Guidelines for Construction of Roller-Compacted Concrete Pavements
2005 Edition

According to IRC SP 68, the approved cement types for Roller-Compacted Concrete Pavements include Ordinary Portland Cement conforming to IS 269 (33 grade), IS 8112 (43 grade), and IS 12269 (53 grade); Portland Slag Cement as per IS 455; Portland Pozzolana Cement (fly ash based) abiding by IS 1489 Part 1; and Sulphate-Resistant Cement in accordance with IS 12230 for soils with soluble sulfate content exceeding 0.5%. Additionally, fly ash meeting IS 3812 Grade I standards is permitted as a partial cement replacement ranging from 20% to 50% by weight. Key properties of fly ash include a fineness of at least 320 m²/kg Blaine, maximum 34% particles retained over 45 microns, lime reactivity of at least 4.5 N/mm², autoclave expansion limited to 0.8%, and drying shrinkage not exceeding 0.15%. Proper storage of cement and fly ash is required to maintain quality, and water used must comply with IS 456 specifications to ensure durability.

The mix design for roller-compacted concrete pavement (RCCP) significantly differs from conventional concrete primarily due to its dry consistency and compaction method. RCCP uses a no-slump mix with water content between 4% and 7% by weight, optimized through trial mixes to maximize density, whereas conventional concrete employs a wetter, slump-controlled mix based on Abram's water-cement ratio. RCCP does not follow the traditional water/cement ratio law; instead, it selects the ratio of cementitious materials, including fly ash, to achieve the desired flexural strength. Coarse aggregates constitute about 52% to 56% of the mix by volume in RCCP, and fly ash replaces 20% to 50% of the cement to enhance durability and workability. Unlike conventional concrete which focuses on compressive strength, RCCP design is primarily based on flexural strength, ensuring the mix can be compacted effectively by vibratory rollers without slump.

For achieving optimal density in Roller-Compacted Concrete Pavements, IRC SP 68 recommends initiating compaction immediately after placing and leveling the RCC mix. The use of a double-drum smooth wheel vibratory roller with a capacity between 80 kN and 100 kN is prescribed. The compaction sequence includes one preliminary static pass without vibration to set the mix, followed by multiple vibratory passes determined through trial to reach maximum density, and concluding with a final static pass without vibration to smooth the surface and remove roller marks. Edge rolling should allow the roller drum to extend 25 to 50 mm beyond the pavement edge to confine the material. For superior surface finish, 2 to 3 passes with a pneumatic tyred roller of approximately 200 kN and minimum tire pressure of 0.56 N/mm² may be employed. Water content should be adjusted carefully at the batching plant to avoid significant mix changes, and compaction must be completed within 90 minutes if temperatures are between 25°C and 30°C, or within 120 minutes if below 25°C, with work halted if temperatures exceed 30°C.

Prior to large-scale RCCP construction, a trial length of at least 30 meters should be built to fine-tune the mix, determine optimal moisture content, test equipment performance, and validate construction procedures. This section uses the water content identified in laboratory trials (typically 4% to 7%) to achieve maximum density. Compaction passes by the vibratory roller are adjusted to ascertain the number required for peak density. Density measurements are taken using the sand replacement method at three locations along a diagonal of the trial section, avoiding edges, with the average density serving as the reference (100%). Only after obtaining satisfactory results in terms of density, compaction, and mix performance should the main pavement construction proceed. If results are unsatisfactory, the trial must be repeated with necessary adjustments. Compaction includes preliminary and final static roller passes without vibration, and the entire mixing to finishing process must be completed within 90 to 120 minutes depending on ambient temperature.

Quality control for Roller-Compacted Concrete Pavements as per IRC SP 68 involves several critical tests. Aggregate grading must conform to specified sieve analysis limits (Table 2), with fine aggregate containing no more than 4% passing the 75-micron sieve for natural sand or 15% for crushed sand. Coarse aggregates should have a maximum size of 25 mm, soundness loss under 12% for sodium sulfate or 18% for magnesium sulfate, and flakiness plus elongation indices below 40%. Trial mixes determine optimum moisture content (4-7%) and target mean flexural strength, with fly ash replacing 20-50% of cement by weight. In-situ density is assessed via the sand replacement method during both trial and actual construction, averaging three samples to establish a reference density of 100%. Compaction is controlled using vibratory rollers (80-100 kN) with passes based on trial results, supplemented by preliminary and final static passes and optional pneumatic roller finishing. Regular tests on cement, fly ash (weekly for physical properties), aggregates, and water quality (per IS 456) ensure ongoing compliance.