HYGROTHERMAL CHARACTERISTICS OF PUMICE AGGREGATE CONCRETE USED FOR MASONRY WALL BLOCKS

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1 HYGROTHERMAL CHARACTERISTICS OF PUMICE AGGREGATE CONCRETE USED FOR MASONRY WALL BLOCKS Kus, Hülya Dr.Eng., Assoc. Professor, Istanbul Technical University, Faculty of Architecture, 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.

In this paper, determination of the water vapour transmission and hygroscopic sorption properties of pumice aggregate concrete is handled in detail.

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 --

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.

2 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 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 Drying of samples in the Sealing of sample samples oven 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 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 KNO 3 solutions in glasses placed in the plastic cups. Table 1: Test conditions and tolerances given in the standard EN ISO Tolerances Conditions Relative Humidity % Set Temperature C - % RH Dry state Wet state C Set point Tolerance Set point Tolerance C 23-50/93 23±0,5 50 ±3 93 ±3

The climate chamber (Weiss WK11 180 model) and the test cups employed in the test are demonstrated in Figure 2.

The temperature and relative humidity within the test chamber were continuously recorded during the test period.

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.

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

3 The climate chamber (Weiss WK 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 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 g me /g = 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/(m 2 s); g is the vapour transmission rate ignoring the masked edge, in kg/( m 2 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: W c = 1/(A Δp v /G)-(d a /δ a ) (Equation 2) where

4 Temperature C, RH %, Absolute moisture gr/kg 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 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 MgCl 2 Mg(NO 3 ) 2 NaCl KNO 3 K 2 SO 4 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) May 25-May 15-Jun 6-Jul 27-Jul 17-Aug Date 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 T RH Abs

5 Mass g for each test condition were determined in accordance with the test procedure given in the standard EN ISO according to the following equation: u = (m m 0 ) / m 0 (Equation 3) where u is the moisture content mass by mass m is the mass of test sample m 0 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/m 3. 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 MASS CHANGE Linear (1) Linear (2) Linear (4) Linear (5) Linear (6) Linear (7) Linear (8) R² = 0,9998 R² = 0,9993 R² = 0,9971 R² = 0,9966 R² = 0,9902 R² = 0,9987 R² = 0, Time (days) 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/m 2 s] W c kg/(m 2 s Pa) Z [m 2 s Pa /kg] thickness d [m] δ [kg/(m s Pa)] μ=δ a /δ - s d = μ d [m] 2.24E E E E E E E E-02 The average dry density of pumice aggregate concrete samples used in the sorption test was found to be about 785 kg/m 3. Figure 6 shows the measured (equilibrium) moisture contents of test samples subjected to increasing relative humidity levels reached by different salt

6 solutions. The moisture adsorption behaviour of pumice aggregate concrete is displayed in Figure 7, as sorption curve reflecting the averages of seven samples. W kg/m average 11 LiCl MgCl2 Mg(NO3)2 NaCl KNO3 K2SO4 Salt Figure 6: The equilibrium moisture contents of pumice aggregate concrete at different salt solutions. 50 y = 0,0001x 3-0,0158x 2 + 0,8508x - 0,02 R² = 0, ,5 W kg/m , Relative Humidity, φ [%] 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.

7 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", 8 th International (8IMS), Dresden, Germany, July 4-7, 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.

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