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
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