Water Vapour Permeability of Clay Bricks

Transcription

1 Water Vapour Permeability of Clay Bricks M. Raimondo 1, M. Dondi 1, F. Mazzanti 1, P. Principi 2, G. Zanarini 3 1 CNR-Istituto di Scienza e Tecnologia dei Materiali Ceramici, via Granarolo 64, Faenza (Italy) 2 Dipartimento di Energetica, Università di Ancona, via Brecce Bianche Ancona (Italy); 3 Consorzio Alveolater, viale A. Moro 16, Bologna (Italy).

2 Why? Cimtec 2002, July 14-18, Florence Absorption of umidity from air Capillary rise Condensation phenomena Formation of superficial moisture Wear and tear

3 Definitions according to UNI 9233 Vapour Flow (kg/s) Quantity of water vapour which, in stady conditions, is transferred to or from a system per unit time, as the effect of a partial vapour gradient Density of water vapour flow rate [kg/(m 2 s)] Water vapour flow rate per unit area and time Water vapour permeance (kg/m 2 s Pa): The moisture permeance is a measure of the permeance with regard to the partial vapour Water vapour permeability (kg/m s Pa) Water vapour permeability is a measure of the mass of moisture penetrating trough a specimen, resulting from the effect of a partial vapour pressure gradient within the specimen, per unit area, time and pressure

4 Water vapour absorption process Non-steady conditions Hygroscopic capacity Diffusion resistance Steady conditions Water vapour permeability Density of vapour flow Pressure gradient

5 State of the art Cimtec 2002, July 14-18, Florence Few data available on thermohygrometric properties of bricks; Bibliographic search Most of them refer to liquid absorption; Some of them concern the equilibrium moisture content; Partically no data on water vapour permeability have been published

6 This study is aimed at drawing a picture representative of the thermo-hygrometric properties of industrial products Through Cimtec 2002, July 14-18, Florence a) an experimental determination of water vapour pemeability of clay bricks obtained without pore forming agents; b) an investigation of the relationship between the water vapour permeability and the microstructure of the ceramic material c) elaboration of a previsional model through the statistical analysis of data

7 Materials Cimtec 2002, July 14-18, Florence Clay mineralogical composition Illite and... Quartz Calcite + Dolomite

8 100...particle size distribution (Sedigraph 5100) Cumulative weight percent A AT CA D 30 F LM 20 SA SL 10 X 0 0,1 1,0 10,0 100,0 LS MA MO S Particle size (µm)

9 Sampling Extruder 30 cm clay block 30 cm 10 cm 2 cm 30 cm cilcular slabs

10 Clay Processing conditions Drying shrinkage (cm m -1 ) Pressure of extrusion (bar) Firing temperature ( C) A AT CA D > F 4.5 n.d. 960 LM LS MA 6.5 n.d. 910 MO S SA SL X n.d. = not determined Cimtec 2002, July 14-18, Florence

11 Open porosity (OP) Characterization of bricks through measurement of Bulk density (BD) Mean pore size (MPS) Pore size selection (PSL) mercury intrusion porosimetry Impervious porosity (IP) Total porosity (TP) ASTM C 329 Pore specific surface (PSS) ASTM C 1069 Water vapour permeability UNI 9233 University of Ancona

12 Results Water vapour permeability of clay bricks (kg m -1 s -1 Pa -1 ) X SL SA S MO MA LS LM F D CA AT A x 10 12

13 Results Cimtec 2002, July 14-18, Florence Porosimetric characteristics of clay bricks Open porosity Closed porosity Total porosity Bulk density Mean pore Pore size selection Specific surface Brick % vol. % vol. % vol. kg m -3 µm adim. m 2 g -1 A AT CA D F LM LS MA MO S SA SL X

14 Statistical analysis Extraction of the main components Variables Water vapour permeability Open porosity Bulk density Mean pore size Pore specific surface Mineralogical composition of bodies Pore size selection

15 Factor 2 1,0 0,8 0,6 0,4 0,2 0,0-0,2-0,4-0,6-0,8 QUARTZ PHYLLOSILICATES PORE SELECTION BULK DENSITY PORE SPEC. AREA CLAYEY FRACTION SANDY FRACTION Factor 1 MEAN PORE SIZE WATER VAPOR PERM. OPEN POROSIT Extraction: principal components Variance maximizing Explained variance: factor 1=42%, factor 2=24% -1,0-1,0-0,8-0,6-0,4-0,2 0,0 0,2 0,4 0,6 0,8 1,0

16 Statistical results: Cimtec 2002, July 14-18, Florence positive Open porosity, Mean pore size Water vapour permeability negative Bulk density, pore specific surface, clay fraction of the body doubtful Pore size selection, mineralogical composition

17 Water vapour permeability vs Open porosity Water vapour permeability (kg/m s Pa) MO CA X AT F LM D LS SA SL MA A S Open porosity (% vol.)

18 Water vapour permeability vs Mean pore size Water vapour permeability (kg/m s Pa) MO CA X AT F D LM LS SA SL MA A S 2 0,0 0,2 0,4 0,6 0,8 1,0 1,2 Mean pore size (µm)

19 Water vapour permeability vs Clayey fraction Water vapour permeability (kg/m s Pa) MO CA X AT F LM D LS SA MA SL A S Granulometric fraction <4 µm (% wt)

20 Water vapour permeability vs Bulk density Water vapour permeability (kg/m s Pa) AT D LS MO CA LM X SA MA 2 1,55 1,65 1,75 1,85 1,95 2,05 2,15 A F SL S Bulk density (g/cm 3 )

21 Water vapour permeability vs Pore specific surface Water vapour permeability (kg/m s Pa) MO CA X AT F LM D LS SA MA SL A S 2 0,4 0,7 1,0 4,0 7,0 10,0 Specific pore surface(m 2 /g)

22 Water vapour permeability vs Pore size selection Water vapour permeability (kg/m s Pa) MO CA X AT F D LM LS SA SL MA A S 2 0,15 0,25 0,35 0,45 0,55 0,65 0,75 Pore size selection

23 Coupling the most significative variables... Water vapor permeability (larger than):

24 Coupling the most significative variables... Water vapor permeability (larger than)

25 Multiple regression analysis... For each selected independent variable are listed: standardized ( )and non standardized coefficients (B) with corresponding standard errors and probability level (p). multiple correlation R = R 2 = probability level number of samples n = 12 Independent variables B p Intercept < 0.01 Open porosity < 0.01 Bulk density < 0.01 Mean pore size Pore Specific Surface Clay fraction (<4 µm) < 0.01

26 Observed scores Number of observations Standard distribution of residues 0-1,5-1,0-0,5 0,0 0,5 1,0 1,5 2,0 SL F LM D LS MA AT CA MO X 4 A S Regression confid. 95% Predicted scores

27 Conclusions Cimtec 2002, July 14-18, Florence The water vapour permeability of clay bricks, manufactured with a wide range of raw materials composition, is in the ; The water vapour permeability depend to a large extent on the microstructure of the ceramic materials, particularly volume, size and tortuosity of pores A previsional model was set up able to predict with reasonable precision and reliability the water vapour permeability on the basis of open porosity, bulk density, mean pore size,pore specific surface of bricks, and the amount of finer fraction in the body.