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EFFECTS OF AGGREGATE SIZES ON THE CONCRETE STRENGTH

ABSTRACT

The effects of aggregate size, and content on the behavior of normal and high-strength concrete, and the relationships between compressive strength, flexural strength, and fracture energy are discussed. The concrete mixtures incorporate either basalt or crushed limestone, aggregate sizes of 12 mm (h in.) or 19 mm (3/4 in.), and coarse aggregate contents with aggregate volume factors (ACI 211, 1-91) of 0.75 and 0.67. Water-to-cementitious material ratios range from 0.24 to 0.50. Compressive strengths range from 25 MPa (3,670 psi) to 97 N'fPa (13,970 psi). Compression test results show that high-strength concrete containing basalt produces slightly higher compressive strengths than high-strength concrete containing limestone, while normal-strength concrete containing basalt yields slightly lower compressive strengths than normal-strength concrete containing limestone. The compressive strength of both normal and high-strength concrete is little affected by aggregate size. High-strength concrete containing basalt and normal-strength concrete containing basalt or limestone yield higher compressive strengths with higher coarse aggregate contents than with lower coarse aggregate contents. The compressive strength of high-strength concrete containing limestone is not affected by aggregate content. Flexure test results show that high-strength concrete containing basalt yields higher flexural strengths than concrete with sirnilar compressive strength containing limestone. The flexural strength of high-strength concrete containing limestone is limited by the strength of the rock and the matrix. The flexural strength of high strength concrete containing basalt is controlled by the strength of the rock and the interfacial strength at the matrix-aggregate interface. The flexural strength of normal strength concrete containing the basalt or limestone used in this study is not affected by aggregate type and is limited by the matrix strength and the strength of the interfacial transition zone. The flexural strength of normal and high-strength concrete is not affected by aggregate size. Normal and high-strength concretes containing basalt yield higher flexural strengths with higher coarse aggregate contents than with lower coarse aggregate contents. Fracture energy test results show that normal and high-strength concretes containing basalt yield significantly higher fracture energies than concretes containing limestone. The fracture energy of high-strength concrete decreases with an increase in aggregate size, while the fracture energy of normal-strength concrete increases with an increase in aggregate size. High-strength concrete containing basalt and normal strength concrete containing limestone yield higher fracture energies with higher coarse aggregate content than with lower coarse aggregate contents. The fracture energy of high-strength concrete containing limestone and normal-strength concrete containing basalt is not affected by aggregate content. There is no well-defined relationship between fracture energy and compressive strength, or fracture energy and flexural strength. However, there is a close relationship between the peak bending stresses obtained in the flexure and fracture tests.