Specifications for Open-Graded Friction Course
2019 Edition

The OGFC mix mandates specific physical characteristics for aggregates: Coarse aggregates must have a nominal maximum size of 9.5 mm, with dry rodded unit weight measured per ASTM C 29. The voids in coarse aggregate (VCA) in dry rodded condition is calculated using the formula VCA_DRC = ((G_ca × Y_w - Y_s) / (G_ca × Y_w)) × 100, where G_ca is the bulk specific gravity, Y_w is water unit weight (998 kg/m³), and Y_s is the dry rodded unit weight. Fine aggregates must meet gradation limits with 20-40% passing 4.75 mm sieve, 5-10% passing 2.36 mm, and 2-4% passing 0.075 mm sieves. The mix is designed to have 18-22% air voids, a minimum 5.5% bitumen content, at least 0.3% cellulose fibers by weight, a VMA ≥ 25%, and the mix’s VCA less than the dry rodded coarse aggregate VCA to ensure permeability and durability.

To achieve the desired air voids and binder content in OGFC, the mix design follows gradation per Table 2 with a nominal maximum aggregate size of 9.5 mm. The VCA in dry rodded condition is computed to ensure the mix’s VCA is lower, indicating dense packing. The mix must have air voids between 18-22%, bitumen content at least 5.5%, and a minimum of 0.3% cellulose fibers to prevent binder drain-down. The voids in mineral aggregate (VMA) should be at least 25%. Compaction is done using the Marshall method with 25 blows per side. This design strategy maintains high air void space for drainage while ensuring sufficient binder for durability without clogging the voids.

OGFC materials should be transported using clean, insulated, and covered vehicles treated with asphalt release agents to prevent sticking. Haul distance should not exceed 56 km or 1 hour to maintain mix temperature and quality. Placement involves spreading the OGFC mix in thin layers of 20 to 40 mm thickness with ±5 mm tolerance. Compaction should be done immediately using an 8-ton static steel-wheeled roller traveling at speeds not exceeding 5 km/h. Pneumatic-tyred rollers should be avoided to protect the porous structure. Uniform fibre dispersion is ensured by increasing dry mixing time by 5-10 seconds and wet mixing time by at least 5 seconds during production.

Drain-down in OGFC mixes is assessed using the ASTM D 6390 Wire Basket test or the Schellenberg Binder Drainage Test. In the wire basket method, a fresh loose mix sample is placed in a wire basket and heated in a forced draft oven at production temperature and 10°C above for one hour. The binder that drains onto a catch plate is weighed, and drain-down percentage is calculated as the mass of drained binder divided by total mix mass times 100. The maximum allowable drain-down is 0.30%. If exceeded, cellulose fibre content is increased, and mixing times are extended to ensure uniform fibre distribution, preventing binder runoff during transport and placement.

OGFC placement requires spreading the mix in lifts 20-40 mm thick with ±5 mm tolerance. Compaction must be performed using an 8-ton static steel-wheeled roller, operating at speeds no more than 5 km/h. Rolling should be longitudinal and as close as possible to the paver (within 15 m), with successive passes overlapping by at least one-third of the rear wheel width. Pneumatic-tyred rollers and standing on uncompacted layers are prohibited. Roller wheels must be lightly moistened to prevent mix adhesion, avoiding excessive water accumulation. These practices ensure uniform compaction, preserve the porous structure, and maintain permeability.

Surface evenness is evaluated using a 3 m straight edge following IRC:SP:16 guidelines. Measurements are taken at intervals of 6.25 m longitudinally and at 0.5 m from each edge and at the center of the pavement width. The pavement is accepted only if all measured deviations lie within specified tolerances. If any section exceeds tolerance limits by being too high or low, the full depth of that pavement layer must be removed and replaced with fresh material that is compacted per specifications to restore surface uniformity.

Critical quality control tests for OGFC include binder quality testing per IS:73 or IRC:SP:53 for each lot; aggregate impact value or Los Angeles abrasion tests at one per 50 m³ aggregate; flakiness index also at one per 50 m³; soundness and water absorption tests for each source or upon quality changes; sand equivalent, plasticity index, and polished stone value tests per source; fractured faces percentage for crushed gravel at one per 50 m²; mix grading, air voids, VMA, and theoretical maximum specific gravity testing twice daily or per 400 tons of mix; binder and mix temperature monitoring regularly; rate of spread checked after every fifth truckload; and density testing of compacted layers at least once per 250 m². These ensure mix consistency, durability, permeability, and adherence to specifications.