Moisture impact on building rocks -Moisture impact on building rocks - the laboratorythe laboratory and and in situin situ investigations investigationsFIDRÍKOVÁ D., KUBIČÁR Ľ.FIDRÍKOVÁ D., KUBIČÁR Ľ.

Institute of Physics SAS, Bratislava, SlovakiaInstitute of Physics SAS, Bratislava, SlovakiaThe work was supported by the project APVV LPP–0442–09

Principle of Hot-ball method: A heat source in the form of ball delivers constant heat flux for t > 0 to the medium and simultaneously the ball surface temperature is measured. Heat flux is in the form of a step-wise function. The stabilized value of temperature Tm is measure and from the parameters of the temperature response the thermophysical parameters can be calculated, according to the model used.

Goal: Rocks are influenced by moisture that in combination with temperature, hydrological conditions, climatic conditions, etc. leads to changes of physical and chemical properties. These changes can be observed in the laboratory, where different conditions can be simulated in which the rocks can be found. This work is focused on water transport and moisture determination in various sandstones observed in laboratory conditions and also directly in environment. Porosity affects transport properties of rocks. Experiments are focused on the mechanism distributing the water in sandstones with different porosities. Measurements were carried out by thermal conductivity sensors (Hot-ball sensor) which measure local temperature and local thermal conductivity. The sensor in connection with the RTM device is used for monitoring of the moisture in various sandstones with different porosity. For in situ measurements a moisture sensor is constructed. The sensor is made of the original stone in a form of the cylinder (diameter and length around 20 mm) in which thermal conductivity sensor is placed. The moisture sensor must be calibrated for dry and water saturated state, and then it is inserted into the original site to start monitoring of the impact of surrounding weather conditions on the rock. Meteorological data are correlated to the measured data. Results from water transport and change of moisture in sandstones at various monitoring conditions are presented.

Working relation: t → ∞ , T = Tm at r = rb

Working regime: steady state

The laboratory The laboratory monitoring of moisture In situIn situ monitoring of moisture in St. Jacob Church in Levoča, Slovakia

Initial and boundary conditions:q = const, t > 0, r = rb

r b

R

Thermal conductivity sensor (Hot-ball sensor)

0 100 200 300 400 500

23,6

23,8

24,0

24,2

24,4

24,6

24,8

End

of

heati

ng

Time [sec]

Tm

Star

t of

heati

ng

Base line

Tem

pera

ture

[°C] )()exp(1),( *2

0 uuTrtT b

approximation

Temperature function:

)(4

tTr

q

mb

Ground water

Rain

Frost

water diffusion

capillary transport

CONCLUSIONS:

Hot-ball sensor (thermal conductivity sensor) allows investigation of processes running in pores that depend on various conditions

The structure of porous materials the most affects moisture transport in samples

Moisture monitoring in porous stones gives a information about deterioration of building and other industrial objects

Change of material stability in laboratory by cycles freezing-thawing, moisture-drying can be studied

By cycles of temperature and humidity we are able to simulate behaviour of material in laboratory devices

By means of above described cycles we are able to predict behavior in material during day-night, summer-winter and in dry-wet enviroment

Hot-Ball method is advantageous for continuous monitoring changes of moisture in rock massive and in historical monuments and for other applications (monitoring of concrete setting, monitoring of polymerization, monitoring of structure transformation in pores, material ageing)

4.8

5.0

5.2

5.4

5.6

5.8

570

575

580

585

590

595

600

605

610

615

620

capillary moisture content

q/Tm

Wei

ght (g

)

q/T

m

Weight [g]

gradually saturation

integral moisture

local moisture

capillary transport

Mechanism sustaining a constant water level

0 20 40 60 80 100

0

5

10

15

20

25

30

35

40

45

Mois

ture

(%

)

Time (hour)

Other monitoring by Hot-ball probe: Spis Castle St. Martin's Cathedral in Bratislava, Slovakia Pravčicka gate in Czech republic

27. 1

2. 201

1

3. 1. 2

012

10. 1

. 201

2

17. 1

. 201

2

24. 1

. 201

2

31. 1

. 201

2

7. 2. 2

012

14. 2

. 201

2

21. 2

. 201

2

28. 2

. 201

2

6. 3. 2

012

-15

-10

-5

0

5

10South

Tem

per

ature

[oC

]

Temperature

70

75

80

85

90

95

100

105

110

M

ois

ture

[%

]

Moisture

24. 1

. 201

2

31. 1

. 201

2

7. 2. 2

012

14. 2

. 201

2

21. 2

. 201

2

28. 2

. 201

2

6. 3. 2

012

-15

-10

-5

0

5

10

Temperature

North

Mois

ture

[%

]

Tem

per

ature

[oC

]

0

10

20

30

40

50

Moisture

Moisture impact to building rocks:

0 20 40 60 80 1007.90

7.95

8.00

8.05

8.10

8.15

Tem

per

ature

arbitra

ry u

nits

Time (hour)

8

10

12

14

16

18

20

22

24

26

Sandstone with 17.8% porosity - cycles of temperature 10-25C by 50% humidity

0 20 40 60 80 1009.20

9.25

9.30

9.35

9.40

9.45

9.50

9.55

9.60

24

26

28

30

32

34

36

38

40

42

44

Tem

per

ature

arbitra

ry u

nits

Time (hour)

Sandstone with 5% porosity - cycles of temperature 25-45C by 80% humidity

Moisture affects the life of building materials and reduced the weathering resistance, so it´s very important to determine of water content in a material in dependence on surrounding conditions

Moisture goes into the material: by capillary transportby water diffusion freezing the wall