Drilled shafts support axial and lateral loads from within the soil. The use of large-size and largediameter drilled shafts is popular now due to the availability of technology and skilled manpower to carry out the task efficiently. Shafts of diameter 4m and length 80m are common these days. Along with the rebars, drilled shafts often contain additional tubes for testing the postconstruction integrity. With such a congested environment, it is difficult for concrete to pass down and set properly by providing the strength it is supposed to provide. In such cases, the use of high-performance concrete is valued. High performance of concrete focuses on the workability of the design mixture and the structural design requirements. The components of a good mixture design, installation plan, passing ability, resistance to bleeding, and low heat of hydration are discussed in this paper. Not only the technology associated with this but also the aggregate properties are important factors to be considered. Errors in such important factors during placement and design lead to anomalies in the structure and the structural performance is underachieved.

1. Introduction
• Deep, cylindrical, cast-in-place concrete foundations – to
support axial and lateral loads.
• Diameter 2 - 30 feet
• Length up to 260 feet
• Dense placement of rebars with additional testing tubes –
difficult to pour concrete.
• Construction of crack-free, and the laitance-free shaft is
challenging.
• High-performance concrete
1

2. High-Performance Concrete
• High-performance concrete for defect-free shafts.
• Workability of design mixture
• Structural design requirements
• Self Consolidating Concrete
• Highly flowable
• Non-segregating
• Better consolidation in congested areas
• Better hardened properties
• Smooth Surfaces
2

3. Objective
• To achieve high-performance concrete
• workability and passing ability
• Workability retention
• Components of good mixture design
• Installation procedure
• Resistance to bleeding
• Control of temperature
3

4. Workability and Passing Ability
• Smooth flow within the shaft under its own buoyant weight
without “piling up” near the tremie.
4

5. Workability and Passing Ability
• Laitance - weak, milky, or powdery layer of cement and sand
fines on the surface – less workable concrete.
5
Figure: Exposure of trapped laitance attributed to inadequate workability.

6. Workability and Passing Ability
• Although workable concrete
but different level.
• Due to inappropriate aggregate
size.
• Aggregate shape and size must
be considered.
6
Figure: Exposure of trapped laitance attributed to
inadequate workability.

7. Workability and Passing Ability
• Tests
• Slump flow test (18- 24 inches)
• L-Box test
7
Figure: L-Box test
Figure: Slump flow test

8. • Use of admixtures –retarders.
• Dosage of retarding control
admixture –completion of tremie
placement.
• Difficulties associated with loss
of concrete workability.
8
Workability Retention
Figure: Effects of loss of workability during
concrete placement

9. Workability Retention
9
Figure: Placement difficulties associated with loss of
concrete workability

10. Resistance to Bleeding
• Minimal bleeding for higher workability
• Soil types
• Cohesive soils – bleeding issue
• Sandy soils – excess water escape
• Hydrostatic pressure – cause
• Effects
• Weak concrete
• Precautions
• Deduction of water-cement ratio
• Use of fly ash / GGBF slag
• Less initial strength higher final strength
10
Figure: bleed water channels on the
exposed surface of a drilled shaft

11. Control of Temperature
• Setting time of concrete and heat of hydration- temperature
dependent.
• High temperature of concrete = high rate of hydration = less
workability.
• Nonlinear effect – 70°F.
• Shafts diameter> 1.2 m – characteristics of mass concrete
• Shaft diameter = 3 m, interior temperature = 180°F.
• Temperature > 158°F, Delayed Ettringite Formation (DEF).
11

12. Control of Temperature
12
Figure 10: The effect of different initial mixture temperatures on the temperature

13. Control of In-Place Temperature
1. Limiting total cementitious material content
2. Fresh concrete placement temperature
3. Selection of cementitious material types
• Type -2 cement, class F fly ash/GGBF slag
13

14. Conclusion
• Fulfillment of requirements
• Workability and Passing ability
• Workability retention
• Resistance to bleeding
• Low heat of hydration
• Measures
• Round gravel aggregates
• Sand to total aggregate ratio – 0.44 to 0.50
• Water-reducing and hydration-control admixtures
• Fly ash/ GGBF slag
• Concrete temperature (75 °F to 80 °F)
• Type -2 cement for reduced DEF 14

15. 15
Any
Queries?