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High strength concrete
The document discusses advancements in high strength concrete (HSC) and high performance concrete (HPC), emphasizing their importance in civil engineering due to their enhanced properties like early strength, durability, and reduced permeability. It highlights the role of various materials and admixtures, such as pozzolanic materials and superplasticizers, in improving the performance of concrete mixtures. The paper also addresses challenges in achieving uniform compaction and workability while presenting different types of high-value concrete and their respective properties.
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High strength 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 becomean 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 rapidsetting 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 wouldbe more durable” did not prove to be right, hence, performance criterion was adopted
- 9. High Performance Concrete(HPC) Possessinghigh 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 StrengthConcrete ◦ High-Strength Concrete ◦ High-Durability Concrete ◦ Self-Consolidating Concrete ◦ Reactive Powder Concrete
- 14. Material Primary Contribution/Desired Property Portlandcement 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 RetardersControl 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 typesof 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 ConcreteMaterials • 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 • flowsand 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.
- 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 RPCis 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 Propertiesof 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 typicalDuctal® 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 typicalDuctal® 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 developingRPC 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 concreteis going to replace normal conventional concrete in future once, codes and guidelines are available.
- 36.