PQC Methodology
PQC Pavement Methodology (M40) – Original + Enhanced Pavement Quality Concrete (PQC) Pavement – M40 Grade 1.0 Scope This methodology shall be applicable for construction of dowel jointed or plain cement concrete of M40 grade pavement in accordance with the lines, grades, camber and thickness as shown in the drawings using fixed forms. Enhancement – Engineering Intent: This clause establishes applicability limits of the methodology and ensures compliance with approved drawings, levels, and pavement thickness essential for structural performance. 2.0 Materials 2.1 Cement These shall consist of Ordinary Portland Cement of approved source. The minimum cement content shall be 350 Kg/m³ and maximum 425 Kg/m³. Best Practice: Cement silos shall be moisture-tight. Batch-wise cement consumption shall be recorded to verify compliance with specified limits. 2.2 Admixtures The admixtures shall conform to IS 6925 and IS 9103 and shall improve the workability of concrete or extension of time and they will not have any effect on the properties of concrete. The performance of these admixtures will be proved both on laboratory trials and in trial paving works. Admixtures containing calcium chloride shall not be used. Quality Control: Each admixture shall be approved by Engineer-in-Charge based on compatibility tests with cement and aggregates used for the project. 2.3 Aggregates The aggregates shall be of crushed stone or naturally available conforming to IS 383. The coarse aggregate shall be clean, hard, strong, dense and durable. The fine aggregate shall be clean natural sand or crushed stone sand or combination of both. These shall be free from clay, shale, loam, mica and other organic matter. Site Control: Aggregate stockpiles shall be segregated by size, kept on paved surfaces and protected from contamination and excessive moisture variation. 2.4 Water Water used for mixing and curing of concrete shall be free from oil, salt, acid and other substances which are harmful to concrete. Compliance: Potable water is generally acceptable. Non-potable sources shall be tested as per IS 456 before use. 2.5 Mild steel bars for dowel and tie bars These shall conform to the requirements of IS: 432, IS: 1139 and IS: 1786 as relevant. The dowel bars shall conform to Grade S 240 and tie bars to Grade S 415 of I.S. Execution Control: Alignment, level, and embedment depth of dowel and tie bars shall be checked before concrete placement to ensure effective load transfer. 2.6 Pre-Molded joint filler To be used for expansion joints abutting structures like bridges, culverts and at end of the day’s work. Thickness 20–25 mm or as shown in drawings, complying to IS 1838. It shall be 25 mm less in depth than the thickness of slab and provided in suitable lengths not less than lane width. Holes shall be made to accommodate dowel bars. Practical Tip: Joint filler boards shall be stored vertically and protected from moisture to prevent warping. 2.7 Joint sealing compound Hot poured elastomeric type as per AASHTO M282 or cold poured polysulphide type as per BS 5212-part2, having flexibility, resistance to age hardening and durability. Durability Aspect: Proper joint sealing prevents ingress of water and incompressible materials, reducing pumping and joint deterioration. 2.8 Separation membrane A separation membrane of impermeable plastic sheeting 125 microns thick shall be laid between the concrete slab and sub-base by nailing with concrete nails to the lower layer. Where overlap is necessary the same shall be at least 300 mm. Purpose: This membrane prevents loss of moisture from concrete and avoids bonding between PQC and underlying layers. 2.9 Concrete Strength The concrete mix design in the laboratory, correlation between flexural and compressive strengths shall be established on the basis of at least thirty tests on samples. Quality control in the field shall be exercised on the basis of flexural strength. Materials and mix proportions shall remain substantially unaltered during daily production. Maximum free water cement ratio: 0.50. The ratio between the 7 and 28 day strengths shall be established in advance by testing pairs of beams and cubes on at least six batches of trial mix. The average 7-day strength divided by average 28-day strength yields ratio R (to three decimals). If any four consecutive 7-day test results fall below the required 7-day strength (derived from R), the cement content shall be increased by 5% by weight (or as agreed by the Engineer) without extra payment. Maintain the increased cement content until four corresponding 28-day strengths have been assessed. Adjust mix to maintain required workability. Technical Explanation: Flexural strength governs rigid pavement performance as it directly reflects slab behaviour under wheel loads. 2.10 Workability Workability requirements at batching plant and site shall be established by slump tests during trial length. Typical slump values: Slip form — 30 ± 15 mm; Fixed form — 50 ± 15 mm. Field Control: Slump variation beyond limits shall trigger immediate mix adjustment and investigation. 3.0 Construction Procedure 3.1 Mixing Materials shall be mixed in a mechanized batching plant with air-conditioned centralized control cabin, minimum 4 bins, weigh hoppers and automatic weighing devices using calibrated load cells. Mixer shall be capable of producing a homogeneous mix without segregation. Mix timing per manufacturer’s recommendations; automatic alarm/timing device recommended. Enhancement – MoRTH Reference: Mixing requirements align with MoRTH Clause 602.3.2 ensuring uniformity, accurate proportioning, and consistency of PQC. 3.2 Joints The location and type of joints shall be as shown in the drawings. 3.2.1 Transverse Joints Transverse joints shall be contraction and expansion joints constructed at the spacing described in the Drawings. They shall be straight within tolerances except at junctions/roundabouts where drawings govern. Engineering Intent: Transverse joints control cracking due to temperature and shrinkage stresses and ensure effective load transfer. 3.2.2 Contraction Joints Contraction joints shall be mechanical saw cut; can start as early as 6–8 hours after paving (initial hardening). Groove width 3–5 mm, depth 1/4 to 1/3 slab depth. Expansion joints shall have joint filler board and prefabricated assemblies. Dowel bars: mild steel as indicated in drawings, positioned at mid-depth within ±20 mm tolerance. MoRTH Clause: Joint cutting and dowel positioning as per