As multistoreyed construction is the need of today, high strength concrete is going to replace normal concrete.

1. HIGH STRENGTH CONCRETE
– CONCRETE OF TOMORROW
Vinay Kumar, Addl. Director General, CPWD,
Mumbai
Dr K M Soni, Chief Engineer, CPWD, Nagpur

2. Concrete
 Has become an essential item of civil engineering
construction.
 Weak in tension hence used in a combination with
reinforcement but if reinforcement bars could have been
avoided or concrete could have tensile strength, it could have
reduced cost, time of construction and structure would be
durable due to no corrosion problem.
 Concrete strength is gained through curing due to heat of
hydration but if curing could have been accelerated, it could
gain early strength which can help in early construction.
 Compaction plays an important role in uniformity but
achieving uniform compaction through vibrators becomes
difficult, particularly when reinforcement is used with
concrete. If compaction could be achieved without vibrators
or concrete could be cast without reinforcing bars, it could
provide uniformity.
 Low w/c ratio leads to high compressive strength but also to
low workability but if w/c ratio could be reduced with required
workability, it could give high compressive strength.

3. High strength concrete
 Low w/c or w/b ratio
 Addition of fine pozzolanic
materials/silica fumes
 Addition of superplasticizers

4. Ettringite-
calcium sulfoaluminate
(delays rapid setting of
cement)
Portlandite is the
major bonding agent in cement
and concrete, formed during
curing process, when
elemental calcium reacts with
water to form calcium hydroxide
(Calcium – silicate- hydrate)

5. High Strength concrete
 Compressive strength;
 Normal structural concrete :20-50
MPa,
 High strength concrete(HSC): 50-100
MPa
 Ultra Strength concrete: 100-150 MPa,
and
 Especial strength concrete > 150
MPa.

6. High-Value Concrete
High-Strength Concrete
Materials
• 9.5 - 12.5 mm nominal maximum size
gives optimum strength
• Combining single sizes for required
grading allows for closer control and
reduced variability in concrete
• For 70 MPa and greater, the FM of the
sand should be 2.8 – 3.2. (lower may
give lower strengths and sticky mixes)
Aggregates —

7. High-Value Concrete
High-Strength Concrete
Materials
• Fly ash, silica fume, or slag often
mandatory
• Dosage rate 5% to 20% or higher by
mass of cementing material.
Supplementary Cementious Materials -
• Superplasticisers for workability

8. “Stronger concrete mixtures
would be more durable” did not
prove to be right, hence,
performance criterion was
adopted

9. High Performance
Concrete(HPC)
 Possessing high workability, high durability and
high ultimate strength.
 As per ACI, HPC is defined as a concrete
meeting special combination of performance and
uniformity requirements that cannot always be
achieved routinely using conventional
constituents and normal mixing, placing, and
curing practices.
 The Strategic Highway Research Program
(SHRP) in the United States defined HPC for
highway structures by three requirements,
namely a maximum w/cm, a minimum durability
factor to cycles of freezing and thawing (ASTM C
666, Method A), and a minimum early-age or
ultimate compressive strength.

10. U.S. Federal Highway
Administration (FHWA) has
revised the definition of HPC for
highway structures. HPC is a
concrete that has been designed
to be more durable and if
necessary, stronger than
conventional concrete.

11. Characteristics of HPC
 High early strength
 High strength
 High modulus of elasticity
 High abrasion resistance
 High durability and long life in severe
environments
 Low permeability and diffusion
 Resistance to chemical attack

12. Characteristics of HPC
 High resistance to adverse climatic
conditions
 Toughness and impact resistance
 Volume stability
 Ease of placement
 Compaction without segregation
 Inhibition of bacterial and mold growth

13. High-Performance?
◦ High-Early Strength Concrete
◦ High-Strength Concrete
◦ High-Durability Concrete
◦ Self-Consolidating Concrete
◦ Reactive Powder Concrete

14. Material Primary Contribution/Desired
Property
Portland cement Cementing material / Durability
Blended cement
Cementing material /
Durability /
High strength
Fly ash / Slag / Silica fume
Calcined clay/ Metakaolin
Calcined shale
Superplasticizers Flowability
High-range water reducers Reduce water-cement ratio
Hydration control admix. Control setting
Materials used in HPC

15. Material Primary contribution/Desired
property
Retarders Control setting
Accelerators Accelerate setting
Corrosion inhibitors Control steel corrosion
Water reducers Reduce cement and water
content
Shrinkage reducers Reduce shrinkage
ASR inhibitors Control alkali-silica activity
Improve workability/reduce paste
Polymer/latex
modifiers

16. HPC
 Four types of HPC were subsequently
developed:
◦ Very Early Strength (14 MPa in 6 hours),
◦ High Early Strength (34 MPa in 24 hours),
◦ Very High Strength (69 MPa in 28 days),
◦ High Early Strength with Fiber-
reinforcement.

17. High-Value Concrete
High-Early-Strength Concrete
• High-early-strength cement
• High cement content 400 to 600 kg/m3
• Low water-cementing materials ratio (0.20 to 0.45
by mass)
• Higher freshly mixed concrete temperature
• Higher curing temperature
May be achieved by;

18. High-Value Concrete
High-Early-Strength Concrete
• Chemical admixtures
• Silica fume (or other SCM)
• Steam or autoclave curing
• Insulation to retain heat of hydration
• Special rapid hardening cements
May be achieved by -

19. High-Value Concrete
High-Strength Concrete Materials
• Use of water reducers, retarders, or superplasticizers
— mandatory in high-strength concrete
• Air-entraining admixtures not necessary or desirable
in protected high-strength concrete.
– Air is mandatory, where durability in a freeze-thaw
environment is required (i.e.. bridges, piers, parking
structures)
– Recent studies:
• w/cm ≥ 0.30—air required
• w/cm < 0.25—no air needed
Admixtures —

20. High-Value Concrete
High-Strength Concrete
• Delays in delivery and placing must be eliminated
• Consolidation very important to achieve strength
• Slump generally 180 to 220 mm
• Little if any bleeding—fog or evaporation retarders
have to be applied immediately after strike off to
minimize plastic shrinkage and crusting
• 7 days moist curing
Placing, Consolidation, and Curing

21. High-Value Concrete
High-Durability Concrete
• 1970s and 1980s focus on — High-
Strength Concrete
• Today focus on concretes with high
durability in severe environments
resulting in structures with long life —
High-Durability HPC

22. High-Value Concrete
High-Durability Concrete
• Abrasion Resistance
• Blast Resistance
• Permeability
• Carbonation
• Freeze-Thaw Resistance
• Chemical Attack
• Alkali-Silica Reactivity
• Corrosion rates of rebar
Durability Issues That HPC Can Address

23. High-Value Concrete
• Cement: 398 kg/m3
• Fly ash: 45 kg/m3
• Silica fume: 32 kg/m3
• w/c: 0.30
• Water Red.: 1.7 L/m3
• HRWR: 15.7 L/m3
• Air: 5-8%
• 91d strength: 60 Mpa
High-Durability Concrete
Confederation Bridge, Northumberland Strait, Prince Edward
Island/New Brunswick, 1997

24. High-Value Concrete
Self-Consolidating/compacting
Concrete
• flows and consolidates on its own
• developed in 1980s — Japan
• Increased amount of
– Fine material i.e. fly ash or limestone filler
– Superplasticizers
• Strength and durability same as
conventional concrete

25. High-Value Concrete
Self-Consolidating Concrete

26. High-Value Concrete
Portland cement (Type I) 297 kg/m3
Slag cement 128 kg/m3
Coarse aggregate 675 kg/m3
Fine aggregate 1,026 kg/m3
Water 170 kg/m3
Superplasticizer ASTM C 494, Type F (Polycarboxylate-based) 1.3 L/m3
AE admixture as needed for 6% ± 1.5% air content
SCC for Power Plant in
Pennsylvania—Mix Proportions

27. Self compacting concrete
 Extreme fluidity
 No need for vibrators to compact the
concrete
 Placement being easier.
 No bleed water, or aggregate
segregation

28. REACTIVE POWDER
CONCRETE
 RPC is composed of very fine
powders (cement, sand, quartz
powder and silica fume), steel fibres
(optional) and superplasticizer.
◦ A very dense matrix is achieved by
optimizing the granular packing of the dry
fine powders. This compactness gives
RPC ultra-high strength and durability.
Reactive Powder Concretes have
compressive strengths ranging from 200
MPa to 800 MPa.

29. High-Value Concrete
Reactive-Powder Concrete
(RPC)• Properties:
– High strength — 200 MPa
(can be produced to 800
MPa)
– Very low porosity
• Properties are achieved by:
– Max. particle size  300 m
– Optimized particle packing
– Low water content
– Steel fibers
– Heat-treatment

30. High-Value Concrete
Mechanical Properties of RPC
Property Unit 80 MPa RPC
Compressive
strength
MPa 80 200
Flexural strength MPa 7 40
Tensile strength MPa 8
Modulus of Elasticity GPa 40 (5.8 x 106) 60 (8.7 x 106)
Fracture Toughness 103 J/m2 <1 30
Freeze-thaw RDF 90 100
Carbonation mm 2 0
Abrasion 10-12 m2/s 275 1.2

31. High-Value Concrete
• Cement
• Sand
• Silica quartz
• Silica fume
• Micro-Fibres - metallic or poly-vinyl acetate
• Mineral fillers - Nano-fibres
• Superplasticizer
• Water
Raw Materials

uctal

32. High-Value Concrete
The typical Ductal® mix
230 kg/m3
710 kg/m3
210 kg/m3
40 - 160 kg/m3
13 kg/m3
140 kg/m3
1020 kg/m3
Cement
Silica fume
Crushed
Quartz
Sand
Fibres
Superplasticizer
Total water
No aggregates !

uctal

33. High-Value Concrete
The typical Ductal® mix
9 – 10%
28 - 30%
8.5 – 9%
1.7 – 6.5%
0.6%
5.5 – 6%
42 –43%
Cement
Silica fume
Crushed
Quartz
Sand
Fibres
Superplasticizer
Total water
No aggregates !

uctal
w/c = 0.20

34. Principles in developing RPC
 Elimination of coarse aggregates
 Utilization of the pozzolanic properties of
silica fume
 Optimization of the granular mixture for the
enhancement of compacted density
 The optimal usage of superplasticizer to
reduce w/c and improve workability
 Application of pressure (before and during
setting) to improve compaction
 Post-set heat-treatment for the enhancement
of the microstructure
 Addition of small-sized steel fibres to
improve ductility

35. Thus, High performance
concrete is going to replace
normal conventional concrete
in future once, codes and
guidelines are available.

36. Thank you