IRC 85:1983 is the Indian Standard (IRC) for recommended practice for accelerated strength testing and curing of concrete. IRC 85:1983 provides methodology for accelerated strength testing and curing of concrete — the practice of using elevated temperature curing to predict 28-day concrete strength from tests at 24 hours or less. This enables faster QA decisions on concrete construction. Four methods: (A) warm water 55°C × 24 hrs, (B) boiling water 100°C × 3.5 hrs, (C) autogenous insulated cure × 48 hrs, (D) high-temperature 93°C + drying. Most common is warm water method. Correlation between accelerated and 28-day strength: warm water ~ 0.65-0.75; boiling water ~ 0.70-0.80. Correlations are mix-specific — must be established for each concrete mix by lab testing. Applications include: pavement opening to traffic (14-day vs 28-day), bridge deck stripping (3-day), concrete acceptance for critical elements. Amendment No. 1 (2018) added alignment with IS 9013 (the IS standard for accelerated testing). Amendment No. 2 (2022) added non-destructive methods (rebound hammer, ultrasonic pulse velocity, maturity meter) as complementary tools. Accelerated testing is widely used on Indian highway and bridge projects — enables faster construction schedules and earlier detection of mix problems. Periodic verification against traditional 28-day test essential for calibration.
Specifies methodology for accelerated strength testing and curing of concrete — methods that estimate 28-day strength from early-age (hours to days) testing using elevated temperature curing, for faster QC decisions on concrete construction.
- Status
- Current
- Usage level
- Specialized
- Domain
- Transportation — Pavement and Road Materials / QA-QC
- Type
- Recommended Practice
- Amendments
- Amendment No. 1 (2018) — alignment with IS 9013; Amendment No. 2 (2022) — non-destructive methods (rebound hammer, UPV, maturity) as complementary tools
Also on InfraLens for IRC 85
Practical Notes
! Accelerated testing is widely used on Indian highway/bridge projects — enables faster construction. Without it, every decision waits 28 days.
! Warm water method (55°C × 24 hrs) is most common due to simplicity and equipment availability. Requires thermostatic water bath (cost ₹20-50k).
! Boiling water method (100°C × 3.5 hrs) faster results but equipment more expensive and handling trickier. Less common in field labs.
! Correlation is mix-specific. Laboratory testing of each new mix design required. Typical: warm water 0.65-0.75 of 28-day; boiling 0.70-0.80.
! Pavement opening to traffic: if design strength 40 MPa at 28 days and correlation 0.70, accelerated strength target = 28 MPa. If achieved, traffic can be opened at 14 days vs 28.
! Bridge deck stripping: critical for construction efficiency. 3-day accelerated data enables formwork removal after 3 days instead of 7. Saves time and equipment cost.
! Correlation verification: periodic 28-day tests confirm correlation. If deviation > 10%, recalibrate. Mix design changes require recalibration.
! Equipment: water bath ₹20-50k; compression tester ₹5-15 lakh; lab setup ₹20-50 lakh total. Payback via faster construction schedules.
! Non-destructive testing (Amendment No. 2, 2022): rebound hammer (₹10-30k), ultrasonic pulse velocity (₹1-3 lakh), maturity meter (₹50k-2 lakh). Complement traditional sampling. Useful for in-situ concrete.
! Maturity method: time-temperature history tracks concrete strength. Real-time temperature sensors in concrete + maturity formula. Particularly useful for mass concrete and bridge decks.
! Temperature accuracy critical: water bath ±1°C; deviations significantly affect correlation. Thermometer verification at each test.
! Cube size 150 mm per IS 516. Specimens standard size for consistency. Smaller (100 mm) cubes permitted but need separate correlation.
! Specimen preparation: same mix as structural concrete; not specially prepared samples. Represents actual in-place concrete.
! Age at test: for warm water, 24 hours; for boiling water, ~6 hours (1 hr cure + 1 hr heat + 3.5 hrs at 100°C).
! Accelerated testing failure: if accelerated strength below target, concrete may still meet 28-day strength. Traditional 28-day test confirms acceptance/rejection.
! When to use traditional 28-day test: for disputes, legal matters, formal acceptance. Accelerated testing is for early decision support, not final acceptance.
! Cost comparison: accelerated testing ₹500-2000 per test vs ₹500 for 28-day traditional. Justified by faster decisions.
! For rural projects: accelerated testing often unavailable (no lab infrastructure). Rely on 7-day traditional strength with correlation.
! For NH/expressway: accelerated testing standard practice. Lab on-site or nearby. QC throughput much higher.
! Modern trend: automated testing (robotic cube testing machines), data logging, cloud-based QA dashboards. Cost ₹20-80 lakh per setup but major efficiency gain.