Question

In the context of construction materials, which of the following statements is/are CORRECT?
 

• A. If the characteristic strength is defined as that value below which not more than 50% results are expected to fall, the target mean strength in mix design will be the same as the characteristic strength irrespective of the degree of quality control expected at the site.
• B. Ten percent fines value is a non-dimensional quantity.
• C. The stress-strain curve of concrete for 1-day duration of loading is associated with a smaller secant modulus of elasticity compared to the stress-strain curve of the same concrete for 10-minutes duration of loading.
• D. The increase of carbon in steel usually leads to an increase in its 0.2% proof stress.

Hint:

Remember: Ten percent fines value has units (it's not dimensionless), and characteristic strength considers 5\% chance of failure, not 50\%.

Answer 1

The Correct Option is A, C, D

Option (A):
This statement is correct. Characteristic strength is defined as the value below which not more than 5% of test results are expected to fall. The target mean strength is calculated based on the characteristic strength and the standard deviation, which depends on the quality control. The given statement is therefore a contradiction and hence CORRECT in pointing out the flaw.
Option (B):
Incorrect. Ten percent fines value has units (typically in terms of load), and hence it is not a non-dimensional quantity.
Option (C):
Correct. With shorter loading durations, concrete exhibits higher stiffness. A longer duration like 1-day results in a smaller secant modulus than that for a quick loading of 10 minutes.
Option (D):
Correct. Increasing the carbon content in steel generally increases its strength characteristics, including the 0.2% proof stress (yield strength).