1. Properties of Fresh Concrete
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

2. Properties of Fresh Concrete
State:
Prior to setting
Fluid like material – plastic concrete
Properties:
Adequate flow for several hours – Workability
No segregation and separation – Uniform
Bleeding
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

3. Properties of Fresh Concrete
Workability – ease with which a fresh concrete mix can be handled – mixing, transporting, compacting, finishing
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

4. Properties of Fresh Concrete
Factors influence Workability
Fine materials - Adequate quantity
Deficiency – harsh mixture (segregation and mixing difficulty)
Coarse aggregate – Low
water content – High
Addition of fine rounded materials – e.g., fly ash, silica fume
Air-entraining admixtures
Ambient temperature
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

5. Water and Aggregate Effects

6. Angular particles – poor workability
Rounded particles – better workability

7. Properties of Fresh Concrete
Factors influence workability
Increase of Max. size of the CA
Rounded
Decrease of Surface area
Workability improves
Increase in ambient temp.
1. Increase in hydration rate
2. Increase in rate of evaporation
Delay in placing or consolidation reduces workability
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

8. Properties of Fresh Concrete
Workability
Consistency – Wetness or fluidity
Measured by slump test
Mobility
Compactibility
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

9. The Slump Test - ASTM C 143 Zero-slump – dry mix with low W/C
The slump test does give some indication of segregation. If the slump is sheared and collapsed, rather than sagged evenly, then segregation and bleeding should be expected of the fresh concrete. The addition of more sand or cement should help provide a greater amount to consistency and cohesiveness to the mixture. Cohesiveness may wane if too much water is added to the mixture.
Zero-slump – dry mix with low W/C
Normal slump – 2-4 inch
Shear slump – non-cohesive / lacks of plasticity,
collapse slump – extremely wet, harsh concrete

10. Properties of Fresh Concrete
Shear slump or collapse slump
segregate and bleed
Causes:
Lack of sufficient content of fines – non-cohesive
High W/C
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

11. Amount of Mixing Water
Relatioship between slump and water content is non-linear
The relationship between slump and water content is not linear, and a small increase in the water content in the wetter mixtures will result in a larger increase in slump than in the stiffer mixtures.

12. Slump decreases with time
% Loss of Slump
Hydration
Evaporation
Rate increases with
increase in ambient
Temp.
Slump loss occurs due to a reduction in free water in the mixture (because of absorption in the aggregates or hydration of the cement) and partly due to evaporation. This effect causes the slump to decrease with time. This is more of a concern during placement in hot weather. Slump loss affects the time available to place and to finish the concrete.

13. Properties of Fresh Concrete
Changes in slump due to variation in
water content
Grading and proportioning of aggregates
Amount, fineness and brand of cement
ambient Temp.
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

14. Workability test

15. T = g + h N
T is the torque
N is the impeller rotational speed
g - flow resistance
h - torque viscosity

16. Properties of Fresh Concrete
Mixing
Machine mixing - Ready mix plant
Pumping and Placing
Finishing
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

17. Placing

18. Properties of Fresh Concrete
Segregation and bleeding
Segregation
separation between large and fine particles
Very wet or deficient in finer particles mixtures
High slump concrete
e.g., Honeycombing, crazing, surface scaling
Air-entrainement or adding finer particles (e.g., fly ash) decreases segregation
The quality of PCC depends on the quality of individual components but also on the concrete production process. The production process consists or mixing, transporting, placing, compacting, and curing. The workability of the concrete must be adjusted for the method of placement (pumping, vibration screed, etc.) and the climatic conditions at the time of placement. The discussion of the concrete properties involves both the fresh and hardened states.

19. Honeycombing

20. Bleeding
During the placing process, the aggregates tend to settle in the form which force any free moisture to move upwards towards the top surface of the finished concrete. This effect is known as bleeding. Bleeding should be held to a minimum but needs to be sufficient to prevent plastic shrinkage cracking. Concrete in the fresh state must also be workable enough to conform to a variety of placing and finishing conditions on the job site.

21. Mixture Design
For a paving project with a 9 inch slab and a minimum strength of 3000 psi, determine using ACI 211:
1) the w/cm
2) the slump
3) # of sacks of cement
4) the CAF
Assume:
FM = 2.9
Agg Size = 1.0 in

22. Concrete Setting Behavior
Initial set – beginning to stiffen (loses fluidity)
Final set – beginning to harden
Concrete shrinkage:
Plastic drying shrinkage - occurs is the evaporation rate exceeds the bleed rate. Shrinkage is controlled to some extent through curing. Curing is the process of maintaining proper moisture levels in concrete during the hardening stages. Several methods are available for curing.
Drying shrinkage - occurs for an extended period of time after the concrete has begun to take on a certain amount of rigidity.
Concrete setting is determined using a laboratory procedure outlined in ASTM C This determines the resistance of the concrete to penetration of a standard probe as a function of time. The procedure itself is rather arbitrary, nonetheless it does provide some insight into the setting behavior concrete. Initial set represents the time when the concrete is nearly capable of supporting human traffic. Final setting is where the concrete begins to develop residue states of stress; it has some compressive strength but zero tensile strength.
ASTM C-403

23. Chemical Admixtures Water-reduction Admixtures
These are surfactants. See next figure. They prevent the cement grains from flocculating in water. More water is available for lubrication the mix and the flow properties are enhanced. These admixtures can be used to reduce the water content. A reduction in w/c will increase strength, lower permeability, and improve durability. They also retart the set time to some extent. The rate of slump loss may also be affected.
Set-retarting Admixtures
These admixtures slow down early hydration and the rate of strength development. May not affect the rate of slump loss.
Accelerating Admixtures
These admixtures accelerate the early hydration process by increasing the calcium ion concentration of the pore water solution. The also affects the hardening stage as well. These admixtures are commonly used in repair work or in other applications where early strength is required. Both chloride and non-chloride accelerators are available.

24. Water Reduction

25. AEA Air-entraining Admixtures
These admixtures acts as surfactants at the air-water interface and work to trap air in individual bubbles. The bubbles must be stabilized within the hardened paste. The tiny bubbles act as reservoirs to accommodate water expelled from the capillary pores during freezing action. Air entrainment will increase workability (especially if fly ash is used) and reduce bleeding action. As long as the air content is below 6%, little loss of strength is experienced. Although there is some concern over compatibility in mixtures containing multiple admixtures, a greater concern exists relative to dosage rates.
AEA

26. Testing for Air Content

27. Type B Pressure Meter

28. Roll-a-Meter

29. Chace Air Indicator

30. Fly Ash and Air Content Effects

31. Unit weight (W), Air content
T = W1/V, Air content = ((T-W) / T) X100

32. Strength Specimen
Preparation

34. Slump, Air, and Cylinder Casting

35. Curing
Maintains favorable condition of Temp. and moisture