Evaluation of strain gage lengths for testing limestone and granite aggregate concretes

An experimental program was conducted to determine an appropriate length of strain gage for use in testing limestone and granite aggregate concretes. Variables in the test program included type and size of aggregate, and length of strain gage. Test specimens consisted of concrete cylinders fitted with a mechanical dial gage, and with multiple electrical resistance strain gages ranging from 120 mm (4.7 in.) to 5 mm (0.2 in.) in length. Cylinders were subjected to compression loading. Strains reported by the strain gages were compared to the strains calculated using dial gage readings. Recommendations are given for appropriate length of strain gages to be used with limestone aggregate and granite aggregate concretes.