ACI Concrete Strength Testing Technician Practice Test

Leather shims are acceptable only when the gap between the specimen surface and the blocks is:

1. Less than 0.010 inches

2. Equal to 0.015 inches

3. Not more than 0.015 inches

4. Greater than 0.020 inches

The correct answer is: Not more than 0.015 inches

Leather shims are permissible for use to ensure proper alignment and surface contact when testing concrete specimens, particularly in hydraulic testing machines. The standard specifies that leather shims can be used to fill gaps, provided that the gap does not exceed a certain size. When the gap between the specimen surface and the blocks is not more than 0.015 inches, the use of leather shims is acceptable. This limitation is to ensure that the shims do not introduce significant deformation or compromise the integrity of the load distribution during testing. If the gap is larger than this threshold, there could be concerns regarding the accuracy of the test results, as the shims would not adequately support the specimen. Thus, the guideline effectively maintains the precision of concrete strength tests by allowing the use of leather shims only when the surfaces can still achieve a reliable connection.