1. “Properties of Concrete” Introduction

2. Overview What is concrete made of? What Is Concrete Used For?
Why Is Concrete Used?
Why Do We Reinforce Concrete?
Curing of concrete

3. What is concrete made of?

4. What is concrete made of?
Concrete is basically a mixture of two components:
Paste
Aggregates
Paste (Portland cement, water, and air)
Aggregates (sand, gravel, crushed stone)

5. CEMENT
Cement (Dry powder of very fine particles) is a building material made by grinding calcined limestone and clay into a fine powder
Portland Cement chemical composition
Limestone, shale and clay
CaO (lime)
Al2O3 (Alumina)
SO3 (Sulfite)

6. CEMENT When mixed with water, forms a paste
it undergoes chemical changes (chemical reaction-Hydration)
Glue paste coats all the aggregates together
hardens and forms a solid mass

7. WATER
Water good for drinking is good for concrete……

8. WATER needed for two purposes:
chemical reaction with cement
workability
only 1/3 of the water is needed for chemical reaction
extra water remains in pores and holes
results in porosity
Good for preventing plastic shrinkage cracking and workability
Bad for permeability, strength, durability.

9. AGGREGATES cheap fillers hard material provide for volume stability
reduce volume changes
provide abrasion resistance

10. AGGREGATE Aggregate are divided into two groups:
Fine - AASHTO M-6 or ASTM C-33
Coarse - AASHTO M-80 or ASTM C-33
Fine aggregate consist of natural or manufactured sand with particle size up to 3/8 inch
Coarse aggregate particles are retained on the #4 sieve and range up to 6 inches

11. COARSE AGGREGATE

12. FINE AGGREGATE

13. CONSTITUENTS paste 25 to 40% Aggregates 60% to 75% Admixtures
portland cement 7% to 15% by Vol.
water 14% to 21% by Vol.
Aggregates 60% to 75%
coarse aggregates
Fine aggregates
Admixtures

14. CONSTITUENTS
Cement Water Air Fine Aggregate Coarse Aggregate
Cement paste constitutes about 25% to 40% volume of concrete

15. AIR ENTRAINED CONCRETE
Why the difference between line #1 and line #2?
Line 1, small size CA, increased H2O and cement
Line 2, larger CA, less H20, air, cement

16. NON-AIR ENTRAINED CONCRETE
Cement Water Air Fine Aggregate Coarse Aggregate
Similar to Air Entrained Concrete slide
See how aggregate size impacts water demand and amount of “paste” in the mix

17. ADMIXTURES
Plastic and hardened properties of concrete may be changed by adding admixtures
Admixtures are commonly used to:
increase set time
decrease set time
increase workability
adjust other concrete properties
reduce water demand
entrain air
inhibit corrosion

18. ADMIXTURES chemical mineral retarders accelerators water reducing
air entraining
mineral
fly ash
silica fume
slags

19. QUALITY OF CONCRETE
Quality of concrete depends on quality of paste and quality of aggregates
each particle of aggregate is completely coated with paste
All spaces between aggregate is filled with paste

20. QUALITY OF CONCRETE Is determined by: W/C Ratio –
Advantage of reducing water
Increased compressive and flexural strength
lower permeability
increased resistance to weathering
reduced shrinkage cracking tendencies
The less water used, the better quality of concrete, provided it can be consolidated properly.

21. Ten cement-paste cylinders with water-cement
ratios from 0.25 to The band indicates that each
cylinder contains the same amount of cement. Increased
water dilutes the effect of the cement paste, increasing
volume, reducing density, and lowering strength.

22. FORMS
A form is the mold for setting concrete into a desired shape

23. What Is Concrete Used For?

24. What Is Concrete Used For?
Construction Material
Art Work

25. Picture of Bench

26. Why Is Concrete Used?

27. Why Is Concrete Used? Economics Material Properties
Inexpensive, readily available
Material Properties
Long Lasting
Molded into a desired shape
Great insulator
Hard

28. Material Properties (cont.)
Great Compressive Strength (up to 8000 psi and even more than that)
Poor Tensile Strength (almost 0)
Reinforcement methods ($)

29. Why Do We Reinforce Concrete?

30. Why Do We Reinforce Concrete?
Prevent cracking due to tension forces

31. Question
What is the difference between tension and compression?

33. Question
Why would concrete never be used in tension?

34. How Do We Reinforce Concrete?
Steel rebar
Excellent in tension, poor in compression

35. CURING OF CONCRETE

36. CURING OF CONCRETE
Over time concrete will cure, which is a hardening process.
Concrete has a 28 day curing time, this is the amount of time it takes to be considered completely cured

37. Curing Critical to durable concrete Increases strength
Decreases permeability
Increases durability

38. Curing Concrete How concrete is cured: Ponding or Immersion
Spraying or Fogging
Wet Coverings
Impervious Paper
Plastic Sheets
Membrane-Forming Curing Compounds

39. Questions? Remember: Use Common Sense
Temperature effects on your body have very similar effects on concrete
If you are not sure, ASK!!!