Concrete tensile strength relationships: flexural (modulus of rupture) and split tensile strength If fck is the characteristic compressive strength of concrete, the flexural/split tensile strength may be expressed as f = a * sqrt(fck). Identify the appropriate value of a for flexural strength.

Introduction:
Concrete is weak in tension. Codes provide empirical relationships linking tensile properties to compressive strength for preliminary design and serviceability checks. This question targets the coefficient used for flexural tensile strength (modulus of rupture).

Given Data / Assumptions:

• Characteristic cube strength fck.
• Relationship of the form f = a * sqrt(fck).

Concept / Approach:

For flexural strength (modulus of rupture), the recommended coefficient is about 0.7. For split tensile strength, a lower coefficient around 0.56 is often used. Recognizing which tensile property is referenced is key.

Step-by-Step Solution:

Verification / Alternative check:

Back-check against test data or code annex values; split tensile is lower (~0.56 * sqrt(fck)), confirming that 0.7 corresponds to flexural strength.

Why Other Options Are Wrong:

0.4, 0.5, and 0.6 are too low for flexural strength; 0.8 is unconservative.

Common Pitfalls:

Confusing split tensile with modulus of rupture; using fck in MPa but forgetting the square-root relationship which is sensitive to units.

Final Answer:

0.7