The ASTM recently clarified the process for sample rejection for the C109 standard. In section 13 “Faulty Specimens and Retests”, a note (#12) was modified to include an example related to the range (lowest to highest) instead of the difference from the average. In the example, three cubes are broken at 31.0, 34.0 and 35.0 MPa. The average strength is 33.3 MPa and the range is 4.0 MPa. According to the 8.7% limit the range should be no greater than 2.9 MPa (33.3 * 0.087). Consequently the value farthest from the average (in this case 31.0) should be rejected. The new average is 34.5 MPa with a range of 2.6 MPa (7.6% for 2 cubes). The remaining cubes (34.0 and 35.0) are within the range, so the data set is accepted.

To test this in your LDMS, use the values given (31.0 MPa ~= 4495 psi, 34.0 MPa ~= 4930 psi, 35.0 MPa ~= 5075 psi) the first cube should be rejected. If Cube 1 is not automatically rejected your calculation may be based on % difference from average.

Figure 1 – Incorrect – 8.7% from average

Figure 2- Correct – 8.7% range, then 7.6% range (5002.5 psi ~= 34.5 MPa)

A product update is available which will revise the rejection calculation for C109 cubes. Please contact the customer care team for additional information.