ASTM C805/C805M-18 PDF Download

ASTM C805/C805M-18 is a standard test method that focuses on determining the rebound number of hardened concrete. The purpose of this test method is to assess the uniformity of concrete in place, identify variations in concrete quality within a structure, and estimate in-place strength if a correlation is established.

The rebound number is influenced by several factors, including the moisture content of the concrete surface, the type of form material or finishing used, the vertical distance from the bottom of the concrete placement, and the depth of carbonation. It is important to consider these factors when interpreting rebound numbers.

It is worth noting that different instruments of the same design may provide varying rebound numbers, ranging from 1 to 3 units. Therefore, it is essential to use the same instrument for comparing results. If multiple instruments are used, comparative tests on typical concrete surfaces should be conducted to determine the expected differences in readings.

The standard emphasizes that the relationships between rebound number and concrete strength provided by instrument manufacturers should only be used as indications of relative strength at different locations within a structure. To estimate strength accurately, it is necessary to establish a correlation between rebound number and strength for a specific concrete mixture and apparatus. This correlation is typically determined by measuring rebound numbers on the structure and testing cores taken from corresponding locations. At least two replicate cores should be taken from a minimum of six locations with different rebound numbers. The surface texture and exposure conditions of the test locations used for correlation should match those of the locations where strength estimates are to be made.

It is important to note that this test method cannot be used for the acceptance or rejection of concrete. Other standards should be consulted for that purpose.