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LOW CARBON LOW COST LOW CAPITALwww.LC3.chwww.LC3.ch

SHRINKAGE AND CREEPLimestone - Calcined Clay CementCharacterization techniques

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Julien Ston 30 June 2015

LOW CARBON LOW COST LOW CAPITALwww.LC3.ch

Outline» Shrinkage

» Types of shrinkage» Theories on mechanisms» How to measure shrinkage» What info can we get?

» Creep» Types of creep » Theories on mechanisms» How to measure creep» What info can we get?

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SHRINKAGE

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Introduction» Chemical shrinkage

» Volume of hydrates < Volume of water + binder» First described by Le Châtelier [1900]

» Autogenous shrinkage» Self-dessication, decrease of inner relative humidity by water consumption» Many protocols, convenient for lab as samples are sealed

» Drying shrinkage» Decrease of RH by water loss to the environment in addition to self-dessication» Kinetics depend on sample size

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Chemical shrinkage» V (Hydrates) ≈ 2 x V (Anhydrous cement)

» Space filling, decrease in porosity» V (Hydrates) < V (Anhydrous cement + water)

» Bound / adsorbed water occupies less space than free water» Empty pores forming

» Typical volume reduction during hydration» 6-7 ml / 100 g of cement» Independent from initial w/c» Only linked to degree of reaction

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Measurement techniques» Buoyancy

» Monitoring the apparent weight of a cement sample in contact with water» Water going into the pore structure will change the volume of the weighted

material, therefore its weight underwater

» Volumetric (ASTM C1608)» Monitoring the volume of water sorbed by cement paste» A known volume of water is provided and its diminution is measured

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Buoyancy method» Weight logging

» Every 5-10 minutes» Temperature control (± 0.25°C)

» Water bath at 20°C or 25°C» Simple equipment

» Balance» Logger or computer» Water bath

» Limitations» Balance precision and stability» Evaporation (use lid)

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Buoyancy method» Weight logging

» Every 5-10 minutes» Temperature control (± 0.25°C)

» Water bath at 20°C or 25°C» Simple equipment

» Balance» Logger or computer» Water bath

» Limitations» Balance precision and stability» Evaporation (use lid)

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Volumetric method» Monitor the height of liquid

» Webcam + image processing» Pay attention to lighting

» Coloured oil on top» Avoid evaporation» Visible to image processing

» Temperature control» Water bath at 20°C or 25°C

» Limitations» Image quality» Image processing

» Direct reading of shrinkage value» Normalize by mass of binder

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Chemical shrinkage» Critical points

» Synthetic pore solution or water?» Possible leaching» Composition of pore solution?

» Air bubbles» Use de-aired water» Mix under vacuum

» Long term stability» Wear of components

» Sample size» Liquid has to diffuse through sample» The thinner, the better

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Chemical shrinkage» What do we get from the results?

» Degree of reaction» Progression of pozzolanic reaction

» Related to strength development

» Indication on autogenous shrinkage» Material would be shrinking if water available

» Useful for predictive models

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Autogenous shrinkage» Water is consumed by the hydration reaction

» Chemical shrinkage causes plastic shrinkage before solid percolation

» After setting empty pores will start appearing

» Tensile force are present at the gas-liquid interface

» Macroscopic strain

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Capillary pressure» Young-Laplace equation

𝑝𝑝𝑐𝑐 = −2𝜎𝜎 cos𝜃𝜃

𝑟𝑟

» Kelvin equation

𝑝𝑝𝑐𝑐 = −𝑅𝑅𝑅𝑅 ln 𝑅𝑅𝑅𝑅

𝑉𝑉𝑚𝑚

» Kelvin-Laplace equation

ln 𝑅𝑅𝑅𝑅 = ln𝑝𝑝𝑝𝑝0

= −2𝜎𝜎 cos𝜃𝜃 𝑉𝑉𝑚𝑚

𝑟𝑟 𝑅𝑅 𝑅𝑅

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pc = capillary tension [N/mm2]r = radius of meniscus [m]σ = surface tension of liquid [N/m]θ = wetting angleR = gas constant [8.314 J/mol K]T = temperature [K]Vm = molar volume of liquid [m3/mol]RH = relative humidity [-]p = vapour pressure over the liquid [N/m2]p0 = saturation vapour pressure [N/m2]


Capillary pressure

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Disjoining pressure» Derives from Van der Waals’ force» Regions of hindered adsorption

» Less than twice the thickness of adsorbed water layer (t)» Constant above 80% RH

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Surface tension» Adsorbed molecules decrease surface tension

» Bangham-Fakhoury Δ𝑙𝑙𝑙𝑙

= 𝜆𝜆 Δ𝜎𝜎

» From Hiller 𝜆𝜆 = Σ 𝜌𝜌𝑠𝑠3𝐸𝐸

» Effective at low RH (< 65%)» ≡ 2 water molecules

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λ = coefficient of proportionality [s2/kg]Σ = pore wall area of empty pores [m2/kg]ρs = solid density [kg/m3]E = Young’s modulus [MPa]


Measurement techniques» Membrane» Corrugated tube» ASTM C157» Free deformation frame» Shrinkage drain» Cylindrical moulds» Vibrating wire

» Others…

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Membrane method» Applies to paste» Volumetric method» Paste is cast in an elastic membrane» Buoyancy is monitored

» Limitations» Type of membrane (osmosis)

» Use non-latex

» Buoyancy liquid used» No water. Paraffin oil

» Membrane pressure» Air entrapment» Temperature control

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Corrugated tubes (ASTM 1698-09)» Applies to paste, mortar, concrete (!)» Linear method» Mix is cast in a flexible tube (longitudinal rigidity < 5∙10-3 N/m)

» Initial volumetric strain is converted to linear» Length is monitored

» Limitations» Friction/locking» Sealing (liquid uptake / paste leaking)» Temperature control» Air entrapment

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ASTM C157 (modified)» Designed for concrete, adaptable to mortar and

paste» Linear method» Sample is cast in a “frictionless” mould» Length is monitored after 24h

» Modifications» Demould and wrap to keep autogenous conditions» Start earlier

» Limitations» Poor temperature control, especially for large

samples

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Free deformation frame» Enhancement of original ASTM C157» Better temperature control

» Limitations» Temperature control for large specimens» Friction» Price

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Schleibinger shrinkage drain» Applies to mortar and concrete» High form factor» Monitoring of T and RH

» Limitation» Proper sealing» Friction

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Cylindrical moulds» Applies to concrete, but also mortars and paste» Very simple linear method

» Limitations» No temperature control» Settlement» Friction

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Vibrating wire» Designed for concrete, could be adapted to mortar and paste» A steel wire is embedded in the sample» Strain will modify its resonant frequency

» Limitations» Sealing» Gauge could influence results

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Comparison» Chemical Vs. Autogenous

» Capture setting

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Comparison» Methods are equivalent, if

carried out properly

» Account for initial offset if not starting at t = 0

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SummaryTest method Type Material Pros Cons

Membrane Volumetric P Temperature control, from casting

Preparation, long term behaviour

Corrugated tubes Linear P, M, C Commercial, fromcasting

Friction, sealing

Mod. ASTM C157 Linear P, M, C Easy to carry out and repeat

Temperature control, sample handling

Free deformation frame

Linear M, C Temperature control, from casting

Friction, complex equipment

Shrinkage drain Linear M, C Commercial, from casting, temperature

Sample preparation

Cylindrical moulds

Linear C, (M, P) Very simple, can be done on site

For comparison only

Vibrating wire Linear C, (M, P) From casting Complex, samplepreparation

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Autogenous shrinkage» What information can we get?

» Maximum shrinkage is imposed by standards» Indication that reaction is going on

» Also linked to porosity, RH, …

» Where is the zero?» Behaviour before setting may not be repeatable» Interesting to start after initial expansions or local maximum

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Drying shrinkage» Most common type in real life» Decrease of internal RH due to loss of water to the environment» Goes on until equilibrium (= almost forever)

» Kinetics highly depend on sample size and geometry» Same driving force than autogenous

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Measurement techniques» ASTM C 157

» Casting» Some curing» Samples place in controlled RH and T environment» Immediate start of measurements

» ASTM C 1581» Cracking ring» Used to compare time before cracking in drying conditions

» ASTM C 1579» Cracking test» Plastic shrinkage, “early age drying shrinkage”

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General guidelines» Science > Standards > Real life

» Shrinkage should not be considered alone (as any technique)» Internal RH» Setting time» Porosity» Creep is also present

» Behaviour of LC3?» Low or none initial expansion» High grade clay: important initial shrinkage, low slope then» Medium grade clay: moderate initial shrinkage, increasing slope?

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CREEP

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Creep“Delayed strain under constant stress”

» Metal» Dislocation creep» Nabarro-Herring creep (diffusion)» Coble creep (diffusion)

» Polymers» Viscoelastic (Kelvin-Voigt)

» Cementitious materials» Movement of water?

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Mechanisms» No consensus on this phenomenon

» Early creep» Reversible» Decohesion mechanisms

» Late creep» Irreversible» Hardening mechanism

» Creep states» Primary: transient state» Secondary: steady state» Tertiary: σ > σcrit

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Most studied


Mechanisms

Theory Decohesion Hardening

Micro-prestress(Bazant, 1997)

Breaking of high-stress atomic bonds

Redistribution of the stress over the microstructure

Nano-granular(Vandamme, 2009)

Displacement of C-S-H grains into empty space

Self-compacting of the microstructure

Micro-crack(Rossi, 2012)

Displacement of water out of existing cracks and pores

Displacement of water into the newly-formed cracks

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Basic creep Vs. Drying creep» Basic creep = autogenous conditions

» Subtract autogenous shrinkage

» Drying creep > Basic creep + Drying shrinkage» Pickett effect

» Drying stress could cause a higher response» Possible effect of aggregates

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Testing guidelines

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» Mix design» Use always the same aggregates» Keep a constant paste fraction

among samples if applicable» Curing

» Conditions? (underwater, fog room, autogenous)

» Duration? (wait for low strain?)» Testing

» Conditions? (autogenous, drying, temperature)

» Applied stress

» Measurements» Samples should have l/d > 5» Measurement points should be

2d away from extremities» Monitor in parallel

» Autogenous shrinkage» Temperature» Relative humidity» (Mass)


Creep & LC3

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0

5

10

15

20

25

0.00 0.01 0.10 1.00 10.00 100.00

Com

plia

nce

[MPa

-1]

Time [days]

LC3-50 Surinam 0.45-340 PC Heidelberg 0.45-340

Compliance = 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 𝑠𝑠𝑠𝑠𝑐𝑐𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑐𝑐𝑐𝑐𝑙𝑙𝑠𝑠𝑐𝑐𝑎𝑎 𝑠𝑠𝑠𝑠𝑐𝑐𝑐𝑐𝑠𝑠𝑠𝑠

60 daysSample 28 days

Strength [MPa]

Elastic modulus [GPa]

PC 64.1 38.9

LC3 68.3 35.3


Creep» Is low creep good?

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Creep» Is low creep good?

» Loss of prestress!

» Is high E good?» Higher stress associated to restrained shrinkage!

» Ideal concrete…» Low E and high creep at young age (3-7 days)» High E and low creep later

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Some names in litterature

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» Hensen P. F» Jensen O.M.» Lura P.» Bentz D.» Weiss » Powers T. C.» Sant G.» Justnes H.» Wyrzykowski M.» RILEM proceedings» Theses

» Chen, EPFL, 2013» Do, EPFL, 2013» Fu, OSU, 2011» Holt, 2001

» Bazant Z.» Pickett G.» Vandamme M.» Rossi P.

» From EPFL» Dunant C.» Hilaire A.» Denarié E.» Guidoum A.

Thank you

LC3 PROJECT

Julien Ston+41 21 69 [email protected]

EPFL STI IMX LMC MXG 211Station 12, Swiss FederalInstitute of TechnologyLausanne, 1015 Lausanne, Switzerland

limestone - calcined clay cement characterization techniquesdocuments.epfl.ch/users/s/st/ston/www/5...

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