Performance assessment of fired bricks incorporating pomegranate peels waste

This research investigated the reuse potential of pomegranate peels waste (PPW) in the production of fired clay bricks with improved thermo-physical and mechanical properties. PPW was used as a substitute for natural clay with different replacement ratios ranging from 0 to 12.5% with a stride of 2.5 wt%. The impact of adding PPW on compressive strength, total porosity, water absorption, bulk density, thermal conductivity and microstructure characteristics has been assessed for bricks fired at 900, 1000 and 1100 °C. With the increase of PPW replacement ratio, the bulk density, thermal conductivity and compressive strength decreased. The obtained results confirm the possibility of using PPW as a sustainable pore forming agent in brick industry. The incorporation of 12.5 wt% PPW showed the lowest bulk density (1230 kg/m3), the lowest thermal conductivity (0.2 W/mK), the lowest compressive strength (5.5 MPa), the highest water absorption (38%), and the highest total porosity (48%) for bricks fired at 1000 °C. The obtained compressive strength satisfies the minimum acceptable requirements for clay bricks. The contribution of the newly developed bricks to the energy consumption performance of a building model has been evaluated by using DesignBuilder energy simulation software. A considerable reduction in the annual energy consumption by about 23.3% has been attained as compared to the traditional bricks.


Introduction
As a result of the massive increase in the population, the demand for building materials has become so unprecedentedly great, that it has become necessary to search for new sources for efficient building materials to meet these increasing requirements. Huge quantities of unmanaged daily waste are the cause of significant environmental problems [1]. The use of this waste in the manufacture of building materials had some environmental and economic benefits. In particular, the manufacture of lightweight masonry bricks offers an excellent opportunity regarding the use of such waste [2]. Furthermore, the development of high-rise buildings is driving global efforts to produce lightweight construction and building materials [3][4][5].
In 2020 the global market size of pomegranate was 236.8 million USD and it is proposed to reach 343.6 million USD in 2027, due to the growing demand for pomegranate products such as table fruit, pomegranate jam, pomegranate juice, seed drinks, pharmaceuticals and beauty products [6]. Along with the global statistics, Iran, USA, China and India are the major producers of pomegranate. Amid them, India as one of the largest pomegranate producer, India alone has a growing rate of 1.14 million tons annually. Peels represent 50% of the weight of the whole pomegranate and are mostly disposed of as waste [7]. In this respect, Chiang et al. [8] evaluated the effect of mixing dried water treatment sludge and rice husk in the production of lightweight bricks using different percentage of rice husk ranging from 0 to 20% wt. totally or partially replaced by sludge waste and sintered at firing temperatures ranging from 900 to 1100 ℃. They found that bricks fired at 1100 ℃ containing 15% wt. rice husk and 5% sludge possessed reasonable mechanical properties and low bulk density that met the standard specifications of lightweight bricks in Taiwan. Da Fonseca et al. [9] studied the possibility of using spent coffee as a secondary raw material with clay in the production of ceramic bricks by adding different percentages ranging from 0 to 20% wt. of spent coffee with clay, dried and fired at the temperatures 900, 1000 and 1100 ℃. Specimens with up to 10% wt. of spent coffee gave the highest mechanical strengths. Moreover, thermal conductivity decreased by about 70% on adding 20% spent coffee to the ceramic bricks. On the other hand, Jambuala et al. [10] incorporated rice husk and its ash in the preparation of porous light weight clay bricks. They fired the produced bricks at 900 ℃ for 3 h and found out that adding 10% rice husk produced bricks with a bulk density of 1.2 g cm −3 and a compressible strength of 4.6 MPa.
The corresponding values obtained on using 10% ash were 1.18 g cm −3 and 5.97 MPa, respectively. Also, Adazabra et al. [11] studied the disposal of spent shea waste in the production of lightweight bricks as secondary raw material. They prepared bricks with different percentage containing 5, 10, 15, 20% wt. of spent shea waste replaced with clay and sintered at different temperatures ranging from 900 to 1200 °C. They found that fired brick at 1000 ℃ containing 15% wt. spent shea waste possessed water absorption of 15.92%, a compressive strength of 6 MPa and a thermal conductivity of 0.31 W m −1 K −1 . On the other hand, the refractory bricks produced from mixing kaolin, grog, beads of polystyrene up to 1.5% wt. and bagasse up to 5% wt. were studied by Hassan et al. [12]. The produced bricks were dried and sintered at 1250 ℃ with soaking time 8 h. The results showed that bricks containing 3% bagasse and 1% polystyrene beads can be utilized in refractory insulation with a bulk density of 1.01 g cm −3 , crushing strength of 4.08 MPa and thermal conductivity of 0.3732 W m −1 K −1 at 800℃. Using the waste produced from the wine industry (stalks, grape seeds, and wine less), Torino et al. [13] obtained lightweight clay bricks with 13% reduction in bulk density and concluded that it was possible to add up to 5% vine waste to the original recipe without impairing its properties. The use of saw dust as addition to clay brick recipes to produce fired porous bricks was recently investigated by Cultrone et al. [14]. Their work showed that up to 10% saw dust was used and the prepared samples fired to temperatures reaching 1100 °C. They concluded that the best insulating refractory bricks were obtained for samples containing 10% wt. sawdust fired at 800 ℃. On the other hand, Siddique et al. [15] mixed 2% cow dung slurry with up to 7.5% saw dust and obtained fired samples which were claimed to have compressive strengths reaching 31.2 MPa. Another abundant waste, namely cigarette butts, was used by Kurmus et al. [16] as additive to clay to prepare porous bricks. Up to 2% waste by weight was incorporated. The samples were fired at temperatures reaching 1100 °C and the results showed that the thermal conductivity of the resulting bodies was lowered by 13%. The authors recommended the use of 1% by weight replacement so as not to alter the mechanical strength of the bricks. The incorporation of water treatment sludge in clay bricks for up to 50% by weight was recently studied by Heniegal et al. [17]. They also tried the addition of some agricultural waste such as rice straw, sugarcane bagasse and wheat straw ashes to the sludge-clay mixture. They concluded that it was possible to obtain lightweight bricks of reasonable properties by firing to 900 °C a mixture of clay and water sludge to which sludge was substituted by 5% vegetable waste. Finally, it is worth mentioning that Murekar et al. [18] and Abed et al. [19] have published comprehensive reviews in the context of using different wastes aiming at producing lightweight bricks. In both works the different types of wastes were discussed and their potential use in the preparation of lightweight bricks evaluated.
In the present study, it is attempted to reuse pomegranate peels waste in the production of lightweight bricks with enhanced insulation properties. By incorporating waste into brick manufacturing not only provide a solution to waste disposal but also leads to resource conservation, and subsequently relieve burden on depleting clay reserves.

Materials
In this study, the primary raw material used for brick manufacturing is a mixture of kaolin and ball clay (1:1 wt.%) obtained from the Sinai region, North East of Egypt. The chemical composition of the clays mixture was determined by X-ray fluorescence (XRF) as demonstrated in Table 1. The mineralogical composition of clay mixture has been determined by X-ray diffraction (XRD) as introduced in Fig. 1. XRD chart revealed that the kaolinite phase is the major mineral phase; in addition, quartz has been detected.
In order to explore the reactions taking place during firing of clay, thermo-gravimetric analysis (TGA) has been conducted up to 1000 °C in nitrogen atmosphere with a purge rate of 20 mL/minute with a heating rate of 10 °C min −1 . Figure 2 displays the TGA-DTG curves. The total weight loss is 12.5% as a result of raising the temperature up to 1000 °C. The moisture content of PPW is released at about 100 °C (i.e., approx. 1%). The main loss due to the dehydroxylation of kaolinite starts at 440 and ends at about 730 °C. It is associated with about 12.5% weight loss, a figure close to the LOI observed.
The waste pomegranate peels were collected from juices factory in Egypt, it was oven dried at 50 °C as per the recommendation of Mphahlele et al. [20]; then after, grounded into powdered form using a mortar and pestle. The obtained PPW powder was utilized without any further treatment. The chemical composition of the prepared PPW powder is illustrated in Table 1. The sieve analyses were performed for both the clay and PPW powder as shown in Fig. 3. As it can be seen, the clay mixture is finer than PPW, their median sizes ( D 50 ) being 0.057 mm and 0.073 mm, respectively.
The TGA pattern of PPW presented in Fig. 4 shows devolatilization of organic material presumably leading to about 50% char formation at approx. 370 °C, followed by its subsequent cracking losing more gases [21]. The high LOI of PPW attributed to its high organic content [22]. Weight loss between temperature ranges of 427-800 °C is assigned to the decomposition of metal carbonates [22].

Samples preparation and testing
The dried PPW was ground by ball milling and mixed at different weight percentages (0, 2.5, 5, 7.5, 10, and 12.5%) with an equal ratio of kaolin and ball clay. The dry raw materials were mixed at a speed of 50 rpm using an electric mixer for 2 min to obtain a homogenous mix. The mixtures were blended with 25 wt.% of water, and then molded in steel cubic molds of dimensions (50 × 50 × 50 mm 3 ). The molds filled with mixtures were vibrated for 1 min to remove entrapped air bubbles. The samples were left to dry in their molds at 25 °C and 50% RH for 24 h, then removed and dried at 110℃ in a drying oven for 6 h. Samples were then fired in a muffle furnace to different firing temperatures (900, 1000, 1100℃) with a soaking time 2 h. The heating rate was kept at 3℃/min to avoid quick escaping of gases which may lead to crack formation. The following tests were performed to determine the characteristics of fired samples: Percentages of water absorption, apparent porosity and bulk density [23], compressive strength [24] and thermal conductivity [25,26].
In all cases, three specimens were tested and the average value of the parameter investigated calculated.

Water absorption
Water absorption was performed according to ISO 5017 standard [23]. The fired bricks were totally immersed in boiled water bath for 5 h then left to cool down for 19 h as shown in Fig. 5. The bricks were removed from water bath to gently wiped using soft cloth to eliminate the excess water present in the surface of the bricks. Finally, the wet bricks were immediately weight recorded using the following equation [26]:

Apparent porosity
Apparent porosity of fired clay bricks is directly related to the water absorption capacity. The fired clay brick with high porosity has a low thermal conductivity which has a good insulating property. Apparent porosity expresses the percentage relationship between the volumes of open pores to the exterior volume and can be calculated using the following equation [27]:

Bulk density
The clay brick density is a significant parameter which indicating the performance of the fired clay bricks. The low (1) Water absorption (%) = Wet bricks − Dry bricks Dry bricks * 100. (2) Apparent Porosity (%) = Wet bricks − Dry bricks Volume of dry bricks * 100. density of fired bricks has a low thermal conductivity and also has a low dead loads for the structure. Bulk density can be calculated using the following equation [27]:

Compressive strength
The fired bricks were tested according to ISO 9652 Standard [19] by applying a perpendicular load to the direction of the pouring brick, which can be calculated by the following equation where C = compressive strength of specimen, N/mm 2 (MPa). W = maximum load, indicated by the testing machine, (N). A = average cross-sectional area of the samples (mm 2 ). The mean value of compressive strength of three samples was determined to be the average compressive strength of the sample.

Thermal conductivity
The thermal conductivity for the brick specimens was measured using the KD2 Pro Thermal Properties Analyzer according to ASTM 5334. The analyzer practices a transitory heat conduction algorithm for digitally recording the (3) Bulk density = Mass offired bricks Volume of fired bricks , gm cm 3 .
(4) C = W A thermal conductivity at ambient temperature. Figure 6 summarizes the samples preparation and testing.

Results and discussion
Bulk density Figure 7 shows the impact of the various PPW percentages on the bulk density of the bricks fired at 900, 1000 and 1100 °C. The plain bricks (without PPW) showed the highest bulk density. These bricks exhibited bulk densities of 1715, 1720 and 1788 kg/m 3 at the firing temperatures of 900, 1000 and 1100 °C, respectively. These densities sharply decreased to 1274, 1240 and 1340 kg/m 3 with the incorporation of 12.5% PPW. Whatever the firing temperature, all PPW-modified bricks showed comparable reduction rates, i.e., an average reduction rate of 26% has been attained. The comparable reduction rates confirm that firing at 900-1100 °C is enough for the pore formation along with clay activation and reaction; therefore, the increase of firing temperature over 1100 °C is useless.
The lowest bulk density of 1230 kg/m 3 can be obtained with the incorporation of 12.5% PPW and firing temperature of 1000 °C. According to ASTM C90 [28], the density for lightweight masonry brick should be less than 1680 kg/m 3 , which means that all the PPW-modified bricks can be considered as lightweight brick. The decrease of the bulk density is attributed to the occurrence of high more pores in the structure of fired bricks as a result of the decomposition of the organic matter and metal hydrates or carbonates in PPW.

Compressive strength
Variations of compressive strength with PPW content for bricks fired at 900, 1000 and 1100℃ are introduced in Fig. 8. The compressive strength values of control bricks were found to be 10.35, 12.91 and 19.37 MPa with respect to firing temperatures of 900, 1000 and 1100 °C, respectively. This agrees with previously published studies concluded that higher firing temperature produces a brick with higher density and mechanical strength [17,34]. As expected, the incorporation of PPW has reduced the compressive strength as a result of the creation of high number of pores and cavities due to the decomposition and combustion of organic matter [29]. The maximum reduction in strengths was found for the bricks with the highest PPW content (12.5%) because of the higher content of PPW provides higher pores ratio. Reductions by about 70.3, 61.2 and 51.6% were found for the bricks fired at 900, 1000 and 1100 °C, respectively. Even for the highest replacement ratio of PPW, the compressive strengths of all PPW-modified bricks are satisfactory and could meet the minimum strength requirement of 5 MPa as specified in many standards and previous studies [30][31][32]. It should be stressed that the dependence of strength on porosity has been the subject of much research work. However, the classical model of Ryshkewitch [33] is still best suited to interpret that relation quantitatively. The relation between strength ( ) and fractional porosity (p) takes the form: where 0 is the strength at zero porosity and k an empirical constant.
This relation was linearized so as to obtain a linear plot for ln against p and the obtained line shown in Fig. 9 (5) = 0 e −kp

Water absorption and apparent porosity
Water absorption is one of the parameters that help in evaluating the durability aspects of bricks as well as the cracks formed by shrinkage [34]; furthermore, it can be used to estimate the brick surface porosity. Porosity is the number of pores in the matrix. It influences the thermal insulation efficiency, mass transport, and strength [35]. The variations of water absorption (WA) and apparent porosity with PPW content for the bricks fired at 900, 1000, 1100 ℃ shown in Figs. 10, 11. Water absorption and total porosity increases with increasing PPW percentages in practically linear manner, which points to the efficiency of PPW as pore forming agent. Replacing the clay with 12.5 Wt.% of PPW resulted in increasing the porosity by 51, 55 and 62%, this is associated with increase in the water absorption by about 107, 119 and 117% with respect to the firing temperatures of 900, 1000 and 1100 ℃ respectively. The increase in total porosity over 50% is effective in providing better insulation properties for fired clay bricks as confirmed by Sutcu and Akkurt [36].
Although the variations in firing temperatures possessed slight differences in WA and porosity, the lowest porosity and water absorption are obtained for the bricks fired at 1100 ℃ this is attributed to their relatively denser structure. Although the formation of pores in the brick structure is responsible for the reduced compressive strength as well as the higher water absorption and total porosity, the increased porosity has a positive effect on the performance of bricks, as these pores facilitate water vapor migration inside brick skeleton and hence provide resistance to crack propagation, especially in the humid climate zones [35].

Thermal conductivity
The variation in thermal conductivity of all fired bricks as function of PPW content is shown in Figure 12. The control brick fired at 1100 °C showed the highest thermal conductivity (0.36W.m -1.K -1) , this is due to the high firing temperature provide more dense bricks. The thermal conductivities of the PPW-blended bricks decrease with increasing the PPW content whatever the firing temperature. Remarkable reductions by about 39, 35 and 22% were obtained for the bricks incorporating 12.5 Wt.% PPW with respect to the firing temperatures 900, 1000 and 1100 °C, respectively. The lowest thermal conductivity (About 0.2W m -1 K -1 ) was obtained for 12.5% PPW-blended brick at firing temperature of 900 °C. The creation of pores as a result of the devolatilization of PPW additives explains the reduction in thermal conductivity with increasing PPW content. As it is well known,  Fig. 12 Variations of thermal conductivity with PPW content for bricks fired at 900, 1000 and 1100 ℃ thermal conduction is heat transfer by microscopic motions of matter. Phonon is a quantized form of atomic vibrations, and phonon transport is responsible for thermal conduction in solid materials. Ceramics and refractories thermal conductivity is mainly promoted by the solid matrix lattice vibrations (i.e., phonons). However, phonons scattering highly affect their mean free path which reduce heat flux/ transfer. Among the sources of scattering (additives, isotopes, etc.), pores are strong phonon scatterers [37]. The pores created via PPW decomposition can increase phonons scattering and this in turn decreases the phonon mean free path and result in decreasing the thermal conductivity of solid brick. It is interesting to note that several models have been suggested to interpret the relation between thermal conductivity (k) and fractional porosity (p) . The Loeb model [38] assumes a relation in the form: On the other hand, the Maxwell-Eucken model [38] predicts a relation in the form: where k 0 is the thermal conductivity at zero porosity and , are empirical constants.
In Fig. 13, the relation between thermal conductivity and fractional porosity is presented for all developed bricks. A generally decreasing trend is apparent and the Loeb model seems to describe best the experimental results with = 1.14 , predicting a zero-porosity conductivity of about 0.5 W.m −1 K −1 . This figure fairly agrees with the findings of Smith et al. [39] who predicted a zero conductivity for kaolin based fired bodies of 0.62 W m −1 K −1 . Figure 14 presents the microstructure characteristics of the bricks incorporating different percentages of PPW at 900 °C firing temperature. As it is clear, the bricks prepared without PPW showed homogeneous and compact structure; however, the incorporation of PPW resulted in the formation of high number of micro-pores uniformly distributed throughout the hardened matrix. The observed pores possessed various shapes like oval and spherical. There is a directly proportional relationship between the PPW content and the number and size of pores. The higher the ratio of PPW is, the higher number and diameter of the micro-pores are. The pores diameters that have been produced are in the range of sub-millimeters. The pore formation can be attributed to the devolatilization process during firing process which involves the emission of the volatile gaseous matters.

Energy simulation
Designbuilder simulation program is a very effective tool in the evaluation of building materials in terms of thermal and energy performances. It has Energy Plus analysis engine and can calculate the energy consumption of buildings. In this study, energy simulations were conducted using Design-Builder (V.3.0.0.105) for two model rooms with dimensions (4 m long × 4 m wide × 3 m high) as shown in Fig. 15. The climate zone of Cairo, Egypt As defined in EREC [40,41] was considered; this zone is characterized by desert moderate climate. The annual energy consumption was assessed for a room built from the newly developed bricks and the results were compared to that made of traditional/dominant cement hollow blocks. Table 2 demonstrates the thermal characteristics of the two wall constructions evaluated in this study. The model room was a North-oriented. The main assumptions of the simulation setup are summarized as following: • The room is air-conditioned-HVAC (split, no fresh air). • Thermal comfort or the set point was 22 °C. • The lightning and the other types of equipment were ignored. • The working time was from 8 am to 6 pm. • Window to wall ratio is 10% with an opening single clear 6 mm glazing material.
The monthly cooling energy consumption (kWh) data obtained for the simulated two room models along with the outdoor dry bulb temperatures (°C) are presented in Fig. 16.
As expected, the newly developed bricks exhibited better energy performance relative to the traditional cement hollow blocks. The annual cooling energy consumption of the room built form the developed bricks is 533 KWh, i.e., 23.3% less than that of the cement hollow blocks which recorded 695 KWh. As compared with the traditional clay bricks, the developed lightweight bricks showed better energy performance [42]. This is attributed to the higher thermal resistance of the developed bricks afforded by the high number of air voids which help in retarding heat flow into the building and hence reducing indoor cooling loads required for attaining acceptable thermal comfort level for its occupants; this in turn, helps in reducing energy consumption for cooling in hot climate regions and minimizing CO 2 emissions [39,40]. These results agree with the findings of a pervious study which confirmed the increase in thermal resistance of cement blocks incorporating varying amounts of date palm ash (DPA) as cement replacement. An increase in thermal resistance by about 47.4% has been obtained for the blocks containing 30% DPA relative to the control block (without DPA). The annual energy consumption and cooling load of the building made with DPA-blended blocks have been reduced by 7.66% and 11%, respectively [43].

Conclusions
Buildings are responsible for a significant percentage of the world's energy consumption and associated CO 2 emission, improving the thermo-physical properties of building envelope materials will help in reducing heat transfer into the building and the electrical cooling energy consumption.
In the current study, the potential of using PPW as a pore forming agent in the production of lightweight bricks with improved thermal insulation and their contribution to energy saving have been assessed, the following conclusions can be drawn: 1. PPW can be utilized as a pore forming agent to produce lightweight fired bricks with reduced thermal conductivity and reasonable/ acceptable compressive strength. 2. The bricks produced with 12.5 Wt.% PPW as partial replacement of clay achieved the lowest bulk density (1240 kg/m 3 ) and the lowest thermal conductivity (0.2 W m −1 K −1 ), this is afforded by the increased total porosity ≈ 48%. 3. Even at the highest PPW percentage, the lowest compressive strength attained is 5.5 MPa, which might satisfy the standard structural requirements load bearing blocks. 4. The SEM analysis of the PPW-modified fired bricks showed that, the higher the ratio of PPW is; the higher number and diameter of the micro-pores are. 5. The newly developed bricks help in reducing electric cooling energy consumption. An energy saving by about 23% has been attained. This is attributed to the high thermal resistance afforded by PPW additives.
Furthermore, future research is recommended to explore the initial energy consumption required for preparing the newly developed bricks. Moreover, feasibility studies to compare the cost with the traditional bricks.

Conflict of interest
The authors declare that they do not have any confict of interest.
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