Testing of No Slump Concrete With Gyratory Compactor

CONCRETE TECHNOLOGY

56 CPI – Concrete Plant International – # 5 – October 2006 www.cpi-worldwide.com

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Pietro Ferrari,Controls S.R.L., Italy

Field of application of testingmachine

The field of application of the GyratoryTesting Machine includes the manufactureof concrete elements, as well as road anddam construction.

Basically the characteristic of compactedfresh no-slump concrete used for concreteelements such as paving blocks, hollowcore blocks, slabs, pipes, roofing tiles andconcrete road pavements, is to be free ofshrinkage effects such as cracks and volu-me change, to maintain its shape afterstripping from the form and to grant andmaintain good aesthetic level of the pro-duct.

As regards concrete dam and road sub-base concrete, the base characteristics isthe consistency of density with mechanicalproperties, as compression and splittingtensile strength at various age.

Small variations of the components of themix cause remarkable change in perfor-mance.Therefore accurate mix design with finetuning of components and frequent QC ofproduction is essential.

The Gyratory Testing Machine is particu-larly useful on the purpose, because itdeals with the subject by examining thevolumetric properties of no-slump concre-te mix during compaction.

To define the optimum mix (mix design)and to perform factory production con-trol, it is necessary to refer to the volume-tric properties of the whole fresh concretewith all its components:• aggregates (sand, gravel, eventual

special aggregate like silica fumes),• cement, • additives and water,in order to control the density and conse-quently the compaction degree and % AirVoids, during and after compaction, inrelation to compaction energy. Volumetric parameters are referred to thetheoretical maximum density of the mixand, during compaction they tend toapproach their numerical values to theones calculated for such max density alsocalled “TMCD” (Theoretical ConstituentMaximum Density).

where:• Pi is percentage of weight of materials

used in the mix;

• RDi is the relative density of each con-stituent in terms of kg/cm3 and “i” isreplaced by the symbols “c”, “f”, “ca”,”fa” and “w” that represent cement,fly ash, coarse aggregate, fine aggre-gate and water respectively;

• % Air Voids are calculated from thepercentage ratio between the measur-ed density of the mix and the theoreti-cal constituent max density (TMCD).

TMCD – dVA% = x 100

TMCD

Principle of the method

A sample of fresh concrete mass is com-pacted by a continuous kneading action,consisting of axial pressure and shear.

Testing of no-slump concrete with gyratory compactor

Controls S.R.L., 20063 Cernusco s/N. (Mi), Italy

Fresh concrete is generally considered no-slump ifit has a slump less than 2 cm and a VeBe time lon-ger than 5 sec. approx. Therefore it consists of astiff mass that has to be compacted by means ofpressure combined with vibration, rolling and/orextrusion, generally a shear movement in order

to grant a good interlocking between the aggre-gate particles. Gyratory Testing Machine wellreproduce in laboratory the compaction of no-slump concrete by mean of vertical pressure com-bined with the gyratory movement.

Gyratory Compactorfrom Controls S.r.L.

Gyratory compaction principle

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02b-Technik_56-75_eng 27.09.2006 15:31 Uhr Seite 56

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www.cpi-worldwide.com CPI – Concrete Plant International – # 5 – October 2006

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As already mentioned, compaction is given by the combination oftwo distinct and essential actions: pressure and shear movement.

• Shear movement under constant pressure allows particles tomove closer one another to reach a higher level of density.

• The constant vertical pressure, applied to a material in themachine, is obtained by compressing the mass in a test cylinder between top and bottom plates. Gyratory movementof the cylinder during a test creates the required shear.Compaction with the gyratory principle can be presented asfollows:• The geometric shape of the work sample is a cylinder with

slightly inclined ends. This “inclination” (�) rotates aroundthe central axis of the sample cylinder during the test

• (Picture 2), one complete rotation being defined as awork cycle (n).

• By the preset gyratory angle “�”, a shear movementinside the sample is produced every work cycle. Internalshear is illustrated by dividing the sample into finite ele-ments. Shear occurs as each element slides relative to theadjoining elements. The related deformation force can befigured out from the moment measurement on the workcylinder lid, where the axis of such reaction moment rotates horizontally with the gyratory movement.

Testing machine versions

Controls S.R.L., the manufacturer of the machine, produces twoversion of the Gyratory Testing Machine:

• standard portable model 54 – C0252/C • research model 54 – C0251/A

Both models are dedicated to no-slump fresh concrete testing andfully comply the specifications of the Nordtest Method NT BUILD427.

Basic specifications are given here below in order to outline thedifference between the standard/portable model and the re-search model:

Both models are driven by portable or desk top computer withtwo software packages included:

1. “Intensive Compaction Testing” WINDOWS® program (Fig. 3) by which the compaction (change in sample height)and density versus number of cycles (gyrations) are recordedin real time and plotted. Shear pressure in kN/m2 is also

Pietro Ferrari (1934), Product Manager of CONTROLS SRL – Milan –Italy, international leading company in the industry of TestingEquipment for construction materials. Graduated in Chemistry atUniversity of Pavia in 1959. Member of UNI Italian standardizationcommittees for testing of bituminous mixes and UNI delegate toEuropean Standards work group CEN/TC227/WG1 for bituminousmaterial testing.

[email protected]


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BETONTOWER

SIMEM

monitored and plotted versus numberof cycles in the Gyratory TestingMachine research model 54 –C0251/A.

2. EXCEL® macro where the followingvolumetric parameters are related tothe number of gyrations:• Height of specimen (mm),• Density (kg/m3),• Air Voids (%) of fresh concrete mix

(AV),• Voids (%) in Mineral Aggregates of

the mix (VMA),• Voids (%) Filled with Cement

(VFC).

Several considerations can be drawnfrom the compaction curve plotted in realtime by the ICT WINDOWS® program,see diagram of density v/s number ofcycles of Fig. 3, green line. :

• Compaction diagram describes theacting of the mix to full degree ofcompaction, max density, versus com-paction energy.

• High workability is indicated by anearly increase of density by givengyratory cycles.

• By converse, low workability mixneeds higher compaction energy,more cycles and/or higher verticalpressure, to reach a certain density.

• Mixes which give a steep densifica-tion curve indicate those with highcompactibility. Their structure, consist-ing of an appropriate dosage ofcement, water, additives and gradedaggregates with high angularity willabsorb a high degree of compactionenergy. Such behaviour is generallyassociated a relative remarkabledimensional stability at the fresh com-pacted stage.

On the contrary, mixes which present adensification curve with a low slope, arecharacterised by lower compactibility andgenerally by lower dimensional stability atthe fresh compacted stage.

Due to high sensitivity of Gyratory TestingMachine it is possible to optimise grada-tion and angularity of aggregate, rate ofcement and eventual silica fumes anddosage of superplasticizer.

Between such opposite behaviours, wellhighlighted by the installed software, thedesigner has the possibility to select theproper mix that better fits the constructionelement, based on its specific require-ment, and to optimise the appropriateworkability.

Various levels of no-slump concrete work-ability:

• Production of concrete tiles requiresrelative higher workability than pro-duction of concrete pipes, slabs andpaving blocks.

• Extruded hollow core elements need aworkability associated with higherlevel of compaction energy and shearaction.

• For road and dam construction theworkability of Rolled CompactedConcrete is optimised to the highestrange of compaction energy.

Generally speaking, high compactibilitycorresponds to good resistance to defor-mation of fresh compacted concrete.

Shear measurement

Shear measurement, continuously moni-tored at each gyration in the Gyratory

Model

Specimen size

Gyratory angle (calibrated by ILS)*

Number of cycles

Rotation speed

Vertical pressure

Max air pressure

5 µ filtered air pressure connection

Vertical pressure auge

Shear measurement

Weight of the unit

Dimensions

54-C0252/C 54-C0251/A

100 mm diameter x 90 ÷ 130 mm height

40 mrad (2° 17”) fixed Adjustable from 0 to 50 mrad (2° 86”)

Adjustable from 2 to 512

30 to 120 cycles /min, adjustable

60 to 320 kPa, adjustable

63 mm diameter twin; 50 mm diameter each

8 bar

max 10 bar

Range 0-10 bar Two ranges; 0-10 and 0-4 bar

55 kg approx. 95 kg approx.

35 x 48 x 93 cm 50 x 60 x 110 cm* Internal LoadSimulator

Example output of the “Intensive Compaction Testing” program

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Testing Machine search model 54 –C0251/A, besides an optional parame-ter not required by the common gyratorytesting volumetric procedure, is a usefultool for finer selection in mix design, as anadditional verification parameter in QCand mix design.

Since the sample is confined within thecylindrical mould and the upper andlower platens are subjected to constantvertical pressure, the deformation force ofthe sample is measured by the reactionmoment due to friction between theaggregate particles. The direction of themoment vector, normal to the rotationaxis, rotates horizontally together with the

gyratory movement, whilst the relativeforce acts against the bases of the cylin-der and is measured by an installed loadcell. Therefore the test report will presenta table with shear force (kN/m2) togetherwith the other parameters normally asso-ciated with the gyratory test.

Generally the shear force increases afterthe start of the test to a maximum valuethat can be reached towards the end ofthe test or before depending on the plasti-city characteristics of the mix as illustratedfurther on.

Standard Specification andliterature

Nordtest Scandinavian Institution hasdeveloped and regulated the testing pro-cedure and the criteria by which a com-paction energy, given by a gyratorytesting machine, can be associated to ano – slump fresh concrete mix (NordtestMethod. NT BUILD 427 – Picture 4)The document indicates the following spe-cifications:

• diameter of the work cylinder: 100 mm• volume of specimen: 0.78 – 0.86 dm3

corresponding to height of specimenof 100 – 110 mm

• air pressure applied by a vertical ram:4 bar (160 kPa on-sample verticalpressure).

• working speed adjusted to 60 rpm• max dimensions of aggregate: 20 mm• gyratory angle: 40 mrad ( 2° 17” )

Other test conditions can be adopted forspecial purposes.

In accordance with the Nordtest Methodthe reference compaction limits are de-fined as follows:

1. At the slurry limit.2. At specified number of cycles of

gyratory machine.3. At a specified density of the sample

Furthermore:

• The “Slurry limit” is defined as thenumber of gyrations where the slurrystarts separation from the sample.

• Since slurry consists of a suspensionof binding matter (components ofhydrated cement), fine aggregate,water and eventual admixtures, theseparation of slurry from the moulddefines the limit beyond which addi-tional compaction, generally close to100%, is no longer possible withouthomogeneity and quality being alter-ed.

• “Specified number of cycles of Gyra-tory machine” at which the test is stop-ped. This compaction limit is bound tothe “ICT index” (Intensive CompactionTest Index) concept. The “ICT index”is defined as the pressure value (i.e.the vertical pressure of Gyratory Test-ing Machine) multiplied by the num-

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ber of gyrations at which slurry come out. For instance, for“Slurry limit” verified at 80 cycles with a vertical pressure of 1,6 Bar, the“ICT index” is equal to 1,6 Bar * 80 cycles = 128. “ICTindex” can be considered a determining variable for thecompaction energy.

• “Specified density of the sample” means that the gyratorymachine makes up the sample at a required level of compac-tion, useful to characterize the compacted sample by othertests such as compression test on hardened sample, to verifymechanical resistance and durability for the convenient cali-bration of the product and of the production plant.

Rather recently in Unites States the interest for concrete GyratoryTesting Machine has got credit. The technical report “ImprovedManagement of RCC Pavement Technology”(Research Paper01231- January 2003), University of Alabama, presents anexhaustive discussion on manufacture and performance of rollercompacted concrete ( RCC ) including an overview on severalmethods of test specimen preparation on the purpose to evidencea method that better “relate the laboratory specimen propertiesto field properties”. This research shows that “strength and densi-ty results for RCC specimens fabricated using the gyratory com-pactor were consistent and that field results indicate that themechanical properties of specimens are consistent with thoseachieved in the field.In the Research Report 105.1, “Summary of Concrete WorkabilityTest Methods”, by Eric P. Kohler and David W. Fowler (from ICAR105, University of Austin, Texas, U.S.A., August 2003), test meth-ods for very low slump concrete have been discussed. Amongstthem, the “Intensive Compaction Test”, as standardized in“Nordtest – Build 427, ISSN 0823 – 7153”, has been quotedas very reliable for measuring the workability of no-slump concre-te and capable of accurately measuring even small changes inmixture proportions.

Conclusions

The target of mix design of no-slump concrete is divided in seve-ral purposes that highlight some characteristics with differentimportance according to the type of the work; for instance:

• good stability before hardening,• product cost optimisation for industrial production of concrete

elements,• high strength and consistent density for Roller Compacted

Concretestructures.

Scandinavian Countries and European industries have based theno-slump concrete mix design and factory production control ofconcrete elements on volumetric properties since many years withgood results.

The reliable result of such a testing approach is evident:

• Optimum compaction energy related to the requisites of theconcrete element, such as durability and mechanical resistance.


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• Calibration of plant compaction ener-gy, on the basis of density data(volumetric properties).

• Immediate means to check the plant’scompaction efficiency.

• Accurate Mix Design easily dupli-cated in the production plant.

• Rationalization of cement andwater/cement ratio, of superplas-ticizers and mineral additive rate.

• Optimum production costs. Correctcompaction energy may lead to arational reduction of cement andcorrect dosage of additives.

• Possibility of continuous QC, accurateindication of any changes in mix pro-duction.

Assessment of sensitivity ofGyratory Testing Machine tosmall change of the mix

Some tests have been carried out withGyratory Testing machine research model54 – C0251/A, in order to assess thesensitivity of the tester with small variationsof water and superplasticizer dosage. Theaggregate mix 0-4 mm and cement con-tent have been kept constant for twogroups of tests.

The first group includes tests carried outon mixes without superplasticizer but withchange in water dosage:

The second group includes tests carriedout on mixes with various rates of super-plasticizer:

All the tests were ended after 80 cycles.

First group of tests without superplasticizer

Comments:

• Slurry lost. It appeared in the mix with0,28 W/C ratio. Due to the amountof water the AV% (air voids) droppedclose to saturation ( 0,9%; 1,3%;2,2%). During the last cycles, due topore pressure development, slurry out-let occurred. Moreover, the shearvalue increased at the same time as

the slurry outlet, for the tests with 1,0and 1,4% AV. Evidently the loss oflubrication effect due to slurry outputincreases the mutual friction of theaggregate particles and hence theshear resistance.

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Group Test Water W/Ccontent ratio

1 1 7.09% 0.281 2 6.58% 0.26

Group Test Super- W/Cplasticizer ratio

2 1 0.50% 0.262 2 0.63% 0.262 3 0.75% 0.262 4 1.00% 0.26

Slurry lost Max Shear N cycles Initial density at N4 final density at Max Shear at N80

5,3 g 145 kN/m2 22 2096 kg/m3 2474 kg/m3

First group of tests without superplasticizer

Subset of tests with W/C ratio of 0,28 ( 7,09 % water); average results.

Subset of tests with W/C ratio of 0,26 ( 6,58 % water); average results.

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Slurry lost Max Shear N cycles Initial density at N4 final density at Max Shear at N80

0 g 151 kN/m2 65 2059 kg/m3 2387 kg/m3


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• N cycles at Max Shear. With 0,28%W/C ratio the max value of shear isreached at N22, rather at the firstpart of the test, whilst, with 0,26%W/C ratio, the max value of shear isreached at N65, towards the end ofthe test. The lubricating action of theslurry starts at quite different level ofcompaction energy.

• Initial density at 4 cycles and finaldensity at 80 cycles. Both densities,initial and final, are bigger for the mixwith 0,28% W/C ratio. Greater watercontent causes easier initial packingof the particles.

Second group of tests with 0,26% W/Cratio and superplasticzer, average values

Comments:

We compare data of initial / final densities,of N cycles at max shear and of max shearvalue by an overview on behaviour ofmixes with the same W/C ratio and varia-ble rate of superplasticizer from 0% to 1%.

• As expected, initial and final densitiesof mixes with superplasticizer show aplain increase in front of the one with-out. Initial and final densities of mixwith 0,5% of superplasticizer are2112 kg/m3 and 2431 kg/m3 against2059 kg/m3 and 2387 kg/m3 withan increase of 2,6% and 1,8%respectively.

• By comparing the same parametersbetween the mixes with superplasti-cizer, we note a smaller variation;initial and final densities of mix with1% of superplasticizer differ from themix with 0,5% by 2,3% and 1,1%.We note moreover that the final den-sity exhausts the increase at 0,75%dosage to remain then constant(2459 kg/m3 with 0,75% and 2458kg/m3 with 1% of superplasticizer ).This is a clear indication for super-plasticizer dosage selection.

• The max shear resistance does notshow a big variation between mixeswith or without superplasticizer, 147kN/m2, for dosages from 0,5% to0,63%, against 150 kN/m2, for 0%

dosage. But we note, nevertheless, anappreciable loss of shear for mixeswith 0,75% and 1%: 146 kN/m2 and144 kN/m2.

• Remarkable is the positioning of themax shear value during the gyratory

test. While the 0% dosage mix showsmax shear value at N65 cycles, mixeswith 0,5%, 0,63%, 0,75%, 1% super-plasticizer dosage show max shear atN32, N25, N25, N16 cycles respec-tively. The addition of superplasticizerhas been clearly pointed out by suchpositioning of max shear. Furthermorewe note max shear advanced to N16for 1% mix, with notable change ofdecrease rate, behaviour that couldbe useful for superplasticizer dosageselection along with final densityincrease rate.

Subsidiary testing equipment

Upon implementation of no-slump concre-te testing by use of the gyratory compac-tor, two small instruments are recommen-ded to check the behaviour of the com-pacted fresh concrete mix:

• “Special Split Tester” (Fig. 8) with600 N measuring cell and mano-meter for determination of the “FreshStrength” according to the NordtestMethod. The sample, freshly compac-ted by the Gyratory Testing Machineand extruded from the mould, is imme-diately tested and the indirect tensilefresh strength recorded. The practicalsignificance of the test is the rankingof possible mixes in order to selectand check the most stable one afterstripping from the form. In steel rein-

Special Split Tester

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6/7:Second group oftests with 0,26%W/C ratio andsuperplasticzer

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Superplastcizer dosage (% on cement content) 0,5% 0,63% 0,75% 1%

Initial density at 4 cycles (kg/m3) 2112 2126 2143 2160Final density at N80 cycles (kg/m3) 2431 2445 2459 2458N cycles at max shear 32 25 25 16Max Shear value (kN/m2) 148 148 146 143


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forced structures, the sticking action offresh compacted mix influences bond-ing to reinforcing wires or bars.

• “Blood pressure tester” (Fig. 9) set upto evaluate the setting time of freshcompacted mix. The sample, freshlycompacted by the Gyratory TestingMachine and extruded from themould, is immediately surrounded bythe pressure band of the apparatusand placed on a stand with a digitaldial gauge that is placed in contactwith the top of the sample. The press-ure transducer of the apparatus andthe digital dial gauge are connectedto a PC. The installed program startsthe test by inflating the pressure bandat pre-set intervals and measuring thevertical deformation of the sample.Vertical deformations are recordedv/s time and a diagram shows thesetting time.

The test, as illustrated and discussed in“method for fresh concrete stability“ byEric Nordenswan (see Reference), givesinformation on the first phase curing: pos-sible amount of early elasto-plastic de-formation and first early indication of thestability of element in relation to amplitudeof recoverable deformation vs time andthe speed (slope) of early setting. Further-more criteria is given in evaluating thetime after which it is possible to move thecompacted mix without perceptiblechange in its dimensions.

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References

[1] Concrete, Fresh: Compactibility With IC – Tester– Method NT BUILD 427, Nordtest ScandinavianInstitution

[2] Improved Management of RCC PavementTechnology, Research Paper 01231– January 2003, University of Alabama

[3] Eric P. Kohler, David W. Fowler; “Summary ofConcrete Workability Test Methods“, research report 105.1, from ICAR 105,University of Austin, Texas, August 2003

[4] Erik Nordenswan, “Method for fresh concretestability“, Nordic Concrete Research(Annual Meeting in Helsingor, Denmark), 2004

Further information:

Controls S.R.L.6, Via Aosta20063 Cernusco s/N (Mi), ITALYT +39 02 921841F +39 02 [email protected]

Blood pressure tester

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Testing of No Slump Concrete With Gyratory Compactor