عنوان مقاله [English]
In the present paper, the detailed mesostructure of concrete is geometrically generated and its compressive strength is numerically estimated using the 3D finite element method. The models contain two phases of mortar and coarse aggregates. The FE models of concrete are cubic in shape, with a side length of 80 mm. Aggregates are assumed to be spherical and behave in a linear elastic manner. The famous Fuller formula is utilized for the aggregate grading curve, and the simple sequential inhibition (SSI) technique is employed to fill the concrete cubes with the particles. Only aggregates bigger than 4.75 mm in diameter (gravel) are modeled, i.e., the particles smaller than 4.75 mm in diameter (sand) are not considered individually and assumed to be part of the
homogenized nonlinear cement paste. A modified version of the plastic-damage model, proposed by Lee and Fenves [J. Lee, G.L. Fenves, International Journal for Numerical Methods in Engineering 50 (2001) 487-506], has been adopted to simulate the inelastic response of the mortar. This constitutive model incorporates two independent hardening variables, namely; equivalent tensile and compressive plastic strains, and, thus, is capable of tracing damage evolution due to both tensile cracking and compressive crushing. In the first stage, the numerical implementation of the plastic-damage model is presented and then its validity is examined in a 3D FE element. Next, the effects of aggregate volume fraction, aggregate maximum diameter, and aggregate elastic
modulus on concrete compressive strength are studied. It is shown that: (1) compressive strength remains constant for specimens with aggregate volume fractions of up to 50%, and then increases significantly with grain content, (2) for the range of aggregate volume fractions studied in this paper, the maximum aggregate size has little influence on compressive strength, and (3) any increase in the elastic modulus of aggregates accentuates stress concentration near the aggregates, and, thus, reduces the compressive strength
of concrete samples. Finally, the results are satisfactorily compared with those presented by other researchers.