1. Civil Engineering Materials
Department of Civil, Structural and Environmental Engineering
Trinity College Dublin
Dr. Roger P. West (TCD)
and Mr. Peter Flynn (ARUP)

2. Section A: Concrete A1 Basic Materials: A2 Fresh Concrete Properties:
A3 Hardened Concrete Properties:
A4 Concrete Mix Design:
A5 Reinforced Concrete:
A6 Pre-stressed Concrete:

3. Section A.2 Fresh Concrete Properties
The first 48 hours are very important for the performance of the concrete structure. It controls the long-term behaviour, influence strength, Young’s Modulus, creep and durability.

4. Section A.2 Fresh Concrete Properties
1. Workability
2. Addition of Water
3. Voids
4. Hydration
5. Segregation
6. Settlement

5. Section A.2 Fresh Concrete Properties
7. Shrinkage
8. Compaction
9. Honeycombing
10. Grout Loss
11. Surface Finishes

6. Section A.2 Fresh Concrete Properties
1. Workability
“the ability of concrete to flow in a mold or formwork, perhaps through congested reinforcement, the ability to be compacted to a minimum volume, perhaps the ability to perform satisfactorily in some transporting operation or forming process, and maybe other requirements as well”

7. Section A.2 Fresh Concrete Properties
1. Workability
The amount of internal work required to produce complete compaction, or the energy required to overcome the internal friction between particles.
But concrete also needs to be “cohesive” in order to resist “segregation” and “bleeding”.
Consistence is the ease with which concrete flows
Consistence which is a combination of workability and cohesion is a measured using the Slump Test.

8. Section A.2 Fresh Concrete Properties
1. Workability
Water Content - higher water content leads to higher workability
Aggregate Type
Aggregate Shape
Grading - uniform grading leads to better workability
Aggregate – Cement Ratio
Admixtures - accelerators / retarders
Fineness of cement - finer cement, faster loss of workability
Time - delay of cement hydration
Temperature - higher temperatures lead to loss of workability

9. Section A.2 Fresh Concrete Properties
1. Workability

10. Section A.2 Fresh Concrete Properties
1. Workability

11. Section A.2 Fresh Concrete Properties
1. Workability

12. Section A.2 Fresh Concrete Properties
1. Workability
A check on the day to day or hour to hour variation in materials or constituents
Increase in slump may indicate increased moisture states of aggregates or added water
Changes in slump may indicate changes in aggregate gradation
Indicates the relative amount of coarse to fine aggregates

13. Section A.2 Fresh Concrete Properties
1. Workability Compacting factor
Best test to measure the amount of work needed to achieve full compaction
Higher the value, the more workable the concrete
- Up to a point!

14. Section A.2 Fresh Concrete Properties
1. Workability

15. Section A.2 Fresh Concrete Properties
2. Bleeding (or “water gain”)
Water in the mix tends to rise to the surface of fresh concrete
Inability of solid constituents to hold all the water together
Top layer becomes too wet, resulting in a porous and permeable layer
Concrete should never be finished until the bleed water has evaporated

16. Section A.2 Fresh Concrete Properties
2. Bleeding (or “water gain”)
Causes of Bleeding
Too much water (high water-cement ratio)
Less fines in the mix (cement, sand)
Poor grading of aggregates
Overworking of concrete

17. Section A.2 Fresh Concrete Properties
2. Bleeding (or “water gain”)
Water is lighter
Leaves pockets of low density
Water may be reabsorbed
No bleeding at all also may be a problem

18. Section A.2 Fresh Concrete Properties
3. Air Voids
Entrapped air
Capillary air
Entrained air

19. Section A.2 Fresh Concrete Properties
3. Air Voids

20. Section A.2 Fresh Concrete Properties
3. Air Voids
There should be sufficient air voids within the concrete mix to ensure sufficient freeze thaw resistance

21. Section A.2 Fresh Concrete Properties
3. Air Voids
Removal of air from concrete by agitating

22. Section A.2 Fresh Concrete Properties
4. Hydration

23. Section A.2 Fresh Concrete Properties
4. Hydration

24. Section A.2 Fresh Concrete Properties
4. Hydration

25. Section A.2 Fresh Concrete Properties
4. Hydration

26. Section A.2 Fresh Concrete Properties
4. Hydration
Curing is the maintenance of satisfactory moisture content and temperature in concrete for a period of time immediately following placing and finishing so as to develop the desired properties of concrete
CONCRETE MUST BE PROPERLY CURED TO DEVELOP OPTIMUM PROPERTIES

27. Section A.1 Basic Materials
4. Hydration

28. Section A.2 Fresh Concrete Properties
4. Hydration

29. Section A.2 Fresh Concrete Properties
4. Hydration

30. Section A.2 Fresh Concrete Properties
4. Hydration

31. Section A.2 Fresh Concrete Properties
4. Hydration

32. Section A.2 Fresh Concrete Properties
5. Segregation
Separation of constituents of the concrete mixture caused by excessive handling or vibration, or improper gradation of aggregates.
Results in a non-uniform distribution
Coarser particles separate out
Cement and water mix separates out
Causes:
Differences in particle sizes
Improper grading

33. Section A.2 Fresh Concrete Properties
5. Segregation
Laitance:
Coarse aggregates separate towards the bottom and cement paste forms a scum on the top
To reduce segregation:
Increase air content
Reduce water-cement ratio
Increase rate of hydration

34. Section A.2 Fresh Concrete Properties
6. Settlement

35. Section A.2 Fresh Concrete Properties
7. Shrinkage (Plastic Cracking)
Cracking that occurs when the concrete is still plastic
Cracks are usually parallel to each other
Moisture loss from the surface is the cause
If bleed water replaces the water lost, no cracking results
Evaporation increased by:
High surface temperatures
High wind speed
Low humidity

36. Section A.2 Fresh Concrete Properties
7. Shrinkage

37. Section A.2 Fresh Concrete Properties
7. Shrinkage
Minimized by:
Moist aggregates
Cover concrete
Dampening sub-grade
Erection of windbreaks & sunshades
Add plastic fibres

38. Section A.2 Fresh Concrete Properties
8. Compaction
Immediately upon placing, the concrete must be compacted by means of hand tools or vibrators.
The compaction by high frequency power driven needle vibrators (frequency : rpm, and amplitude : mm) has the advantage that they allow the use of stiff mixes for the same strength.
The spacing of needle vibrator and its duration depend upon several factors. It requires an experienced operator to make the necessary judgement at the actual site. The spacing of needle vibrator depends upon its radius of influence in concrete. It may be used for about 30 sec to 60 sec at each location. Such compaction ensures more impermeable and dense concrete.
Under compaction as well as over compaction are bad for concrete.

39. Section A.2 Fresh Concrete Properties
9. Honeycombing
Honeycombing occurs when voids are left in concrete due to failure of the mortar to effectively fill the spaces among the coarse aggregate particles. It occurs due to lesser quantity of fine sand leading to a harsh concrete mix. 

40. Section A.2 Fresh Concrete Properties
10. Grout Loss

41. Section A.2 Fresh Concrete Properties
11. Surface Finishes

42. Section A.2 Fresh Concrete Properties
11. Surface Finishes