Many road owners in India want to keep asphalt. Their consultants know it, their contractors build it, and their approvals expect it. The question we hear is whether a GridMats grid can still help while the asphalt materials and the contractor above the base stay the same.
That is what GridMats S5 does: OC-LW 40 laid at the GSB/WMM interface and filled with the same aggregate, with at least 100 mm of compacted WMM above it (OC-HD 40 for the heaviest traffic). The bituminous layers follow MoRTH and your specification. To find out what the grid does down there, we asked IIT Hyderabad to test it.
What was tested
- Large-scale tank tests at IIT Hyderabad, with OC-LW 40 at the GSB/WMM interface (report, October 2025)
- Two subgrades: CBR 5% and CBR 10%
- The work was presented at TGS2026, IISc Bengaluru, in July 2026, for publication by Springer
What it found
The grid made the base stiffer. IIT Hyderabad measured the modulus improvement factor (MIF): how much stiffer the granular base is with the grid than without it.
| Subgrade | Modulus improvement factor, OC-LW 40 at the GSB/WMM interface |
|---|---|
| CBR 5% | 2.00 |
| CBR 10% | 1.63 |
The weaker the subgrade, the more the grid adds. That is where a conventional design would otherwise add aggregate.
What a stiffer base means for the layers
IIT Hyderabad then worked through design examples, checked in IITPAVE to IRC:37:
- At 3.5 MSA: a pavement 14% thinner overall, with 22–24% less bituminous and 11% less granular material.
- At 50 MSA on CBR 5%: 80 mm thinner.
Less bituminous thickness means less bitumen bought, heated and laid. Less granular material means less quarried aggregate hauled to site.
What stays the same
- Your contractor. The asphalt scope, plant and crew stay the same; the layers above the grid are the same materials, at the thinner thicknesses of the GridMats design.
- The programme. The grid adds about one shift per 1,000 m²; the asphalt opens as it always does.
- The surfacing. Bituminous concrete, SMA, mastic asphalt, cold mix or a RAP mix, as specified.
The limits
- Soil. The results hold for subgrades of CBR 5–10%. Outside that range an engineer has to verify the design; we do not assume the same gain.
- Grid position. The tests put the grid at the GSB/WMM interface. Other positions need their own engineering.
- Cost. The grid is an added material. Whether the thinner layers pay for it depends on your traffic, soil and local rates, so every S5 design is priced against your own conventional section. Where asphalt is not required, S1 or S2 usually costs less.
In service
At Orxa Energies, Bengaluru, OC-HD 40 went in at the WMM/GSB interface as a rut-resistance layer under the campus road and parking. The client's contractor built it on its normal schedule, and the road was photographed in service in 2024.
How we design it
The GridMats Design Engine 72 uses layered-elastic analysis, checked against Boussinesq and the two IITPAVE sections in the IIT Hyderabad report, with IRC:37-2018 checks. An engineer reviews every design before it goes out.
Your road
Send us the length and width, the heaviest vehicle and how many a day, the soil CBR if you have it, and your asphalt specification. Ask for your free estimate: our engineers follow with the design, the bill of quantities and the cost comparison against your conventional section.