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Effect of temperature on water capillary rise coefficient of building materials
Accepted Manuscript Effect of temperature on water capillary rise coefficient of building materials N. Karagiannis, M. Karoglou, A. Bakolas, A. Moropoulou PII:
S0360-1323(16)30262-1
DOI:
10.1016/j.buildenv.2016.07.008
Reference:
BAE 4563
To appear in:
Building and Environment
Received Date: 18 March 2016 Revised Date:
12 July 2016
Accepted Date: 12 July 2016
Please cite this article as: Karagiannis N, Karoglou M, Bakolas A, Moropoulou A, Effect of temperature on water capillary rise coefficient of building materials, Building and Environment (2016), doi: 10.1016/ j.buildenv.2016.07.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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EFFECT OF TEMPERATURE ON WATER CAPILLARY RISE COEFFICIENT OF BUILDING MATERIALS
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N. Karagiannis1, M. Karoglou1, A. Bakolas1*, A. Moropoulou1
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ABSTRACT
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Dept. of Materials Science and Engineering, School of Chemical Engineering, National Technical University of Athens, Zografou Campus 15780, Athens, Greece * tel:+30210772715, fax:+302107723215, email: [email protected]
The presence of water is one of the main decay factors in buildings. Capillarity is the most usual mechanism of water penetration into building materials in liquid phase. Free capillary water uptake experiment, utilized for the estimation of the capillary rise coefficient Aw, a crucial hygrothermal materials property, is widely used for the characterization of building materials.
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The main aim of this work was to investigate the effect of temperature on the capillary water absorption coefficient. Different categories of building materials such as stones, bricks and mortars of various compositions, for three different levels of air temperature (20, 25 and 30 °C) were studied. A linear dependence of the capillary water absorption coefficient with temperature was found for all examined materials, however with different slope values for each material. In order to assess the validity of the linear dependence of the capillary water absorption coefficient on the temperature, capillary rise experiments were performed at the temperature of 15oC and a very good agreement between experimental and predicted values of the Aw was obtained. Finally, other models correlating the capillary water absorption coefficient Aw with temperature suggested by other researchers were evaluated.
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KEYWORDS
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Building materials, capillary rise, temperature, sorptivity.
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INTRODUCTION
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The role of water in the mechanism of deterioration of porous building materials has been recognized from ancient times [1]. Water enters building materials in water or vapor phase but the major moisture transfer mechanisms are at liquid phase [2]. Water penetrates into a building material’s pores with several ways. Potential sources of water are: the ground, the environment (rain, sea, water vapor etc.), possible water sewage leakages, use of water for the production of building materials, interventions with the use of extensive quantities of water, salts’ hygroscopicity etc. [3-5]. The most common way by which ground water can rise into the pore structure of a building material is by force of capillarity. Capillary rise is, by definition, the upward vertical movement of ground water through a permeable wall structure causing the appearance of rising damp into the structure.
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ACCEPTED MANUSCRIPT Building materials usually contain an amount of physically bound water without affecting their durability. But if the material’s moisture content is above a certain percentage, the deterioration effect of moisture is activated causing an amount of physical, chemical and biological effects [6-7].
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The knowledge of the water movement within a building material is of great importance to determine the degradation mechanism in question and moisture migration is by far the most important control function to be addressed. Moisture related problems in buildings are common and broadly vary in types and consequences affecting their overall durability [8]. Illustrating the moisture impact to buildings durability, numerous hygrothermal models have been developed [9-21]. Heat and moisture flow into or out of a building have also a significant impact on the insulating properties of the building envelope and on the energy efficiency of the construction [22-26] decreasing the life-time of the building [27-29]. Furthermore, as many people spend most of their time indoors, moisture can affect the quality of indoor air and consequently their health and comfort [30-36].
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Describing the capillary rise phenomenon, several parameters related with the hydric properties of porous building materials have been introduced and widely used. Capillary water absorption coefficient Aw, or A-coefficient, is one of the most important features of a building material because it governs the liquid moisture movement through the capillary pores into it. A-coefficient expresses the rate of absorption of water due to capillary forces for building materials and is a measure of the tendency of a material to absorb and transmit water by capillarity. Capillary water absorption coefficient has a significant impact and many applications not only at the traditional but at the contemporary building materials, thus, it must be taken into consideration when determining the hydrometric properties of the material.
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Capillary water absorption coefficient Aw is also connected with water sorptivity S coefficient which is another equally important material property. Water sorptivity S is another way to express the tendency of a material to absorb and transmit water by capillarity and it is connected with the water absorption coefficient Aw of a building material through the equation:
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Aw = S ρw
(1)
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where ρw is the density of the water.
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In recent years, many researchers dealt with the estimation of the capillary water absorption coefficient [37-42]. Furthermore, several studies have been carried out regarding the influence of the temperature on hydric properties of building materials. Reinhardt and Jooss examined the influence of temperature on capillary rise coefficient of concretes with different types of cement and aggregates, at three different ambient temperatures. They measured the capillary absorption coefficients of 9 kinds of concrete in the temperature range of 20-80°C and they found that the capillary absorption coefficient increased almost linearly with temperature [43]. Gummerson et al. made measurements of the sorptivity of one clay brick for four organic liquids and for water at several temperatures in the range 5-36°C finding a linear dependence of the sorptivity with the temperature [44]. Mukhopadhyaya et al. determined the water 2
ACCEPTED MANUSCRIPT absorption coefficients of three commonly used building materials, at four different water temperature levels, while the specimen remained at ambient room temperature [45]. They found that the surface temperature of the sample has an effect on the water absorption coefficient of materials with a small A-coefficient while for materials with high A-coefficients the temperature impact is very small. Feng and Janssen also conducted measurements on the hygric properties of autoclaved aerated concrete, calcium silicate board and ceramic brick in the temperature range of 10-40°C. They measured the capillary water absorption coefficient and they found that capillary absorption coefficient is strongly temperature-dependent and it can be estimated from a linear equation for each building material [46].
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As far as the sorptivity coefficient, Philip first introduced the term of sorptivity S in soil science and since then many researchers have adopted it in their research [47-49]. Hall used it for building materials and gathered a large amount of data on sorptivity [50-52]. Over the last 30 years, the water sorptivity measurement has been considered to be a well-established method for liquid water transport characterization, and was regularly used for a variety of building materials [37], [38], [43], [53], [54]. Presenting the sorptivity S as a quantity deriving from the unsaturated flow theory, Hall and Hoff suggested that water sorptivity S of a building material should be given from the following equation:
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(2)
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where σ is the surface tension of the water, η is the water viscosity and S is the intrincic sorptivity which depends on each material’s characteristics and is independent of temperature [52]. The capillary absorption of liquid water by a building material depends not only on the hydric properties of water (surface tension σ and viscosity η) but also on the microstructure of the material. The dependence of temperature on the surface tension and viscosity of the water indicate that sorptivity S and thus, capillary water absorption coefficient Aw, can be written as [44], [46], [52]:
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S = (σ/η)1/2 S
Aw ∝ (σ/η)1/2
(3)
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For the estimation of the capillary water absorption coefficient of building materials, many European and international standards and recommendations are used. The majority of these standards are related to building materials and materials used in cultural heritage protection. European standard EN 1925 refers to natural stones [55], while EN 1015-18 refers to hardened mortars [56]. European standard EN 13057 describes the measurement of the capillary water absorption of hardened concrete [57]. Normal 11/85 refers to materials and conservation interventions of cultural heritage and it was replaced by the UNI 10859 standard, which refers to natural and artificial stones [58], [59]. EN 15801 refers to porous inorganic materials used for and constituting cultural property and the European standard EN 480-5, describes the determination of the water capillary absorption coefficient of concrete, mortars and grouts [60], [61]. Finally, EN ISO 15148 is applied in the determination of the water absorption 3
ACCEPTED MANUSCRIPT coefficient by partial immersion with no temperature gradient [62]. This method is suitable for renders or coatings tested in conjunction with the substrate on which they are normally mounted.
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However, regarding the experimental conditions, these European and International standards do not take into account environmental factors, such as air temperature and air humidity. Specifically, the describing procedure indicates that the specimens shall be kept in a room temperature of 20 ± 5oC [55]. Additionally, several established studies refer to the European standards above but none of them consider the dependence of the A-coefficient on temperature. While the experimental procedure estimating the capillary water absorption coefficient of building materials remains unquestionable, the comparison of A-coefficient values is difficult mostly because of the different estimation methods. Consequently, there is an argument among researchers regarding the dependence or not of the A-coefficient with the environmental parameters and especially with temperature. One main reason for such an argument is the unavailability of data that would define the moisture transport properties of common building materials as a function of temperature.
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The aim of this work was firstly to investigate the effect of the temperature on the capillary water absorption coefficient Aw of a variety of building materials. For this reason, the capillary water absorption coefficient was measured at three different ambient temperatures (20, 25 and 30oC) and a linear model describing the effect of temperature on the capillary water absorption coefficient was found. Moreover, other researchers’ models were examined in order to evaluate the validity of these models.
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MATERIALS AND METHODS
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In the present study, three categories of building materials were studied (bricks, stones, and natural hydraulic mortars). Bricks are symbolized with codes starting with the letter “B”, stones with “S” and mortars with “m”. More specifically, two different types of clay brick have been investigated. One was a typical solid clay brick (BRI) and the other one was a traditional handmade clay brick (BRM). Two sedimentary quarry stones originated from Rhodes Island (SRH) and from Rethymno, Crete Island (SRY) respectively were the stones investigated. The mortars examined were prepared by using two different types of natural hydraulic lime (NHL2 & NHL3.5) in accordance to EN 459-1 [63], in 3 different binder/aggregate ratios. The specific mortars choice was made because mca and mcb mortars are different building materials, with different binder type and with different b/a ratio. These mortars are widely used at the restoration of traditional and historic buildings as well as for the construction of sustainable buildings. The materials dimensions were 5×5×5±0.1 cm3. The materials characteristics are summarized in Table 1.
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Table 1: Materials characteristics
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No
Materials
Description
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BRI BRM SRH
Typical solid clay brick Traditional handmade clay brick Rhodes quarry stone 4
ACCEPTED MANUSCRIPT SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
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Rethymno quarry stone 20% NHL 2 & 80% river sand 25% NHL 2 & 75% river sand 30% NHL 2 & 70% river sand 20% NHL 3.5 & 80% river sand 25% NHL 3.5 & 75% river sand 30% NHL 3.5 & 70% river sand
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In order to investigate the dependence of the capillary water absorption coefficient on the temperature, a series of capillary rise tests were carried out at 20oC as the majority of the standards and recommendations suggest. Afterwards, a series of capillary rise tests were performed at 25°C and 30°C for all the examined materials. All the capillary rise experiments were performed at controlled relative humidity conditions. The water temperature was determined about 2±0.5oC lower than the air temperature while the relative humidity was 45 ± 5% during the experiments. At least, three specimens of each material were tested for each one of the selected air temperatures. Each specimen was tested three times. The side surfaces of each specimen were sealed with a transparent tight epoxy sealant, which did not significantly penetrate into the pore network of the material. The water level was kept constant and each specimen was partially immersed, at a depth of 3±0.5 mm above the highest point on the base of the specimen, while an effort was made to ensure that air bubbles were not trapped below the specimen.
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The experimental setup for the capillary rise experiment was quite common and it was divided in two stages [50]. During the first stage, the position of the waterfront was gradually approaching the opposite side of the sample and the water intake was governed by capillary and viscous forces. The quantity of the absorbed water was measured at standard time intervals by weighing the specimen. During the second stage, the waterfront had reached the upper end of the sample and no other increase in specimen weight was observed because moisture content had reached the capillary moisture content wcap.. The capillary water absorption coefficient was determined according to Italian Normal 11/85 in which the two tangents method is described. According to this method, the capillary water absorption coefficient should be determined according to the following equation:
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Aw=
M*
(4)
t*
where Aw (kg/m2s1/2) is the capillary water absorption coefficient, M* (kg/m2) is the asymptotic value of the absorbed water per unit area of the sample (water reach the capillary moisture content) and t* (s) is the abscissa of the point of intersection between the straight line passing through the asymptote and the tangent to the straight portion of the curve measured in seconds.
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RESULTS AND DISCUSSION
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In Table 2 the capillary water absorption coefficient values according to the two tangents method, at the air temperature of 20oC are presented for all examined materials.
0.002 0.002 0.005 0.002 0.004 0.001 0.003 0.002 0.001 0.001
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Bricks presented the highest capillary water absorption coefficient values (>0.20) and they are the most hydrophilic of the examined materials. As far as mortars, they exhibit different Aw values because of their different binder type and their different mix design. The main results of the capillary rise kinetics for all the examined materials at the temperatures of 20, 25 and 30oC are summarized in Fig. 1. The values plotted refer to the same specimen of each material at three different temperatures. From the diagrams in Fig.1, a dependence of the A-coefficient with the temperature is observed in all the samples. More specifically, the water absorption coefficient increases with the increase of temperature. In the case of BRI and BRM bricks kinetics, the initial part is very well defined by a straight line at all the temperatures and their curve shape is the same at every temperature examined. Moreover, BRI brick exhibits higher capillary saturation moisture content than BRM brick. SRH stones exhibit a first stage not sufficiently defined by a straight line (see Fig. 1). SRY stones present lower A-coefficient values than SRH stones [64]. Some irregularities are also observed in the curve shape of some mortars (mca25/75, mcb25/75 and mcb30/70 mortars) probably due to their different microstructure.
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0.252 0.206 0.123 0.083 0.176 0.106 0.160 0.106 0.071 0.065
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BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
SD
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Materials Aw (kg/m2 s1/2) (20 oC)
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Table 2 Water absorption coefficient Aw (kg/m2s1/2) values according to the two tangents method for building materials at 20oC and its Standard Deviation (SD)
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Figure 1: Cumulative mass of capillary water uptake versus time for different building materials. 7
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Α linear regression analysis between Aw values and temperature T was conducted and the extracted equations with their R-squared values are presented in Figs. 2, 3 and 4. BRI
0.30
BRM
SRH
SRY y = 0.0009x + 0.2353 R² = 0.996
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y = 0.0026x + 0.1493 R² = 0.9933
0.20
0.15
y = 0.0056x + 0.0036 R² = 0.9988
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Capillary Rise Coefficient (kg /m2s1/2 )
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y = 0.0016x + 0.0513 R² = 0.9933
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Figure 2: Water absorption coefficients at various temperatures for bricks and stones
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y = 0.0015x + 0.1457 R² = 0.9962
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y = 0.002x + 0.1089 R² = 0.9828
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Capillary Rise Coefficient (kg/m2 s1/2)
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y = 0.001x + 0.0856 R² = 0.9847
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25 Temperature (oC)
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Figure 3: Water absorption coefficients at various temperatures for mca mortars
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mcb 25/75
mcb30/70
y = 0.001x + 0.0867 R² = 0.9953
0.10
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y = 0.0009x + 0.0539 R² = 0.9957
y = 0.0006x + 0.0546 R² = 0.9956
0.05
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Capillary Rise Coefficient (kg/m2 s1/2)
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Figure 4: Water absorption coefficients at various temperatures for mcb mortars
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According to the results presented in Fig. 2, 3 and 4, it is evident that the capillary water absorption coefficient exhibits a linear dependence with temperature in all samples which indicates the dependence of the Aw on the hydric properties of the water (see equation (3)). It is also apparent from Fig. 2, 3 and 4 that there is a slope differentiation for every building material which suggests that Aw is also dependent on the intrinsic properties of each material such as porosity, pore size distribution etc.
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For the validation of the linear regression equations, a capillary water absorption coefficient measurement was performed at 15oC for all the examined materials. Also, a calculation of the water absorption coefficient was made, using the equations obtained from the linear regression analysis given in Figs 2, 3 and 4.
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The results from the comparison of the experimental values with the predicted values of the capillary water absorption coefficient are shown in Table 3.
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Table 3 Experimental and predicted estimation of the capillary water absorption coefficient A at 15oC.
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Temperature 15oC Predicted A-coefficient (kg m-2s-1/2) 0.249 0.188 0.087 9
Experimental A-coefficient (kg m-2s-1/2) 0.249 0.188 0.088
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0.076 0.169 0.100 0.139 0.102 0.067 0.063
0.077 0.169 0.101 0.141 0.102 0.068 0.064
From the above reported results is evident that experimental values of the A-coefficient are in very good agreement with the predicted ones using the equations given in Figs 2, 3 and 4. Furthermore, the equations given in Figs 2, 3 and 4 should be utilized to predict capillary water absorption coefficient at any other temperature which is in the experimental range of 15 to 30oC, and consequently, the aforementioned linear regression model can be utilized as a very useful tool for the design and simulation of the hydric behavior of the specific building materials examined in this work.
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An effort was made to compare the linear regression model with other models existing in the literature. Feng and Janssen (2016) took into account equation (3) and suggested that capillary water absorption coefficient Aw shall be estimated as following:
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Aw = C . [0.095.(T-273.15)+6.566]
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where C is a coefficient which is dependent only on the material microstructure, and can be calculated when the A-coefficient value at a specific temperature T is known.
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Following the methodology suggested in Feng and Janssen’s paper, the C coefficient was estimated from equation (5), using the Aw values at the temperature of 20oC for each material and the estimated results with their standard Deviation are illustrated in Table 4.
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Table 4 C-coefficient values with Standard Deviation, according to Feng and Janssen’s paper at 20oC.
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(5)
Materials BRI
C-coefficient (kg/m5/2) 0.030±0.001
BRM
0.024±0.002
SRH
0.015±0.001
SRY
0.010±0.001
mca20/80
0.021±0.001
mca25/75
0.009±0.001
mca30/70
0.019±0.002
mcb20/80
0.013±0.001
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0.008±0.001
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mcb30/70
0.008±0.001
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Afterwards, C-coefficient values were applied in equation (5) for each material and an estimation of Aw-coefficient values was made at the temperature of 30oC. Finally, a comparison was performed between Aw values estimated from equation (5) with the experimental Aw values at the temperature of 30oC, as measured in the current study. The Aw values estimated from equation (5) and the experimental Aw values with their Standard Deviations are shown in Table 5.
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Table 5 Comparison of the experimental A-coefficient values with those estimated from equation (5) at 30oC.
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Experimental Aw values ± SD (kg/m2 s1/2)
BRI
0.280±0.002
0.263±0.002
0.229±0.002
0.228±0.001
0.137±0.004
0.172±0.006
0.092±0.002
0.101±0.002
BRM SRH
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Aw values ± SD according to equation (5) (kg/m2 s1/2)
0.195±0.004
0.191±0.004
mca25/75
0.089±0.001
0.116±0.002
mca30/70
0.178±0.003
0.170±0.003
mcb20/80
0.118±0.002
0.117±0.002
mcb25/75
0.079±0.001
0.081±0.002
mcb30/70
0.072±0.001
0.073±0.001
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It is clearly reflected in Table 5 that in some cases (BRM, mca20/80, mcb20/80, mcb25/75 and mcb30/70), Aw estimated according to equation (5) is very close to the experimental results and the difference in values was under 4%. On the contrary, in some other cases (BRI, SRH, SRY, mca25/75 and mca30/70), the predicted Aw values exhibit a significant deviation from the experiment results, as the difference in values was above 4%. Therefore, although equation (5) gives adequate results for some materials, it cannot be widely applied for all building materials.
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ACCEPTED MANUSCRIPT Additionally, Hall and Hoff suggested an adequate model to predict the dependence of the sorptivity S with the temperature in all building materials. More specifically, they took into account the fact that viscosity η of the water falls more rapidly with increasing temperature than in the case of surface tension σ and they suggested that a change in temperature from 20oC to 30oC should cause an increase of (σ/η)1/2 for water and hence an increase of about 10.6% in sorptivity S of every building material [52]. In order to evaluate the aforementioned forecasts, an estimation of water sorptivity S at 20 and 30oC according to the equation (1) was performed, as well as an estimation of the % experimental change of S with its Standard Deviation (SD). The results are presented in Table 6.
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Table 6 Experimental % change of water sorptivity S from 20 to 30oC and its Standard Deviation for all the materials
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S30 − S20 (%) S 20 6.6±1.0 11.9±0.8 53.2±7.1 23.2±3.0 8.8±3.0 31.6±2.4 12.2±3.0 10.7±2.6 14.4±2.5 12.6±2.0
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It is evident from Table 6 that water sorptivity S increases with the temperature in all the examined materials. However, this increase is different for each material and depends on each material’s characteristics. Moreover, all generalizations regarding the influence of temperature on the capillary water absorption coefficient include high risk if they do not take into account each material’s microstructure and characteristics. Without a doubt, material microstructure is a very crucial issue which is strongly related to each material hydric properties and this issue has not adequately been investigated up to present.
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S30 (m/s1/2) (x10-4) 2.60 2.30 1.70 1.00 1.90 1.20 1.70 1.20 0.81 0.73
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BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
S20 (m/s1/2) (x10-4) 2.54 2.00 1.10 0.82 1.80 0.89 1.50 1.10 0.71 0.65
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CONCLUSIONS
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The effect of air temperature on the progress of capillary rise of various building materials was investigated. A linear relationship between capillary water absorption coefficient values and temperature was observed. Moreover, an evaluation of the capillary water absorption coefficient values at a temperature of 15oC was performed, in order to validate the linear dependency of the A-coefficient with temperature. Experimental values of the capillary water 12
ACCEPTED MANUSCRIPT absorption coefficient were found in very good agreement with the predicted ones for all of the examined materials. Hence, a prediction of the value of the A-coefficient in every air temperature which is in the temperature range examined in this work, using appropriate linear equations could be made. Moreover, the assumption of a constant water absorption coefficient, independent of temperature, that is often adopted, is clearly inaccurate.
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In addition, A-coefficient experimental values, as resulted by this research study, were compared with the values estimated through the equations suggested by other researchers. It was found that up to date models cannot predict the A-coefficient values adequately in all cases. This is because capillary water absorption coefficient is dependent not only on the hydric transport properties but it is also strongly influenced by the intrinsic properties of each building material. This dependence must be taken into account, through a simulation based on real experimental results and can be utilized as a useful tool for the design, simulation and decision-making community who use the capillary water absorption coefficient as a mean to characterize a building material and predict its hydric behavior.
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REFERENCES
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[1] Marcus Vitruvius Pollio: de Architectura, Book VI, chapter IV. [2] Torraca, G. (1981) Porous building materials. ICCROM, Rome.
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[3] Oxley, T.A., Gobert, E.G. (1998): Dampness in buildings: diagnosis, treatment, instruments, 2nd edn. Biddles Ltd Guilford and King’s Lynn, Great Britain. [4] Arnold, A. (1982): Rising damp and saline minerals. In: Fourth international congress on the deterioration and preservation of stone objects, Louisville, 11–28.
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[5] Karoglou M, Moropoulou A, Giakoumaki A, Krokida M. (2005): Capillary rise kinetics of some building materials, Journal of Colloid and Interface Science, 284, 260–264.
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[6] Moropoulou, A., Karoglou, M., Bakolas, A., Krokida M. and Maroulis, Z. B. (2014): Moisture Transfer Kinetics Building Materials and Components: Modeling, Experimental Data, Simulation. In: Drying and Wetting of Building Materials and Components. Springer International Publishing Switzerland. [7] Oliver A. (1997): Dampness in buildings. In: Douglas J, Sterling JS (eds) 2nd edn. Blackwell Science, Great Britain. [8] Connoly JD. (1993): Humidity and building materials. In: Rose WB, Tenwolde A (eds) Bugs, mold and rot II, proceedings of a workshop by the building environment and thermal envelope council of the National Institute of Building Sciences, Washington DC, NIBS, pp 29–36. [9] Mukhopadhyaya, P. and Kumaran, M. K. (2001): “Prediction of moisture response of wood frame walls using IRC’s advanced hygrothermal model (hygIRC),” 2nd Annual
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ACCEPTED MANUSCRIPT Conference on Durability and Disaster Mitigation in Wood-Frame Housing, Wisconsin, Madison, USA, 221-226. [10] Mukhopadhyaya, P., Kumaran, M. K., van Reenen, D. and Tariku F. (2001): “Influence of sheathing membrane and vapour barrier on hygrothermal response of stucco walls,” International Conference on Building Envelope Systems and (ICBEST), Ottawa, Canada, Vol. 1, 269-274.
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[11] Kumaran M. K., Mukhopadhyaya P., Cornick S. M., Lacasse, M. A., Maref W., Rousseau M., Nofal M., Quirt J. D. and Dalgliesh W. A. (2002): “A methodology to develop moisture management strategies for wood-frame walls in North America: application to stucco-clad walls,” 6th Nordic Building Physics Symposium, Trondheim, Norway.
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[12] Nofal, M., Straver, M. and Kumaran, M. K. (2001): “Comparison of four hygrothermal models in terms of long-term performance assessment of wood-frame constructions,” Proceedings of the 8th conference of Canadian building science - Solutions to moisture problems in building enclosures, Toronto, Canada, Straube J., (Ed.), 118-138.
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[13] Candanedo L, Derome D. (2005): Numerical simulation of water absorption in softwood. In: Ninth international IBPSA conference, Montréal, Canada. [14] Moonen, P. and Carmeliet, J. (2013): Modelling moisture transport in intact and fractured concrete. In: J. Weerheyn (ed.), Understanding the tensile properties of concrete, Woodhead Publishing Limited, Cambridge, UK.
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[15] Stuck H., Plagge R., Siegesmund S. (2013): Numerical modeling of moisture transport in sandstone: the influence of fabric and clay content, Environmental Earth Science, 69 (4), 1161. doi: 10.1007/s12665-013-2405-0
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[16] Ioannou I., Andreou A., Tsikouras B., Hatzipanagiotou K. (2009): Application of the Sharp Front Model to capillary absorption in a vuggy limestone. Engineering Geology, 105, 20-23. [17] Scheffler, G.A.; Plagge, R. (2010): A whole range hygric material model: modelling liquid and vapour transport properties in porous media, International Journal of Heat and Mass Transfer, 53, 286–296.
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[18] Guizzardi, M. , Derome, D., Carmeliet, J. (2016): Water uptake in clay brick at different temperatures: Experiments and numerical simulations, Journal of Building Physics, 39, 4, 373-389. [19] Kunzel H. (1995): Simultaneous heat and moisture transport in building components. PhD Thesis, Fraunhofer-IBP, Stuttgart. [20] Kubilay A, Derome D, Blocken B, et al. (2014): Numerical simulations of wind-driven rain on an array of low-rise cubic buildings and validation by field measurements, Building and Environment, 81, 283–295.
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ACCEPTED MANUSCRIPT [21] Chari, M. N., Shekarchi, M., Sobhani, J., Chari M. N. (2016): The effect of temperature on the moisture transfer coefficient of cement-based mortars: An experimental investigation, Construction and Building Materials, 102, 1, 306–317. [22] Walker, I.; Sherman, M.; Les, B. (2014): “Houses Are Dumb Without Smart Ventilation. ACEEE Summer Study on Energy Efficiency in Buildings.” Washington DC: ACEEE. at: http://aceee.org/files/proceedings/2014/data/papers/1-239.pdf.
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[23] Levinson, R. M.; Akbari, H. (2010): “Potential Benefits of Cool Roofs on Commercial Buildings: Conserving Energy, Saving Money, and Reducing Emission of Greenhouse Gases and Air Pollutants.” Energy Efficiency, 3(1), 53-109.
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[24] Martínez-Molina, A.; Tort-Ausina, I.; Cho, S.; Vivancos, J.L. (2016): Energy efficiency and thermal comfort in historic buildings: A review, Renewable and Sustainable Energy Reviews, 61, 70–85.
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[25] Chenari, B.; Carrilho, J. D.; da Silva, M. G. (2016): Towards sustainable, energy-efficient and healthy ventilation strategies in buildings: A review, Renewable and Sustainable Energy Reviews, 59, 1426–1447. [26] Litti, G.; Khoshdel, S.; Audenaert, A.; Braet, J. (2015): Hygrothermal performance evaluation of traditional brick masonry in historic buildings, Energy and Buildings, 105, 393411.
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[27] Ismail, M.; Yew, C. K.; Muhammad B. (2016): Life-span prediction of abandoned reinforced concrete residential buildings, Construction and Building Materials, 112, 10591065. [28] Nicolae, B.; Vlad B. G. (2015): Life cycle analysis in refurbishment of the buildings as intervention practices in energy saving, Energy and Buildings, 86, 74-85.
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[29] Ruparathna, R.; Hewage, K.; Sadiq, R. (2016): Improving the energy efficiency of the existing building stock: A critical review of commercial and institutional buildings, Renewable and Sustainable Energy Reviews, 53, 1032-1045. [30] ASHRAE Standard 62: “Ventilation for Acceptable Indoor Air Quality”.
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[31] Environmental Protection Agency. Indoor Air Quality (IAQ). EPA, 2014. [32] Environmental Protection Agency (EPA). “Energy Savings Plus Health: Indoor Air Quality Guidelines for School Building Upgrades.” Washington, DC, 2014. at: http://www.epa.gov/iaq/schools/pdfs/Energy_Savings_Plus_Health_Guideline.pdf. [33] Lourenço, P. B.; Luso, E.; Almeida M. G. (2006): Defects and moisture problems in buildings from historical city centres: a case study in Portugal, Building and Environment, 41, 2, 223-234. [34] Pietrzyk K. (2015): A systemic approach to moisture problems in buildings for mould safety modelling, Building and Environment, 86, 50-60.
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ACCEPTED MANUSCRIPT [35] Carrer, P.; Wargocki, P.; Fanetti, A.; Bischof, W.; Fernandes, E.; Hartmann, T.; Kephalopoulos, S.; Palkonen, S.; Seppänen O. (2015): What does the scientific literature tell us about the ventilation–health relationship in public and residential buildings?, Building and Environment, 94, 1, 273-286.
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[36] Huang, K.T.; Huang, W.P.; Lin, T.P.; Hwang R.L. (2015): Implementation of green building specification credits for better thermal conditions in naturally ventilated school buildings, Building and Environment, 86, 141-150. [37] Bomberg, M., Pazera, M. and Plagge, R. (2005). Analysis of Selected Water Absorption Coefficient Measurements, Journal of Thermal Envelope and Building Science, 28: 227–243.
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[38] Roels, S., Carmeliet, J., Hens, H., Adan, O., Brocken, H., Cerny, R., Pavlik, Z., Hall, C., Kumaran, K., Pel, L. and Plagge, R. (2004): Interlaboratory Comparison of Hygric Properties of Porous Building Materials, Journal of Thermal Envelope and Building Science, 27: 307– 325.
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[39] Vejmelkova, E.; Pavlikova, M.; Jerman, M. and Cerny, R. Free Water Intake as Means of Material Characterization. Journal of Building Physics, Vol. 33, No. 1-July 2009. [40] Aggelakopoulou, E., Bakolas, A. and Moropoulou, A. (2011): Hygric Properties of Lime Based Mortars used for Restoration Interventions on Historic Structures, XII DBMC, Porto, Portugal.
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[41] Raimondo, M., Dondi, M., Gardini, D., Guarini, G., Mazzanti, F. (2009): Predicting the initial rate of water absorption in clay bricks, Construction and Building Materials, 23: 2623– 2630. [42] Tsunazawa, Y., Yokoyama, T. and Nishiyama, N. (2016): An experimental study on the rate and mechanism of capillary rise in sandstone, Progress in Earth and Planetary Science, 3,8.
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[43] Reinhardt H-W, Jooss M. (1998): Permeability, Diffusion, and Capillary Absorption of Concrete at Elevated Temperature in the Service Range, Otto-Graf-Journal, 34-47. [44] Gummerson, R.J., Hall, C. and Hoff, W. D. (1980): Water movement in porous building materials II. Hydraulic suction and sorptivity of brick and other masonry materials, Building and Environment, 15, 101-108.
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[45] Mukhopadhyaya, P., Kumaran, K., Normandin, N. and Goudreau, P. (2002): Effect of Surface Temperature on Water Absorption Coefficient of Building Materials, Journal of Thermal Envelope and Building Science, 26, 179–195. [46] C. Feng, H. Janssen (2016): Hygric properties of porous building materials (II): Analysis of temperature influence, Building and Environment, doi: 10.1016/ j.buildenv.2016.01.016. [47] Philip, J.R. (1957). The Theory of Infiltration: 4. Sorptivity and Algebraic Infiltration [48] Martys, N.S. Ferraris, C.F. (1997): Capillary transport in mortars and concrete, Cement and Concrete Research, 27 (5), 747–760. 16
ACCEPTED MANUSCRIPT [49] Pia, G., Sassoni, E., Franzoni, E., Sanna, U. (2014): Predicting capillary absorption of porous stones by a procedure based on an intermingled fractal units model, International Journal of Engineering Science, 82, 196–204. [50] Hall, C. (1989): Water Sorptivity of Mortars and Concretes: A Review, Magazine of Concrete Research, 41, 51–61.
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[51] Hall, C. (1977): Water Movement in Porous Building Materials–I. Unsaturated Flow Theory and its Application, Building and Environment, 12, 117–125. [52] Hall, C. and Hoff, W.D. (2002): Water Transport in Brick, Stone and Concrete, Taylor & Francis Group., London.
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[53] Kumaran, M.K. (1999): Moisture Diffusivity of Building Materials from Water Absorption Measurements, Journal of Thermal Envelope and Building Science, 22, 349–355. [54] Nambiar, E.K.K. and Ramamurthy, K. (2007): Sorption Characteristics of Foam Concrete, Cement and Concrete Research, 37, 1341–1347.
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[55] EN 1925 (1999). Natural stone test methods. Determination of water absorption coefficient by capillarity. [56] EN 1015-18 (2002): Methods of test for mortar for masonry - Part 18: Determination of water absorption coefficient due to capillarity action of hardened mortar.
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[57] EN 13057 (2002): Products and systems for the protection and repair of concrete structures - Test methods. Determination of resistance of capillary absorption.
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[58] Normal 11/85 (1985): Assorbimento d’ acqua per capillarità – Coefficiente di assorbimento capillare, CNR-ICR.
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[59] UNI 10859 (2000): Cultural Heritage – Natural and Artificial Stones - Determination of Water Absorption by Capillarity.
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[60] EN 15801 (2009): Conservation of cultural property - Test methods. Determination of water absorption by capillarity. [61] EN 480-5 (2005): Admixtures for concrete, mortar and grout - Test methods. Determination of capillary absorption. [62] ISO 15148 (2002): Hygrothermal performance of building materials and products Determination of water absorption coefficient by partial immersion. [63] EN 459-1 (2010): Building lime. Definitions, specifications and conformity criteria. [64] Togkalidou, T., Karoglou, M., Bakolas, A., Glakoumaki, A., Moropoulou A. (2013): Correlation of water vapor permeability with microstructure characteristics of building materials using robust chemometrics, Transport in Porous Media, 99, 273–295.
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ACCEPTED MANUSCRIPT Table 1: Materials characteristics Materials
Description
1 2 3 4 5 6 7 8 9 10
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
Typical solid clay brick Traditional handmade clay brick Rhodes quarry stone Rethymno quarry stone 20% NHL 2 & 80% river sand 25% NHL 2 & 75% river sand 30% NHL 2 & 70% river sand 20% NHL 3.5 & 80% river sand 25% NHL 3.5 & 75% river sand 30% NHL 3.5 & 70% river sand
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RI PT
No
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Table 2 Water absorption coefficient Aw (kg/m2s1/2) values according to the two tangents method for building materials at 20oC and its Standard Deviation (SD) Materials Aw (kg/m2 s1/2) (20 oC)
SD
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
0.002 0.002 0.005 0.002 0.004 0.001 0.003 0.002 0.001 0.001
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0.252 0.206 0.123 0.083 0.176 0.106 0.160 0.106 0.071 0.065
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Table 3 Experimental and predicted estimation of the capillary water absorption coefficient A at 15oC.
Materials
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
Temperature 15oC Predicted A-coefficient (kg m-2s-1/2) 0.249 0.188 0.087 0.076 0.169 0.100 0.139 0.102 0.067 0.063
Experimental A-coefficient (kg m-2s-1/2) 0.249 0.188 0.088 0.077 0.169 0.101 0.141 0.102 0.068 0.064
ACCEPTED MANUSCRIPT Table 4 C-coefficient values with Standard Deviation, according to Feng and Janssen’s paper at 20oC. C-coefficient (kg/m5/2) 0.030±0.001
BRM
0.024±0.002
SRH
0.015±0.001
SRY
0.010±0.001
mca20/80
0.021±0.001
mca25/75
0.009±0.001
mca30/70
0.019±0.002
mcb20/80
0.013±0.001
mcb30/70
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mcb25/75
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Materials BRI
0.008±0.001 0.008±0.001
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Table 5 Comparison of the experimental A-coefficient values with those estimated from equation (5) at 30oC. Aw values according to equation (5) (kg/m2 s1/2)
Experimental Aw values ± SD (kg/m2 s1/2)
0.280±0.002
0.263±0.002
BRM
0.229±0.002
0.228±0.001
SRH
0.137±0.004
0.172±0.006
SRY
0.092±0.002
0.101±0.002
mca20/80
0.195±0.004
0.191±0.004
mca25/75
0.089±0.001
0.116±0.002
mca30/70
0.178±0.003
0.170±0.003
mcb20/80
0.118±0.002
0.117±0.002
mcb25/75
0.079±0.001
0.081±0.002
mcb30/70
0.072±0.001
0.073±0.001
Materials
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BRI
ACCEPTED MANUSCRIPT Table 6 Experimental % change of water sorptivity S from 20 to 30oC and its Standard Deviation for all the materials
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BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
S 30 − S 20 (%) S 20 6.6±1.0 11.9±0.8 53.2±7.1 23.2±3.0 8.8±3.0 31.6±2.4 12.2±3.0 10.7±2.6 14.4±2.5 12.6±2.0
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MATERIALS
S30 (m/s1/2) (x10-4) 2.60 2.30 1.70 1.00 1.90 1.20 1.70 1.20 0.81 0.73
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S20 (m/s1/2) (x10-4) 2.54 2.00 1.10 0.82 1.80 0.89 1.50 1.10 0.71 0.65
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ACCEPTED MANUSCRIPT
Figure 1: Cumulative mass of capillary water uptake versus time for different building materials.
ACCEPTED MANUSCRIPT BRI
0.30
BRM
SRH
SRY y = 0.0009x + 0.2353 R² = 0.996
y = 0.0026x + 0.1493 R² = 0.9933
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0.20
0.15
y = 0.0056x + 0.0036 R² = 0.9988
0.10
y = 0.0016x + 0.0513 R² = 0.9933
0.05
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Capillary Rise Coefficient (kg /m2s1/2 )
0.25
0.00
25 Temperature (oC)
M AN U
20
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Figure 2: Water absorption coefficients at various temperatures for bricks and stones mca20/80
mca30/70
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0.20
EP
0.15
0.10
AC C
Capillary Rise Coefficient (kg/m2 s1/2)
0.25
mca25/75
y = 0.0015x + 0.1457 R² = 0.9962
y = 0.002x + 0.1089 R² = 0.9828 y = 0.001x + 0.0856 R² = 0.9847
0.05
0.00
20
25 Temperature (oC)
Figure 3: Water absorption coefficients at various temperatures for mca mortars
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ACCEPTED MANUSCRIPT mcb20/80
mcb 25/75
mcb30/70
y = 0.001x + 0.0867 R² = 0.9953
0.10
RI PT
y = 0.0009x + 0.0539 R² = 0.9957
y = 0.0006x + 0.0546 R² = 0.9956
0.05
SC
Capillary Rise Coefficient (kg/m2 s1/2)
0.15
M AN U
0.00 20
25 Temperature (oC)
30
AC C
EP
TE D
Figure 4: Water absorption coefficients at various temperatures for mcb mortars
ACCEPTED MANUSCRIPT
Highlights: • The effect of temperature on capillary water absorption coefficient of various building materials was investigated. • Capillary rise tests were carried out at different air temperatures and a linear correlation between capillary rise coefficient and temperature was made.
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• An evaluation was made comparing our linear regression equations with other researchers’ models.
S0360-1323(16)30262-1
DOI:
10.1016/j.buildenv.2016.07.008
Reference:
BAE 4563
To appear in:
Building and Environment
Received Date: 18 March 2016 Revised Date:
12 July 2016
Accepted Date: 12 July 2016
Please cite this article as: Karagiannis N, Karoglou M, Bakolas A, Moropoulou A, Effect of temperature on water capillary rise coefficient of building materials, Building and Environment (2016), doi: 10.1016/ j.buildenv.2016.07.008. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT 2
EFFECT OF TEMPERATURE ON WATER CAPILLARY RISE COEFFICIENT OF BUILDING MATERIALS
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N. Karagiannis1, M. Karoglou1, A. Bakolas1*, A. Moropoulou1
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ABSTRACT
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Dept. of Materials Science and Engineering, School of Chemical Engineering, National Technical University of Athens, Zografou Campus 15780, Athens, Greece * tel:+30210772715, fax:+302107723215, email: [email protected]
The presence of water is one of the main decay factors in buildings. Capillarity is the most usual mechanism of water penetration into building materials in liquid phase. Free capillary water uptake experiment, utilized for the estimation of the capillary rise coefficient Aw, a crucial hygrothermal materials property, is widely used for the characterization of building materials.
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The main aim of this work was to investigate the effect of temperature on the capillary water absorption coefficient. Different categories of building materials such as stones, bricks and mortars of various compositions, for three different levels of air temperature (20, 25 and 30 °C) were studied. A linear dependence of the capillary water absorption coefficient with temperature was found for all examined materials, however with different slope values for each material. In order to assess the validity of the linear dependence of the capillary water absorption coefficient on the temperature, capillary rise experiments were performed at the temperature of 15oC and a very good agreement between experimental and predicted values of the Aw was obtained. Finally, other models correlating the capillary water absorption coefficient Aw with temperature suggested by other researchers were evaluated.
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KEYWORDS
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Building materials, capillary rise, temperature, sorptivity.
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INTRODUCTION
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The role of water in the mechanism of deterioration of porous building materials has been recognized from ancient times [1]. Water enters building materials in water or vapor phase but the major moisture transfer mechanisms are at liquid phase [2]. Water penetrates into a building material’s pores with several ways. Potential sources of water are: the ground, the environment (rain, sea, water vapor etc.), possible water sewage leakages, use of water for the production of building materials, interventions with the use of extensive quantities of water, salts’ hygroscopicity etc. [3-5]. The most common way by which ground water can rise into the pore structure of a building material is by force of capillarity. Capillary rise is, by definition, the upward vertical movement of ground water through a permeable wall structure causing the appearance of rising damp into the structure.
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ACCEPTED MANUSCRIPT Building materials usually contain an amount of physically bound water without affecting their durability. But if the material’s moisture content is above a certain percentage, the deterioration effect of moisture is activated causing an amount of physical, chemical and biological effects [6-7].
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The knowledge of the water movement within a building material is of great importance to determine the degradation mechanism in question and moisture migration is by far the most important control function to be addressed. Moisture related problems in buildings are common and broadly vary in types and consequences affecting their overall durability [8]. Illustrating the moisture impact to buildings durability, numerous hygrothermal models have been developed [9-21]. Heat and moisture flow into or out of a building have also a significant impact on the insulating properties of the building envelope and on the energy efficiency of the construction [22-26] decreasing the life-time of the building [27-29]. Furthermore, as many people spend most of their time indoors, moisture can affect the quality of indoor air and consequently their health and comfort [30-36].
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Describing the capillary rise phenomenon, several parameters related with the hydric properties of porous building materials have been introduced and widely used. Capillary water absorption coefficient Aw, or A-coefficient, is one of the most important features of a building material because it governs the liquid moisture movement through the capillary pores into it. A-coefficient expresses the rate of absorption of water due to capillary forces for building materials and is a measure of the tendency of a material to absorb and transmit water by capillarity. Capillary water absorption coefficient has a significant impact and many applications not only at the traditional but at the contemporary building materials, thus, it must be taken into consideration when determining the hydrometric properties of the material.
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Capillary water absorption coefficient Aw is also connected with water sorptivity S coefficient which is another equally important material property. Water sorptivity S is another way to express the tendency of a material to absorb and transmit water by capillarity and it is connected with the water absorption coefficient Aw of a building material through the equation:
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Aw = S ρw
(1)
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1 2 3 4
30
where ρw is the density of the water.
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In recent years, many researchers dealt with the estimation of the capillary water absorption coefficient [37-42]. Furthermore, several studies have been carried out regarding the influence of the temperature on hydric properties of building materials. Reinhardt and Jooss examined the influence of temperature on capillary rise coefficient of concretes with different types of cement and aggregates, at three different ambient temperatures. They measured the capillary absorption coefficients of 9 kinds of concrete in the temperature range of 20-80°C and they found that the capillary absorption coefficient increased almost linearly with temperature [43]. Gummerson et al. made measurements of the sorptivity of one clay brick for four organic liquids and for water at several temperatures in the range 5-36°C finding a linear dependence of the sorptivity with the temperature [44]. Mukhopadhyaya et al. determined the water 2
ACCEPTED MANUSCRIPT absorption coefficients of three commonly used building materials, at four different water temperature levels, while the specimen remained at ambient room temperature [45]. They found that the surface temperature of the sample has an effect on the water absorption coefficient of materials with a small A-coefficient while for materials with high A-coefficients the temperature impact is very small. Feng and Janssen also conducted measurements on the hygric properties of autoclaved aerated concrete, calcium silicate board and ceramic brick in the temperature range of 10-40°C. They measured the capillary water absorption coefficient and they found that capillary absorption coefficient is strongly temperature-dependent and it can be estimated from a linear equation for each building material [46].
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As far as the sorptivity coefficient, Philip first introduced the term of sorptivity S in soil science and since then many researchers have adopted it in their research [47-49]. Hall used it for building materials and gathered a large amount of data on sorptivity [50-52]. Over the last 30 years, the water sorptivity measurement has been considered to be a well-established method for liquid water transport characterization, and was regularly used for a variety of building materials [37], [38], [43], [53], [54]. Presenting the sorptivity S as a quantity deriving from the unsaturated flow theory, Hall and Hoff suggested that water sorptivity S of a building material should be given from the following equation:
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(2)
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where σ is the surface tension of the water, η is the water viscosity and S is the intrincic sorptivity which depends on each material’s characteristics and is independent of temperature [52]. The capillary absorption of liquid water by a building material depends not only on the hydric properties of water (surface tension σ and viscosity η) but also on the microstructure of the material. The dependence of temperature on the surface tension and viscosity of the water indicate that sorptivity S and thus, capillary water absorption coefficient Aw, can be written as [44], [46], [52]:
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S = (σ/η)1/2 S
Aw ∝ (σ/η)1/2
(3)
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For the estimation of the capillary water absorption coefficient of building materials, many European and international standards and recommendations are used. The majority of these standards are related to building materials and materials used in cultural heritage protection. European standard EN 1925 refers to natural stones [55], while EN 1015-18 refers to hardened mortars [56]. European standard EN 13057 describes the measurement of the capillary water absorption of hardened concrete [57]. Normal 11/85 refers to materials and conservation interventions of cultural heritage and it was replaced by the UNI 10859 standard, which refers to natural and artificial stones [58], [59]. EN 15801 refers to porous inorganic materials used for and constituting cultural property and the European standard EN 480-5, describes the determination of the water capillary absorption coefficient of concrete, mortars and grouts [60], [61]. Finally, EN ISO 15148 is applied in the determination of the water absorption 3
ACCEPTED MANUSCRIPT coefficient by partial immersion with no temperature gradient [62]. This method is suitable for renders or coatings tested in conjunction with the substrate on which they are normally mounted.
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However, regarding the experimental conditions, these European and International standards do not take into account environmental factors, such as air temperature and air humidity. Specifically, the describing procedure indicates that the specimens shall be kept in a room temperature of 20 ± 5oC [55]. Additionally, several established studies refer to the European standards above but none of them consider the dependence of the A-coefficient on temperature. While the experimental procedure estimating the capillary water absorption coefficient of building materials remains unquestionable, the comparison of A-coefficient values is difficult mostly because of the different estimation methods. Consequently, there is an argument among researchers regarding the dependence or not of the A-coefficient with the environmental parameters and especially with temperature. One main reason for such an argument is the unavailability of data that would define the moisture transport properties of common building materials as a function of temperature.
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The aim of this work was firstly to investigate the effect of the temperature on the capillary water absorption coefficient Aw of a variety of building materials. For this reason, the capillary water absorption coefficient was measured at three different ambient temperatures (20, 25 and 30oC) and a linear model describing the effect of temperature on the capillary water absorption coefficient was found. Moreover, other researchers’ models were examined in order to evaluate the validity of these models.
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MATERIALS AND METHODS
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In the present study, three categories of building materials were studied (bricks, stones, and natural hydraulic mortars). Bricks are symbolized with codes starting with the letter “B”, stones with “S” and mortars with “m”. More specifically, two different types of clay brick have been investigated. One was a typical solid clay brick (BRI) and the other one was a traditional handmade clay brick (BRM). Two sedimentary quarry stones originated from Rhodes Island (SRH) and from Rethymno, Crete Island (SRY) respectively were the stones investigated. The mortars examined were prepared by using two different types of natural hydraulic lime (NHL2 & NHL3.5) in accordance to EN 459-1 [63], in 3 different binder/aggregate ratios. The specific mortars choice was made because mca and mcb mortars are different building materials, with different binder type and with different b/a ratio. These mortars are widely used at the restoration of traditional and historic buildings as well as for the construction of sustainable buildings. The materials dimensions were 5×5×5±0.1 cm3. The materials characteristics are summarized in Table 1.
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Table 1: Materials characteristics
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TE D
M AN U
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1 2 3
No
Materials
Description
1 2 3
BRI BRM SRH
Typical solid clay brick Traditional handmade clay brick Rhodes quarry stone 4
ACCEPTED MANUSCRIPT SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
4 5 6 7 8 9 10
Rethymno quarry stone 20% NHL 2 & 80% river sand 25% NHL 2 & 75% river sand 30% NHL 2 & 70% river sand 20% NHL 3.5 & 80% river sand 25% NHL 3.5 & 75% river sand 30% NHL 3.5 & 70% river sand
RI PT
1
In order to investigate the dependence of the capillary water absorption coefficient on the temperature, a series of capillary rise tests were carried out at 20oC as the majority of the standards and recommendations suggest. Afterwards, a series of capillary rise tests were performed at 25°C and 30°C for all the examined materials. All the capillary rise experiments were performed at controlled relative humidity conditions. The water temperature was determined about 2±0.5oC lower than the air temperature while the relative humidity was 45 ± 5% during the experiments. At least, three specimens of each material were tested for each one of the selected air temperatures. Each specimen was tested three times. The side surfaces of each specimen were sealed with a transparent tight epoxy sealant, which did not significantly penetrate into the pore network of the material. The water level was kept constant and each specimen was partially immersed, at a depth of 3±0.5 mm above the highest point on the base of the specimen, while an effort was made to ensure that air bubbles were not trapped below the specimen.
15 16 17 18 19 20 21 22 23 24 25
The experimental setup for the capillary rise experiment was quite common and it was divided in two stages [50]. During the first stage, the position of the waterfront was gradually approaching the opposite side of the sample and the water intake was governed by capillary and viscous forces. The quantity of the absorbed water was measured at standard time intervals by weighing the specimen. During the second stage, the waterfront had reached the upper end of the sample and no other increase in specimen weight was observed because moisture content had reached the capillary moisture content wcap.. The capillary water absorption coefficient was determined according to Italian Normal 11/85 in which the two tangents method is described. According to this method, the capillary water absorption coefficient should be determined according to the following equation:
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Aw=
M*
(4)
t*
where Aw (kg/m2s1/2) is the capillary water absorption coefficient, M* (kg/m2) is the asymptotic value of the absorbed water per unit area of the sample (water reach the capillary moisture content) and t* (s) is the abscissa of the point of intersection between the straight line passing through the asymptote and the tangent to the straight portion of the curve measured in seconds.
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ACCEPTED MANUSCRIPT 1
RESULTS AND DISCUSSION
2 3 4 5 6 7
In Table 2 the capillary water absorption coefficient values according to the two tangents method, at the air temperature of 20oC are presented for all examined materials.
0.002 0.002 0.005 0.002 0.004 0.001 0.003 0.002 0.001 0.001
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Bricks presented the highest capillary water absorption coefficient values (>0.20) and they are the most hydrophilic of the examined materials. As far as mortars, they exhibit different Aw values because of their different binder type and their different mix design. The main results of the capillary rise kinetics for all the examined materials at the temperatures of 20, 25 and 30oC are summarized in Fig. 1. The values plotted refer to the same specimen of each material at three different temperatures. From the diagrams in Fig.1, a dependence of the A-coefficient with the temperature is observed in all the samples. More specifically, the water absorption coefficient increases with the increase of temperature. In the case of BRI and BRM bricks kinetics, the initial part is very well defined by a straight line at all the temperatures and their curve shape is the same at every temperature examined. Moreover, BRI brick exhibits higher capillary saturation moisture content than BRM brick. SRH stones exhibit a first stage not sufficiently defined by a straight line (see Fig. 1). SRY stones present lower A-coefficient values than SRH stones [64]. Some irregularities are also observed in the curve shape of some mortars (mca25/75, mcb25/75 and mcb30/70 mortars) probably due to their different microstructure.
AC C
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
0.252 0.206 0.123 0.083 0.176 0.106 0.160 0.106 0.071 0.065
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BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
SD
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Materials Aw (kg/m2 s1/2) (20 oC)
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Table 2 Water absorption coefficient Aw (kg/m2s1/2) values according to the two tangents method for building materials at 20oC and its Standard Deviation (SD)
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1 2
Figure 1: Cumulative mass of capillary water uptake versus time for different building materials. 7
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Α linear regression analysis between Aw values and temperature T was conducted and the extracted equations with their R-squared values are presented in Figs. 2, 3 and 4. BRI
0.30
BRM
SRH
SRY y = 0.0009x + 0.2353 R² = 0.996
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y = 0.0026x + 0.1493 R² = 0.9933
0.20
0.15
y = 0.0056x + 0.0036 R² = 0.9988
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0.10
0.05
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Capillary Rise Coefficient (kg /m2s1/2 )
0.25
0.00 20
25 Temperature (oC)
3 4
y = 0.0016x + 0.0513 R² = 0.9933
30
Figure 2: Water absorption coefficients at various temperatures for bricks and stones
0.25
mca30/70
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0.20
y = 0.0015x + 0.1457 R² = 0.9962
0.15
y = 0.002x + 0.1089 R² = 0.9828
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Capillary Rise Coefficient (kg/m2 s1/2)
mca25/75
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mca20/80
0.10
y = 0.001x + 0.0856 R² = 0.9847
0.05
0.00 20
5 6
25 Temperature (oC)
30
Figure 3: Water absorption coefficients at various temperatures for mca mortars
8
ACCEPTED MANUSCRIPT mcb20/80
mcb 25/75
mcb30/70
y = 0.001x + 0.0867 R² = 0.9953
0.10
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y = 0.0009x + 0.0539 R² = 0.9957
y = 0.0006x + 0.0546 R² = 0.9956
0.05
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Capillary Rise Coefficient (kg/m2 s1/2)
0.15
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0.00 20
25 Temperature (oC)
1
30
Figure 4: Water absorption coefficients at various temperatures for mcb mortars
3 4 5 6 7 8 9
According to the results presented in Fig. 2, 3 and 4, it is evident that the capillary water absorption coefficient exhibits a linear dependence with temperature in all samples which indicates the dependence of the Aw on the hydric properties of the water (see equation (3)). It is also apparent from Fig. 2, 3 and 4 that there is a slope differentiation for every building material which suggests that Aw is also dependent on the intrinsic properties of each material such as porosity, pore size distribution etc.
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For the validation of the linear regression equations, a capillary water absorption coefficient measurement was performed at 15oC for all the examined materials. Also, a calculation of the water absorption coefficient was made, using the equations obtained from the linear regression analysis given in Figs 2, 3 and 4.
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The results from the comparison of the experimental values with the predicted values of the capillary water absorption coefficient are shown in Table 3.
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Table 3 Experimental and predicted estimation of the capillary water absorption coefficient A at 15oC.
AC C
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TE D
2
Materials BRI BRM SRH
Temperature 15oC Predicted A-coefficient (kg m-2s-1/2) 0.249 0.188 0.087 9
Experimental A-coefficient (kg m-2s-1/2) 0.249 0.188 0.088
ACCEPTED MANUSCRIPT SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
0.076 0.169 0.100 0.139 0.102 0.067 0.063
0.077 0.169 0.101 0.141 0.102 0.068 0.064
From the above reported results is evident that experimental values of the A-coefficient are in very good agreement with the predicted ones using the equations given in Figs 2, 3 and 4. Furthermore, the equations given in Figs 2, 3 and 4 should be utilized to predict capillary water absorption coefficient at any other temperature which is in the experimental range of 15 to 30oC, and consequently, the aforementioned linear regression model can be utilized as a very useful tool for the design and simulation of the hydric behavior of the specific building materials examined in this work.
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An effort was made to compare the linear regression model with other models existing in the literature. Feng and Janssen (2016) took into account equation (3) and suggested that capillary water absorption coefficient Aw shall be estimated as following:
12
Aw = C . [0.095.(T-273.15)+6.566]
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where C is a coefficient which is dependent only on the material microstructure, and can be calculated when the A-coefficient value at a specific temperature T is known.
15 16 17
Following the methodology suggested in Feng and Janssen’s paper, the C coefficient was estimated from equation (5), using the Aw values at the temperature of 20oC for each material and the estimated results with their standard Deviation are illustrated in Table 4.
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Table 4 C-coefficient values with Standard Deviation, according to Feng and Janssen’s paper at 20oC.
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(5)
Materials BRI
C-coefficient (kg/m5/2) 0.030±0.001
BRM
0.024±0.002
SRH
0.015±0.001
SRY
0.010±0.001
mca20/80
0.021±0.001
mca25/75
0.009±0.001
mca30/70
0.019±0.002
mcb20/80
0.013±0.001
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mcb25/75
0.008±0.001
2
mcb30/70
0.008±0.001
3
Afterwards, C-coefficient values were applied in equation (5) for each material and an estimation of Aw-coefficient values was made at the temperature of 30oC. Finally, a comparison was performed between Aw values estimated from equation (5) with the experimental Aw values at the temperature of 30oC, as measured in the current study. The Aw values estimated from equation (5) and the experimental Aw values with their Standard Deviations are shown in Table 5.
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Table 5 Comparison of the experimental A-coefficient values with those estimated from equation (5) at 30oC.
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Experimental Aw values ± SD (kg/m2 s1/2)
BRI
0.280±0.002
0.263±0.002
0.229±0.002
0.228±0.001
0.137±0.004
0.172±0.006
0.092±0.002
0.101±0.002
BRM SRH
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SRY
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Materials
Aw values ± SD according to equation (5) (kg/m2 s1/2)
0.195±0.004
0.191±0.004
mca25/75
0.089±0.001
0.116±0.002
mca30/70
0.178±0.003
0.170±0.003
mcb20/80
0.118±0.002
0.117±0.002
mcb25/75
0.079±0.001
0.081±0.002
mcb30/70
0.072±0.001
0.073±0.001
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mca20/80
It is clearly reflected in Table 5 that in some cases (BRM, mca20/80, mcb20/80, mcb25/75 and mcb30/70), Aw estimated according to equation (5) is very close to the experimental results and the difference in values was under 4%. On the contrary, in some other cases (BRI, SRH, SRY, mca25/75 and mca30/70), the predicted Aw values exhibit a significant deviation from the experiment results, as the difference in values was above 4%. Therefore, although equation (5) gives adequate results for some materials, it cannot be widely applied for all building materials.
11
ACCEPTED MANUSCRIPT Additionally, Hall and Hoff suggested an adequate model to predict the dependence of the sorptivity S with the temperature in all building materials. More specifically, they took into account the fact that viscosity η of the water falls more rapidly with increasing temperature than in the case of surface tension σ and they suggested that a change in temperature from 20oC to 30oC should cause an increase of (σ/η)1/2 for water and hence an increase of about 10.6% in sorptivity S of every building material [52]. In order to evaluate the aforementioned forecasts, an estimation of water sorptivity S at 20 and 30oC according to the equation (1) was performed, as well as an estimation of the % experimental change of S with its Standard Deviation (SD). The results are presented in Table 6.
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Table 6 Experimental % change of water sorptivity S from 20 to 30oC and its Standard Deviation for all the materials
13
21
S30 − S20 (%) S 20 6.6±1.0 11.9±0.8 53.2±7.1 23.2±3.0 8.8±3.0 31.6±2.4 12.2±3.0 10.7±2.6 14.4±2.5 12.6±2.0
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It is evident from Table 6 that water sorptivity S increases with the temperature in all the examined materials. However, this increase is different for each material and depends on each material’s characteristics. Moreover, all generalizations regarding the influence of temperature on the capillary water absorption coefficient include high risk if they do not take into account each material’s microstructure and characteristics. Without a doubt, material microstructure is a very crucial issue which is strongly related to each material hydric properties and this issue has not adequately been investigated up to present.
AC C
14 15 16 17 18 19 20
S30 (m/s1/2) (x10-4) 2.60 2.30 1.70 1.00 1.90 1.20 1.70 1.20 0.81 0.73
TE D
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
S20 (m/s1/2) (x10-4) 2.54 2.00 1.10 0.82 1.80 0.89 1.50 1.10 0.71 0.65
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CONCLUSIONS
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The effect of air temperature on the progress of capillary rise of various building materials was investigated. A linear relationship between capillary water absorption coefficient values and temperature was observed. Moreover, an evaluation of the capillary water absorption coefficient values at a temperature of 15oC was performed, in order to validate the linear dependency of the A-coefficient with temperature. Experimental values of the capillary water 12
ACCEPTED MANUSCRIPT absorption coefficient were found in very good agreement with the predicted ones for all of the examined materials. Hence, a prediction of the value of the A-coefficient in every air temperature which is in the temperature range examined in this work, using appropriate linear equations could be made. Moreover, the assumption of a constant water absorption coefficient, independent of temperature, that is often adopted, is clearly inaccurate.
6 7 8 9 10 11 12 13 14
In addition, A-coefficient experimental values, as resulted by this research study, were compared with the values estimated through the equations suggested by other researchers. It was found that up to date models cannot predict the A-coefficient values adequately in all cases. This is because capillary water absorption coefficient is dependent not only on the hydric transport properties but it is also strongly influenced by the intrinsic properties of each building material. This dependence must be taken into account, through a simulation based on real experimental results and can be utilized as a useful tool for the design, simulation and decision-making community who use the capillary water absorption coefficient as a mean to characterize a building material and predict its hydric behavior.
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REFERENCES
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[60] EN 15801 (2009): Conservation of cultural property - Test methods. Determination of water absorption by capillarity. [61] EN 480-5 (2005): Admixtures for concrete, mortar and grout - Test methods. Determination of capillary absorption. [62] ISO 15148 (2002): Hygrothermal performance of building materials and products Determination of water absorption coefficient by partial immersion. [63] EN 459-1 (2010): Building lime. Definitions, specifications and conformity criteria. [64] Togkalidou, T., Karoglou, M., Bakolas, A., Glakoumaki, A., Moropoulou A. (2013): Correlation of water vapor permeability with microstructure characteristics of building materials using robust chemometrics, Transport in Porous Media, 99, 273–295.
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ACCEPTED MANUSCRIPT Table 1: Materials characteristics Materials
Description
1 2 3 4 5 6 7 8 9 10
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
Typical solid clay brick Traditional handmade clay brick Rhodes quarry stone Rethymno quarry stone 20% NHL 2 & 80% river sand 25% NHL 2 & 75% river sand 30% NHL 2 & 70% river sand 20% NHL 3.5 & 80% river sand 25% NHL 3.5 & 75% river sand 30% NHL 3.5 & 70% river sand
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Table 2 Water absorption coefficient Aw (kg/m2s1/2) values according to the two tangents method for building materials at 20oC and its Standard Deviation (SD) Materials Aw (kg/m2 s1/2) (20 oC)
SD
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
0.002 0.002 0.005 0.002 0.004 0.001 0.003 0.002 0.001 0.001
TE D
0.252 0.206 0.123 0.083 0.176 0.106 0.160 0.106 0.071 0.065
AC C
EP
Table 3 Experimental and predicted estimation of the capillary water absorption coefficient A at 15oC.
Materials
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
Temperature 15oC Predicted A-coefficient (kg m-2s-1/2) 0.249 0.188 0.087 0.076 0.169 0.100 0.139 0.102 0.067 0.063
Experimental A-coefficient (kg m-2s-1/2) 0.249 0.188 0.088 0.077 0.169 0.101 0.141 0.102 0.068 0.064
ACCEPTED MANUSCRIPT Table 4 C-coefficient values with Standard Deviation, according to Feng and Janssen’s paper at 20oC. C-coefficient (kg/m5/2) 0.030±0.001
BRM
0.024±0.002
SRH
0.015±0.001
SRY
0.010±0.001
mca20/80
0.021±0.001
mca25/75
0.009±0.001
mca30/70
0.019±0.002
mcb20/80
0.013±0.001
mcb30/70
SC
M AN U
mcb25/75
RI PT
Materials BRI
0.008±0.001 0.008±0.001
TE D
Table 5 Comparison of the experimental A-coefficient values with those estimated from equation (5) at 30oC. Aw values according to equation (5) (kg/m2 s1/2)
Experimental Aw values ± SD (kg/m2 s1/2)
0.280±0.002
0.263±0.002
BRM
0.229±0.002
0.228±0.001
SRH
0.137±0.004
0.172±0.006
SRY
0.092±0.002
0.101±0.002
mca20/80
0.195±0.004
0.191±0.004
mca25/75
0.089±0.001
0.116±0.002
mca30/70
0.178±0.003
0.170±0.003
mcb20/80
0.118±0.002
0.117±0.002
mcb25/75
0.079±0.001
0.081±0.002
mcb30/70
0.072±0.001
0.073±0.001
Materials
AC C
EP
BRI
ACCEPTED MANUSCRIPT Table 6 Experimental % change of water sorptivity S from 20 to 30oC and its Standard Deviation for all the materials
AC C
EP
TE D
M AN U
BRI BRM SRH SRY mca20/80 mca25/75 mca30/70 mcb20/80 mcb25/75 mcb30/70
S 30 − S 20 (%) S 20 6.6±1.0 11.9±0.8 53.2±7.1 23.2±3.0 8.8±3.0 31.6±2.4 12.2±3.0 10.7±2.6 14.4±2.5 12.6±2.0
RI PT
MATERIALS
S30 (m/s1/2) (x10-4) 2.60 2.30 1.70 1.00 1.90 1.20 1.70 1.20 0.81 0.73
SC
S20 (m/s1/2) (x10-4) 2.54 2.00 1.10 0.82 1.80 0.89 1.50 1.10 0.71 0.65
AC C
EP
TE D
M AN U
SC
RI PT
ACCEPTED MANUSCRIPT
Figure 1: Cumulative mass of capillary water uptake versus time for different building materials.
ACCEPTED MANUSCRIPT BRI
0.30
BRM
SRH
SRY y = 0.0009x + 0.2353 R² = 0.996
y = 0.0026x + 0.1493 R² = 0.9933
RI PT
0.20
0.15
y = 0.0056x + 0.0036 R² = 0.9988
0.10
y = 0.0016x + 0.0513 R² = 0.9933
0.05
SC
Capillary Rise Coefficient (kg /m2s1/2 )
0.25
0.00
25 Temperature (oC)
M AN U
20
30
Figure 2: Water absorption coefficients at various temperatures for bricks and stones mca20/80
mca30/70
TE D
0.20
EP
0.15
0.10
AC C
Capillary Rise Coefficient (kg/m2 s1/2)
0.25
mca25/75
y = 0.0015x + 0.1457 R² = 0.9962
y = 0.002x + 0.1089 R² = 0.9828 y = 0.001x + 0.0856 R² = 0.9847
0.05
0.00
20
25 Temperature (oC)
Figure 3: Water absorption coefficients at various temperatures for mca mortars
30
ACCEPTED MANUSCRIPT mcb20/80
mcb 25/75
mcb30/70
y = 0.001x + 0.0867 R² = 0.9953
0.10
RI PT
y = 0.0009x + 0.0539 R² = 0.9957
y = 0.0006x + 0.0546 R² = 0.9956
0.05
SC
Capillary Rise Coefficient (kg/m2 s1/2)
0.15
M AN U
0.00 20
25 Temperature (oC)
30
AC C
EP
TE D
Figure 4: Water absorption coefficients at various temperatures for mcb mortars
ACCEPTED MANUSCRIPT
Highlights: • The effect of temperature on capillary water absorption coefficient of various building materials was investigated. • Capillary rise tests were carried out at different air temperatures and a linear correlation between capillary rise coefficient and temperature was made.
AC C
EP
TE D
M AN U
SC
RI PT
• An evaluation was made comparing our linear regression equations with other researchers’ models.