ASTM C469 testing provides a stress to strain ratio value and a ratio of lateral to longitudinal strain for hardened cylindrical concrete at whatever age and curing conditions may be designated. ASTM C469 is a compression test whereby a load is applied with a Constant-Rate of-Traverse (CRT) type machine until a specified stress. The modulus of elasticity and Poisson’s ration values will be found within the working stress range (0 to 40% of the ultimate strength). These values are used to determine the size of structural members, the quantity of reinforcements, and to compute the stress for observed strains. The modulus of elasticity under static rate will be less than values found under dynamic or seismic rate and greater than values under slow load application. Before conducting ASTM C469, it is important to read the entire specification in the relevant ASTM publication.
Determine the ultimate strength of a companion specimen by following ASTM C39. This involves applying a compressive axial load until failure occurs. Place the specimen on the platen so the axis of the specimen is aligned with the center of thrust of the spherically seated bearing block. Apply the load specified in the standard continuously and without shock until failure. Ensure the specimen fails within the prescribed permissible time tolerances in the specification.
Attach the required strain-measuring equipment (compressometer-extensometers). Place the specimen on the lower platen. Align the axis of the specimen with the center of thrust of the spherically seated bearing block and slowly bring the block to bear load on the specimen. This will ensure uniform seating is obtained. Apply the load at a constant rate within the range specified by the standard until it reaches 40% of the ultimate load. Return the load to zero at the same rate. The first loading is primarily used to seat the strain measuring equipment and should not be recorded.
ASTM C469 recommends completing at least two subsequent loadings to ensure repeatability. If repeatable, average the results. Apply the load at a constant rate within the range specified by the standard until it reaches 40% of the ultimate load. Return the load to zero at the same rate. During loading, record applied load, longitudinal, and transverse strain when the strain reaches 50 millionths and when the applied load is equal to 40% of the ultimate load. Ambient temperature and humidity should be maintained as constant as possible through the duration of this test.