Equipment selection — compacting a plain concrete road slab (< 20 cm thick) For compaction of a plain cement concrete pavement or road slab of thickness less than 20 cm, which type of vibrator is most appropriate?

Introduction / Context:
Pavement-quality concrete (PQC) and thin slab concretes require rapid and uniform compaction over wide areas. Choosing the right vibration equipment improves finish quality, reduces honeycombing, and ensures adequate density without damaging edges or forms.

Given Data / Assumptions:

• Plain concrete slab thickness < 20 cm.
• Continuous placement along a road bay with guide forms.
• Goal: uniform compaction and surface finish across the full width.

Concept / Approach:

A screed vibrator spans across the forms and provides distributed vibration while also striking off the surface to grade. For thin slabs, this method is superior to internal needle vibrators, which are localized and can leave uneven consolidation lines. External form vibrators mainly stiffen forms and are not ideal for full-width slab compaction alone.

Step-by-Step Solution:

Verification / Alternative check:

Standard road construction practices employ vibrating screeds or fixed-form pavers for slabs up to typical pavement thicknesses, ensuring both compaction and surface tolerance.

Why Other Options Are Wrong:

• Internal vibrators risk over/under-vibration zones and do not level the surface.
• Form vibrators are supplementary; they do not compact the slab body effectively.
• “None” is incorrect because an appropriate tool exists.

Common Pitfalls:

• Dragging the screed too fast, reducing effective consolidation.
• Failing to maintain consistent head of concrete ahead of the screed.

Final Answer:

Screed vibrator.