Construction steps of cement concrete pavement

Cement concrete pavement (Pavement Quality Concrete, PQC) is built as a slab on a sub-base following IRC:15 (construction of concrete roads), IRC:58 and MoRTH Section 600; Nepal DoR specifications follow the same steps.

Materials: ordinary Portland cement (OPC 43/53, IS:269) or PPC; fine aggregate (zone II sand); crushed stone coarse aggregate of maximum size 31.5 mm (usually 20-26.5 mm), abrasion value below 35 percent, flakiness below 25 percent; potable water; admixtures if needed; dowel bars (plain mild steel), tie bars (deformed), joint filler and sealant (hot or cold poured), curing compound. The concrete has a flexural strength of about 4.5 MPa (M40, w/c ratio below 0.45).

Construction steps

1. Sub-grade and sub-base: prepare and compact the subgrade; lay a Dry Lean Concrete (DLC) or granular sub-base with a separation layer of polythene sheet (125 micron) on top.
2. Setting out and forms: fix steel side forms (for fixed-form paving) rigidly to line and level, or set string lines for a slip-form paver.
3. Dowels and tie bars: fix dowel bars on cradles/baskets at transverse joints and tie bars at the longitudinal joint before concreting (or insert them with the paver's dowel inserter).
4. Batching and mixing: batch aggregates and cement by weight in a batching plant and mix in a central plant (or transit mixer); slump about 25-50 mm (workability suited to the paver).
5. Placing: place the concrete in a uniform layer, slightly above the final level, without disturbing the dowel baskets.
6. Compaction: use needle vibrators along edges and joints, and a screed or surface vibrator; a slip-form paver compacts, shapes and finishes in one pass.
7. Finishing: float, check with a straight edge, and texture (broom or tining) for skid resistance; surface tolerance 3 mm under a 3 m straight edge.
8. Curing: spray a curing compound immediately, then cover with wet hessian or polythene; keep moist for at least 14 days, and protect from rain, sun and wind.
9. Joints: saw-cut contraction joints (about 3-5 mm wide, 1/4 to 1/3 of the slab depth) within about 6-18 hours of laying; form expansion and construction joints; seal them with sealant after cleaning.
10. Opening: allow traffic after the concrete attains the specified strength, generally after 28 days (light vehicles may be allowed earlier, at about 75 percent of the design strength).

Quality control: tests on cement, aggregate and water; slump (every batch/truck); cube strength (3 cubes per 30 m3 at 7 and 28 days) and flexural beam tests; temperature of concrete (between 5 and 30 C); thickness by levels or cores (+-5 mm); level and evenness with a straight edge; checks on dowel alignment, joint depth and curing records.