Minimum cement content by weight for durable cement concrete (road works) For achieving good strength and durability in cement concrete used for road construction, the recommended minimum cement content by weight of the concrete is typically around:

Introduction / Context:
Cement content in concrete influences strength, durability, and workability. Road concrete must resist abrasion, weathering, and cycles of wetting and drying. A minimum cement content (by weight of the concrete) helps ensure adequate paste volume for full aggregate coating and durable matrix formation.

Given Data / Assumptions:

• Ordinary Portland cement concrete for road slabs and related works.
• Typical target: balance between economy and performance.
• Proper water–cement ratio and curing practices are assumed.

Concept / Approach:
While modern specifications often prescribe minimum cement content in kg/m^3 (e.g., 300–360 kg/m^3 depending on exposure), traditional percentage-based teaching approximates the cement proportion in normal concrete near 1:2:4 mixes to about 15% by weight of the total concrete. This thumb rule aligns with achieving adequate paste for compaction and durability, provided w/c ratio is controlled.

Step-by-Step Solution:

Verification / Alternative check:
Converting common mix proportions to mass fractions under realistic specific gravities yields cement fractions near this value for general-purpose mixes, confirming the order of magnitude.

Why Other Options Are Wrong:
Much higher values (25–33%) are uneconomical and may cause shrinkage and thermal cracking; lower than this benchmark risks inadequate paste and poor durability.

Common Pitfalls:
Assuming high cement alone guarantees durability; neglecting w/c control and curing undermines performance despite adequate cement.

Final Answer:
15%