ASTM C873/C873M-15 PDF Download

The ASTM C873/C873M-15 standard is a test method that is used to determine the compressive strength of concrete cylinders that have been molded in place using special molds attached to formwork. The concrete cylinder mold assembly consists of a mold and a tubular support member that is fastened within the concrete formwork before the concrete is placed. The elevation of the mold upper edge is adjusted to match the finished slab surface. The mold support ensures that there is no direct contact between the slab concrete and the outside of the mold, making it easy to remove the mold from the hardened concrete.

The strength of the cast-in-place cylinders can be used for various purposes, such as estimating the load-bearing capacity of slabs, determining the time for form and shore removal, and evaluating the effectiveness of curing and protection measures. The consolidation of the concrete in the mold can be adjusted to simulate the conditions of placement, but internal vibration of the concrete in the mold is generally not allowed unless there are special circumstances.

The standard also notes that there is not a unique relationship between the strength of cast-in-place cylinders and cores of the same age, due to differences in moisture condition, consolidation, specimen size, and length-diameter ratio. However, when undamaged cores can be drilled and tested in the same moisture condition as the cast-in-place cylinders, the strength of the cylinders can be expected to be on average 10% higher than the cores at ages up to 91 days, assuming the specimens are of the same size and length-diameter ratio.