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, kushu@itu.edu.tr

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.