ThermoCem – Naturally good - the dry mortar with ...

Naturally good – the dry mortar with outstanding thermal conductivity

THERMOCEM®

2

CONTENTS

1. Product description 3

2. Achievability of thermal conductivity levels 3

3. Suspension properties 4 3.1 Marsh time 4

3.2 Water separation 5

4. Advice on working with the product 6 4.1 Adding water 6

4.2 Quality assurance on the building site 7

5. Machinery and equipment 8 5.1 Mixing operation 8

6. Backfilling the borehole 10 6.1 Backfilling operation using an underwater concreting process 10

6.2 Ending the backfilling operation 11

7. Development of strength and hydration heat 12 7.1 Setting process 12

7.2 Development of early strength and end-strength 13

8. Borehole resistance 14

9. Chemical resistance to aggressive groundwater 15 9.1 Classifying the level of the attack 15

9.2 Resistance to sulphate and lime-dissolving carbonic acid 16

10. Frost-thaw resistance 18

11. Magnetic Susceptibility 20

3

1. Product description for ThermoCem® PLUS■■ ThermoCem PLUS comes in a pure powder form.■■ ThermoCem PLUS contains no quartz sand and is non-abrasive in mixers/pumps.■■ ThermoCem PLUS is a premixed product and is ready-to-use after the specified

quantity of water has been added.■■ ThermoCem PLUS contains swellable clay minerals that enable it to swell in situ.■■ ThermoCem PLUS contains a special binder that exhibits particularly high resistance

to concrete-aggressive waters (e.g. sulphates, carbonic acid).■■ ThermoCem PLUS is subject to internal and external quality monitoring, meaning that

consistently high quality is assured.■■ ThermoCem PLUS comprises selected raw materials and is accordingly suitable for

use in groundwater protection areas, having regard to water hygiene.

For projects with a lower requirement on thermal conductivity for the

backfilling material, we offer an ideal alternative in ThermoCem Light,

which has a thermal conductivity of λ ≈ 1.0 W/mK

2. Achievability of thermal conductivity levelsVarious options are available for increasing the

thermal conductivity of a construction material. One

basis for this, for example, could be to add graded

quartz sand, that is to say aggregates. In order to

come close to achieving reliable thermal conductivity

of 2.0, this requires a relatively high share by weight

of the aggregate. It is a completely different story

with our ThermoCem PLUS product. We employ

a selected additive to ensure that we reliably achieve

thermal conductivity (λ) of approx. 2.0 W/mK. The

volume of the product required and the rheology are

then matched to the specific application.

ThermoCem 04λ ≈ 4,0 W/(m*K)

Suspension density

Ther

mal

con

duct

ivity

ConcreteThermoCem PLUSλ ≈ 2,0 W/(m*K)

ThermoCem Basicλ ≈ 0,8 W/(m*K)

W/(m*K)

4

3,75

3,5

3,25

3

2,75

2,5

2,25

2

1,75

1,5

1,25

1

0,75

0,5

0,25

0

1000 1200 1400 1600 1800 2000 2200 kg/m3

THERMOCEM | Naturally good

4

3. Suspension properties

3.1 MARSH VISCOSITY

This figure serves as an estimate of the viscosity or working property of a suspension. The variable measured

is the time required for a litre of the suspension to flow from the cone funnel (funnel contents approx. 1.5 l)

with an exit diameter of approx. 5 mm.

Guide values for Marsh viscosity■■ Water: approx. 28 seconds■■ Marsh viscosities of 40-100 seconds generally mean that the material works easily

The clay components contained in ThermoCem induce tixotropy in the suspension after a while, i.e. the

minerals in the clay absorb the free part of the water in the suspension like a sponge. This causes the

suspension to gradually become “stiffer” in its resting state. This is a particular advantage when undertaking

vertical backfilling in the sub-soil.

Good workability,Cavity-free backfilling,Good probe-to-soil bonding

<

Onset of tixotropy.

<

Tixotropy effect after resting state has been achieved.

5

Keeping to the formulation,Stabilisation using clay minerals,Matching the mixer to the construction material

<Determining the Marsh viscosity after mixing.

3.2 WATER SEPARATION

Water separation serves as a measure of the stability of a suspension. The higher the water separation, the

less stable the suspension. The limit value for a consistency that is good for working should be around 1 to

max. 2 %.

Possible reasons for high water separation■■ Contents in the materials not suitably matched■■ Too high water/solid-ratio (W/S ratio)■■ Insufficient intensity of mixing■■ Insufficient mixing time

Possible consequences of high water separation■■ Loss of suspension on the filled column in the

borehole■■ Collapse of the filled column and defective points

in the borehole■■ Increased sedimentation of possible additives

<

Determining water separation of ThermoCem PLUS with W/S ratio 0.8.

<

Determining water separation of a cementsuspension with W/S ratio 0.8.

Water separation


6

No. of sacks

Quantity of ThermoCem

Volume of water to be added

Suspensionvolume

[Stck.] [kg] [l] [l]

1 25 20 31

2 50 40 62

3 75 60 93

4 100 80 124

5 125 100 155

6 150 120 186

Mixing table for ThermoCem with W/S ratio 0.8.

4. Advice on working with the product

4.1 ADDING WATER

ThermoCem PLUS is a pre-mixed product that only requires water to be added to it on the building site. The technical properties we indicate for ThermoCem PLUS can only be achieved if the material is admixed with the designated quantity of water.

This means that the most important factor during admixing is what is known as the water/solid ratio (W/S

ratio). It is the quotient by mass of the required amount of water and of the construction material. The W/S

ratio is determined by our formulation. If the ThermoCem is being admixed using a batch mixer, please note

the fill volume per batch. The formulation should be laid on to approx. 85 % of the mixer volume. In that way,

it is possible to avoid the suspension from “spilling over”.

Example: working volume of mixer 150 l x 0.85 = 127.5 l

The construction material feed is ideally always geared to whole sacks, as part quantities are relatively difficult

to estimate. For this example, the feed is calculated as follows:

First put in 80 litres of water and then add 4 sacks of ThermoCem. This produces around 124 litres of the suspension.

To fill a 1,000-litre cavity requires the following: 810 kg ThermoCem

and 650 litres water > Suspension density approx. 1,460 kg/m3. Using

the W/S ratio, it is then also possible to calculate the water required per

25 kg sack: 25 kg ThermoCem x 0.8 = 20 litres water. The resulting yield

per 25 kg sack of ThermoCem is approximately 31 litres.

7

4.2 QUALITY ASSURANCE ON THE BUILDING SITE

To check on the correct mixing ratio, the only reliable measure is the suspension density. Regular checking

during the backfilling operation is essential to ensure the quality of the filling. The DVGW study (2003) on

investigations to determine quality criteria in well construction, “Untersuchungen zur Bestimmung von Qualität-

skriterien im Brunnenbau”, has demonstrated that it is also sensible to compare the suspension density in the

mixer with the suspension discharged at the head of the borehole. If both density values agree, it can be

assumed that the cavity has been uniformly filled.

The following procedures for measuring density on-site are commonplace:■■ Determination of density using an areometer■■ Determination of density using a mud balance■■ Determination of density using household scales (5 kg) and a defined litre vessel

4.3 CHANGE IN W/S RATIO

But what happens if the W/S value is changed? The table below is intended to provide a brief overview of the

changes in the technical properties if the specified proportion of water is not observed correctly:

Technical properties Increasing the proportion of water: Reducing the proportion of water:

Viscosity Reduces viscosity Increases viscosity

Water separation Increases water separation Reduces water separation

Thermal conductivity Reduces thermal conductivity Increases thermal conductivity

Strengths Reduces strengths Increases strengths

Resistance to frost-thaw Lower resistance Improved resistance

Water permeability Increases water permeability Reduces water permeability

Quantity of construction material required

Reduces consumption of material Increases consumption of material

<Mud balance

<5 kg Household scales

<Areometer

TARGET ACTUAL


8

5.1 MIXING PROCEDURE

The quality of the suspension to be worked is not demonstrated solely in the deliberate choice of the individual components. The stated properties can only be achieved, and even enhanced, using the mixing procedure that is suited to it.Fundamentally, it is possible to distinguish between the following types of mixing:

5. Machinery and equipment

MIXING PROCEDURE

MUD TANKLOW-SPEED HIGH-SPEED

BATCH MIXERFLOW MIXER SOLELY BATCH MIXER

9

Low-speed mixers are mainly designed for the mixed-particle range, where pump-conveyed consistencies are admixed or pumped. Flow mixing (or continuous mixing) systems are often used for geothermal construction sites. Depending on the manufacturer, the quality of the admixed ThermoCem suspension may be adequate. However, if purchasing a new machine it is advisable to test for suitability.

By contrast, colloidal mixers work with very high shearing forces and turbulences. ThermoCem PLUS

suspensions that have been dispersed in this way achieve optimum consistency.

The additional advantage is that colloidal mixers are always batch mixers. This means that the user is always

able to maintain practically identical W/S ratio mix for mix.

In addition, the suspension can be subjected to a sight check. If suspensions have to be set to be more

viscous, due to the geological conditions (fissures, pore chambers), this can be adjusted not only by reducing

the W/S ratio (which means a simultaneous increase in the materials requirement), but in this case also by

adjusting the mixing time in the colloidal mixer.

Viscosity of ThermoCem PLUS as a function of mixing speed(mixing time: 2 min.)

Viscosity of ThermoCem PLUS as a function of mixing time(mixing speed: 1250 rpm)

As a special type of “mixer”, the classic mud tank also merits a mention. Depending on the design of

the tank size and circulating spiral pump, the mixing results achieved range from good to very good.

The advantage lies in the mixing time.

Given the time necessary to prepare a mix in the tank, the ThermoCem PLUS suspension is

thoroughly mixed through. In view of the viscosity and suspension density achieved, it is possible

to backfill geothermal boreholes to a qualitatively high standard using ThermoCem PLUS. Adequate

suspension volumes (e.g. 1000 l), together with a very high pump rate, are advantageous in forcing

out any drilling fluid that may be present.

Mar

sh v

isco

sity

[s]

Mar

sh v

isco

sity

[s]

Mixing speed [rpm] Mixing time [min]


10

6. Backfilling the borehole

6.1 BACKFILLING OPERATION USING AN UNDERWATER CONCRETING PROCESS

Essentially, the backfilling of a geothermal borehole should be carried out as an underwater concreting

process. This means that an additional backfilling hose, mounted on the foot of the probe, or a compression

pipe lowered down to the bottom of the borehole, must be employed as the starting-point for backfilling.

The backfilling operation, which now takes place protected by its own suspension, is a precondition for:■■ Controlled expulsion of any drilling fluid that may be present■■ Preventing demixing of the suspension■■ Cavity-free backfilling

<

Illustration to show the underwater concreting process; homogeneous suspension.

<

Illustration to show “falling” through the water = demixing.

If this method of procedure is not

respected, the material will demix.

In other words, the suspension

“falling” through the standing

water in the borehole or the mud

mix necessarily brings about a

thinning effect.

The proportion of water in the

suspension increases, and can

increase to a level where in some

cases the material fails to harden off.

��

��

��

��

Before the backfilling operation

During the backfilling operation

Backfilling pipe

Geothermal probe

Groundwater

ThermoCem

11

6.2 ENDING THE BACKFILLING OPERATION

During the backfilling process, the mix ratio is to be checked at regular intervals using the suspension density.

The DVGW study (2003) on investigations to determine quality criteria in well construction, “Untersuchungen

zur Bestimmung von Qualitätskriterien im Brunnenbau“, has demonstrated that it is sensible, particularly with

jetting drilling, to compare the suspension density in the mixer with the suspension discharged at the head of

the borehole. If both density values agree, it can be assumed that the drilling fluid has been completely

expelled.

> www.dvgw.de/fileadmin/dvgw/wasser/gewinnung/w1_01_02.pdf

<

Overflow of water/ThermoCem mixture.

<

Overflow of the water expelled from the borehole.

<

Overflow of pure ThermoCem suspension.


12

7. Development of strength and hydration heat

Erosion resistance, Response test,Secure bedding of probes

Source: Stark et al. 2001

7.1 SETTING PROCESS

After admixing ThermoCem with water, an easily-worked suspension is obtained.The clay minerals contained in ThermoCem mean that a tixotropy effect occurs once the suspension ceases to move. It is only some time after that when the actual solidification process starts, i.e. crystals form on the surface of the binder particles.

Where these crystals bridge the spaces between the particles, the material suspension

solidifies and then hardens. This hydration is an exothermic reaction, i.e. heat is generated

during the setting process (hydration heat).

Temperature trend in a ThermoCem test sample under adiabatic conditions.

The estimate of the temperature generated

during the setting process for ThermoCem is

made under adiabatic conditions. This measure-

ment covers the case scenario.

Using the laboratory result, given a start temper-

ature of 24° C a maximum temperature increase

of 5° C can be determined. In the borehole, a

temperature rise of this order is not expected,

since the ambient conditions are different – i.e.

the start temperature is generally lower and the

heat that develops can flow out into the sur-

rounding soil.

SUSPENSION PHASE (liquid) > TIXOTROPIC PHASE (gel) > SOLIDIFICATION (solid) > HARDENING (solid)

22

23

25

27

28

13:00 30:00 38:00 47:00 50:00 55:00

24

26

29

Time [h]

ThermoCem PLUS

Tem

pera

ture

[°C]

13

7.2 DEVELOPMENT OF EARLY STRENGTH AND END-STRENGTH

The development of strength in the ThermoCem is decisively dependent on the ambient

temperature. As a general rule, the colder the ambient temperature, the slower the rate at

which strength develops.

Development of early strength in ThermoCem PLUS at 10° C ambient temperature(shear resistance).

Development of compressive strength in ThermoCem PLUS at 20° C ambient temperature.

1

10

02 1

100

3


Time [d]

Shea

r stre

ngth

[kPa

]

4 kPa threshold

for puncture resistance

Age [d]

Com

pres

sive

stre

ngth

[N/m

m2 ]

14

8. Borehole resistance

System safety, Thermal transfer, Optimisation

The transport of heat on geothermal probes from the

thermal carrier liquid to the subsoil and vice versa

depends on the geometry of the borehole, the

installation of the probe pipes in the borehole and

the properties of the materials used. To be able

to transfer heat, a sufficient temperature drop is

required as the driving force. For thermal transfer via

heat conduction, the determining factor is thermal

conductivity. The higher the conductivity, the lower

the temperature drop needed.

Accordingly, the overall resistance acting on the system is dependent on the following factors:■■ Thermal conductivity of the backfilling material■■ Probe material■■ Distance to the side of the probes■■ Borehole geometry

This overall resistance is also described as the

borehole resistance Rb. In a purely analytical study,

it relates to a point at any depth. With a Thermal

Response Test, the effective borehole resistance

Rb* can be determined over the entire length of the

borehole.

The borehole resistance determines the necessary

temperature drop to transfer a given output.

Example:■■ Extraction output: 50 W/m■■ Borehole resistance Rb* (thermal conductivity of

backfilling material λ ≈ 0.8 W/mK) = 0.12 K/(W/m)■■ Borehole resistance Rb* (thermal conductivity of

ThermoCem PLUS λ ≈ 2.0 W/mK) = 0.07 K/(W/m)

■■ 50 W/m x 0.12 K/(W/m) = 6 K■■ 50 W/m x 0.07 K/(W/m) = 3,5 K

In the example shown here, the temperature loss

between the thermal carrier medium and the rock

in a borehole backfilled with ThermoCem is around

2.5 K lower than for backfilling with a standard

material. Depending on the particular instance,

whether heating or cooling, improving the borehole

resistance can contribute to a significant improve-

ment in the performance capability of a geothermal

plant.

Source: M. Reuss, ZAE

Backfilling material Rock

Flow

Tem

pera

ture

T

Distance rrPipe

rBorehole

dPipe wall

15

9. Chemical resistance to aggressive groundwater

Reliable separation of different groundwater storeys and adherence-actuated stabilisation of the annular space can only be achieved for the long term if the backfilling material used exhibits adequate chemical resistance to the waters found on site. In the case of ce-ment-bound backfill materials, the strength of a chemical attack can be estimated as a provi-sional measure using DIN EN 206.

This standard indicates contents in the water and

pH values that are to be classified as aggressive to

concrete. Concentration ranges are defined for

each concrete-aggressive content material in

water, corresponding to the exposure categories

XA1 (weak attack), XA2 (moderate attack) or XA3

(strong attack). The highest exposure category

identified when studying each of the individual

aggressive materials determines the overall

classification. If a chemical attack is present, this

needs to be taken into account in the choice of

backfilling material.

We point out that the potential aggressiveness to

construction materials of localised groundwater

must always be examined specific to the individual

project, by means of suitable water analysis. To

assess the potential aggressiveness of the ground-

water, as part of the analysis the following should

be determined as a minimum: pH value, electrical

conductivity, and the concentrations of water

contents to be classified pursuant to DIN EN 206

as aggressive to concrete – sulphate, magnesium,

ammonium and lime-dissolving carbonic acid.

Durability, Resistance, Ground - w ater aggressive to concrete

9.1 CLASSIFYING THE LEVEL OF THE ATTACK

Exposure category

XA1 XA2 XA3

Content in water weakly aggressive moderately aggressive strongly aggressive

SO42- [mg/l] 200-600 > 600-3000 > 3000-6000

NH4+ [mg/l] 15-30 > 30-60 > 60-100

Mg2+ [mg/l] 300-1000 > 1000-3000 > 3000 to saturation

pH value 6.5-5.5 < 5.5-4.5 < 4.5 and 4.0

CO2(aq) [mg/l] 15-40 > 40-100 > 100 to saturation

Concrete-aggressive contents in water; limits for exposure categories pursuant to DIN EN 206. Source: DIN


16

To achieve the high chemical resistance of ThermoCem PLUS and ThermoCem Light to waters containing sulphate, these products make exclusive use of a cement with a high sulphate resistance pursuant to DIN 1164. In addition to this, the formulations for these construction materials are designed such that they exhibit significantly increased chemical resistance to acid attacks (e.g. carbonic acid) compared with a standard backfilling material (e.g. Dämmer – Das Original).

The chemical resistance of ThermoCem PLUS and

ThermoCem Light against carbonic acid attack was

investigated in our laboratories in a comprehensive

series of tests. A core part of these investigations

were storage tests whereby water containing

carbonic acid was passed round samples of the

construction materials over a period of 90 days and

the surface softening of the test samples docu-

mented. The measurement of surface softening

was carried out using Vicat needle penetration

depth pursuant to DIN EN 196-3.

The carbonic acid concentration of the storage

water was 100 mg per litre, thereby corresponding

to exposure category XA3 (strong chemical attack).

The permanent flow of water around the test

samples, using fresh water containing carbonic

acid, simulates a “worst-case” scenario.

By comparison with the situation on a real construc-

tion measure, the storage test accordingly provokes

accelerated softening of the construction material,

thereby producing an effect of time compression.

This makes it possible to estimate the influence of

the contaminant over a longer period, despite the

limited duration of the test.

Even under these extreme test conditions,

ThermoCem PLUS and ThermoCem Light exhibit

only slight surface softening.

9.2 RESISTANCE TO SULPHATE AND CARBONIC ACID

9. Chemical resistance to aggressive groundwater

17

Chemical resistance to lime-dissolving carbonic acid. Trend over time for softening of the surface.Carbonic acid concentration of the storage water 100 mg/l (exposure category XA3, strong chemical attack).

Both construction materials satisfy the endurance criterion customary

for sealing wall applications for a needle penetration depth of < 2mm

after 90 days in storage.

By contrast, the surface softening of a standard backfilling material

(Dämmer – Das Original) exceeds this endurance criterion by more

than a factor of three.

Vica

t nee

dle

pene

tratio

n de

pth

[mm

]

Long-term test [days]

Endurance criterion: Vicat needle penetration depth < 2mm

Dämmer – das Original

ThermoCem PLUS

ThermoCem Light


18

10. Frost-thaw resistance of ThermoCem® PLUS and ThermoCem® Basic

Triaxial cell pursuant to DIN 18130 (from Horst 1997).

If more heat is extracted from the subsoil by the geothermal probe than is able to flow continuously (e.g. incorrectlydimensioned plant or altered conditions of use), there is an increase in cooling and, possibly, freezing of the area immediately around the probe. If operating conditions of this kind come about several times over due to temporarily high extraction yields to cover peak loads, then the backfilling material surrounding the probe is subjected to frost-thaw stressing. With backfilling materials lacking sufficiently high frost-thaw resistance, this results in crack formation and damage to joints occurring.

To date, there have been no binding guidelines for assessing the frost-thaw resistance of backfilling

materials for geothermal probes. For that reason, we have developed a frost-thaw test based on compa-

rable tests for concretes and adapted for the special requirements relating to geothermal probes.

In this frost-thaw test, 28-day old cylinders of the construction material (height 100 mm; diameter 100 mm)

are subjected to 10 frost-thaw cycles.

EACH INDIVIDUAL CYCLE WITHIN THIS CORRESPONDS TO A TEMPERATURE PROFILE BASED ON THE AUSTRIAN CONCRETE STANDARD B3303:

> 8 hours cooling down from +10° C to -10°C> 4 hours constant -10°C> 8 hours warming up from -10° C to +10°C> 4 hours constant +10°C

Feed tank Feed volume flow meter Triaxial cell with sample

19

The test samples are stored in a manner to protect against evaporation.

For this, the base of the test sample is kept permanently in a water-bath.

The water contact simulates groundwater penetration into the area around

the geothermal probe affected by the alternating frost-thaw.

The permeability coefficient (kf value) of the frosted test samples is used

as a test criterion. To that end, the permeability coefficient of the test

sample is determined before and after the frost-thaw test in a triaxial cell

pursuant to DIN 18130 with a hydraulic gradient of i = 30.

A backfilling material can only permanently perform its sealing function if it

exhibits low permeability before and after the frost-thaw test.

<

ThermoCem PLUS after 10 frost-thaw cycles;permanent water storage.

< ThermoCem Basic after 10 frost-thaw cycles;permanent water storage.

In the test series conducted in our laboratory

under the rigorous test conditions described

above, ThermoCem PLUS and ThermoCem Basic

demonstrated a permeability coefficient before

and after the frost-thaw test of ≤ 1·10 -10 m/s.

The frost-thaw stressing did not result in the

emergence of damage to joints, nor in impair-

ment of the sealant effect of the construction

materials.


20

11. Geophysical verification of the annular space backfilling

Headline:Verfüllkontrolle mit magnetisch dotiertem ThermoCem PLUS

Bildunterschrift:Beispielhafte Messwertdarstellung

Sond

entie

fe [m

unt

er G

OK]

Magnetsignal [–] Geschwindigkeit [m/Min.]

50

0

-50

-100

-150

-200

-2500 2 4 6 8 10 -2 -1 0 1 2

<

Proof of the annular space backfilling.

SUPERVISION OF THE BACKFILLING PROCESS WITH MAGNETICALLY-DOPED THERMOCEM® PLUS

SENSYS GmbH

21

The more-advanced quality-control directives for the construction of geothermal heat probes require the verification of a complete annular space backfilling.

One possibility is the verification with the aid of geophysical methods. For example,

magnetically- doped backfilling construction materials can be verified unambiguously by the

employment of magnetometer probes. The miniaturization of this measurement technology

makes it possible to drive the tubes of usual soil warming probes, with miniature-design

magnetometers, to the depth required.

ThermoCem PLUS “doped” is a magnetically-doped backfilling construction material. In this

way, the presence or non-presence of the backfilling construction material in the annular space

can be verified unambiguously, using the measurement technology described, by means of the

measurement of the magnetic susceptibility.

As well as the measurement of the rise of the suspension column during the annular space

backfilling, the utilization of ThermoCem PLUS “doped” also enables repeated measurements

at a later time.

< Example of measurement presentation.

< Sensor, Incremental encoder, Data collection. SENSYS GmbH

< Probe. SENSYS GmbH

Headline:Verfüllkontrolle mit magnetisch dotiertem ThermoCem PLUS

Bildunterschrift:Beispielhafte Messwertdarstellung

Sond

entie

fe [m

unt

er G

OK]

Magnetsignal [–] Geschwindigkeit [m/Min.]

50

0

-50

-100

-150

-200

-2500 2 4 6 8 10 -2 -1 0 1 2

Speed [M/min.]Magnetic signal [–]

Dept

h of

the

prob

e [m

bel

ow g

roun

d le

vel]


23THERMOCEM | Naturally good

WWW.HEIDELBERGCEMENT.DE

0219

/SD3

228U

K/Re

v.2

We would like to stress that achieving the mentioned

properties require a suitable production and processing of

the building material as well as a proper, state-of-the art

preparation on the construction site.

HeidelbergCement AGZur Anneliese 7

D-59320 Ennigerloh

Phone +49 2524 29-51700

Fax +49 2524 29-51715

E-Mail [email protected]

www.heidelbergcement.de/spezialtiefbau

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