Hydrated Lime in BC and DBM Road Mix: Uses, Benefits & Dosage
Hydrated lime is a proven anti-stripping agent and modifier in Bituminous Concrete (BC) and Dense Bituminous Macadam (DBM) road mixes. Learn how it works, correct dosage rates, and why NHAI specifies it for premium highways.
Hydrated Lime in BC and DBM Road Mix: Uses, Benefits & Dosage
Frequently Asked Questions
Why is hydrated lime used in BC and DBM road mixes?
Hydrated lime is used as an anti-stripping agent in Bituminous Concrete (BC) and Dense Bituminous Macadam (DBM) mixes. It chemically bonds with aggregate surfaces, converts them from hydrophilic to hydrophobic, and prevents moisture from displacing bitumen — the main cause of pothole formation and early pavement failure in India.
What is the correct dosage of hydrated lime in BC/DBM mix?
As per MoRTH specifications, hydrated lime is added at 1.0–1.5% by weight of aggregate as a dry filler replacement. For a 1,000 kg aggregate batch, this means 10–15 kg of hydrated lime. Exceeding 1.5% can over-stiffen the mix and reduce workability.
Which grade of hydrated lime is required for road construction?
For BC and DBM mixes, Premium Grade (88–92% Ca(OH)₂) or Ultra Grade (93–95% Ca(OH)₂) hydrated lime is required. Minimum 90% fineness passing 350 mesh (43 micron) and moisture content below 2% are essential. IS 712 certification is mandatory for NHAI and state highway projects.
Is hydrated lime better than liquid anti-stripping agents for roads?
Yes, for long-term performance. Hydrated lime creates a permanent chemical bond with aggregate (lasting 10–15 years), improves rutting resistance by stiffening the bitumen film, and costs ₹80–120 per tonne of mix versus ₹150–250 for liquid agents. It is also fully specified in MoRTH and NHAI standards.
Does NHAI specify hydrated lime for bituminous road mixes?
Yes. MoRTH Clause 507 (BC) and 508 (DBM) permit hydrated lime at 1.0–1.5% by weight of aggregate as an anti-stripping measure. The treated mix must achieve a Tensile Strength Ratio (TSR) of ≥ 0.80 as per AASHTO T 283. IRC:111 also recommends lime for Warm Mix Asphalt (WMA) projects.
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