Properties of hardened concrete Flashcards
What are the three main phases of hardened concrete?
Aggregate particles
Hardened cement paste
Interfacial transition zone (ITZ)
What are the three primary properties of hardened concrete?
Strength
Deformation
Durability
Flashcard 3
Front: Why is compressive strength the most specified property for concrete?
It serves as an index for other concrete properties and is critical for structural design.
Flashcard 4
Front: What are the intrinsic factors affecting concrete strength?
Aggregate (strongest component)
Hardened cement paste
ITZ (weakest component)
What are the extrinsic factors affecting concrete strength?
Specimen parameters: Dimensions, shape, moisture state
Loading parameters: Direction, stress type, rate
How is compressive strength calculated?
Compressive strength (MPa)= Maximum load (N)/
Cross-sectional area (mm²)
What are the methods to measure tensile strength?
Direct tensile test (rare)
Tensile split test (Brazilian test)
Flexural strength test
Define stress and strain.
Stress (σ): Force per unit area (N/mm²)
Strain (ε): Dimensional change per original length (mm/mm)
What is elastic modulus (E)?
E=
Stress (σ)/ Strain (ε)
Differentiate elastic vs. plastic deformation.
Elastic: Reversible; returns to original shape after load removal.
Plastic: Irreversible; permanent deformation after elastic limit.
What are the two categories of concrete deformation?
Load-dependent: Elastic deformations, creep
Load-independent: Shrinkage, thermal movements
What is creep in concrete?
Time-dependent deformation under sustained load, partly reversible. Occurs in cement paste; aggregates restrain it.
List beneficial and detrimental effects of creep.
Beneficial: Relieves stress, imparts ductility.
Detrimental: Increases deflection, causes prestress loss.
What causes drying shrinkage?
Time-dependent volume reduction due to moisture loss in hardened concrete (paste content, water content, environment).
How does thermal movement affect concrete?
Cyclic deformation from temperature changes (daily ambient shifts, hydration heat, fire).
What is the formula for elastic deformation (ΔL)?
ΔL= F⋅L/ A⋅E
Where:
F = Load (N)
L = Original length (mm)
A = Cross-sectional area (mm²)
E = Elastic modulus (GPa)
How to calculate long-term creep strain (εₙ)?
ε c =ε e ×ψ=(Stress/ E) ×Creep factor
What is the coefficient of thermal expansion (α)?
Material’s length change per unit temperature change (units: K⁻¹). For steel:
10×10−6K^-1.
How to calculate thermal stress if expansion is restrained?
σ=E⋅α⋅ΔT
Where
ΔT = Temperature change (K).
