{'fraction_non_alphanumeric': 0.025919552591955258, 'fraction_numerical': 0.011830501183050119, 'mean_word_length': 4.9153944020356235, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Coupled heat and moisture transport in building material – water absorption coefficient and capillary water content

At present, restoration of historic buildings is a difficult process. The most common problem of historic buildings is increased moisture, because waterproofing is missing and thanks that water can be transported in porous material by capillary forces. There is several simulation software available, which can include many factors such as water transport from the ground, sun radiation, impact of driven rain. Also it includes thermal conductivity, specific heat capacity and water vapor diffusion factor, which are depended on content of water. For correct assessment of hygrothermal behaviour of these buildings and find suitable retrofit strategies, hygric and thermal properties are needed. When we want to use simulation software for assessment of hygrothermal behaviour of historic structures, we need to know heat and water transmission parameters of sandstones. In this paper are presented two water transmission parameters and that water absorption coefficient and capillary water content. For the test measurement of these parameters was used clay brick. The water absorption and capillary water content are obtained by experiment of one-dimensional transport water. The results are compared with values of clay brick, which are presented in German material database.


Introduction
The moisture is one of the most common issue of existing buildings. It can affect not only service life and buildings energy efficiency but also their air quality in interior of buildings [1]. Water transport is crucial factor in terms of building design. When designing new buildings, civil engineers consider with transport water only as transport water vapor from the interior to the exterior. It is correct, because they can consider with waterproof insulations against ground water or waterproof plasters on the facades of buildings envelopes, but in historical buildings are usually missing and thanks that water can be transported to the porous materials of historical constructions. There is simulation software available, which can include influence of water to materials properties, sun radiation, driven rain, orientations of walls, wind and many others important factors. To use this software, it is necessary to know heat and water transmission parameters of historical materials [2]. In eastern Slovakia, sandstone was used in large quantities for construction of buildings. It was used for its compressive strength, good workability and aesthetic appearance. By the end of the 19 th century, 336 quarries for sandstone mining were registered in the territory of eastern Slovakia [3]. Only a few scientists have studied the hygrothermal properties of sandstones. Transmission parameters of sandstones were studied by scientist in Canada [4], Czech Republic [5], and Germany [6] [7]. Capillary absorption coefficient (Acap) and the capillary moisture content (wcap) are important material properties. They can be determined by capillary absorption test, which is one of the most frequently performed material characterization test. There are many international and regional standards prescribing the procedures of the capillary absorption test [12], [13], [14], [15], but there are still some differences between procedures and rules. These differences include questions about sample size, area of bottom surface, sealing materials to providing onedimensional transport water, temperature impact on Acap, operational factors, weighing method. In this

Characterization of material
For test measurement was used common clay brick. It was chosen, because it has a typical tubular pore structure [8] and it is weak in hygroscopicity but strong in [9], this makes it suitable for capillary absorption test measurement.

Sample preparation
The size of the sample and the area of the bottom surface that is in contact with the water surface are one of the most disputable factors. The standard ISO 15148 requires, that a bottom surface area of sample should has minimum of 50 cm 2 for each sample [16]. The standard EN 1925 requires cubic sample with dimension 50, 70 mm or cylinder sample with diameter 50,70 mm and with height 50, 70 mm. Although there are several standards that set minimum dimensions of samples, many researchers often use much smaller samples with bottom surface areas ranging from 10 to 30 cm 2 [5], [9], [10], [11]. For test measurement were used cylindric samples with diameter 50 mm and height 60 mm figure 1. Two samples were made from one homogenous batch by core drilling machine and the bottom surface was treated by emery paper.

Principle of one-dimensional water transport experiment
By performing a water absorption test also called one dimensional water transport experiment, it is possible to determine the water absorption coefficient and capillary moisture content. The principle of this method is that the measured sample is immersed in the water and mass gain over time is monitored. The bottom surface of sample is in contact with water level to allow water absorption [16]. To providing only one-dimensional water transport, it is necessary to seal lateral sides and upper surface of the samples. The insulation must be perfect, because water can move in gap between sample and insulation material. Before the testing, samples must be dried at defined temperature 105°C [16] or 70°C [17]. After cooling down to temperature of the room in desiccator, oven-dried sample can be used for measurement. The test can be performed either with automatic or manual weighing. Some studies show a good agreement between the results of manual and automatic weighing [10]. For this test was used apparatus with automatic weighing shown in figure 2. This apparatus was constructed according measuring device stated in [20]. It consists of a water container, a container lifter, a weighing machine, a rod for suspending sample, a data logger, which is connected to computer for monitoring temperature, relative humidity and weight gain.

Waterproof insulation
To reduce evaporation of water from the sample, it is necessary to insulate lateral sides of the sample. Insulation material must be vapor-proof and waterproof. Upper surface of the sample, must be vaporproof but air-permeable, because of air leakage. In general, there are two sealing methods. Samples can be sealed by adhesive, non-adhesive film or by epoxy resin. According standard ASTM C1585 [18], both methods are acceptable. Bomberg et al. [10] stated that the self-adhesive tape should not be used, but without any theoretical explanations. Two different insulating materials were used for the test measurement, self-adhesive tape commonly used to insulate the gap between the walls and openings, and a heat shrink tube commonly used to insulate electrical cables. Both materials are shown in figure  3.

Determining of water absorption coefficient and capillary moisture content
One-dimensional water transport experiment can be divided into two stages. The first stage is characterized by a linear mass gain as a function of square root of time. During this stage, water absorption is governed by capillary forces. Water absorption coefficient Acap is defined as the slope of the cumulative water inflow versus square root of time in the first stage of the test figure 4. Second stage is characterized by non-linear mass gain and mass gain is slower. This stage takes a several days or months [19].
where Acap is water absorption coefficient (kg/(m 2 .s 1/2 ), mwet weight of the wet sample (kg/m 2 ) per unit area S (m 2 ), mdry is weight of the dry sample (kg/m 2 ) per unit area S (m 2 ), t is time of experiment. Capillary moisture content wcap is defined as the moisture content at the transition from the 1st to the 2nd stage. More specifically, it is the moisture content, which correspond to the cross point with the fitting of the 1st and 2nd stages, as it is illustrated in figure 4. The capillary moisture content wcap can be determined by using following equation (2)

Results and conclusion
The resulting water absorption courses in the experiment with two different sealing materials are presented in figure 5 and figure 6. Weight gain recording was performed by automatic weighing at defined times. The weight gain of clay brick with self-adhesive tape is shown in figure 5. The linear course of weight gain is not entirely perfect. It is not because the sample was lifted during the experiment. In figure 6 is shown weight gain of the clay brick with heat shrink tube. The linear course of weight is much better. Such a course is typical of an ordinary clay brick. match can be observed between values of Acap and wcap of brick Wienerberger 1 and values of measured brick with heat shrink tube. But on the other side, there is a bigger difference between values of bulk density. In the case of measurement with self-adhesive tape, the good match can be observed between Acap of brick ZD and measured brick. Also there is a small difference between values of bulk density. The measurement and comparison of the results indicates that there are significant differences between measurements with different sealing material and therefore further measurements are required.