| Summary: | Substitution of Styrofoam balls on coarse aggregates reduced concrete self-weight. Coating on Styrofoam ball surface makes ball has shell on its surface and could increase the adhesive strength between ball surfaces and cement paste. The coating materials made by mixing of Portland cement and RCC-15 (Residual Catalytic Cracker-15) as pozzolanic material. 20 mm diameter Styrofoam balls are used. Coarse aggregates substituted by 5%, 15%, and 20% Styrofoam balls. The test specimens used three 10x20cm cylinders for each variant. Beam specimens of 15x15x60cm used for bending strength test by third point loading method. The testing of mechanical properties were 7, 14, and 28 days compressive strengths, 28 days split-tensile strengths and 28 days flexural strengths. The experimental results of concrete with various Styrofoam ball substitutions of 5%, 15%, and 20% at 28 days show the average compressive strengths are 27.6 MPa, 24.3 MPa, and 20.3 MPa, the splittensile strengths are 2.5 MPa, 2.2 MPa, and 1.7 MPa, and the flexural strengths are 5 MPa, 4.5 MPa, and 3.8 MPa, respectively. The compression strength could be predicted by density ratio method and air content method. The experimental results show that all of the variants of Styrofoam ball coarse aggregates concrete are adequate to achieve structural strength, and have nearly compressive strengths compared with the prediction by density ratio method and air content method. Styrofoam balls substitution content could be increased to make the concrete density below 1,900 kg/m3 and compressive strength above 17.5 MPa to reach structural lightweight concrete performance.
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