isothermal calorimetry of cement - institute for transportation · 2018-08-07 · hydration process...

Isothermal Calorimetryof Cement

• The hydration process of cement is highly exothermic and is typically measured in the milliwatt (mW) range.

• TAM Air was originally designed for use in cement calorimetry research.

• TAM Air combines eight channels with a sensitivity of about ±4 µW.

TAM Air

Calorimetric Unit

General Heat Balance Equation

After calibration the following holds:Rate of Heat Production

(dQ/dt)=

Heat flow Monitoredby TAM

dtdTC+=

dtdQ

Rate of Heat Accumulation+Rate of Heat

ExchangeRate of Heat Production =

dtdQ To

TS

dtdTC

The measured property

TAM Air

Fan

Heat detector

Fan

Heat detector

8 Channel calorimeter blockThermostat

Air in

TAM Air Heat Detectors

• Consist of small plates with thermopiles (Seebeck Modules)

• When the two sides of the plate are exposed to different temperatures, heat will flow from the warm to the cold side– Same principle as TAM III

• Sensitivity in µW-mW range

Heat sink in contact with the air thermostat

Static Calibration

P (µW)

Time

CalibrationPower OFF

Calibration Power ON = set µW pulse

Empty calorimeter or Accessory and Reference in position.

How to obtain The time until P/Po = 1/e = 0.37

)exp(tPP o

P/Po = 1/e

Exponential heat exchange

Heatflow and Dynamically Corrected Data

• For reactions where the slope of the heat flow time curve (dPRaw/dt) is changing slowly the first part of the following formula can be used to calculate the true response in heat flow (PHF) from the heat flow monitored by the heat detector (PRaw) using the following formula. For fast reactions an additional term is used to calculate PDyn.

2

2

2121 dtdP

dtdPPP RawRaw

RawDyn

dtdPPP Raw

RawHF

The hydration process undergoes a number of phases (Young, 1985)

• (I) Rapid initial processes• (II) Dormant period• (III) Acceleration period• (IV) Retardation period• (V) Long term reactions

The phases have been described in more detail (Sandberg, 2002)• (I) Dissolution of ions and initial hydration• (II) Formation of ettringite• (III) Initiation of silicate hydration• (IV) Depletion of sulphate

Dr. P. Sandberg, Grace Construction Products, US (2002)

Basics of Cement Calorimetry

Portland Cement Basics

• Silicates hydrate to give strength giving gel, “glue”

• Aluminate and ferrite phases necessary to get a molten phase during production of cement

• Aluminates react rapidly, interact with admixtures, workability, set, early strength development

• Gypsum added during grinding to slow down aluminate hydration rate

– Higher C3A , lower C4AF generally more reactive

– Different sulfate forms have different solubility

• ASTM Standard Method drafts available in 2008

–– C1679 (kinetics)C1679 (kinetics)

–– WK 4922 (heat of hydration)WK 4922 (heat of hydration)


• Isothermal calorimetry is sensitive and versatile tool for studying the hydration process of cement.

– The shape of the heat flow versus time curve reflects the hydration process(es) of cement

– The effect of an admixture is reflected in a change of the hydration curve

– The integrated heat flow time curve, i.e. the energy evolved is related to the extent of hydration

• Excellent experimental reproducibility.

Isothermal Calorimetry for Cements

Typical Cement Applications for Isothermal Calorimetry

• Setting time and premature stiffening

• Effect of contaminations

• Effect of admixtures

• Temperature dependency of cement hydration

• Quality control

• R&D


• Closed ampoules for long term reactions.

• Admix ampoule for early reactions i.e. first 30-45 minutes.– Refer to EN 302 (Lars Wadsö)

Sample Handling

How to Perform Cement Hydration Measurements

• Weigh ampoule and/or lid

• Weigh cement powder (1-10g) and water (1-10g)

• Mix well and mix for a consistent time (~1-3min)

– Stirring rate can be important

– Time zero important

– Load and weigh cement paste into the ampoule

• Load into TAM Air and come back in a few days

– Most common test is 72 hour (or 3 day) hydration

– Cement hydration completion after 28 days

• ASTM Methods in 2008 - WK4922 or C1679 (kinetics)

Dr. Moro , Holcim Group Support, Switzerland (2002)

Isothermal Calorimetry Reproducibility

• Only small differences between cement lots when tested without admixture

• Very large differences between cement lots when tested withsame admixture!!!

Water/cement ratio 0.5, 23 C, water only

Water/cement ratio 0.5, 23 C, 1.0% water reducing admixture by weight of cement in all samples


Effect of Admixtures

Kinetics of Cement Hydration

Measurements at 20, 25 and 30 C

P reflects the rate of the process

Q reflects the extent of the process

P (m

W)

Q (W

)Time (h)

Dr. P. Vikegard, Thermometric AB, Sweden (2002)

Admix Ampoule Experiment Reproducibility

0.46hr

0.04hr

0.39hr

0.14hr

0.04hr

0.00

0.05

0.10

0.15

0.20

0.25N

orm

aliz

ed H

eat F

low

(W/g

)

0.0 0.2 0.4 0.6 0.8 1.0

Time (hr)

Stucco_w/c 0.50_1––––––– Stucco_w/c 0.50_2– – – – Stucco_w/c 0.50_5% Salt–––––––

Universal V4.4A TA Instruments

Calcium Sulfate Hemihydrate 1-2 g powder mixed at w/c 0.50

5% NaCl solution

DI water

Admix Ampoule Experiment

0.00

0.02

0.04

0.06

0.08

0.10

0.12N

orm

aliz

ed H

eat F

low

(W/g

)

0.0 0.5 1.0 1.5 2.0

Time (hr)

Stucco w/c 0.35––––––– Stucco w/c 0.50– – – –


w/c = 0.50

Calcium Sulfate Hemihydrate 1-2 g mixed with DI water at w/c 0.50 and 0.35

w/c = 0.35

Normalized Heat of Wetting/Mixing

(mW

/g)

Time (min)100 120 140 160 180

0

10

20

30

FPC 9 FPC 9 FPC 3 FPC 3

Heat of wetting and stirring

Mix ~2.85 g cement solid with 1.38 mL water

Differences in the heat of wetting/mixing observed for two different cement powders. Mixed with DI water at w/c 0.48. Hydration plot shown on next slide.

Normalized Heat of Hydration

(mW

/g)

Time (hour)12 24 36 48 60 72

0

1

2

3

4

5

FPC 9 FPC 9 FPC 3 FPC 3

Heat of hydration

Differences in the cement hydration profile observed. Mixed with DI water at w/c 0.48.

Mix ~2.85 g cement solid with 1.38 mL water

Normalized Heat

(J/g

)

Time (hour)12 24 36 48 60 72

0

50

100

150

200

250

300

FPC 9 FPC 9 FPC 3 FPC 3Mix ~2.85 g cement solid with 1.38 mL water

Differences in the cement hydration profile observed. Mixed with DI water at w/c 0.48.

Mortar – Normalized Heat of Wetting

0.00

0.01

0.02

0.03

0.04

Nor

mal

ized

Hea

t Flo

w_2

(mW

/g)

0.00

0.01

0.02

0.03

0.04

Nor

mal

ized

Hea

t Flo

w (W

/g)

1.00 1.25 1.50 1.75 2.00

Time (hr)

FPC 9_RMS 4 mortar––––––– FPC 9_RMS 5 mortar–––––––


Cement 1 w/ Sand B

Cement 1 w/ Sand A

1 g cement: 2.75 g sand: 0.475 mL water

Injected DI water

Mortar – Normalized Heat of Hydration

0.000

0.001

0.002

0.003

Nor

mal

ized

Hea

t Flo

w_2

(mW

/g)

0.000

0.001

0.002

0.003

Nor

mal

ized

Hea

t Flo

w (W

/g)

0 10 20 30 40 50 60 70

Time (hr)

FPC 9_RMS 4 mortar––––––– FPC 9_RMS 5 mortar–––––––


Cement 1 w/ Sand B

Cement 1 w/ Sand A

1 g cement: 2.75 g sand: 0.475 mL water

Repeatability

Three different samples

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0 0.5 1 1.5 2 2.5 3 3.5 4

Time (weks)

Rel

ativ

e sp

ecifi

c he

at fl

ow

Solid sample

Microhygrostat

Glass tube with pure solvent or a solvent saturated by a salt (e.g. sat. NaCl (aq))

Developed independently by: Angberg, Uppsala University and Byström, Astra Zeneca (1992)

Other Calorimetric Methods for the Study of Cement

• Adiabatic calorimetry or semi-adiabatic calorimetry

– Sample is placed in insulation made of polystyrene. One example of a semi-adiabatic calorimeter is the Nordic “hökassen” that was investigated in NORDTEST-studies: NT 821 and NT Build 388.

• Solution calorimetry– ASTM C186 – Total heat of hydration at a certain time is determined as the

difference between the liberated heat when an un-hydrated sample and the sample under investigation is dissolved in a mixture of hydrofluoric acid and nitric acid.

– This old measurement technique is described in ASTM C186, prEN196-8, and SS B1 1960.

– This method is time-consuming, costly and dangerous, but still in use.

Isothermal Calorimetry (heat flow) versus Semi-Adiabatic

• Isothermal calorimeters directly measure the heat production rate that is proportional to the rate of the reaction – adiabatic calorimeters measure temperature change and

that is recalculated to give heat produced– Heat capacity of the sample is required for adiabatic

calorimetry and not for isothermal• Isothermal calorimeters are very stable and need not be

calibrated more than a few times a year – adiabatic calorimeters are often calibrated before each run.

• The temperature never increases to unrealistic temperatures in an isothermal calorimeter. The structure and thus the properties of the hardened cement paste depend on the temperature of hydration.

• A main benefit of isothermal calorimetry is that the hydration process of the cement is monitored continuously with multiple samples from the start of the measurements.

• Analysis in laboratory environment• Multiple channels (sample and reference) for parallel

analysis• Built in calibration heaters for automated calibrations• Sample temperature can be assumed isothermal• Very sensitive calorimeter(s) with the ability to load up to

20 mL volume samples– Compare heat flow stability/sensitivity.

• Admix accessory to study initial hydration.– Software includes data analysis

Isothermal Calorimetry

• AN 22014 Hydroscopic powders – a microcalorimetric assessment of cement

• AN 314-01 The Study of Cement Hydration by Isothermal Calorimetry • AN 314-05 Optimization of sulfate - Part I without admixture • AN 314-06 Optimization of cement sulfate Part II with admixture • AN 314-07 Effect of carboxylic acids on the hydration of calcium sulfate

hemihydrate pastes• EN 302 Using the Admix ampoule for cement hydration measurements

• ASTM Methods in 2008 - WK4922 or C1679 (kinetics)

• Applications of an eight-channel isothermal conduction calorimeter for cement hydration studies. By Lars Wadsö, Cement International 2005

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isothermal calorimetry of cement - institute for transportation · 2018-08-07 · hydration process...

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