An Urban Planning Approach to the Climatization of Space Using Natural Resources Based on Ceramic Clay , Zeolite and Bentonite

An advantage of this approach is that tiles made of heterogeneous natural materials can be built into urban objects of different architecture and energy profiles. Their right position in a room would enable natural ventilation based on changes in the air composition that would reduce the exchange of air with the environment, reduce heating costs during the winter and provide cooling during the summer while at the same time maintaining relatively similar air composition. The research showed that sand and ceramic clay enable quicker drying of the sample in comparison to bentonite clay, polyphosphate and a plasticizer enable.


Introduction
Today there are many different types of material used during construction of technical facilities and buildings [1,2].Natural materials (e.g.wood, stone, sand, gravel and clay) are used in the state as found in nature without any prior processing.Bentonite clay as one of them is very important for manufacturing of building materials [3].The physicochemical properties of bentonite clay are commonly modified by addition of polymers in order to improve its characteristics [4,5].Over the last few decades, natural construction materials have lost their leading role in the market and have been replaced by synthetic materials (e.g.concrete, bricks, metal, glass, polymers, synthetic compounds, etc.), which have a damaging effect on both the health of people and the environment [6].Recycled materials with technologically advanced levels of radioactivity is also used quite often, including phosphoplaster, coal ash, slag, thermoplastic synthetic resin, cellulose fiber etc. [7,8].Many of these are valuable industrial by-products which can be reused in construction.Recent studies have been trying to improve and apply the natural materials with modified properties for both cooling and solar heat storage.Vardoulakis et al. [9] prepared, characterized and tested various modified clay materials for solar cooling.Apart from those, Jänchen et al. [10] systematically modified zeolites and mesoporous materials by ion exchange and impregnation with hygroscopic salts to improve their thermal energy storage capacity.
In a well-designed house, main problem is air quality which can be improved if one fifth of the air exchanges every hour.The air humidity is controlled by an appropriate air exchange rate [11] that can be achieved only by ventilation [12].However in many houses the degree of air exchange through the building structure is a big problem.According to Robert and Brend an accepTab.air exchange rate is 0.45 per hour [13].
The presence of moisture and carbon monoxide makes one feels warm or cold in room [14].Thus, in a room or an apartment with volume of 100 m 3 it could be found up to 10 kg of water without condensation in the form of steam and from 3 to 6 kg of carbon dioxide depending on the number of rooms, which is, the number of gas locations and other sources of carbon-dioxide [15].A cubic meter of air can contain from 30 to 70 g of steam even in conditions of relative moisture of 40-80% and temperature of 18-25 °C.In order to bind the excess moisture approximately 200 kg of adsorbents are needed under the condition that they bind 5% moisture in relation to their mass.If the thickness of the adsorbent is 1 cm, and its density is approximately 2.5 kg/L, then the surface of approximately 8 m 2 is required.The distribution of the adsorbents is very important considering that the molecule mass of water is 18 kg/kmol.The adsorbents in the room should be set up, glued or fixed in the vicinity of the ceiling [15].This paper will analyze the influence of the composition of tiles including ceramic clay, bentonite clay, plasticizers, wood chips, and zeolite on the processes of adsorption, i.e. moisture desorption.The experiment was designed to determine an optimal composition of the tiles which provides the so-called "breathing" of the walls without condensation.The experiment included the process of drying -desorption of moisture from raw tiles until it reaches a constant mass.In addition, the process of desorption over a period of 2 hours was studied on a sample of tiles resoaked in demineralized water.

2.Experimental 2.1 Tile Preparation Procedure
The process of water adsorption and desorption is evaluated on the model of a porous object -a tile.In order to study the influence of the tile composition on the adsorption process, i.e. desorption of water, tiles with various composition were made in 7 series with 4 samples per each.The content of each series is shown in Tab.I.The tiles were made from ceramic clay with an addition of sand, bentonite clay, zeolite, wood chips, plasticizers and polyphosphates [15].In order to make tiles, carboxymethylcellulose was used as a plasticizer.The overall mass of all analyzed tiles within each series was 330 g.The formed mass from one series was covered with 132 mL of demineralized water.The overall mass of the freshly modelled samples was 462 g, while the average mass of one tile was 115.5 g.The size of the wet tiles was 8×8×1 cm.

Drying of tile
Previously prepared tiles were dried in a convex four-level laboratory dryer, shown in Fig. 1.The tile mass was measured during 170 h in predetermined intervals.Following the convex drying, the tiles were exposed to 105 °C in a laboratory dryer until constant mass.Following this treatment, they were resoaked in water (150 mL) for 2 min and dried again in a convex dryer under the same conditions.In this case the water represented the component which was adsorbed, i.e. desorbed from the tiles.
A vertical dryer has dimensions of 1×0.15×0.25 m with levels made of wooden frames, wire mesh, and radius of 2 mm, set at distance of 15 mm.Using this wire construction, a non-hygroscopic cloth was set up.On the bottom of the dryer a 1200 W heater with a thermostat was fixed and connected.In the door of the dryer, which was positioned frontally along its entire length, a 220 W ventilator was positioned, which enabled the air flow of 108 L/h and an air current stream of 0.8 m/s.On its inner side, the dryer was impregnated with aluminium foil.

Fig. 1. Scheme of the convective dryer
The drying process in a convex dryer after wetting the tiles was modeled using the OriginPro 8.5.0 SR1 software.Following the drying process in a convex dryer, experimental data obtained for moisture content in the analyzed tiles were fitted with a general exponential equation y = a + b exp(-k x).The coefficients in the equation were determined using the least squares method.

Results and Discussion
In this paper, various series of tiles were made with the aim of studying the influence of their composition on the process of adsorption, i.e. moisture desorption.In this study, during the drying process in a convex dryer, the changes in the moisture content in precisely defined time intervals was monitored.The drying process of fresh made tiles for various series is shown in Fig. 2, while the profile of the drying rate is shown in Fig. 3.The existence of various changes in the amount of moisture in the composite materials used in the experiment is shown in diagrams 1 and 2. The greatest release of moisture was determined for the material from series 1, since it contained the greatest amount of ceramic clay with a small addition of sand.Relatively small amounts of the plasticizer and adsorbents did not have any significant effect on the removal of the water over time.In the case of the composite mixture from series 2, the addition of greater amounts of sand and wood chips should facilitate the removal of the water from the material.The role of bentonite clay is reflected in the fact that it enables the binding of moisture in the form of inter-layer water, which significantly slows down the drying process.
In the case of the samples with the composite mixture from series 3, zeolite was used as an adsorbent instead of bentonite clay.In series 2 and 3, similar behavior during the first two hours of the drying process can be seen (Tab.II).Introducing additional amounts of energy into the material being dried, a sudden desorption of water occurs.Similar behavior, in the sense of moisture desorption from the material, is found in the composite mixtures from series 4 and 7.In both cases the mixtures with great amounts of bentonite clay and zeolite were used.In the case of the series 7, ceramic clay was left out, but not the plasticizer which enabled shaping of tiles as well as maintenance of their consistency.Series 4 had no added plasticizers, but contained a small percentage of ceramic clay with plastic features.The clay content has proven to be insufficient for the preservation of consistent forms of tile samples.The content of ceramic clay is greater in the samples of composite mixtures from series 5.The presence of plasticizers enables a better removal of moisture from the material, while in the case of series 6 the removal of moisture is more difficult due to the presence of polyphosphates which bind water molecules.The second part of the experiment referred to the process of water desorption from the resoaked tile samples.The profile of the desorption rate from water for various series in shown in Fig. 4. Change in the moisture content over time in the studied samples is shown in Fig. 5.It has been found that the presence of zeolite in the mixture increases the process of water desorption (Tab.III).In the samples of the composite mixtures from series 2 the process of desorption is significantly slower.The experimental method has also indicated that the presence of polyphosphates in the mixture decreases the desorption in the case of the tiles from series 6 which even after 120 min from the start of the follow-up drying process had 81.01%moisture.Due to the ability of phosphate to build hydrates with water molecules, the moisture remains bound in the mixture so that it is not desorbed in the sample tiles from series 6.The drying rate is smaller in comparison to the drying rates for the other series of tiles.

Tab. II Drying rate of different material combination samples
The tiles from series 1 have the highest content of kaolinite which represents a connection between irons whose hydrides have the ability to bind water.Due to its presence, the tiles have a very high drying rate at the beginning, and then at one point that value becomes constant.This sort of behavior of the analyzed system in essence represents the basic characteristic of the system with an excess of ceramic clay.In the beginning, the iron hybrids, due to their relatively weak links, easily release water from the structure of the composite.By being submerged again and dried for 120 min the water content is reduced to approximately 78.22%.Due to a great amount of bentonite clay and the lack of plasticizers, the tiles from series 4 swell when in contact with water, increasing their volume and completely disintegrating.The percentage of bentonite clay is high in the composite mixture from series 6 with the difference that in this series, due to presence of kaolinite and a plasticizer, the sample does not disintegrate, i.e. the tiles do not change their shape.

Fig. 6. Drying and desorption rate comparison of different experiment series
The tiles from series 5 do not contain bentonite clay, but do contain kaolinite, wood chips and a plasticizer.Such a composition increases the material capillarity, so that at the very beginning the desorption rate is faster.In this series the moisture content was approximately 90.18% after 120 min.The tiles from series 7 have shown a different functional dependence, since they do not contain any kaolinite whose hydrides could bind the water molecules.Through comparative graphic analysis of the data about both drying and moisture desorption rate of the materials from each series used in the above mentioned experiments, a relatively big difference in these two rates can be found at the beginning.Later on, i.e. after 2 -2.5 h the rates become almost same as shown in Fig. 6.

Tab. III
Deviations from this type of behavior were only noted for the composite mixtures from series 5 and 7, which contain greater percentage of zeolite.In these two cases, the lines of drying and moisture desorption intersected in the period between 1.0 -1.5 h from the experiment start, after which the rate decreased, but still continued their trend unlike the classic drying process which was relatively constant.Mathematical modelling of the data collected led to a conclusion that the moisture content in the tiles changes exponentially as function of time.A general equation used to adequately describe the process of moisture desorption can be represented in the form of y = a + b exp(-k x).All the coefficients in this exponential equations related to different series of tiles were obtained by the least squares method and are shown in Tab.IV.The Tab. also shows the values of standard errors (S.E.) for all calculated parameters.Based on the calculated values for the adjusted R 2 parameters, the validity of the set equations was defined.Since these values were mainly above 0.99, it can be concluded that the above equation was a right choice for description of the moisture desorption process.Slight deviations of the suggested functional dependencies from the experimentally obtained values can be clearly seen in Tab.IV.

Conclusion
In this paper, the obtained results indicate that the combination of bentonite clay, zeolite and unfired ceramic clay can be used to make adsorbents that are moisture desorbents, which can be further successfully used in the construction of buildings.The influence of adsorption and moisture desorption increases by increase of the zeolite content in the analyzed tiles.The significance of the bentonite clay is reflected in the fact that it increases moisture adsorption, but slows down its desorption.Sand in combination with wood chips increases porous nature of the tiles, which further decreases their ability to bind moisture.The optimization of the content of ceramic clay, bentonite clay, zeolite, wood chips, sand and plasticizers was realized using appropriate mathematical model of the process studied.

Fig. 4 .Fig. 5 .
Fig. 4. Moisture alteration in different resoaked samples during the desorption process Content of the analyzed tiles Desorption rate of different material combination samples Coefficients of the exponential equations obtained by modelling the moisture desorption process for various series of tiles