Fresh concrete is generally considered lowworkability (No –Slump), if it has a slump less than 2 cmand a VeBe time longerthan 5 sec. approx.

Therefore it consists of a stiff mass that has to be compacted bymeans of pressure combined with vibration, rolling and/orextrusion.

The field of application includes:� Manufactureof concreteelements� Manufactureof concreteelements

• paving blocks• hollow core blocks• Slabs• Pipes• Roofing tiles

� Road construction� Dam construction.

Basically the characteristics of compacted fresh low workabilityconcrete used for concrete elements is to be free of shrinkage effectssuch as cracks and volume change, and to maintain its shape afterstripping fromthe form.

While for Road and Damconstruction the base characteristic is theconsistency with mechanical properties, compression and splittingtensile strength at various age.

To define the optimummix (mix design) and to performfactoryproductioncontrol, it is necessaryto examinethevolumetricpropertiesproductioncontrol, it is necessaryto examinethevolumetricpropertiesof the whole fresh concrete with all its components:

� aggregates (sand, gravel)� eventual special aggregate (like silica fumes)� cement� additives� water

in order to control the compaction degree (density) during and aftercompaction.

Reference Standard:Nordtest MethodNT BUILD 427 (approved 1994-11)

States the testing procedure and the criteria by which acompaction energy can be associated to a no – slump freshconcrete mix.

Nordtest Method NT BUILD 427

Such compaction energy isgiven by GyratoryCompaction, by which a

Principle of the method:• Vertical static compression• Dynamic gyratory action withfixed angle

Compaction, by which afresh concrete mass sample(approx. 0.8 dm3) iscompacted using acontinuous kneadingaction, that is pressure andshear.

In accordance with the Nordtest Method, reference compactionlimits are defined.

They are:� At the slurry limit.� At specified number of cycles of gyratory machine.� At aspecifieddensityof thesample.� At aspecifieddensityof thesample.

The “Slurry limit” defined as the number of gyrations needed for thestart of separation of slurry fromthe sample. As slurry consists of asuspension of binding matter (components of hydrated cement), fineaggregate, water and eventual admixtures, the separation of slurryfrom the mould defines the limit beyond which additionalcompaction, generally close to 100% compaction grade, is no longerpossible without the homogeneity and quality being altered.

“Specified number of cycles of Gyratory machine”. From the“Specified number of cycles of Gyratory machine”. From the“Slurry limit”, according to the definition of “Nordtest Method”,descends the “ICT index” ( Intensive Compaction Test index), acompaction energy parameter defined as the pressure value (i.e. thevertical pressure of Gyratory Testing Machine) multiplied by thenumber of gyrations required for the visual observation andevaluation of slurry come out (loss of weight is ca. 5 – 10 g) .Therefore the “ICT index” is a determining variable for thecompaction energy.

“Specified density of the sample” means that the gyratory machinemakes up the sample at a required level of compaction, useful tocharacterize the compacted sample by other tests such ascompression test on hardened sample, to verify mechanicalresistance and durability for the convenient calibration of theproduct and of the production plant.

Reference List

Reference List

Scandinavian Countries and European industries have based the no-slump concrete mix design and factory production control ofconcrete elements on volumetric properties for many years with goodresults.The reliable result of such a testing approach is evident:• Optimumcompaction energy correlated to the requirement of theconcrete element, such as durability and mechanical resistance.• Density data based (volumetric properties), calibration of plantcompactionenergy.compactionenergy.• Immediate means to check the plant’s compaction efficiency.• Accurate Mix Design easily duplicated in the production plant.• Optimum production costs. Correct compaction energy maylead to a rational reduction of cement and correct dosage ofadditives.• Possibility of continuous QC, accurate indication of anychanges in mix production (tracking of problems).

54-C0252/C Specifications

Compacted specimen size:- diameter mm: 100- height mm: typically 90 to 120, - can be reduced for special purposes

Mould dimensions:- internal diameter mm: 100- height mm: ca. 200

Gyratory angle: 40 mradNumber of cycles: 2 - 512

54-C0252/CGYRATORYINTENSIVE COMPACTION TESTER

Number of cycles: 2 - 512Gyratory rate: 30 - 120 work cycles/minVertical load: adjustable from 60 to 320 kPaOverall dimensions: 350x480x930 mmWeight approx.: 55 kg

54-C0251/C Specifications

Same as 54-C0252/C plus:- adjustable angle (0 to 50 mrad)- shear measurement by load cell

54-C0252/C gyratory compactor fully complies to thespecifications of the Nordtest Method NT BUILD427 and iscontrolled by PC.

Two programs are supplied:

� “Intensive Compaction Testing” Windows program

� EXCEL macro� EXCEL macro

“Intensive Compaction Testing” Windows program

by which the behaviourof compaction (changein sample height) anddensity versus numberof cycles (gyrations)isof cycles (gyrations)isrecorded in real timeand plotted.

Excel Macro

Excel Macro

The evolution of all the volumetric parameters are related to the nr.of gyrations:

• Height of specimen (mm)

• Density (kg/m3)

• Air Voids % of fresh concrete mix (AV)

• Voids % in MineralAggregatesof themix (VMA)• Voids % in MineralAggregatesof themix (VMA)

• Voids % Filled with Cement (VFC)

• Shear during compaction(optional parameter not expressly required by the NordtestMethod, butavailable on request – see 54-C0251/C model)

Upon implementation of no-slump concrete testing by use of the gyratory compactor, two small instruments are recommended to check the behaviour of the compacted fresh concrete mix:

� Special Split Tester with 600 N measuring cell

Behaviour of compacted fresh concrete mix

� Special Split Tester with 600 N measuring cell

� “Blood pressure tester”

Fresh concreteconsistence

to check fresh concrete consistence after stripping from the form

Special Split Tester

For determination of the “Fresh Strength”, as foreseen by theNordtest Method.

The sample, freshly compacted by the Gyratory Testing Machineand extruded from the mould, is immediately tested and the

Special Split Tester

with 600 N measuring cell and manometer

and extruded from the mould, is immediately tested and theindirect tensile fresh strength recorded.

The practical significance of the test is the ranking of possiblemixes in order to select and check the most stable one afterstripping fromthe form. It has also to be considered that in steelreinforced structures the sticking action of the fresh compactedmix influences bonding to reinforcing wires.

“Blood pressure tester”

Setting time

set up to evaluate the setting time of the fresh compacted mix

The sample, freshly compacted by the Gyratory Testing Machine andextruded fromthe mould, is immediately surrounded by the pressureband of the apparatus and placed on a stand with a digital dialgauge thatis placed in contact with the top of the sample.

The pressure transducer of the apparatus and the digital dial gauge areconnected to a p.c.

The installed programstarts the test which consists of inflating thepressure band at pre-set intervals and measuring the vertical deformationof thesample. Thep.c. recordsthedeformationv/s time dataalongwithof thesample. Thep.c. recordsthedeformationv/s time dataalongwitha diagramthat shows the setting time.

The test gives information on the first phase curing: possible amount ofearly elasto/plastic deformation and first early indication of the stabilityof element in relation to amplitude of recoverable deformation versustime and the speed (slope) of early setting.Furthermore criteria is given in evaluating the time after which it ispossible to move the compacted mix without perceptible change in itsdimensions.