Test of Wet and Hardened Concrete

2 6 TESTING WET AND2.6 - TESTING WET AND HARDENED CONCRETE

• 2.6.1 Workability• 2.6.2 Bleeding and segregation• 2 6 3 Air content• 2.6.3 Air content• 2.6.4 Test cubes / Cylinder• 2.6.5 Other mechanical tests

W k bilitWorkability

• Workability is defined as: "The amount of useful internal work necessary to produceuseful internal work necessary to produce full compaction".

• Note that "consistence" is the European wordfor workability and is used in all the newyEuropean Standards etc.

Low Slump pConcrete

Workability Tests

• Slump Test• Degree of Compactability Test• VB Test• VB Test• Flow Table Test• Slump Meters

Rh l i l T t• Rheological Tests• Self Compacting Concrete Testsp g• Slump Loss

Slump Test

Concrete Slump Apparatus

When carrying out the slump testy g p• Ensure that the base on which the test is to be carried out is

flat, level, clean and free from vibration and of adequateflat, level, clean and free from vibration and of adequatesize to stand the cone next to the slumped concrete formeasurement.

• Check that the cone is not bent or dented and the insidesurface is clean.

• Check that a length of 16 mm diameter steel bar is availablefor tamping.

• Obtain a representative sample. Do not use the first or lastfraction from the mixer.

• Fill the cone carefully tamping it in three layers. Lift it offvertically.

• Record the result carefully with details of the date, concretebatch etc.

Slump Conep

When carrying out the slump testy g• Ensure that the base on which the test is to be carried out is

flat level clean and free from vibration and of adequateflat, level, clean and free from vibration and of adequatesize to stand the cone next to the slumped concrete formeasurement.


• Check that a length of 16 mm diameter steel bar is availablefor tamping.p g


• Fill the cone carefully tamping it in three layers. Lift it offvertically.y


How do you get a sample from y g pthis?

Concrete Sampling

When carrying out the slump testy g• Ensure that the base on which the test is to be carried out is

flat level clean and free from vibration and of adequateflat, level, clean and free from vibration and of adequatesize to stand the cone next to the slumped concrete formeasurement.


• Check that a length of 16 mm diameter steel bar is availablefor tamping.p g


• Fill the cone carefully tamping it in three layers. Lift it offvertically.y


Slump Test

Workability Tests



Degree of Compactability (compaction Index) test

h1h

hc 1

1s sh 1

h1

Workability Tests



The V-B Test

Workability Tests



Flow TableFlow Table TestTest

Flow Distance

Workability Tests



Problems with single-point tests

Viscosity (see section 1.6 of the notes)

Shear Stress y

Fluid velocity V1

h i i i

BinghamShear

Fluid velocity V2 The viscosity e is defined as:

Bingham Fluid

Shear Stress e = y Pa s

v1 - v2

yield N t iGradient of

where is the shear stress

yieldstress

NewtonianFluid

this line =viscosity (e)

Shear rate

Rheometers

Results from viscometer test

Torque

hShear Rate

Si RhSite Rheometer

Rheology of Concrete Mixes

Effect of increasing:

yield stress g %fines

PFA, GGBS

ViscosityModifyer

%fines

y

Plasticiser or ib ti

Water

vibration

gradient h of shear stress vs shear rate ( fi 1 6 1)(see fig 1.6.1)

EffectsEffects of Silicaof Silica Fume on Rheology

Workability Tests



Tests for Self Compacting Concretep g

L Box test Normal concrete SCCL Box test Normal concrete, SCC

V Funnel test Normal concrete SCCV Funnel test, Normal concrete, SCC

Workability Tests



Effect of Temperature on Slump

Slump Loss

2 6 TESTING WET AND2.6 TESTING WET AND HARDENED CONCRETE

• 2.6.1 Workability• 2.6.2 Bleeding and segregation• 2 6 3 Air content• 2.6.3 Air content• 2.6.4 Test cubes• 2.6.5 Other mechanical tests

Segregation of concreteWhen Poured One hour later

Bleed water

Depletion ofDepletion of coarse aggregate

Accumulation of coarse aggregategg g

The consequences of Segregationq g g• Segregation will reduce the strength both in areas

where there is a lack of aggregate and in areaswhere there is a lack of aggregate and in areaswhere there is a surplus of aggregate. The lack ofaggregate may produce cracking and the surplusgg g y p g pmay produce voidage.

• A small amount of bleeding will be harmlessgbecause it will reduce the effective water/cementratio and provide some water on the surface forcuring. Larger amounts of water loss will causeplastic settlement and cracking. If the rising water

i t ith it d t fcarries cement with it a dusty porous surface mayresult. Bleed water trapped under reinforcementetc will reduce bond and cause voidageetc. will reduce bond and cause voidage.

Measurement of Bleed

• Bleed measurement with the bleed waterreplaced after measurement. It willnormally all be reabsorbed within 24 hours.y

• Bleed measurement with the water removedand not replaced This is often a betterand not replaced. This is often a bettersimulation of site conditions where sun andwind will dry it off

Types of air void

• Accidental air voidage. Typical void size 1-3 mm but any size possible.

• Entrained air Typical size 0 05 mmEntrained air. Typical size 0.05 mm.Entrained to give resistance to freeze/thaw.

ill i l i 7• Capillary pores. Typical size 10-7 m

Air Content M tMeasurement

When preparing cubes check the f ll ifollowing

Ch k h h b ld l d l• Check that the cube moulds are clean and properlybolted together. Note that moulds may beexpensive but bolts are cheap so always have aexpensive but bolts are cheap so always have abox of spare bolts and nuts. Never use woodenmoulds or steel moulds held together with tie wiremoulds or steel moulds held together with tie wire.

• Oil the moulds carefully. Always use propershutter oilshutter oil.

• Check that a steel tamping bar is available.• Get a good representative sample (as for slump• Get a good representative sample. (as for slump

test).• Always compact the concrete in layers• Always compact the concrete in layers.

Cube moulds metal and plasticCube moulds, metal and plastic

When preparing cubes check the f ll ifollowing

Ch k h h b ld l d l• Check that the cube moulds are clean and properlybolted together. Note that moulds may beexpensive but bolts are cheap so always have aexpensive but bolts are cheap so always have abox of spare bolts and nuts. Never use woodenmoulds or steel moulds held together with tie wiremoulds or steel moulds held together with tie wire.

• Oil the moulds carefully. Always use propershutter oilshutter oil.

• Check that a steel tamping bar is available.• Get a good representative sample (as for slump• Get a good representative sample. (as for slump

test).• Always compact the concrete in layers• Always compact the concrete in layers.

Storage and Despatchg• This part of cube testing is often overlooked and can

lead to unnecessary failures.lead to unnecessary failures.• Always cover the cubes with wet hessian covered with

polythene after casting. Note that hessian alone ispolythene after casting. Note that hessian alone isvirtually useless because it has to be continually wetted.

• Always ensure that some form of heating is provided inways e su e t at so e o o eat g s p ov dedcold weather in the area where the cubes are storedovernight.

• Try to get the cubes collected by the day after casting.If this is not possible a heated curing tank must be used.

• Always keep good records of the cubes and ensure thatthey are properly labelled in at least two places.

Temperature matched

icuring

The observed cube strength willThe observed cube strength will depend on:depend on:

• The original concrete (w/c ratio, age, curingconditions etc )conditions etc.)

• Factors in manufacture and storage (see above)Th l li f h l• The cleanliness of the platens

• The alignment of the platens (should be onh i h i l i hi h l k l di )hemispherical seating which locks on loading)

• The rate of loading. Faster loading gives higherh EN 12390 ifi i fstrength. EN 12390 specifies a stress increase of

0.2-1.0 N/mm2/sTh d f f il Th f il d b h ld b• The mode of failure. The failed cube should be two pyramids.

C b d C li d S iCube and Cylinder Specimen MoldMold

Compression of cube specimen

Compression of cylinderCompression of cylinder specimenp


• The original concrete (w/c ratio, age, curing conditions etc )conditions etc.)





Effect of loading rate on cube test

10 seconds

Duration of test

10 seconds

3 minutesStress

3 minutes

30 minutes30 minutes

StrainStrain


• The original concrete (w/c ratio, age, curingconditions etc )conditions etc.)





Effect of testing method on strengthEffect of testing method on strengthObserved strength lossg

• Insufficient consolidation: 61%• Seven days on site: 26%• Plastic mould: 14%• Plastic mould: 14%• Eccentric loading: 12%• Mix subject to vibration while setting: 5%

R b t i 2%• Rebar tamping: 2%

Equivalent Cube TestEquivalent Cube Test

Tensile Strength Measurement

Hardboard pads

Load P

Hardboard pads

Stress Concrete=2PlD

Diameter D

Concrete test cylinder

C k f

Diameter D cylinderLength L

Crack forms here

Cylinder Splitting

Large scale gsplitting

Flexural Strength MeasurementLoad P

L/3L/3L/3

width b

depth d

Span LCrack forms in this regionCrack forms in this regionFlexural stress = PL

bd2

Modulus of rupture = flexural stress at failure

Flexural strength g(modulus of rupture) test

Test of Wet and Hardened Concrete

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