QUIZ 2 HARDENED PROPERTIES Flashcards
Entrapped Voids
From Mixing (1-2% by volume)
Rock Pockets or Honeycomb or voids of incomplete consolidation
Macro Cracks
What is effect on Concrete ?
Visible cracks
- Structural
- Thermal
- Plastic Shrinkage (rapid moisture loss)
- Drying Shrinkage (follow hardening)
Severe effect on concrete durability
Entrained Voids
Entrained Intentionally for freeze thaw durability
Significant reduction in concrete strength (this is compensated through w/c ratio)
Bubbles not connected (therefore do not result in more permeable concrete
Micro Cracks
Naturally occur around agg from restraint shrinkage forces
Increased with increasing load
Influence durability and strength
Transition Zone
Weak Porous zone around agg particles
Large Oriented Ca(OH)2 crystals
Reduced by add SCM’s
Capillary Voids
Residue of the original water filled spaces in the fresh concrete
Primary path which water and aggressive ions penetrate concrete matrix, resulting in durability problems by corroding steel
Significantly reduce strength
Concrete Strength Tests
Compressive strength
Flexural Strength
Modulus of Elasticity
Density
Compressive Strength
GU = 20-40 MPA
High Strength = > 70 MPA
Strength of Concrete is a function of
Porosity - w/c ratio, degree of hydration, entrained air content, degree of compaction
Type of cement
Type of admixtures
Cracks and when they start
25 percent ultimate strength = micro cracks
50 percent strength = New cracks
75 percent strength = cracks become unstable and merge into continuous cracks
Type of tests
In-situ : Shmidt Hammer test
In-situ: Pull-out test
Concrete drilling: Compressive strength, splitting tensile, flexural
Splitting Tensile: 5 to 15 percent higher than direct tensile
Flexural test: 40 to 100 percent higher than direct tensile
Maturity Concept
- Development of strength vs maturity graph in lab
- Embedment of temperature sensors
- Retrieve data and computation of maturity index
- Estimate of in strength concrete using graph
