How many times must each layer be rodded when using a standard 6 x 12 inch cylinder?

In the context of concrete testing using a standard 6 x 12 inch cylinder, rodding is an important method used to compact the concrete in the mold. The purpose of rodding is to eliminate air pockets and ensure an even and dense mixture, which is critical for achieving accurate strength test results.

The correct answer indicates that each layer of concrete placed in the cylinder must be rodded 25 times. This number is based on established guidelines which specify that for every 2-inch lift of concrete, a consistent number of rodding takes place to compact that layer effectively. The 25 rodding actions ensure sufficient compaction and are a standard practice to ensure uniformity and reliability in strength testing.

Rodding with the specified number helps in achieving a homogenous sample which will impact the reliability of test results in subsequent strength evaluations. Without proper rodding, the results can be skewed due to inconsistencies in the density and distribution of the mix within the cylinder. Thus, following the proper rodding procedure is crucial to meet the standards laid out by ASTM specifications and to ensure that the test results are valid.