ACI Concrete Strength Testing Technician Practice Test

Why should neat cement paste caps not be used on dry specimens?

1. They may absorb moisture

2. They may shrink and crack

3. They can increase weight

4. They may not bond properly

The correct answer is: They may shrink and crack

Using neat cement paste caps on dry specimens is generally discouraged because these caps are prone to shrinkage as they cure. When applied to a dry specimen, the paste can lose moisture to the underlying concrete, leading to excessive drying as the curing process continues. This loss of moisture can cause the neat cement paste to shrink and crack, which can adversely affect the integrity of the test results. The presence of cracks may lead to inconsistent transfer of load between the concrete sample and the testing apparatus, ultimately resulting in unreliable compressive strength measurements. While the other options present valid concerns about the use of neat cement paste caps, they do not directly address the primary issue associated with applying these caps to dry specimens in the context of tests for concrete strength.