Incorporation of coffee grounds into clay brick production

Incorporation of coffee grounds into clay brick production D. Eliche-Quesada*, L. Pe´rez-Villarejo, F. J. Iglesias-Godino, C. Martıńez-Garcıá and F. A. Corpas-Iglesias This present study has been conducted to assess the viability of mixing increasing amounts of coffee ground as a solid waste material (1–5 wt-%) with raw clay. Samples have been compressed, dried and fired at 950uC for 24 h to laboratory scale. Using coffee grounds as organic residue has been proven to be effective for pore formation in clay body, increasing its insulating properties yet maintaining acceptable mechanical properties. Small amounts of waste (1–2 wt-%) were found to be effective at forming open cell porosity in clay bricks, which results in worse mechanical and thermal insulating properties. However, bricks with higher amounts of coffee grounds (3–5 wt-%) showed lower density levels and, therefore, higher porosity, which is mainly closed cell porosity, which shows higher insulating capacity and suitable mechanical resistance. Optimal results have been found in bricks with 3 wt-% coffee grounds, showing good mechanical, physical and thermal properties. Keywords: Coffee waste, Pore forming, Clay bricks, Environment, Physical, mechanical and thermal properties

Introduction At present, the need for a progressive reduction in human produced waste has been reasserted by both social pressure for preserving the environment and high cost for the final disposition of waste. This implies a newly generated interest in using products whose raw material is waste, which may lead to product diversification and final cost reduction, as well as to provide some industrial sectors with an alternative material. These factors explain why appreciation towards waste materials is an increasingly important current issue, which is necessary to clear up problems derived from current development. Once waste has been generated, a wide range of techniques must be applied for its reintegration. The European Union and, in general, developed countries tend to the so called ‘3Rs’ waste hierarchy: reducing the amount of waste one produces and recovering waste which can be reused, recycling by means of multiple available techniques and reusing, directly or indirectly, materials.1 Building is an excellent industry for the absorption of considerable amounts of solid waste material, not only in the form that they are found but also after being adapted.2 Building offers several advantages, among which are as follows: being able to absorb huge amounts of material and admitting an enormous range of qualities, which allows setting a wide range of

Departamento de Ingenierıá Quı´mica, Ambiental y de los Materiales, EPS de Linares, Universidad de Jaeń, Linares, Jaeń 23700, Spain *Corresponding author, email [email protected]

ß 2011 Institute of Materials, Minerals and Mining Published by Maney on behalf of the Institute Received 27 January 2011; accepted 29 January 2011 DOI 10.1179/1743676111Y.0000000006

materials, each showing its standardised quality and suitability for a specific use. Research has discovered that base materials, such as polymer, cement and ceramic materials, are those most suitable for inertising and neutralising residues by means of encapsulation in their matrix.3–6 Ceramic products, mainly bricks and tiles, are really heterogeneous since they are formed by clay, with a wide range in their composition.7 Owing to this, these materials may tolerate considerable amounts of different types of residue,8 which may help reduce the costs in the building industry. Owing to the environmental regulations, the demand for high insulation capacity bricks is increasing. The decrease in thermal conductivity is a decisive factor for limiting energy demand. One way to increase the insulation capacity of the brick is to generate porosity in the clay matrix.9,10 One of the most conventional ways to reduce the thermal conductivity in the ceramic material is to modify its microstructure by incorporating lightening, pore forming, organic additives into the clay matrix.11,12 Coffee grounds are a solid organic residue, widely generated by the service sector, which, at present, is not recycled or is used as a fertiliser in agriculture or for compost production. Therefore, it is necessary to research new applications on this kind of residue. Porous ceramic production may be a significant application for coffee waste. Besides, coffee waste may contribute to autothermal combustion due to its high heating power, which involves lower fuel consumption during firing. Uses of organic residues in brick production in order to obtain porous ceramic bodies with better

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Incorporation of coffee grounds into clay brick production

insulating properties have been studied by other authors.13–19 Garcıá-Ten et al.14 studied the feasibility of reducing the thermal conductivity of ceramic material by incorporating lightening additives like agricultural residues: olive oil waste, paper industry waste, sewage and coke. Results have shown that additives subject to study may be put in the following effectiveness based order: sewage.olive oil waste. coke.paper, in order to achieve a thermal conductivity value of 0?43 W mK21. However, the resulting samples show a decrease in mechanical properties, which may require a change in the production process or its composition. Demir15 investigated the utilisation potential of organic residues, such as sawdust and tobacco residues (0–10 wt-%) in clay bricks. The author has found that incorporating up to 5 wt-% of residue produces a suitable decrease in real density and increase in open porosity of clay, but the compression strength of the samples decreases. Later, Demir16 investigated the use of used tea (0, 2?5 and 5 wt-%) in clay bricks. The addition of residue increases open porosity, causing a reduction in total density and improving the thermal insulating properties of bricks. The compression resistance of bricks also grows when the amount of residue is increased. Duckman and Kopar17 produced brick clay with up to 30 vol.-% of sawdust and/or papermaking sludge as pore forming agents. A highly porous ceramic structure was obtained after firing at 920uC. Monteiro et al.18 investigated the use of oily wastes (up to 5 wt-%) incorporated into red ceramic products. The oily wastes were crude sludge derived from the petroleum separation process and its inert treated form. The results showed that practically no change occurred in the main technological properties required to specify porous red ceramic products. Mekki et al.19 investigated the possibility of incorporating the effluent resulting from olive oil extraction activity, known as olive oil mill wastewater, in the brick making process. Results have shown that despite the solid content of residues, replacing waste water with the residue in brick making had no adverse effects on extrusion performance, maintaining or even improving their physical and mechanical properties. The incorporation of the residue resulted in a significant increase in volume shrinkage (10%) and water absorption (12%), whereas tensile strength remained constant. By incorporating different proportions of organic residue into the ceramic matrix, the required thermal and acoustic insulation levels may be achieved. Consequently, a lightening, pore forming residue like coffee grounds may provide economic benefits for the building industry and ecological benefits due to the lack of problems regarding residue depletion. In view of these precedents, the main aim of this research is to obtain a good building material, pursuant to current regulations, using waste obtained from coffee grounds as an additive. The use of coffee grounds as a lightening additive for ceramic material allows modifying the clay microstructure and improving its insulating properties since it is an organic, pore forming residue. For this study, the residue was incorporated into raw clay progressively up to 5 wt-%, and the objective of the study is to analyse its impact on physical, mechanical and thermal properties.

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Materials and method Preparation of samples Clay was supplied by the local plant of the company ‘Arcillas Bailen S.L.’, in Bailen, Jaen, Spain. The initial preparation consists of shredding clay in a hammer mill in order to obtain particles with a suitable size to be sifted through a 150 mm sieve. In order to determine the effect on the clay matrix caused by the pore formation of organic waste material, different amounts of coffee grounds (1–5 wt-%) with a humidity level of 44?8% in clay were added. After weighing the suitable amounts of clay and coffee grounds, raw material and lightening additive were mixed in a mortar to obtain good homogenisation. In order to obtain comparative results, a series of 10 samples of 40 g, each containing 0–5 wt-% of coffee grounds, were prepared for the tests. The necessary amount of water (7–10 wt-% of moisture) was added to obtain adequate plasticity and absence of defects, mainly cracks, during the semidry compression moulding stage. At this stage, uniaxial pressures of 54?5 MPa were applied. Conformed bricks with 30610 mm crosssections and a length of 60 mm were obtained. After moulding, the bricks were dried for 48 h at 110uC to reduce the moisture content, so that no cracks would appear on samples at a later stage. Eventually, the dried bricks were fired in a laboratory type electrically heated furnace at a rate of 10uC min21 up to 950uC for 24 h. This temperature is usually used in the fabrication of clayey bricks. The bricks were then cooled to room temperature by natural convection inside the furnace after being turned off. The conformed bricks will be designated as A for the brick without residue and AC-x for mixtures, where x denotes the coffee ground weight percentage in the matrix clay (C).

Characterisation of brick raw material X-ray diffractometry of clay and ash coffee ground (the coffee grounds were fired up to 950uC) was carried out by using an automatic diffractometer (Siemens D5000), with Bragg–Brentano geometry (h/2h), and using Ka1,2 radiation, provided with a graphite monochromator to eliminate Cu Kb radiation. The chemical composition was determined by X-ray fluorescence in a Philips Magix Pro (PW-2440) equipment. Raw material and lightening additive, i.e. coffee grounds, were analysed by thermogravimetric analysis (TGA) and differential thermal analysis (DTA) using a Mettler Toledo 850e equipment, where the samples were placed in a platinum crucible and heated at a rate of 10uC min21 within the range between room temperature and 900uC. The shown data reflect the percentages of loss of weight depending on the temperature and DTA diagram simultaneously. A CHNS chemical elemental analysis was carried out to determine the total amount of carbon, hydrogen, nitrogen and sulphur in samples by using a CHNS-O Thermo Finnigan Elementary Analyser Flash EA 1112 via combustion (950uC) under an O2 atmosphere. Bernard calcimeter was used to determine the carbonate content in clay by quantifying the CO2 released after attacking clay with diluted hydrochloric acid.


Characterisation of conformed bricks A series of tests and inspections were performed to determine the physical (weight loss on ignition, linear shrinkage, bulk density, water absorption and water suction), mechanical properties (compressive strength and frost resistance) and thermal properties (thermal conductivity) of the bricks to ensure that they would meet the specifications regulated by the UNE Standards. Bulk density is defined as the ratio of the mass of dry solids to their bulk volume. The measurements were carried out after drying at 110uC for 24 h (dry) and after firing. The bulk density was calculated as the ratio of dry mass of the conformed brick to its standard volume. Weight loss on ignition was obtained by measuring the weight after the drying stage at 110uC and after the firing stage at 950uC. Linear shrinkage was obtained by measuring the length of the samples before and after the firing stage using a calliper with a precision of ¡0?01 mm. Water absorption capacity is defined as the measurement of moisture when a solid (brick) is completely immersed in water during a prolonged time. A test on determining the water absorption capacity was implemented according to the standard procedure UNE 67-027. The bricks are dried up on an oven at 110uC for 24 h. Once they are dry, the bricks are weighed repeatedly until the weigh difference is lower than 1%. As a result, a Gs weight is obtained. After cooling the samples for 24 h, they are slowly introduced in water until they are completely immersed. After 24 h from initial immersion in water, the bricks were taken out of the water, dried with a damp cloth and weighed again. The bricks are weighed every 24 h until the difference between the weights is lower than 0?1% for two consecutive times, resulting in a constant weight Ge. Water absorption is the difference between weights Ge and Gs. The water absorption of samples was calculated according to equation (1) Ge {Gs |100% WA~ Gs

(1)

Water suction of a brick is the volume of water absorbed during a short partial immersion. A test on determining the water suction was implemented according to the standard procedure UNE 67-031. The bricks are dried up at a temperature between 100 and 110uC until their weights are at constant Pi. The surface of the face introduced into the water is measured. A tray is filled with water until reaching the level where only 3 mm of samples will be covered for 1 min. After that, the bricks are dried with a cloth and weighed Qi (g). Water suction (g cm22 min21) of the bricks was calculated according to equation (2) Qi {Pi (2) A The compressive strength of the bricks is the bulk unit charge against breakage under axial compressive strength. For this trial, six fired bricks were studied. Tests on the compressive strength were carried out according to the standard UNE 67-026 for marble and limestone on a Suzpecar CME 200 SDC laboratory press. WS~


The area of both bearing surfaces is measured, and the average is taken. A progressively increasing normal strength was applied for all the bricks, applying the load centred on the upper surface of the sample until breakage. The compressive strength of each brick is obtained by dividing the maximum load by the average surface of both bearing surfaces, which is expressed in megapascals with a 0?1 MPa accuracy. Determining, on an experimental basis, the thermal conductivity of bricks involves experimentally determining the heat flow, going through the sample, in which after an initial variation in temperature, the steady state is obtained. The brick is placed on a hot plate, heated until reaching a specific temperature and then switching off the heat source. When the hot plate reaches some determined temperature, the brick’s temperature is measured. The thermal conductivity is obtained from equation (3) k~

hc bc(T1 {Tamb ) hc bc { c(T1 {T2 ) c

(3)

where k is the thermal conductivity of the brick, b and c are the length and width of the brick respectively, T1 is the hot plate temperature, Tamb is the ambient temperature, T2 is the brick temperature and hc is the air convection coefficient (10 W mK21). The effect of frost resistance is carried out according to the standard UNE 67028 by means of a manual system, having bricks undergo 25 icing/deicing cycles (18 h for icing and 8 h for deicing) using a freezer and having saturated bricks in water previously for 48 h. The microstructure of the conformed pieces is observed by means of a scanning electron microscope (SEM), using a high resolution transmission electron microscope (JEOL SM 840). The samples were placed on an aluminium grate and coated with gold using an ion sputtering device (JEOL JFC 1100).

Results and discussion Material composition analysis Table 1 shows the chemical composition and the loss on ignition of clay and ash coffee ground, and according to Table 1 Chemical compositions of clay and ash coffee grounds Oxide content/% SiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2O TiO2 P2O5 SO3 CuO SrO NiO Rb2O ZnO Zr/ppm Loss on ignition

Clay 55.82 12.13 4.83 0.03 1.49 9.21 0.49 2.78 0.83 0.12 … … … … … … 279.3 10.55


Ash coffee grounds 1.09 0.79 1.26 0.38 22.93 13.73 8.42 23.87 0.14 23.66 3.30 0.28 0.06 0.03 0.02 0.01 … …

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1 X-ray diffraction patterns of a powdered clay and b ash coffee grounds

the X-ray diffraction pattern of clay dust (Fig. 1a), it mainly contained quartz (SiO2), clay minerals, mainly phyllosilicates, such as kaolinite [aluminium silicate, Al4Si4O10(OH)8], illite [potassium aluminium silicate, KAl2(Si3Al)O10OH], montmorillonite (aluminium magnesium silicate, MgOAl2O35SiO2xH2O), chlorite [a laminar silicate containing magnesium hydroxide and micaceous layers (Al,Fe,Mg)4–6(Al,Si,Fe)4O10(OH,O)8], calcite (CaCO3) and hematite (Fe2O3). Phyllosilicates are responsible for the clay plasticity when mixed with appropriate water proportions, as well as for hardening over drying or firing.20 From the corresponding X-ray diffraction graphs of the ash coffee grounds (Fig. 1b), it can be concluded that the major component is oxide magnesium, and they also contained dicalcium silicate [Ca2(SiO4)] and potassium and magnesium silicate (K2MgSiO4), smaller amounts of halite (NaCl), pyrodhyllite [Al2Si4O10(OH)2] and dolomite ferroan [Ca(Mg,Fe)(CO3)2] containing traces of bayerite [(Al(OH)3]. The chemical composition of the coffee ash reveals that the fired coffee grounds provide the clay body and the presence of amorphous potassium oxide or silicate, amorphous phosphorus pentoxide and crystalline magnesium oxide. The calcium and sodium oxides are a lower proportion as silicates and chlorides respectively. The high contents of fluxing oxides (K2OzNa2O) and auxiliary fluxing oxides (CaOzMgOzFe2O3) in the waste are suitable to the

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low temperature firing process for the preparation of bricks. The results of TGA and DTA of both clay and coffee grounds (used as an additive) are shown in Fig. 2. In the case of clay (Fig. 2a), an endothermic peak has been found at 51?4uC, assigned to moisture loss, obtaining, consequently, 2% weight loss. As the temperature is raised, a virtually constant weight is observed, with a weight loss of 2?8% from 100uC up to 600uC. In the interval from 400 to 600uC, a weak endothermic peak is found, which is assigned to dehydration (loss of water of constitution) due to a breakage in the silicate lattice structure. Finally, a strong endothermic peak is found at 750uC, due to the thermal decomposition of CaCO3 (calcite) into CaOzCO2, with a consequent weight loss of 9?8%. A DTA-TGA curve analysis of coffee grounds (Fig. 2b) is typical for solid combustibles, where the residue in clay body is found to be completely fired at low temperatures and within the range from 200 to Table 2 Analysis (CHNS) of raw materials (%) Sample

C

H

N

S

Clay 2.14¡0.13 0.34¡0.01 0.025¡0.01 0.0¡0.00 Coffee 49.80¡0.35 6.65¡0.05 3.02¡0.18 0.0¡0.00 grounds



2 Analyses (DTA-TGA) of a clay and b coffee grounds

600uC. Two exothermic peaks and weight loss are observed, which are due to combustions. The total weight loss is almost 94%, showing that ashes are barely produced (only 6%) during combustion. Ashes are later incorporated into the ceramic matrix. The results of elemental analysis on C, H, N and S content in both clay and coffee ground residue have been determined (Table 2). The organic matter content in clay is low. However, the high content of carbon and hydrogen in the residue must be highlighted, thus conferring the residue material a high calorific power similar to that of the fuel coke. The particular difference is that coffee grounds do not contain sulphur. Carbonate content has been determined by Bernard’s calcimeter method. The carbonate content is another relevant factor for determining material production process and boiled sample properties. Calcium carbonates represent the vast majority of carbonates in clay (22?4%). Carbonates have whitening properties and increased water absorption, and they delay the fusion point of clay mineral. Consequently, chalky clay is preferably used for porous coatings, whereas clay with a carbonate low content (,5%) is used for manufacturing glazed products.

Characterisation of conformed materials During thermal treatment, samples show variations in their mass and dimension. During both the drying stage of conformed samples and after the firing stage, no defect, such as cracks, was observed. A series of 10 samples were used for each test. The average results of the tests are presented and discussed in this section. The weight loss of the conformed sample happening after sintering is related to the porosity and densification and, occasionally, has an effect on the compressive strength of thermally treated samples.21,22 During sintering, both open and closed pores are formed. A

weight loss after sintering clay at 950uC reaches 14?2% can be assigned to the elimination of organic matter by means of combustion and to the elimination of water content from clay mineral due to dehydroxylation reactions. As the temperature is increased, the carbonate content in clay (22?4%) will decompose into CO2, causing a loss of weight in bricks. The addition of increasing amounts of coffee grounds to clay causes a linear increase in weight loss after sintering. The more waste coffee is used, the bigger the weight loss will be. Weight loss after sintering grows from 14?5 to 16?0% when 1 and 5 wt-% of waste coffee are added respectively (Table 3). As TDA-TGA has shown, this happens because the organic matter contained in the residue burns, forming CO2 and increasing the porosity in the clay matrix. These results show the compatibility between clay and coffee, and consequently, coffee grounds may be incorporated into the clay in order to increase the porosity. During sintering, the results show little variation in linear contraction of samples for the residue percentage tried, going from 20?2% in the case of clay to 20?62% in the case of sample AC-4 (Table 3). Therefore, clay samples, as well as samples containing coffee grounds, expand slightly when fired at 950uC, resulting in a typical behaviour of porous bodies, in which a low amount of liquid is generated. This can be due to the high content in quartz of the clay that is inert in the studied range of temperatures that reduces the contraction of the piece, as well as to the increase in porosity due to the high content of calcium carbonate in clay (22?4%) and the high content in organic matter in the coffee grounds. The bulk density of raw samples containing only clay was 2090 kg m23, whereas the value reported by samples after thermal sintering at 950uC was 1810 kg m23. Thermal treatment of clay at 950uC causes the density to decrease by 13?42%. The addition of increasing amounts

Table 3 Characteristics of construction bricks made from coffee grounds Sample

Coffee grounds/wt-%

Weight loss on ignition/%

Linear shrinkage/%

Suction water/kg m22 min21

Thermal conductivity/W m21 K21

A AC-1 AC-2 AC-3 AC-4 AC-5

0 1 2 3 4 5

14.2¡0.09 14.5¡0.18 15.1¡0.17 15.3¡0.15 15.9¡0.25 16.0¡0.21

20.20¡0.07 20.25¡0.08 20.50¡0.09 20.46¡0.07 20.62¡0.10 20.59¡0.08

2.76¡0.19 3.00¡0.06 2.84¡0.09 2.55¡0.21 2.28¡0.27 2.29¡0.15

2.78¡0.02 3.89¡0.04 1.73¡0.04 1.43¡0.10 1.36¡0.15 1.04¡0.05


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3 Bulk density for dry ( ) and fired bricks (¤) as function of coffee ground addition

of coffee grounds causes a linear decrease in bulk density, both of raw and fired samples (Fig. 3). Such impact on raw samples may result from the low bulk density level of coffee waste against that of clay and from the change in particle packing of the clay mix originated by incorporating a lightening additive. Contrary to fired clay, the addition of 1 wt-% coffee grounds after thermal treatment decreases the bulk density by 4% to 1740 kg m23, which diminishes linearly by up to 6?5% when 5 wt-% of coffee waste (1690 kg m23) is added. Therefore, the residue’s lightening force is due to the increased loss of organic material over combustion during firing, generating higher levels of total porosity in clay. Pursuant to current regulations, the bulk density in bricks may not be lower than 1050 kg m23. The total porosity of fired samples might be either open or closed. Open porosity shall be determined by water absorption values. The lower the water absorption value is, the more durability and resistance to the natural environment are expected. Tests on water absorption have shown that open porosity increases by adding coffee ground residue, even though no linear relation between the open porosity and the added residue percentage has been found. According to Fig. 4, incorporating small amounts of additive (1– 2 wt-%) into clay with 16?8% absorption value increases the open porosity. A maximum absorption value of 18?2% is reached by samples where 1 wt-% of coffee waste has been added. In samples with coffee waste addition higher than 2 wt-%, open porosity is barely

4 Effect of amount coffee grounds on water absorption

increased, showing water absorption values similar to those of pure clay. According to data on weight loss and bulk density of bricks, samples with higher residue content (3–5 wt-%) show higher total porosity values, and since data on water absorption indicate that these samples have low open porosity value, the porosity must be mainly closed. The results of water suction variation, depending on the percentage of coffee grounds added, are shown in Table 3. Water suction in the case of pure clay is 2?76 kg cm22 min21, and again, a maximum suction value (3?00 kg m22 min21) is obtained in samples with the lowest residue content (1 wt-%). Adding increasing coffee ground amounts decreases the water suction to 2?84 kg m22 min21 in samples with 2 wt-% residue content and even lower in the case of samples with higher residue content (3–5 wt-%), reaching water suction values lower than that of pure clay. These results show that the superficial interconnected porosity decreases when adding amounts of coffee grounds higher than 2 wt-%, as expected according to the absorption data. The increase in the samples’ closed porosity is therefore caused by the formation of unconnected pores due to the increase in lightening additive. Morphological study of samples containing clay, as well as that of samples containing smaller or bigger amounts of coffee grounds (AC-1% and AC-5%), has been obtained by means of SEM, as shown in Fig. 5.

5 Images (SEM) of a clay samples and those containing b 1 wt-% and c 5 wt-% of coffee waste

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6 Thermal conductivity as function of open porosity (indirect measurement obtained from water absorption)

Clay porosity (Fig. 5a), either small sized and closed (micropores), resulting from intergrain porosity, or open (macropores), over the pores placed in the surface, changes due to the presence of coffee grounds. However, the different impacts of residue amounts on porosity can be observed. While small amounts of coffee grounds (1 wt-%) cause a significant increase in open porosity as a result of macropore connection (Fig. 5b) according to the water absorption data, bigger amounts (5 wt-% of coffee grounds) cause an increase in closed porosity and micropores (Fig. 5c). The thermal conductivity values of fired samples in relation to coffee ground content are shown in Table 3. The higher the percentage of additive is added, the more the thermal conductivity decreases. An exception has been found for the composition with 1% addition of coffee grounds, which provides the highest thermal conductivity value (3?88 W mK21), due to a higher level of open porosity found in this sample, according to water absorption data. Thermal conductivity depends not only on the porosity of fired samples, since no linear relation between such property and bulk density, when fired, has been found, but also on the kind of porosity of samples (open or closed) and on pore size. The thermal conductivity as a function of water absorption (indirect measurement of open porosity) for fired samples containing coffee grounds is shown in Fig. 6. A sample containing 1 wt-% coffee grounds has been rejected since it shows an anomalously high conductivity value. Results show that all the compositions fit one straight, positive sloped line, showing that the conductivity in samples increases as porosity does. Therefore, closed porosity must be generated by incorporating coffee ground contents higher than 2 wt-% in order to improve thermal insulation. The compressive strength of ceramic materials is the most relevant engineering quality index for building materials, since such materials have structural functions in buildings. According to the UNE-67?046-88 standard, the compressive strength of bricks must be 10 MPa. Test results on the compressive strength of clay bricks and of clay–coffee ground mixtures are shown in Fig. 7. The mechanical resistance of fired materials is partially determined by material porosity, even though it depends

7 Compressive strength of bricks as function of amount of coffee grounds added

on the kind of porosity developed by the sample. For small amounts of added coffee grounds (1 wt-%), a minimum compressive strength is observed, yet this sample is the one with the highest water absorption value and, therefore, the highest open porosity value. As the results indicate, higher open porosity values show lower compressive strength values (49?6–55?3 MPa) than bricks containing only clay (65?2 MPa). On the opposite side, samples containing bigger amounts of residue (4–5 wt-% coffee grounds) can be found. These samples show higher levels of total porosity, mostly closed, due to their lower bulk density, and lower compressive strength values than pure clay (60?0 and 55?9 MPa respectively). Only the sample containing 3 wt-% waste coffee shows a higher strength value (70?7 MPa). Such sample shows a reduction of 4?8% in bulk density and has better mechanical properties than pure clay due to its closed porosity and small sized pores. Frost resistance is an index showing the ability to withstand a series of consecutive freeze–thaw cycles. Frost resistance is characterised by a decrease in compressive strength of samples before and after undergoing a series of 25 freeze–thaw cycles. After a visual examination of the samples, once all 25 cycles were carried out, no exfoliation, fissures or spalls were found (Fig. 8). Following the examination, a comparative trial on compressive strength was implemented. Results showed that mechanical resistance barely varied (Fig. 9).

8 Samples a before and b after frost resistance trial


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mainly closed porosity (coffee grounds .2 wt-%) barely show changes in mechanical properties, compared with bricks consisting only of clay, resulting in a better thermal insulation capacity. The proportion of added coffee grounds is, therefore, a key factor affecting brick quality. Optimal results are achieved by incorporating 3 wt-% coffee grounds into the clay, since mechanical resistance is then higher than that of the clay, resulting in a decreased bulk density and an increased total porosity and thermal insulation capacity.

References 9 Compressive strength before and after frost resistance trial

Conclusion The present work was conducted to verify the feasibility of incorporating coffee grounds into clay bodies as lightening raw material for ceramic brick production. Such proposal has been presented to offer an alternative use of undervalued organic residue as well as to produce a higher porosity ceramic material in order to improve its thermal insulation ability. Coffee grounds have been chosen since, being organic residue, they may be easily combusted during the firing stage and incorporated into the clay body without causing defects like cracks. In addition, such material does not cause efflorescence in samples since no sulphur is found in its composition. According to the results obtained, incorporating coffee ground amounts of up to 5 wt-% causes an increase in total porosity of the clay body, as shown by bulk density values (a decrease of 6?63%). As a consequence, the residue causes an increase in total porosity of the sample, in open and closed porosity and in absorption and suction values. However, the kind of porosity produced by this residue depends on its concentration. Bricks with lower coffee waste percentage (,2 wt-%) show lower insulation capacity and lower compressive strength according to water absorption data and SEM images. On the contrary, bricks with

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1. X. Elıás: in ‘Reciclaje de Residuos Industriales’, 27–59; 2000, Madrid, Dıáz de Santos, S.A. Ed. 2. R. R. Menezes, G. A. Neves and H. C. Ferreira: Rev. Bras. Eng. Agric. Ambient., 2002, 6, 303–313. 3. M. J. Ribeiro, D. U. Tulyaganov, J. M. Ferreira and J. A. Labrincha: Ceram. Int., 2002, 28, 319–326. 4. D. M. S. Couto, R. F. Silva, F. Castro and J. A. Labrincha: Ind. Ceram., 2001, 21, 163–168. 5. D. A. Pereira, J. B. Aguiar, F. P. Castro, M. F. Almeida and J. A. Labrincha: Cem. Concr. Res., 2000, 30, 1131–1138. 6. J. A. Pe´rez, R. Terradas, M. R. Manent, M. Sejas and S. Martinez: Ind. Ceram., 1996, 16, 7–10. 7. D. M. Couto, A. Ringuede´, R. F. Silva, J. A. Labrincha and C. M. S. Rodriguez: Am. Ceram. Bull., 2003, 82, 9101–9103. 8. M. Dondi, M. Marsigli and B. Fabbri: Tile Brick Int., 1997, 13, 218–225. 9. Ch. Schmidt-Reinholz: Tile Brick Int., 1990, 6, (3), 23–27. 10. M. Dondi, M. Masigli and B. Fabbri: Tile Brick Int., 1997, 13, 218– 225. 11. M. Dondi, M. Masigli and B. Fabbri: Tile Brick Int., 1997, 13, 302– 309. 12. S. Krebs and H. Mo¨rtel: Tile Brick Int., 1999, 15, (1), 23–27. 13. V. Duchan and T. Kopar: Ind. Ceram., 2001, 21, (2), 81–86. 14. J. Garcıá-Ten, G. Silva, V. Cantavella and M. Lorente: Conarquitectura, 2005, 324, 89–96. 15. I. Demir: Waste Manage., 2007, 28, 622–627. 16. I. Demir: Build. Environ., 2006, 41, 1274–1278. 17. V. Duckman and T. Kopar: Ind. Ceram., 2001, 21, (2), 81–86. 18. S. N. Monteiro, C. M. F. Vieira, M. M. Ribeiro and F. A. N. Silva: Constr. Build. Mater., 2007, 21, 2007–2011. 19. H. Mekki, M. Anderson, M. Benzina and E. Ammar: J. Hazard. Mater., 2008, 158, 308–315. 20. L. Sańchez-Munõz and J. B. Carda-Castello`: ‘Materias primas y aditivos cera´micos’; 2003, Castelloń, Faenza Editrice Ibe´rica S. L. 21. D. F. Lin, H. L. Luo and Y. N. Sheen: J. Air Waste Manage., 2005, 55, 163–172. 22. C. H. Weng, D. F. Lin and P. C. Chiang: Adv. Environ. Res., 2003, 7, 679–685.