Rigid pavements – expansion joint spacing from thermal movement A cement concrete pavement uses expansion joints with a joint gap width of 2.5 cm. For a maximum rise in slab temperature of 25 °C and a coefficient of thermal expansion for concrete α = 10 × 10^-6 per °C, determine the appropriate spacing between expansion joints (in metres).

Introduction:
Concrete slabs expand with temperature. Expansion joints are provided to prevent compressive closing at joints from inducing blowups or excessive stresses. The joint spacing should limit the maximum thermal expansion of a slab panel to the available joint gap width.

Given Data / Assumptions:

• Joint gap width w = 2.5 cm = 0.025 m.
• Temperature rise ΔT = 25 °C.
• Thermal coefficient α = 10 × 10^-6 per °C.
• Linear, uniform expansion along the length.

Concept / Approach:

Free thermal expansion of a slab of length L is ΔL = α * L * ΔT. To avoid joint closure, set ΔL ≤ w and solve for L. Thus L ≤ w / (α * ΔT). Use consistent SI units to compute the maximum spacing.

Step-by-Step Solution:

Verification / Alternative check:

Using metres throughout avoids unit errors; the result is typical of expansion-joint spacings adopted historically for plain jointed concrete pavements with dowels.

Why Other Options Are Wrong:

5 m and 25 m are far too small for the stated thermal movement; 50 m is conservative but not implied by the calculation; 200 m would exceed the permitted expansion and risk joint closure.

Common Pitfalls:

Forgetting to convert centimetres to metres; mixing up α units; neglecting other movements like drying shrinkage (handled separately in design).

Final Answer:

100 m