The work shall consist of construction of (zero slump) DLC sub-base for cement concrete pavement in accordance with the requirements of MoRTH Specifications Clause 601 and in conformity with the lines, grades and cross sections shown on the drawings.
The Contractor shall indicate to the AE the source of all materials with relevant test data to be used in DLC work sufficiently in advance and the approval of the AE for the same shall be obtained before the scheduled commencement of the work in trial length.
Cement to be used may preferably be obtained in bulk form. Cement shall be transported, handled and stored on the site in such a manner as to avoid deterioration or contamination. Cement shall be stored above ground level in perfectly dry and water-tight sheds and shall be stacked to a height of not more than eight bags.
Wherever bulk storage containers are used, their capacity should be sufficient to cater to the requirement at site. The containers shall be cleaned at least once every 3 months. MTC or laboratory test certificate shall be maintained for each and every batch of cement received.
Following types of cement may be used with prior approval of the AE:
| S. No. | Type of Cement | Conforming To |
|---|---|---|
| 1 | Ordinary Portland Cement | IS:269 |
| 2 | Portland Slag Cement | IS:455 |
| 3 | Portland Pozzolana Cement | IS:1489 Part-I |
If subgrade soil contains soluble sulphates in a concentration more than 0.5%, sulphate resistant cement conforming to IS:12330 or Portland Slag Cement with slag up to 50% shall be used.
Fly ash up to 20 percent by weight of cementitious material (Cement + Fly Ash) may be used as replacement of OPC cement and in such case the cement content shall not be less than 120 kg/cum.
Fly ash shall conform to IS:3812 Part-I.
Aggregates for DLC shall be natural material complying with IS:383. The aggregates shall not be alkali reactive. The limits of deleterious materials shall not exceed the requirements set forth in Table 600-2 of MoRTH Specifications.
Coarse aggregate shall comply with Clause 602.2.6.2, except that the maximum size of the coarse aggregate shall be 26.5 mm, and aggregate gradation shall comply with Table 600-1.
The fine aggregate shall comply with Clause 602.2.6.3.
The curing compound shall be white pigmented or transparent type with water retention index of 90% when tested in accordance with BS:7542.
Water used for mixing and curing shall comply with Clause 602.2.7.
The mix shall be proportioned with a maximum aggregate cementitious material ratio of 15:1 (as per MoRTH). The water content shall be adjusted to the optimum as per Clause 601.3.2 for facilitating compaction by rolling.
The strength and density requirements of concrete shall be determined in accordance with Clause 601.7 and Clause 601.8 by making trial mixes. Care should be taken to prevent one size of aggregate falling into other size of the hopper of the feeding bin while loading the individual size of the aggregates into the bins.
The OMC shall be determined and demonstrated by rolling during trial length construction and the OMC and degree of compaction shall be got approved from AE.
While laying in the main work, the DLC shall have a moisture content between the optimum and optimum +2 percent, keeping in view the effectiveness of the compaction achieved and to compensate for evaporation losses.
The cement content in the DLC shall be such that the strength specified in Clause 601.3.4 of MoRTH is achieved.
Clause 601.3.4 of MoRTH shall be applicable.
The subgrade shall conform to the grades and cross-sections shown on the drawings and shall be uniformly compacted to modified Proctor density not less than 97%.
The lean concrete sub-base shall not be laid on a subgrade softened by rain after its final preparation. Surface trenches and soft spots, if any, shall be properly backfilled and compacted to avoid weak spots.
A day before placing of the sub-base, the subgrade surface shall be given a fine spray of water and rolled with one or two passes of a smooth wheeled roller after a lapse of 2-3 hours in order to stabilise loose surface.
If found necessary, another fine spray of water may be applied just before placing the sub-base.
A drainage layer conforming to Clause 401 shall be laid above the subgrade before laying the DLC sub-base.
The DLC shall be laid on the prepared granular drainage layer. The DLC sub-base shall be overlaid with concrete pavement only after 7 days of sub-base construction.
The batching plant shall be capable of proportioning the materials by weight, each type of material being weighed separately in accordance with Clause 602.9.2, Clause 602.9.3.1 and Clause 602.9.3.2 of MoRTH Specifications.
Plant mix DLC shall be discharged immediately from the mixer, transported directly to the point where it is to be laid and protected from weather by covering the tipping trucks with tarpaulin during transit, if necessary.
DLC shall be placed by a paver with electronic sensor on the drainage layer.
The compaction shall be carried out immediately after the material is laid and levelled.
Rolling shall be continued on the full width till there is no visible movement under the roller and the surface becomes well closed.
The spreading, compacting and finishing of lean concrete shall be carried out rapidly to ensure that the time between mixing of first batch and final finishing does not exceed:
| Concrete Temperature | Maximum Time Limit |
|---|---|
| 25°C to 30°C | 90 Minutes |
| Less than 25°C | 120 Minutes |
This period may be reviewed by the Engineer based on trial run results, but in no case shall it exceed 120 minutes.
Construction and longitudinal joints shall be provided as per approved drawings.
Curing shall be carried out by any one of the following methods:
The surface shall be covered with wet gunny bags or hessian cloth and kept continuously moist for 7 days by regular sprinkling of water.
Approved resin-based aluminized reflective curing compound shall be sprayed in accordance with Clause 602.9.12.
After the curing compound loses tackiness, the surface shall be covered with wet hessian for 3 days.
Wax-based white pigmented curing compound having water retention index not less than 90% shall be used.
The compound shall be applied uniformly using a mechanical sprayer fitted with wind protection hood.
Control of quality of materials and workmanship shall be exercised by the Engineer in accordance with Section 900 of MoRTH Specifications.
| Test | Standard | Frequency | Requirement |
|---|---|---|---|
| Normal Consistency | IS 4031 | Each batch | IS 12269 / IS 8112 / IS 1489 |
| Initial & Final Setting Time | IS 4031 | Each batch | Initial ≥ 30 min, Final ≤ 600 min |
| Soundness | IS 4031 | Each batch | Max 10 mm |
| Compressive Strength (Mortar) | IS 4031 | Each batch | 28-day strength as per grade |
| Chemical Test | IS 4031 | Every 6 months | As per IS 269 / IS 1489 |
| Test | Standard | Frequency | Requirement |
|---|---|---|---|
| Phenolphthalein Test | IS 3025 | Every 3 months | Max 5 ml of 0.02N NaOH |
| Methyl Orange Test | IS 3025 | Every 3 months | Max 25 ml of 0.02N H₂SO₄ |
| pH | IS 3025 | Every 3 months | ≥ 6 |
| Organic | IS 3025 | Every 3 months | Max 200 mg/l |
| Inorganic | IS 3025 | Every 3 months | Max 3000 mg/l |
| Sulphate | IS 3025 | Every 3 months | Max 400 mg/l |
| Chlorides | IS 3025 | Every 3 months | Max 500 mg/l |
| Suspended Matter | IS 3025 | Every 3 months | Max 2000 mg/l |
| Test | Standard | Frequency | Requirement |
|---|---|---|---|
| Sieve Analysis | IS 2386 Part-1 | 1 Test/day/plant |
26.5mm: 100% 19mm: 75–95% 9.5mm: 50–70% 4.75mm: 30–55% 2.36mm: 17–42% 0.600mm: 8–22% 0.300mm: 7–17% 0.150mm: 2–12% 0.075mm: 0–10% |
| Aggregate Impact Value | IS 2386 | 1/day | Max 45% (30% for wearing surface) |
| Los Angeles Abrasion | IS 2386 | As required | Max 35% |
| Flakiness & Elongation | IS 2386 | Weekly | Max 35% |
| Soundness | IS 2386 | Once/source | 12% Na₂SO₄ / 18% MgSO₄ |
| Water Absorption | IS 2386 | Once/source | Max 2% |
| Test | Standard | Frequency | Requirement |
|---|---|---|---|
| Alignment, Cross Section & Level | Standard Survey Practice | Regular | As per specification |
| Field Compaction | IS 2720 | 3 density tests / 2000 m² | ≥ 98% of trial density (≥96% edges) |
| Test | Standard | Frequency | Requirement |
|---|---|---|---|
| Strength of Concrete | IS 516 | Min 3 samples / 1000 m² | Min 10 MPa at 7 days |
| Surface Level Tolerance | Standard Survey Practice | Every 10 m | ±6 mm |
| Problem | Cause | Solution |
|---|---|---|
| Low Density | Inadequate roller passes | Increase vibration and adjust moisture |
| Segregation | Poor plant control | Ensure proper aggregate blending |
| Cracking | Early moisture loss | Immediate curing |
| Thickness Variation | Improper paver calibration | Sensor check and trial adjustment |
The following records shall be maintained:
Proper documentation ensures audit compliance and quality assurance.
Dry Lean Concrete is a critical structural layer in rigid pavement construction. Proper mix design, moisture control, compaction, curing, and quality testing are essential to ensure pavement durability and performance.
Strict compliance with MoRTH Section 600, supported by systematic field verification and documentation, ensures long-term success of highway infrastructure projects.
Kishor Kumar is a Highway QA/QC Engineer specializing in MoRTH compliant construction methodologies, pavement quality control, and infrastructure testing practices. He shares practical, field-oriented engineering knowledge for highway professionals and construction teams.
