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Several years ago the Alabama State Highway Department decided to investigate the applicability of reef shell as aggregate for concrete. Considerable difficulties were encountered in the investigation in attempting to produce a shell concrete with acceptable technical properties. The main problem was the inadequate workability of the shell concretes. Finally, a combination of crushed reef shell and beach sand was found that appeared to provide adequate concrete for selected structural purposes.
These results indicate that concrete of suitable strengths for certain purposes can be produced from reef shell and beach sand aggregates even though these aggregates do not meet the usual requirements concerning grading, particle shape, and abrasion loss. Concrete with a compressive strength of 2500 psi, flexural strength of 550 psi, and adequate workability can be obtained by combining 40 percent (by weight) of sand, 60 percent (by weight) crushed reef shell, 6 bags/yd3 (564 lb/yd3 = 335 kg/m3) cement, and suitable amounts of fly ash and air entraining agents.
The reef shell and beach sand are available in areas where there is a scarcity of suitable aggregates for concrete. The use of reef shell and beach sand in these areas would be less costly than “imported” aggregates to produce concrete for uses where high strength and high abrasive resistance is not required. These uses could include retaining walls, structure foundations, subpavements, and construction involving massive concrete.
abrasion loss, aggregates, angularity, beach sand, compressive strength, concretes, consistency, flexural strength, grading, internal structure, reef, slump, splitting strength, water-cement ratio
Professor and research coordinator of Engineering, Northern Arizona University, Flagstaff, Ariz.