The ultimate creep coefficient of concrete:
Correct Answer: B. Decreases with age at loading
📚 Detailed Explanation: Creep Coefficient Decreases with Age at Loading
Why B (Decreases with age at loading) is correct: The creep coefficient (φ) is defined as the ratio of total creep strain (εcr) to initial elastic strain (εe): φ = εcr/εe. When concrete is loaded at an early age, the hydration is incomplete, paste is porous, and creep is high. As concrete matures, C-S-H gel thickens, porosity reduces, and resistance to time-dependent deformation increases — thus, the creep coefficient decreases with increasing age at loading.
Creep Coefficient vs. Age at Loading
| Age at Loading | Typical Creep Coefficient (φ) | Reason |
|---|---|---|
| 7 days (early loading) | φ = 3.0–4.0 | Low hydration; porous paste; easily deforms under sustained stress |
| 28 days | φ = 2.2–2.5 | Standard reference; moderate hydration |
| 90 days | φ = 1.5–2.0 | Higher hydration; denser paste; less creep |
| 1 year | φ = 1.0–1.5 | Nearly full hydration; dense microstructure; minimum creep |
Creep Coefficient: φ = εcr / εe
where:
εcr = creep strain (time-dependent)
εe = immediate elastic strain on loading
IS 456:2000: φ = 1.6 for loading at 28 days
φ = 2.2 for loading at 7 days
φ = 1.1 for loading at 1 year
where:
εcr = creep strain (time-dependent)
εe = immediate elastic strain on loading
IS 456:2000: φ = 1.6 for loading at 28 days
φ = 2.2 for loading at 7 days
φ = 1.1 for loading at 1 year
Factors That Influence Creep
| Factor | Increase in Creep | Decrease in Creep |
|---|---|---|
| Age at loading | Earlier loading → more creep | Later loading → less creep |
| w/c ratio | Higher w/c → more porous paste → more creep | Low w/c → dense paste → less creep |
| Stress level | Higher stress → more creep | Low stress → less creep |
| Humidity | Lower humidity → more drying creep | High humidity or sealed conditions → less creep |
| Cement content | Richer mix (more paste) → more creep | Lean mix with high aggregate → less creep |
- Ultimate creep coefficient decreases with increasing age at loading.
- IS 456:2000 tabulates creep coefficients by age at loading for use in structural design.
- Creep is entirely a paste phenomenon; aggregate particles are essentially inert to creep.