HIGH PERFORMANCECONCRETE - HPC

Fahim Al-Neshawy & Esko Sistonen23.10.2015

Outlines• Introduction• Materials used in HPC• Methods used for making HPC• HPC - mix design• Properties of HPC• Advantages and disadvantages• Applications

Introduction• Based on the compressive strength; concrete

is normally classified asØ normal strength concrete,Ø high strength concrete andØ ultra strength concrete.

• High performance concrete is necessary forthe construction of high rise building and longspan bridges.

• To achieve high strength, it necessary to use:− high cement content− with the lowest possible W/C ratio which

invariable affect the workability of the mix.

Introduction• It is important to note the high-strength and high-

performance concrete are not synonymous.

• Concrete is defined as “high-strength concrete”solely on the basis of its compressive strengthmeasured at a given age.

• In the 1970’s, any concrete mixtures thatshowed 40 MPa or more compressive strengthat 28-days were designed as high-strengthconcrete.

• Later, 60-100 MPa concrete mixtures werecommercially developed world.

• Mehta used the term, high- performanceconcrete (HPC) for concrete mixturespossessing:− high workability,− high durability and− high ultimate strength

• ACI defined high-performance concrete as aconcrete meeting special combinations ofperformance and uniformity requirements thatcannot always be achieved routinely usingconventional constituents and normal mixing,placing, and curing practice.

Definition - HPC

P.K. Mehta and P.J.M. Monteiro, Concrete: Microstructure, Properties, and Materials

HPC classification

• Normal Strength 20-50 MPa

• High Strength 50-100 MPa

• Ultra High Strength 100-150 MPa

• Especial > 150 MPa

Microstructure

MATERIALSUSED IN HPC

Material SelectionThe main ingredients of HPC are almost the sameas that of conventional concrete. These are:

1) Cement2) Fine aggregate3) Coarse aggregate4) Water5) Mineral admixtures (fine filler and/or

pozzolanic supplementary cementationmaterials)

6) Chemical admixtures (plasticizers,superplastisizers, retarders, air-entrainingagents)

Material Primary contribution/Desired propertyPortland cement Cementing material/durabilityBlended cement

Cementing material/durability/highstrength

Fly ashSlagSilica fumeSuperplasticizers FlowabilityHigh-range water reducers Reduce water to cement ratioHydration control admixtures Control settingRetardersAccelerators Accelerate settingCorrosion inhibitors Control steel corrosionWater reducers Reduce cement and water contentShrinkage reducers Reduce shrinkageASR inhibitors Control alkali-silica reactivityPolymer/latex modifiers Durability

Optimally graded aggregate Improve workability and reduce pastedemand

Materials Used in High-Performance Concrete

Cements• There are two important requirements for any

cement:a) Strength development with time

• Cement with compressive strength up to 60MPa for HSC

b) Facilitating appropriate rheologicalcharacteristics for the fresh concrete

• Experience has shown that low-C3A cementsgenerally produce concrete with improvedrheology.

• Cement contents between 400 and 550 kg/m3

• Cement should compatible with the chemicaladmixtures

Aggregates• The higher the targeted compressive strength,

the smaller the maximum size of coarseaggregate.

• Up to 70 MPa compressive strength can beproduced with a good coarse aggregate of amaximum size ranging from 20 to 28 mm.

• To produce 100 MPa compressive strengthaggregate with a maximum size of 10 to 20mm should be used.

• Concretes with compressive strengths of over125 MPa have been produced, with 10 to 14mm maximum size coarse aggregate.

Mineral admixturesn GGBS, fly ash and natural pozzolans, not only

reduces the production cost of concrete, butalso addresses the slump loss problem.

n While silica fume is usually not necessary forcompressive strengths under 70 MPa, mostconcrete mixtures contain it when higherstrengths are specified.

n Dosage rate 5% to 20% or higher by mass ofcementing material.

n Some specs. – silica fume 10% max.

Admixturesn Use of admixtures is mandatory in high-performance

concrete:n water reducers,n retarders,n superplasticizers

n Air-entraining admixtures not necessary or desirablein protected high-strength concrete.u Air is mandatory, where durability in a freeze-thaw

environment is required ie. bridges, piers, parkingstructures

u Recent studies:H w/cm ≥ 0.30 - air requiredH w/cm < 0.25 - no air needed

Requirements of ingredients for HPC

METHODS USEDFOR MAKING HPC

Special methods for making HSC

1. Seeding

2. Re-vibration

3. High Speed Slurry

4. Use of admixtures

5. Inhibition of Cracks

6. Sulphur Impregnation

7. Use of Cementitious aggregates

Special methods for making HSC1. Seeding:

This involves adding a small percentage offinely ground, fully hydrated Portland cement tothe fresh concrete mix.

2. Revibration:Controlled revibration removes all the defectslike bleeding, water accumulates , plasticshrinkage, continuous capillary channels andincreases the strength of concrete.

3. High speed slurry [liete] mixing:This process involves the advance preparationof cement - water mixture which is then blendedwith aggregate to produce concrete.

Special methods for making HSC4. Use of admixtures:

Use of water reducing agents are known toproduce increased compressive strength.

5. Inhibition of cracks:If the propagation of cracks is inhibited, thestrength will be higher.Concrete cubes made this way have yieldedstrength up to 105MPa.

Special methods for making HSC

6. Sulphur Impregnation:Satisfactory high strength concrete havebeen produced by impregnating low strengthporous concrete by sulphur.The sulphur infiltrated concrete has givenstrength up to 58 MPa.

7. Use of Cementitious aggregates:Cement fondu is kind of clinker.Using a slag as aggregate, strength up to 25MPa has been obtained with water cementratio 0.32.

Air-cooled blast furnace slag(ABS), coarse aggregate

Granulated blast furnace slag(GBS), fine aggregate

HPC MIX DESIGN

Mix design• A generalized systematic approach to the selection

of mix proportions of HPCs has not yet beendeveloped

• Specific requirements to considered:− Water content should be chosen on the basis of

the required w/c ratio (from strengthconsiderations)

− Excessive content of cementitious materialshould be avoided (to control shrinkage)

− Compatibility between Portland cement and thesuperplasticizer

− If air entrainment is to be used, mix proportionshave to be modified by trial and error

Mix design1. Define proportioning strength

Average strength + effect of deviationex. fcr = fc + 1.3swhere σ is the standard deviation in MPaThe equation ensures that there is a 99% probability that the average of allsets of three consecutive compressive strength tests must be equal to orgreater than f’c.

2. Define the amount of binder

C = cementSi = Silica fumeLt = Fly ashMk = Blastfurnace slag

From the report:”Korkealujuuksisten betoniensuhteitus”; Penttala V. et. al.(1990). Publication 108. Figurefrom page 40.

Mix design3. Calculate the amount of cement and

additional bindersBinder amount (C+2,5∙Si+0,3∙Lt+Mk)

4. Define the amount of (super)plasticizer as apercentage of binder

Mix design5. Define the water amount

Mix design6. Calculate the amount of aggregate with

the basic equation of concrete.The amount of air is assumed to be 10dm3/m3

C = cementSi = Silica fumeLt = Fly ashMk =Blastfurnace slagI = air contentNt = PlasticizerW = WaterR = Aggregates

7. Define the components of the batch8. Combine the aggregate9. Make a trial batch

Example of HPC mix design

PROPERTIES OF HPC

Properties of HPC• High modulus of elasticity• High abrasion resistance• High durability and long life in severe environments• Low permeability and diffusion• Resistance to chemical attack• High resistance to frost and deicer scaling damage• Toughness and impact resistance• Ease of placement• Chemical Attack• Carbonation

High modulus of elasticity

Low permeability and diffusion

• The durability and service life of concrete exposed to weather isrelated to the permeability of the cover concrete protecting thereinforcement.

• HPC typically has very low permeability to air, water, and chlorideions.

• The dense pore structure of high-performance concrete makes itso impermeable

• HSC is considerably more brittle than NSC.• HSC behaves linearly up to a stress level which is about

90% of the peak stress, whereas lower strengthconcrete shows nearly no linear part at all

• When the peak stress has been reached, the stressdecays rapidly in high strength concrete.

Durability parameters1. Water/ (cement + mineral admixture) ratio2. Strength3. Densification of cement paste4. Elimination of bleeding5. Homogeneity of the mix6. Particle size distribution7. Dispersion of cement in the fresh mix8. Stronger transition zone9. Low free lime content10.Very little free water in hardened concrete

High abrasion resistance• Abrasion resistance is directly related to the

strength of concrete.• This makes high strength HPC ideal for

abrasive environments.• The abrasion resistance of HPC incorporating

silica fume is especially high.• This makes silica fume concrete particularly

useful for spillways and stilling basins, andconcrete pavements or concrete pavementoverlays subjected to heavy or abrasive traffic.

High durability and long life in severeenvironments

• Durability problems of NSC can be associated withthe severity of the environment and the use ofinappropriate high water/binder ratios.

• HPC that have a water/binder ratio between 0.30and 0.40 are usually more durable than NSC notonly because they are less porous, but alsobecause their capillary and pore networks aresomewhat disconnected due to the development ofself-desiccation.

• In high-performance concrete (HPC), thepenetration of aggressive agents is quite difficultand only superficial

High resistance to frost and deicerscaling damage• Because of its very low W/C ratio (<0.30), HPC

should be highly resistant to both scaling andphysical breakup due to freezing and thawing.

Resistance to chemical attack• For resistance to chemical attack on most

structures, HPC offers a much improvedperformance.

• Resistance to various sulfates is achievedprimarily by the use of a dense, strongconcrete of very low permeability and lowwater-to-cementing materials ratio; these areall characteristics of HPC.

• Similarly resistance to acid from wastes isalso much improved.

Carbonation• HPC has a very good resistance to carbonation

due to its low permeability.• In practical terms, non-cracked HPC cover

concrete is immune to carbonation to a depththat would

Properties - summaryFlowability/pumpability EasierWorkability/compactability EasierBleeding None or negligibleFinishing QuickerSetting time Slower up to 2 hEarly strength (up to 7-day) Lower but can be acceleratedUltimate strength- 90day + HigherCrack resistance Higher• Plastic shrinkage Higher (if unprotected)• Thermal shrinkage Lower• Drying shrinkage LowerResistance to penetration of chloride ions Very high after 3 monthsElectrical resistivity Very high after 3 monthsDurability• Resistance to sulfate attack Very high• Resistance to alkali-silica expansion Very high• Resistance to reinforcement corrosion HighEnvironmental benefits(reduced CO2 emission) Very high

ADVANTAGES /DISADVANTAGES

Advantages of using HPC• Reduction in member size, resulting in increase in

plinth area/useable area and direct savings in theconcrete volume saved.

• Reduction in the self-weight and super-imposedDL with the accompanying saving due to smallerfoundations.

• Reduction in form-work area and cost with theaccompanying reduction in shoring and strippingtime due to high early-age gain in strength.

• Construction of High –rise buildings with theaccompanying savings in real-estate costs incongested areas.

Advantages of using HPC• Longer spans and fewer beams for the same

magnitude of loading.• Reduced axial shortening of compression

supporting members.• Reduction in the number of supports and the

supporting foundations due to the increase inspans.

• Reduction in the thickness of floor slabs andsupporting beam sections- which are a majorcomponent of the weight and cost of the majorityof structures.

Advantages of using HPC• Superior long-term service performance under

static, dynamic and fatigue loading.• Low creep and shrinkage.• Greater stiffness as a result of a higher

modulus,Ec

• Higher resistance to freezing and thawing,chemical attack, and significantly improved long-term durability and crack propagation.

• Reduced maintenance and repairs.• Smaller loss in value as a fixed cost.

DisadvantagesThe current disadvantages of HPC pointed outby some engineers include:

− the initially higher construction bid prices tobe expected with the use of any newtechnology

− quality control concerns related to variousmaterial selection, testing methods in useand the number of tests

− Instabilities concerns that could resultfrom reduced stiffness

− Fire resistance concerns

HSC APPLICATIONS

The East Bridge of the Great Belt Linkin Denmark, (1994)

• Concrete structuresà 100 years• High-quality precast concrete segments were

fabricated on dry docks under controlled environment.• Even for the 50,000-tonne precast concrete units,

construction tolerances were within a few centimeters

The Confederation Bridge in Canada (1997)

http://www.ce.berkeley.edu/~paulmont/241/high_performance_concrete.pdf

The Confederation Bridge in Canada (1997)

The Normandie Bridge in France (1993)

The Normandie Bridge in France (1993)

• Approximately 35,000 m3 of 60-Grade HPC(60 MPa specified strength at 28 days) wereused in the construction of pylons andcantilever beams.

• The concrete mixture was composed of:− 425 kg/m3 blended Portland cement− containing 8% silica fume,− 770 kg/m3 fine aggregate,− 1065 kg/m3 coarse aggregate of 20mm

max. size,− 153 kg/m3 water (w/cm=0.36), and− 11 L/m3 of melamine-type superplasticizer.

http://www.ce.berkeley.edu/~paulmont/241/high_performance_concrete.pdf

Water Tower Place: Shopping mall inChicago (1975 )

Water Tower Place: Shopping mall inChicago (1975)

Summary• Definition of HPS, HSC and NSC• Materials used in HPC (cement, mineral and

chemical admixtures, aggregates)• Methods used for making HPC• HPC - mix design• Advantages and disadvantages of the use of

HPS• HPC Applications