2.6 TESTING WET AND HARDENED CONCRETE2.6.1 Workability2.6.2 Bleeding and segregation2.6.3 Air content2.6.4 Test cubes2.6.5 Other mechanical tests

WorkabilityWorkability is defined as: "The amount of useful internal work necessary to produce full compaction".Note that "consistence" is the European word for workability and is used in all the new European Standards etc.

Low Slump Concrete

Workability TestsSlump TestDegree of Compactability TestVB TestFlow Table TestSlump MetersRheological TestsSelf Compacting Concrete TestsSlump Loss

Slump Test

When carrying out the slump test Ensure that the base on which the test is to be carried out is flat, level, clean and free from vibration and of adequate size to stand the cone next to the slumped concrete for measurement.Check that the cone is not bent or dented and the inside surface is clean.Check that a length of 16 mm diameter steel bar is available for tamping.Obtain a representative sample. Do not use the first or last fraction from the mixer.Fill the cone carefully tamping it in three layers. Lift it off vertically.Record the result carefully with details of the date, concrete batch etc.

Slump Cone

When carrying out the slump test Ensure that the base on which the test is to be carried out is flat, level, clean and free from vibration and of adequate size to stand the cone next to the slumped concrete for measurement.Check that the cone is not bent or dented and the inside surface is clean.Check that a length of 16 mm diameter steel bar is available for tamping.Obtain a representative sample. Do not use the first or last fraction from the mixer.Fill the cone carefully tamping it in three layers. Lift it off vertically.Record the result carefully with details of the date, concrete batch etc.

How do you get a sample from this?

Concrete Sampling

When carrying out the slump test Ensure that the base on which the test is to be carried out is flat, level, clean and free from vibration and of adequate size to stand the cone next to the slumped concrete for measurement.Check that the cone is not bent or dented and the inside surface is clean.Check that a length of 16 mm diameter steel bar is available for tamping.Obtain a representative sample. Do not use the first or last fraction from the mixer.Fill the cone carefully tamping it in three layers. Lift it off vertically.Record the result carefully with details of the date, concrete batch etc.

Slump Test

Workability TestsSlump TestDegree of Compactability TestVB TestFlow Table TestSlump MetersRheological TestsSelf Compacting Concrete TestsSlump Loss

Degree of Compactability (compaction Index) test sh1

Workability TestsSlump TestDegree of Compactability TestVB TestFlow Table TestSlump MetersRheological TestsSelf Compacting Concrete TestsSlump Loss

The V-B Test

Workability TestsSlump TestDegree of Compactability TestVB TestFlow Table TestSlump MetersRheological TestsSelf Compacting Concrete TestsSlump Loss

Flow Table TestFlow Distance

Workability TestsSlump TestDegree of Compactability TestVB TestFlow Table TestSlump MetersRheological TestsSelf Compacting Concrete TestsSlump Loss

Problems with single-point tests

Viscosity (see section 1.6 of the notes)Shear Stress yieldstressNewtonianFluidBingham FluidShear Stress yFluid velocity V1Fluid velocity V2Gradient of this line = viscosity (e)The viscosity e is defined as:e = y Pa s v1 - v2where is the shear stressShear rate

Rheometers

Results from viscometer testTorqueShear Rate

Site Rheometer

Rheology of Concrete Mixes

Effects of Silica Fume on Rheology

Workability TestsSlump TestDegree of Compactability TestVB TestFlow Table TestSlump MetersRheological TestsSelf Compacting Concrete TestsSlump Loss

Tests for Self Compacting ConcreteL Box test Normal concrete, SCCV Funnel test, Normal concrete, SCC

Workability TestsSlump TestDegree of Compactability TestVB TestFlow Table TestSlump MetersRheological TestsSelf Compacting Concrete TestsSlump Loss

Effect of Temperature on Slump

Slump Loss

2.6 TESTING WET AND HARDENED CONCRETE2.6.1 Workability2.6.2 Bleeding and segregation2.6.3 Air content2.6.4 Test cubes2.6.5 Other mechanical tests

Segregation of concreteWhen Poured One hour laterBleed waterDepletion of coarse aggregateAccumulation of coarse aggregate

The consequences of SegregationSegregation will reduce the strength both in areas where there is a lack of aggregate and in areas where there is a surplus of aggregate. The lack of aggregate may produce cracking and the surplus may produce voidage.A small amount of bleeding will be harmless because it will reduce the effective water/cement ratio and provide some water on the surface for curing. Larger amounts of water loss will cause plastic settlement and cracking. If the rising water carries cement with it a dusty porous surface may result. Bleed water trapped under reinforcement etc. will reduce bond and cause voidage.

Measurement of BleedBleed measurement with the bleed water replaced after measurement. It will normally all be reabsorbed within 24 hours.Bleed measurement with the water removed and not replaced. This is often a better simulation of site conditions where sun and wind will dry it off

2.6 TESTING WET AND HARDENED CONCRETE2.6.1 Workability2.6.2 Bleeding and segregation2.6.3 Air content2.6.4 Test cubes2.6.5 Other mechanical tests

Types of air void Accidental air voidage. Typical void size 1-3 mm but any size possible.Entrained air. Typical size 0.05 mm. Entrained to give resistance to freeze/thaw.Capillary pores. Typical size 10-7 m

Air Content Measurement

2.6 TESTING WET AND HARDENED CONCRETE2.6.1 Workability2.6.2 Bleeding and segregation2.6.3 Air content2.6.4 Test cubes2.6.5 Other mechanical tests

When preparing cubes check the following Check that the cube moulds are clean and properly bolted together. Note that moulds may be expensive but bolts are cheap so always have a box of spare bolts and nuts. Never use wooden moulds or steel moulds held together with tie wire.Oil the moulds carefully. Always use proper shutter oil.Check that a steel tamping bar is available.Get a good representative sample. (as for slump test).Always compact the concrete in layers.

Cube moulds, metal and plastic

When preparing cubes check the following Check that the cube moulds are clean and properly bolted together. Note that moulds may be expensive but bolts are cheap so always have a box of spare bolts and nuts. Never use wooden moulds or steel moulds held together with tie wire.Oil the moulds carefully. Always use proper shutter oil.Check that a steel tamping bar is available.Get a good representative sample. (as for slump test).Always compact the concrete in layers.

Storage and DespatchThis part of cube testing is often overlooked and can lead to unnecessary failures.Always cover the cubes with wet hessian covered with polythene after casting. Note that hessian alone is virtually useless because it has to be continually wetted.Always ensure that some form of heating is provided in cold weather in the area where the cubes are stored overnight.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 that they are properly labelled in at least two places.

Temperature matched curing

The observed cube strength will depend on: The original concrete (w/c ratio, age, curing conditions etc.)Factors in manufacture and storage (see above)The cleanliness of the platensThe alignment of the platens (should be on hemispherical seating which locks on loading)The rate of loading. Faster loading gives higher strength. EN 12390 specifies a stress increase of 0.2-1.0 N/mm2/sThe mode of failure. The failed cube should be two pyramids.

Compression of cube

The observed cube strength will depend on: The original concrete (w/c ratio, age, curing conditions etc.)Factors in manufacture and storage (see above)The cleanliness of the platensThe alignment of the platens (should be on hemispherical seating which locks on loading)The rate of loading. Faster loading gives higher strength. EN 12390 specifies a stress increase of 0.2-1.0 N/mm2/sThe mode of failure. The failed cube should be two pyramids.

Effect of loading rate on cube testStressStrain10 seconds3 minutes30 minutesDuration of test

The observed cube strength will depend on: The original concrete (w/c ratio, age, curing conditions etc.)Factors in manufacture and storage (see above)The cleanliness of the platensThe alignment of the platens (should be on hemispherical seating which locks on loading)The rate of loading. Faster loading gives higher strength. EN 12390 specifies a stress increase of 0.2-1.0 N/mm2/sThe mode of failure. The failed cube should be two pyramids.

Effect of testing method on strengthObserved strength lossInsufficient consolidation: 61%Seven days on site: 26%Plastic mould: 14%Eccentric loading: 12%Mix subject to vibration while setting: 5%Rebar tamping: 2%

Equivalent Cube Test

2.6 TESTING WET AND HARDENED CONCRETE2.6.1 Workability2.6.2 Bleeding and segregation2.6.3 Air content2.6.4 Test cubes2.6.5 Other mechanical tests

Tensile Strength MeasurementHardboard padsLoad PCrack forms hereStress =2P lDDiameter DConcrete test cylinderLength L

Cylinder Splitting

Large scale splitting

Flexural Strength MeasurementL/3L/3L/3width bdepth dSpan LLoad PCrack forms in this regionFlexural stress = PL bd2Modulus of rupture = flexural stress at failure

Flexural strength (modulus of rupture) test