Concrete

Question 1

What are the material properties of concrete?

Answer 1

Tensile Strength - 400 psi (LOW)
Compressive Strength - 3 - 5 ksi (HIGH)
Density - 150 lbs/ft^3
Mod of Elasticity - 3600 ksi

Question 2

What are the constituents of concrete?

Answer 2

Portland Cement (Type I and Type II)
Aggregate (Coarse & Fine)
Potable Water
But also can add:
Supplementary Cementitious Materials & Chemical Admixtures

Question 3

What are the three big terms?

Answer 3

Paste = Cement + Water
Mortar = Paste + Fine Aggregate
Concrete = Mortar + Coarse Aggregate

Question 4

What are different types of admixtures and what do they do?

Answer 4

Water reducers - Increase slump w/o water
Set retarder - Hot weather placement
Accelerator - Cold weather
Air entrainer - Increase workability

Question 5

Typical proportions of a concrete mix?

Answer 5

60 - 75% aggregate
10 - 15% cement
15 - 20% water
4 - 8% Air
(1 part cement, 2 parts sand, 3 parts gravel)

Question 6

What is the single largest variable in concrete strength?

Answer 6

Water: Cement Ratio - Airfield mix is 0.45

Question 7

Entrained versus Entrapped air?

Answer 7

Entrained - stable air voids that provide freeze/thaw durability
Entrapped - large unstable air voids created during mixing

Question 8

What is the importance of concrete workability?

Answer 8

Stiff - lower w/c and stronger mix but more difficulty with entrapped air and consolidation