CONCRETE
Creep Coefficient of Concrete (θ)
Ratio of creep strain to elastic strain under sustained load — per IS 456 Cl. 6.2.5.1 — depends on age at loading and humidity.
Also calledcreep coefficientcreep concretecreep strainis 456 creeplong-term deformation
Related on InfraLens
CODES
Definition
Creep coefficient θ per IS 456 Cl. 6.2.5.1: θ_28 = 1.6 (loaded at 28 days); θ_7 = 2.2 (loaded at 7 days); θ_1y = 1.1 (loaded at 1 year). Used in long-term deflection: Ec,long = Ec / (1 + θ). Creep is the time-dependent strain under constant stress — concrete deforms slowly over months/years.
Typical values
Age at loading = 7 daysθ = 2.2
Age at loading = 28 daysθ = 1.6
Age at loading = 1 yearθ = 1.1
Typical long-term Ec reduction1 / (1+θ) ≈ 0.38
Where used
- Long-term deflection check
- Prestress loss calculation
- Composite-section analysis
- Differential settlement assessment
Acceptance / threshold
Per IS 456 Cl. 6.2.5.1 — apply creep coefficient based on actual age at loading; reduce Ec accordingly for sustained-load deflection.
Site example
Slab loaded at 28 days (θ=1.6): long-term elastic deflection multiplier = (1 + 1.6) = 2.6× short-term. Deflection that's 8 mm immediately becomes ~21 mm after years.
Frequently asked
What is creep coefficient θ?
θ is the ratio of creep strain to elastic strain. Per IS 456 Cl. 6.2.5.1: 2.2 at 7 days, 1.6 at 28 days, 1.1 at 1 year. Drives long-term deflection.
Related concrete terms
Concrete Mix Design
Proportioning of cement, water, aggregates per IS 10262
Concrete Grades (M15-M80)
M20=20 N/mm² characteristic strength at 28 days
Water-Cement Ratio (w/c)
Mass of water to mass of cement. 0.40-0.55 typical.
Concrete Cover
Min concrete from rebar to surface (15-50mm per exposure)
Concrete Curing
Min 7 days for OPC, 10 days for PPC, 14 days for sulphate-resistant
Slump Test / Workability
25-150mm slump per application (IS 1199)
Cube Test (Compressive Strength)
150mm cube compressive strength test at 7/28 days (IS 516)
Concrete Admixtures
Plasticizers, accelerators, retarders per IS 9103