15th International Brick and Block
Masonry Conference
Florianópolis – Brazil – 2012
HYGROTHERMAL CHARACTERISTICS OF PUMICE AGGREGATE
CONCRETE USED FOR MASONRY WALL BLOCKS
Kus, Hülya
Dr.Eng., Assoc. Professor, Istanbul Technical University, Faculty of Architecture, [email protected]
In recent years, computer simulation programs have been increasingly utilized for
performance analysis of building and its parts. Despite the databases incorporated into the
simulation programs, it is sometimes required to have measured data related to material
properties in order to get more accurate results and thus to make better interpretations and
assessments. In the context of an extensive research, water vapour transmission and
hygroscopic moisture adsorption properties of pumice aggregate concrete composite material
were measured for such purposes. In this paper, tests are described in detail and the
measurement results are presented. Beside careful consideration and long periods of time
required for conducting reliable tests, the heterogeneous material characteristics in particular
necessitate further tests and analysis on hygrothermal properties.
Keywords: Hygrothermal characteristics, pumice aggregate concrete, vapour transmission, sorption
INTRODUCTION
Pumice aggregate concrete (PAC) hollow block, a relatively new product, is observed to be
utilized increasingly as an alternative infill masonry wall unit to autoclaved aerated concrete
block and hollow brick, in the construction of both residential and commercial buildings of
Turkey. In order to develop the technical data and enhance the scientific knowledge about the
characteristics of PAC blocks and the hygrothermal performance of external walls built with
these blocks, an extensive research based on laboratory measurements, numerical analyses,
and field observations was conducted (Kus et.al. 2010). Laboratory studies of: (i) material
characteristics tests for determining thermal and moisture related properties of pumice
aggregate concrete composite; and (ii) hot-box measurements for investigating heat and
moisture flow through PAC block walls under various indoor and outdoor testing conditions
constituted an important part of the research program.
The pore structure plays an important role in the hygrothermal performance of pumice
aggregate concrete composite like for other inorganic mineral materials. Therefore, studies on
moisture related properties were considered important for: (i) proper understanding the
characteristics of pumice aggregate concrete and thus to make accurate assessments and
interpretations on the hygrothermal behaviour based on the hot-box measurement results
obtained by monitoring of temperature and relative humidity in PAC block test walls; and (ii)
improving the material database of hygrothermal simulation softwares in order to increase the
accuracy of calculation results.
15th International Brick and Block
Masonry Conference
Florianópolis – Brazil – 2012
In this paper, determination of the water vapour transmission and hygroscopic sorption
properties of pumice aggregate concrete is handled in detail. The test results are presented and
discussed based on the test procedure; preparation of test samples, the testing equipment, and
the measurement course.
WATER VAPOUR TRANSMISSION TEST SET-UP
Water vapour transmission test was conducted in compliance with the standard “EN ISO
12572 Hygrothermal performance of building materials and products -- Determination of
water vapour transmission” [EN ISO 12572] according to “wet cup” method. Tests lasted
over a period of five weeks including one week for the preparation of test samples and cups,
and four weeks for the measurement period.
Ten plates were first cut (with wet saw) from original wall blocks having one-row of hollows,
since these blocks were the most appropriate for the dimensions of test samples required.
Discs having a diameter of 88mm were then drilled out from these plates. The thickness of the
hollow walls, i.e. pumice aggregate concrete solid parts of the blocks, constituted the
thickness of the samples. Seven samples were selected among ten, having the proper shapes to
be used in the tests. The dimensions were then measured by means of a digital caliper and the
sample surface areas of both sides were accurately calculated through copying the sample
surfaces on a millimetre-squared sheet of graph paper.
All samples were conditioned under 23 °C and 50% RH before conducting the test. The edges
of the samples were sealed with elastic putty, and then they were mounted on top of plastic
circular cups in which saturated salt solutions were placed in a glass prior to closing the open
mouth with the sample. The tightness of the edges was controlled and the cups were put in the
climate chamber. The preparations before the vapour transmission test are seen in Figure 1.
Wall
Block
Drilling out of disc
samples
Drying of samples in the
oven
Sealing of sample
edges
Figure 1: Preparation of samples for vapour transmission test
Test conditions were arranged as 93% RH in the test cup, and %50 RH and 23°C in the
climate chamber in compliance with EN ISO 12572 standard according to set “C” given in
“Table 1”. Test conditions and tolerances are given in Table 1. 94% relative humidity in the
test cups was obtained using saturated KNO3 solutions in glasses placed in the plastic cups.
Table 1: Test conditions and tolerances given in the standard EN ISO 12572
Set Conditions
°C - % RH
Tolerances
Temperature
°C
Relative Humidity %
Dry state Wet state
Set point Tolerance Set point Tolerance
C 23 - 50/93 23±0,5 50 ±3 93 ±3
15th International Brick and Block
Masonry Conference
Florianópolis – Brazil – 2012
The climate chamber (Weiss WK11 180 model) and the test cups employed in the test are
demonstrated in Figure 2. The accuracy of conditions in the climate chamber displayed on the
digital screen was controlled with a protimeter. The temperature and relative humidity within
the test chamber were continuously recorded during the test period. Test cups placed in the
preconditioned climate chamber were periodically weighed and rotated. The mass changes in
time were measured, and the water vapour transfer rates and the water vapour resistance
factor were calculated according to EN ISO 12572.
Climate chamber Preliminary controls before conducting test Test cups on the shelf
Figure 2: Climate chamber and the samples
Screen – set conditions Graphical display of realized
conditions
Weighing
Figure 3: Measurements of water vapour transmission test
Before the calculation of average values based on the test data, the corrections were made for
the masked edge effect of the samples using Equation 1, as given in the standard EN 12572.
gme/g = 1 + 4·d/π·S · ln (2/(1+exp(-2 · π · b/d))) (Equation 1)
where
gme is the vapour transmission rate with masked edge, in kg/(m2·s);
g is the vapour transmission rate ignoring the masked edge, in kg/( m2·s);
d is the thickness of the specimen, in m;
b is the width of the masked edge, in m;
S is the hydraulic diameter, in m, (four times the test area divided by the perimeter).
Since the pumice aggregate concrete is highly permeable, the corrections were also made for
the resistance of air layer thickness between the saturated salt solution and the base of the
sample. Following equation was used to obtain the final results:
Wc = 1/(A·Δpv/G)-(da/δa) (Equation 2)
where
15th International Brick and Block
Masonry Conference
Florianópolis – Brazil – 2012
da is the thickness of the air layer;
δa is the water vapour permeability of air.
HYGROSCOPIC SORPTION TEST SET-UP
Hygroscopic sorption property of pumice aggregate concrete was determined using desiccator
method in accordance with the standard EN ISO 12571 “Hygrothermal performance of
building materials and products – Determination of hygroscopic sorption properties” (EN ISO
12571). The test period including the determination of dry densities of test samples lasted
over four months. Test method is based on precise weighing of test samples attained
equilibrium state under controlled temperature and relative humidity conditions. In adsorption
isotherm, defined by the wetting process of oven dry sample under increasing equilibrium
relative humidities at a specified temperature, sorption curves through moisture adsorption are
measured. In desorption isotherm, defined by the drying process of water saturated sample
under decreasing equilibrium relative humidities at a specified temperature, sorption curves
through moisture desorption are measured. In this study, in order to be used in the computer
simulation programs, only adsorption curve was determined for pumice aggregate concrete.
Seven test samples measuring 24mm × 102mm × 60mm were cut with wet saw from original
pumice aggregate concrete hollow blocks. Dry densities were determined after drying in the
oven at 105 °C. Oven dried samples were then put in the desiccator in which specified relative
humidity conditions were attained with different saturated salt solutions. Salts used in the test
and the corresponding relative humidity values are given in Table 2.
Table 2: Salts and RH values used in the sorption test LiCl MgCl2 Mg(NO3)2 NaCl KNO3 K2SO4
12% 33% 54% 75% 92% 96%
The tightness of the desiccator was ensured by means of a non-hardening butyl mastic strip
(Figure 4a). Temperature and relative humidity conditions in the desiccator were monitored
using a humidity sensor and the data was recorded by a datalogger throughout the test (Figure
4b).
a) Test samples in the desiccator. b) Monitored conditions inside the desiccator.
Figure 4: Sorption test
Test samples were periodically weighed with minimum 24 hours of intervals at specified RH
conditions until they attained an equilibrium state with constant mass. Adsorption isotherms
0
10
20
30
40
50
60
70
80
90
100
4-May 25-May 15-Jun 6-Jul 27-Jul 17-Aug
Tem
pe
ratu
re C
, RH
%,
Ab
solu
te m
ois
ture
gr/
kg
Date
T RH Abs
15th International Brick and Block
Masonry Conference
Florianópolis – Brazil – 2012
for each test condition were determined in accordance with the test procedure given in the
standard EN ISO 12571 according to the following equation:
u = (m – m0) / m0 (Equation 3)
where
u is the moisture content mass by mass
m is the mass of test sample
m0 is the mass of dry test sample.
RESULTS
The average oven-dry density of the samples employed in the water vapour transmission test
was determined as 786 kg/m3. The mass change over time (vapour transfer rate) measured
during the vapour transmission test is demonstrated in Figure 5. As it is seen in the diagram,
the steady state conditions for each sample were obtained at different times during the test
period.
Figure 5: Vapour transfer rate of pumice aggregate concrete samples
In Table 3, the vapour transmission test results are presented. The values represent the mean
values of seven pumice aggregate concrete samples.
Table 3: Average results of samples in the vapour transmission test.
G [kg/s] g=G/A
[kg/m2s]
Wc
kg/(m2·s·Pa)
Z
[m2·s·Pa /kg]
thickness
d [m]
δ
[kg/(m·s·Pa)]
μ=δa/δ
-
sd= μ·d
[m]
2.24E-
08
3.78E-
06 2.15E-09 4.75E+08 2.38E-02 5.11E-11
3.92E+0
0 9.33E-02
The average dry density of pumice aggregate concrete samples used in the sorption test was
found to be about 785 kg/m3. Figure 6 shows the measured (equilibrium) moisture contents of
test samples subjected to increasing relative humidity levels reached by different salt
R² = 0,9971
R² = 0,9993
R² = 0,9966
R² = 0,995
R² = 0,9902
R² = 0,9998
R² = 0,9987
435
440
445
450
455
460
465
470
475
480
485
0 2 4 6 8 10 12 14 16 18 20 22
Time (days)
1 2 4 5 6 7 8 Linear (1) Linear (2) Linear (4) Linear (5) Linear (6) Linear (7) Linear (8)
Mas
s g
MASS CHANGE
15th International Brick and Block
Masonry Conference
Florianópolis – Brazil – 2012
solutions. The moisture adsorption behaviour of pumice aggregate concrete is displayed in
Figure 7, as sorption curve reflecting the averages of seven samples.
Figure 6: The equilibrium moisture contents of pumice aggregate concrete at different
salt solutions.
Figure 7: Adsorption curve for pumice aggregate concrete.
CONCLUSIONS
Tests and analysis conducted to determine the hygrothermal characteristics of porous building
materials is important for a correct understanding of the characteristics of pumice aggregate
concrete composite. Thus, more accurate performance assessments and interpretations can be
made through input of measured data both in (i) the experimental studies and (ii) computer
simulations performed on hygrothermal behaviour of walls built with pumice aggregate
concrete hollow blocks. Since there is very limited scientific data and technical information
on pumice aggregate concrete in general, and also limited data available in the international
literature will not directly reflect the properties of the national products, test results obtained
in the context of the research project were found to be quite useful.
11
14
17
20
23
26
29
32
LiCl MgCl2 Mg(NO3)2 NaCl KNO3 K2SO4
W k
g/m
3
Salt
1 2
3 5
6 7
8 average
y = 0,0001x3 - 0,0158x2 + 0,8508x - 0,02 R² = 0,9944
0
12,5
25
37,5
50
0 50 100
W k
g/m
3
Relative Humidity, φ [%]
15th International Brick and Block
Masonry Conference
Florianópolis – Brazil – 2012
ACKNOWLEDGEMENTS
The material characteristics tests of pumice aggregate concrete were conducted within the
research project, TUBITAK 107M532 “Hygrothermal Performance of External Walls Made
of Pumice Agregate Concrete Blocks, Energy and Economic Efficiency through Life Cycle”
supported by The Scientific and Technical Research Council of Turkey. BMG-HIG is greatly
acknowledged for opening their laboratories to conduct the vapour transmission test.
REFERENCES
Kus, H., Edis, E., Özkan, E., and Göçer, Ö. "Performance assessment of pumice aggregate
concrete block walls", 8th
International Masonry Conference (8IMS), Dresden, Germany, July
4-7, 2010.
EN ISO 12572: 2001 Hygrothermal performance of building materials and products --
Determination of water vapour transmission properties.
EN ISO 12571: 2000 Hygrothermal performance of building materials and products --
Determination of hygroscopic sorption properties.