IRC SP 70 : 2005Guidelines for the Use of Cement Treated and Recycled Materials in Road Construction

IRC SP 70 specifies guidelines for the use of cement-treated and recycled materials in road construction — stabilisation of weak soils with cement / lime / industrial by-products, and the use of reclaimed asphalt pavement (RAP) and recycled concrete aggregate (RCA) in new road layers.

Use IRC SP 70 when: - Subgrade CBR is too low to support pavement (< 4 %); cement-treat to lift CBR - Sub-base or base course needs more strength than untreated granular material can deliver - Existing pavement is being reconstructed; reuse asphalt millings (RAP) as recycled aggregate - Old concrete pavement is being demolished; reuse as RCA in sub-base - Industrial by-products (fly ash, GGBS, lime sludge) are available locally and reduce cost vs imported materials - Sustainability / circular-economy targets in NHAI Bharatmala or state highway projects

This code addresses two related themes: 1. Cement / lime / fly-ash treatment of in-situ or borrowed soil to improve strength and durability 2. Recycled material (RAP / RCA) incorporation into new pavement layers

Both approaches reduce import / mining of fresh aggregate and cement, lower carbon footprint, and often provide cost savings — though they require careful design and quality control.

This is a guideline (SP series), not a binding standard; project specifications cite IRC SP 70 as the recommended practice for the specific cement-treated / recycled material being used.

Common cement treatments: - Cement-modified soil — 1-3 % cement; minor strength improvement, mainly waterproofing and fines binding - Cement-stabilised soil — 4-7 % cement; significant strength gain (UCS 1-3 MPa typical) - Cement-treated base / sub-base — 5-10 % cement; pavement-quality treated material (UCS 3-7 MPa)

Soil suitability: - Best: well-graded sand or sandy clay (PI < 15) - Acceptable: silty soils, lateritic gravel - Poor: highly plastic clay (PI > 30), organic soils, sulphate-rich soils

Lime treatment alternative: - For high-PI clays (PI 20-50): lime is more effective than cement - 4-6 % hydrated lime - Works by ion exchange + pozzolanic reaction - Best in tropical climates (warm temperatures accelerate reaction)

Fly ash + lime / cement (PFA stabilisation): - Class C fly ash (high-CaO) self-cementing in moisture; can replace some cement - Class F fly ash (low-CaO) needs lime activator - Common in industrial-by-product utilisation projects

Strength acceptance (Clause 4): - 7-day UCS for cement-treated base: ≥ 3 MPa (low-volume) / ≥ 4.5 MPa (high-volume) - 28-day UCS: typically 1.5-2× of 7-day - Durability test: 12 cycles wet-dry, mass loss ≤ 14 % per ASTM D559 / IRC SP 70

Construction: - Mix at site (windrow + grader spreader + cement add) OR plant-mix (more uniform) - Compaction at OMC of treated mix; maximum delay between mixing and compaction: 2-3 hours (set begins after this) - Cure for 7-14 days (typically wet hessian or curing compound) - Crack control: dummy joints sometimes provided for thick treated layers (> 200 mm)

Reclaimed Asphalt Pavement (RAP): - Source: existing bituminous pavement removed for reconstruction (millings + slabs) - Processing: crushed, screened to specified gradation; aged bitumen content typically 4-5 % - Use: - In new BC / DBM (10-30 % RAP by mass) — supplements virgin aggregate + bitumen - In bituminous emulsion cold-recycling (in-place or central-plant) — full pavement reconstruction - As granular sub-base (with cement / bitumen stabilisation)

RAP acceptance criteria: - Source: previously paved road with known bitumen grade - Quality: aged bitumen recoverable, aggregate sound (LA ≤ 35-40 %) - Test: extract bitumen + aggregate gradation analysis; verify no contamination - Use limit: 10-15 % RAP in surface course (BC); up to 30 % in binder course (DBM)

Recycled Concrete Aggregate (RCA): - Source: demolished concrete (building, pavement) - Processing: crushed, screened, contamination removed - Use: in sub-base or as coarse aggregate replacement (10-30 %) in new concrete - Limited to non-structural / sub-base concrete; not for high-strength or critical structural pours

RCA acceptance: - Compressive strength of source concrete ≥ 25 MPa - LA abrasion: ≤ 40 % - Water absorption: ≤ 7 % (vs ≤ 2 % for virgin aggregate) - Sulphate / chloride content within IS 383 limits - Trial mix to verify performance

Industrial by-products: - Fly ash (Class F or C from coal-fired thermal power plants) - GGBS (ground granulated blast-furnace slag) - Steel slag aggregate (specific compatibility checks) - Lime sludge from steel / sugar industries

Cement content guide (cement-stabilised soil for sub-base / base):

| Soil type | Cement (%) | Achievable UCS (MPa) | |---|---|---| | Well-graded sand | 4-6 | 3-5 | | Sandy gravel | 4-6 | 3-5 | | Silty soil (PI 10-15) | 5-7 | 2-4 | | Sandy clay (PI 15-25) | 6-8 | 2-3 | | High-PI clay | use lime instead | — |

Lime content guide (lime-treated soil):

| Soil PI | Lime (%) | Treatment outcome | |---|---|---| | 15-25 | 3-4 | Modification (no significant strength gain) | | 25-40 | 4-6 | Stabilisation (UCS 0.5-2 MPa) | | > 40 | 6-8 | Stabilisation (UCS 1-2 MPa); may need supplementary cement |

Mix design protocol (per IRC SP 70 Clause 4.4): 1. Identify soil (gradation, plasticity, classification) 2. Trial mixes at 3-5 cement/lime contents 3. Compact at OMC, cure 7 days 4. UCS test 5. Select dose that meets target UCS with minimum binder 6. Verify with 28-day strength + durability (wet-dry cycles)

RAP usage limits: - Surface BC: 10-15 % RAP (preserve surface quality) - Binder DBM: up to 30 % RAP - Granular sub-base: up to 100 % RAP (with cement/bitumen stabilisation) - Cold-mix base course: up to 100 % RAP (with bitumen emulsion)

Cost savings (typical, vs virgin aggregate / cement): - Cement-treated sub-base vs imported GSB: 20-30 % savings on long-haul material - 30 % RAP in DBM: 15-20 % savings on virgin bitumen + aggregate - RCA sub-base for demolition projects: 30-50 % savings + disposal cost saving

Carbon savings: - Cement-treatment of weak soil avoids 100-200 km imported aggregate haul: ~5 kg CO₂ per tonne saved - 30 % RAP in DBM: ~10 % CO₂ savings vs all-virgin mix

• IRC:37:2018 — flexible pavement design (cement-treated layers can be designed as semi-rigid base in IRC:37 framework).
• IRC SP 72:2015 — flexible pavement design for low-volume rural roads (cement-treated subgrade is common rural intervention).
• IRC:36:2010 — earth embankment construction (subgrade preparation).
• IRC SP 89 — guidelines for the design and construction of cement concrete pavements (CC pavements over treated subgrade).
• IS 8112:1989 / IS 12269:2013 / IS 1489 Part 1 — cement standards for stabilisation.
• IS 712 — building lime specification (for lime treatment).
• IS 3812 (Part 1 / 2):2003 — pulverised fuel ash (fly ash) specification.
• IS 12089 — granulated slag for cement.
• IS 2720 Part 4 — soil grain-size analysis.
• IS 2720 Part 5 — Atterberg limits.
• IS 2720 Part 7 / 8 — Proctor compaction.
• IS 2720 Part 10:1991 — UCS test (acceptance for cement-treated soil).
• IS 2386 Part 1 / 4 — aggregate test methods (for RCA acceptance).
• ASTM D559 — wet-dry cycle durability.
• MoRTH Specifications for Road and Bridge Works (5th Revision) Section 400 — granular sub-base / WBM / WMM.

1. Sulphate-rich soil + cement = expansive reaction. Sulphate in soil reacts with cement aluminates, forms ettringite, expansion + heave occurs. Test soil sulphate before cement treatment; for SO₄ > 1000 ppm, switch to lime + fly ash treatment. 2. Mixing not uniform on site. Patches with too little cement = strength shortfall; patches with too much = brittle, cracking. Use PMM (plant-mix) for critical jobs; mix-in-place only for routine subgrade improvement. 3. Compaction delayed beyond set time. Cement-treated mix sets in 2-3 hours; compaction after this gives reduced density and strength. Plan production and laydown for short window. 4. Curing skipped. 7-14 days curing critical for cement hydration; without it, strength is 40-50 % of design. Wet hessian or curing compound mandatory. 5. Cracks in cement-treated base reflected through bituminous surface. Thick (> 250 mm) cement-treated layers crack from shrinkage; cracks reflect upward. Use thinner layers (150-200 mm), provide stress-absorbing membrane interlayer (SAMI) over treated base. 6. RAP source contamination. Construction debris, organics, or excessive aged bitumen in RAP. Source should be uniform, age-known, no contamination. 7. Excessive RAP in surface course. > 15 % in surface mix degrades workability and finish. Stick to limits. 8. No lab trial mix for cement-treated material. Soil chemistry is variable; assumed cement dose may not deliver target UCS. Always do trial mix per project soil. 9. RCA used in critical structural concrete. Higher water absorption, variable strength source. Use only in non-structural sub-base or low-grade concrete. 10. No durability check on treated layers. UCS at 7-28 days is one thing; durability under wet-dry cycles is another. Specify wet-dry test for layers exposed to moisture changes (water-table fluctuation, monsoon). 11. Heat of hydration in thick cement-treated layers. Thermal cracking. Limit layer thickness or use lower cement content + longer cure.

Cement-treated / recycled material project considerations:

1. Project site survey — identify weak subgrade, available borrow material, demolition material on adjacent project sites. 2. Material selection strategy: - Subgrade weak: cement-treat or lime-treat top 200-500 mm - GSB cost high: stabilise local material with cement - Existing pavement scheduled for reconstruction: capture RAP, plan reuse - Industrial by-products available locally: factor in fly ash / GGBS 3. Trial mix design: - Cement / lime dose optimisation - 7-day, 28-day strength + durability test 4. Field trial section (1-2 km): - Verify mix-design strengths achievable in field - Check construction quality, compaction - Decide final acceptance specifications 5. Procurement: - Cement / lime / fly ash sources qualified - RAP processing plant identified 6. Construction: - Plant-mix or mix-in-place (per project criticality) - Spread and compact within set window - Cure 7-14 days 7. Quality acceptance: - Cement / lime content per delivery / batch - Compaction density per layer - 7-day / 28-day UCS on field samples - Durability check on representative samples 8. Pavement layers above — flexible pavement per IRC:37 or rigid per IRC:58, accounting for the structural contribution of the treated layer.

IRC SP 70 enables substantial cost and sustainability gains when the right soil + binder combination is identified and quality controls are followed. The single biggest implementation issue is uneven field mixing with mix-in-place; plant-mix is more reliable for critical applications.