Rigid pavement sizing (interior case): For a cement concrete pavement with a design wheel load of 6300 kg and a permissible flexural stress of 21 kg/cm², what is the approximate interior slab thickness?

Introduction / Context:
Slab thickness in cement concrete pavements is governed by flexural (tensile) stress induced by wheel loads. For the interior loading condition, the slab is fully surrounded by concrete, usually making it less critical than edge or corner loading. The question asks for a practical interior thickness corresponding to a moderate wheel load and a given allowable flexural stress.

Given Data / Assumptions:

• Design wheel load W = 6300 kg.
• Permissible flexural stress σ_allow = 21 kg/cm².
• Interior loading condition (not edge/corner).
• Conventional material and support conditions typical of highway rigid pavements.

Concept / Approach:

Interior stresses are checked using established rigid pavement analysis (e.g., Westergaard-based relations or charts) correlating load, contact area, subgrade reaction, and slab stiffness. For standard ranges of support and materials, charts/tables map the permissible stress to a required slab thickness. A wheel load of about 6.3 tonnes (single wheel 6.3 kN*1000/9.81 ≈ 61.8 kN; using classic highway units) with 21 kg/cm² allowable flexural stress leads to interior thickness near the lower end of typical highway slabs.

Step-by-Step Solution (Conceptual):

Verification / Alternative check:

Pavement design examples with similar wheel loads and flexural strengths frequently yield slab thickness between 15 cm and 20 cm for interior checks; 17 cm is a representative, economical value for interior locations (edge/corner checks generally control higher thickness when included).

Why Other Options Are Wrong:

• 25.5–50.0 cm: far thicker than typical for the stated load and stress limit; uneconomical.
• 34.0–50.0 cm options match heavy-duty industrial or airfield slabs, not standard road interior cases.

Common Pitfalls:

• Using corner-load thickness for interior condition; corner is more critical and yields greater thickness than interior.

Final Answer:

17.0 cm.