effects of the aggregate shape, maximum aggregate diameter, aggregate gradation and aggregate area fractions on the nearest surface distance distribution and two-point probability function are evaluated in a quantitative manner. Second, based on the simulated distribution of octagonal aggregates, a numerical algorithm is developed for the ITZ area fraction in concrete by the Monte Carlo method. The validity of the numerical algorithm is verified by the approximate analytical solution. A numerical method is presented for the coordination number and aggregate area fraction threshold of ITZ percolation in concrete. The effects of key factors on the coordination number and aggregate area fraction threshold are quantitatively evaluated. Finally, as an application, a numerical method is presented for predicting the chloride diffusivity of concrete with aggregate shape. By comparing with the experimental results obtained from the literature, the validity of the numerical method is verified. The effects of the aggregate shape, maximum aggregate diameter, aggregate gradation, aggregate area fraction, ITZ thickness and ITZ chloride diffusivity on the chloride diffusivity of concrete are evaluated in a quantitative manner.