Testing the Effects of Sample and Grain Sizes on Mechanical Properties of Concrete

Lohrasb Faramarzi¹ and Hooman Rezaee²

¹ Associate Professor, Dept. of Mining Engineering, Isfahan Univ. of Technology, 84156-83111 Isfahan, Iran (corresponding author).

² Rock Mechanics Graduate, Dept. of Mining Engineering, Isfahan Univ. of Technology, 84156-83111 Isfahan, Iran

Doi:10.1061/(ASCE)MT.1943-5533.0002249  

Abstract: Concrete specimens used in this study as artificial rock samples were created to investigate the effects of grain size and specimen size on the mechanical properties of cementitious material. For this purpose, three concrete blocks were produced in which grain sizes of 12, 20, and 25 mm were used. The cylindrical specimens of diameter 56, 68, 72, and 94 mm were prepared. Nine concrete beams were created to determine the fracture toughness of the specimens. Results showed that enhancement in the uniaxial compressive strength of the specimens with diameter 56, 68, and 72 mm was monotonic as a result of the increased grain size, whereas it took a monotonic but decreasing trend in those 94 mm in diameter. Moreover, the results of bending tests indicated that fracture toughness and toughness factor increased with increasing grain size from 12 to 20 mm, whereas fracture toughness was found to decrease slightly when grain size increased from 20 to 25 mm. The findings presented here suggest that the SEL-I model predicted robust increases in strength with increasing size in specimens with a grain size of 12 mm, resulting in a fit of good quality for a grain size of 12 mm (R² = 0.90), whereas the coefficients of determination of R² = 0.69 and R² = 0.43 were reasonably obtained for specimens with grain sizes of 20 and 25 mm, respectively. Moreover, tensile strength decreased monotonically with increasing length-to-diameter ratio, whereas an opposite trend was observed with increasing grain size.   

keywords: Uniaxial compressive strength; Tensile strength; Fracture toughness; Bending; Grain size; Specimen size