The Effect of Bone Ash on the Physio-Chemical and Mechanical Properties of Clay Ceramic Bricks

: Bone ash waste can be used to fabricate clay ceramic bricks, consequently managing their pollution of the environment. This is because bone ash (BA) and clay predominantly consist of calcium and alumina-silicate, respectively, which are components of clay ceramic brick (CCB) materials. This study aims to investigate the effect of bone ash and temperature on the physio-chemical and mechanical properties of CCB. Different percentages of bone ash (5%, 10%, 15%, and 20%) were added to clay and heat treated at temperatures of 100 ◦ C, 300 ◦ C, 600 ◦ C, and 900 ◦ C, and their compressive strengths were measured. Prior to the determination of their mechanical properties, the CCB chemical and phase compositions were characterized using FTIR spectroscopy and X-ray diffraction (XRD). The CCB microstructure was evaluated with scanning electron microscopy (SEM) and the compressive strength was tested. The results suggest that the addition of bone ash (10% and 15%) improves the compressive strength and water absorption properties after heat treatment of CCB at higher temperatures. the decrease in apparent porosity from sample 100C to 20BAC is due to the decrease in the evolution of pores as the interstice is occupied, the packing fraction of bricks increases, and thus the porosity reduces. The 100C, 5BAC, and 10BAC samples heat-treated at 900 ◦ C had porosities of 35%, 33%, and 31%, respectively, which was congenial to clay bricks [49]. The slight increase in apparent porosity from samples 15BAC to 20BAC might be a result of the increase in pozzolanic and cementitious reaction in 20BAC at 600 ◦ C. The apparent porosity increased with the increase in heat treatment temperature from 600 ◦ C to 900 ◦ C. This might have been a result of the loss of organic compounds at higher heat-treated samples at 900 ◦ C in the brick material that caused extra pores, leading to a higher porosity.


Introduction
Environmental pollution and climate change awareness has increased in recent years. The emission of CO 2 from cement production is a major concern for environmentalists [1,2], which calls for an alternate cement material for construction companies [3,4]. Pozzolanic and cementitious materials are less costly and have the needed mechanical strength to serve as construction material for building purposes. A further advantage is that CCB production releases less CO 2 into the environment compared with Portland cement [5,6], which is partly owing to bone ash being an agricultural waste material [7].
Clay ceramic bricks are potential building materials that can be strengthened by the addition of some environmental waste materials. Clay ceramic bricks (CCB) are materials formed as a result of partial replacement of clay with other mineral waste such as fly ash [8], marble sludge [9], and bone ash [10], which improves the materials' mechanical properties. Typically, the mechanical properties depend on the type of mineral addition and processing temperature [11].
An increase in agricultural activities has caused an increase in agricultural waste products, resulting in environmental pollution. Consequently, research to reduce environmental

Characterization of Materials
X-ray fluorescence (XRF) Thermo Scientific (ARL Quant'x model) Epsilon Spectrometer was used for the chemical composition analysis of clay and bone ash. Fourier-transform infrared (FT-IR) spectroscopy Thermo Scientific (Nicolet™ iS™5 model) was used for functional group analysis of clay, bone ash, and clay ceramic bricks (CCB). X-ray diffraction (XRD) Thermo scientific model (ARL'XTRA X-ray, Rotreuz) was used for phase analysis of the materials using the following set parameters. The XRD patterns were measured at 40 mA and 45 kV under CuKα radiation (λ = 1.5406 Å) from 5 to 75° 2θ with the scan step rate of 0.03° 2θ/min. The surface morphology and elemental composition of the clay ceramic bricks were determined with scanning electron microscope (SEM/EDX) using Carl Zeiss Model Evo LS10 after polishing and coating samples with gold to prevent sample charging.

Physio-Chemical and Mechanical Properties of Clay Ceramic Bricks' Measurement
The bulk density, water absorption, and apparent porosity of clay ceramic bricks at 600 °C and 900 °C were determined using the British Standards for clay ceramics (1985) [34]. The clay ceramic bricks (CCB) were soaked completely for 24 h in water, the samples were removed from water, and excess water was wiped from the surface of CCB. The bricks were suspended in water for a minute, removed, and re-weighed. Water absorption measurements were done for brick samples only heat-treated at 600 °C and 900 °C . The dry weight (Ms), the saturated weight of wet bricks in air (W), and the suspended weight in water (Mw) of the samples were noted. The bulk density, apparent porosity, and water absorption were calculated from Equations (1)- (3). The compressive strength of CCB was determined using the compressive testing machine model ELE ADR (series No.1912-3-00282, UK). A replicate of five samples for each clay/bone ash composition was measured (Table 1) and the average compressive strength was recorded. The samples were pre-dried at room temperature (26 °C ) for 21 days before heat treatment. The weight of each brick was measured using an electronic balance and the actual size of each sample was taken using a Vernier Calipers before and after heat treatment. The clay ceramic bricks were fired at temperatures of 100 °C , 300 °C , 600 °C , and 900 °C . The compressive testing was done at a 0.250 MPa/s loading rate under monotonic failure. Compressive strength (CS) was calculated from the failure load (F) divided by surface area (A) of the bricks (Equation (4)).

Characterization of Materials
X-ray fluorescence (XRF) Thermo Scientific (ARL Quant'x model) Epsilon Spectrometer was used for the chemical composition analysis of clay and bone ash. Fourier-transform infrared (FT-IR) spectroscopy Thermo Scientific (Nicolet™ iS™5 model) was used for functional group analysis of clay, bone ash, and clay ceramic bricks (CCB). X-ray diffraction (XRD) Thermo scientific model (ARL'XTRA X-ray, Rotreuz) was used for phase analysis of the materials using the following set parameters. The XRD patterns were measured at 40 mA and 45 kV under CuKα radiation (λ = 1.5406 Å) from 5 to 75 • 2θ with the scan step rate of 0.03 • 2θ/min. The surface morphology and elemental composition of the clay ceramic bricks were determined with scanning electron microscope (SEM/EDX) using Carl Zeiss Model Evo LS10 after polishing and coating samples with gold to prevent sample charging.

Physio-Chemical and Mechanical Properties of Clay Ceramic Bricks' Measurement
The bulk density, water absorption, and apparent porosity of clay ceramic bricks at 600 • C and 900 • C were determined using the British Standards for clay ceramics (1985) [34]. The clay ceramic bricks (CCB) were soaked completely for 24 h in water, the samples were removed from water, and excess water was wiped from the surface of CCB. The bricks were suspended in water for a minute, removed, and re-weighed. Water absorption measurements were done for brick samples only heat-treated at 600 • C and 900 • C. The dry weight (Ms), the saturated weight of wet bricks in air (W), and the suspended weight in water (Mw) of the samples were noted. The bulk density, apparent porosity, and water absorption were calculated from Equations (1)-(3). The compressive strength of CCB was determined using the compressive testing machine model ELE ADR (series No.1912-3-00282, UK). A replicate of five samples for each clay/bone ash composition was measured (Table 1) and the average compressive strength was recorded. The samples were pre-dried at room temperature (26 • C) for 21 days before heat treatment. The weight of each brick was measured using an electronic balance and the actual size of each sample was taken using a Vernier Calipers before and after heat treatment. The clay ceramic bricks were fired at temperatures of 100 • C, 300 • C, 600 • C, and 900 • C. The compressive testing was done at a 0.250 MPa/s loading rate under monotonic failure. Compressive strength (CS) was calculated from the failure load (F) divided by surface area (A) of the bricks (Equation (4)).
Water absorption (%) = M − Ms Ms × 100 The chemical composition of bone ash (BA) and kaolin clay (KC) is presented, as shown in Table 2. The result showed that P 2 O 5 (34.50%) and CaO (42.87%) were the major chemical constituents in BA. This suggests that the major inorganic component of bone ash may be hydroxyapatite (Ca 5 (PO 4 ) 3 OH). The major components of KC are alumina (54.81%) and silica (22.72%); Table 2. This result was consistent with the chemical composition of BA and KC from the obtained SEM-EDX analysis shown in Figure 2. The combined constituent of ferric oxide (Fe 2 O 3 ), potassium oxide (K 2 O), titanium oxide (TiO 2 ), manganese oxide (MgO), calcium oxide (CaO), and titanium oxide (TiO 2 ) was more than 10%, suggesting the clay to be a low refractive material [9]. The Ca(OH)2 formed during cementitious reactions from the chemical components of BA and water is also suggested to improve compressive strength. Calcium hydroxide [Ca(OH)2], also known as portlandite, is then further reacted with silicate from the alumina-silicate clay to give a calcium silicate hydrate (CaSiO3·2H2O) [36] as a cementitious compound, leading to the increase in the compressive strength of the ceramic clay bricks (Equation (7)).
Ca(OH)2(aq) + H2SiO3(aq)→ CaSiO3·2H2O(s) 3.1.2. XRD Analysis Figure 2 shows diffraction patterns of bone ash (BA), kaolin clay (KC), and clay ceramic bricks (CCB). The XRD patterns showed that the two major phases are kaolinite and quartz in KC. Hydroxyapatite is the major crystalline phase in bone ash (BA) and has some traces of quartz that are also present in sample 15BAC [37,38]. The control sample 100C (0% bone ash) showed that the three phases of XRD patterns are quartz, biotite, and montmorillonite. The ceramic clay bricks (15BAC) present three XRD patterns of hydroxyapatite, chloritoid, and quartz. The XRF (Table 2) also suggested hydroxyapatite in bone ash, as well as Mg, Fe, and K in kaolin clay, which is consistent with the XRD results [35].  The rich alumina-silicate chemical composition in clay indicated that the material is kaolinite clay, and this was further confirmed by the XRD analysis ( Figure 2). The chemical composition of a material contributes to the compressive strength. The increased in compressive strength was a result of cementitious properties owing to the pozzolanic reactions between the calcium oxide in bone ash, alumino-silicate in the clay, and water (Equation (5)) [35].
The reaction between calcium oxide and water has cementitious properties, which enables the clay ceramic bricks' strength to increase (Equation (6)).
The Ca(OH) 2 formed during cementitious reactions from the chemical components of BA and water is also suggested to improve compressive strength. Calcium hydroxide [Ca(OH) 2 ], also known as portlandite, is then further reacted with silicate from the alumina-silicate clay to give a calcium silicate hydrate (CaSiO 3 ·2H 2 O) [36] as a cementitious compound, leading to the increase in the compressive strength of the ceramic clay bricks (Equation (7)).
3.1.2. XRD Analysis Figure 2 shows diffraction patterns of bone ash (BA), kaolin clay (KC), and clay ceramic bricks (CCB). The XRD patterns showed that the two major phases are kaolinite and quartz in KC. Hydroxyapatite is the major crystalline phase in bone ash (BA) and has some traces of quartz that are also present in sample 15BAC [37,38]. The control sample 100C (0% bone ash) showed that the three phases of XRD patterns are quartz, biotite, and montmorillonite. The ceramic clay bricks (15BAC) present three XRD patterns of hydroxyapatite, chloritoid, and quartz. The XRF (Table 2) also suggested hydroxyapatite in bone ash, as well as Mg, Fe, and K in kaolin clay, which is consistent with the XRD results [35].

FTIR Analysis
The FTIR spectra were conducted in the range 400-4000 cm −1 . The observed bands for bone ash, clay, and clay ceramic bricks (CCB) are presented in Figure 3. The characteristic spectra bands around 3556 cm −1 correspond to the hydroxyl (H-O-H, O-H) stretching bonds of hydroxyapatite in bone ash. The H-O-H stretching group showed two peaks close to each other at 3620 cm −1 and 3695 cm −1 in the clay spectra that shift to 3472 cm −1 broad bands in the CCB spectra. The vibrational bands at 2022 cm −1 are due to the presence of the CO 2 group in the bone ash. A similar vibration band at 2361 cm −1 , corresponding to clay, appeared at the same intensity as the CO 2 group [39]. The 1650 cm −1 and 1636 cm −1 bands are associated with amide (NH 2 ) stretching groups on bone ash and CCB, respectively. The band at 1412 cm −1 assigned to bone ash spectra is due to CO 3 −2 vibrations. The bone ash PO 4 −2 stretching vibrational bands were observed at 1094 cm −1 , 1058 cm −1 , 630 cm −1 , and 561 cm −1 , and is in agreement with the XRF (Table 2)  quartz in the XRD of clay (Figure 1). The band at 912 cm −1 corresponds to Al-O stretching bonds in kaolin clay. The bands at 537 cm −1 and 428 cm −1 are attributed to O-H bending bonds of clay. The band at 460 cm −1 is assigned to Al-O-Si vibration bonds on the CCB spectra [42].    Figure 5 illustrates SEM micrographs of brick materials that have been heat-treated at 100 °C , 300 °C , 600 °C , and 900 °C. It can be seen from this figure that the ceramic bricks became denser as temperature increased from 100 °C to 900 °C ; Figure 5. The irregular crystalline particles of bone ash bonded and fused eventually with the irregular sphere particles of clay, decreasing the apparent porosity as the temperature increased. Generally, bone ash addition increased the quantity of hydroxyapatite and, therefore, increased the cementitious reaction as the temperature became higher [35]. The surface of the ce- particles of clay, decreasing the apparent porosity as the temperature increased. Generally, bone ash addition increased the quantity of hydroxyapatite and, therefore, increased the cementitious reaction as the temperature became higher [35]. The surface of the ceramic brick produced at 100 °C became smoother owing to an improved cementation reaction within the clay ceramic brick ( Figure 5) [35]. Dense crystalline phases on CCB at 600 °C and 900 °C were due to sintering clay bone ash composite, as observed by Johari et al. (2010) [27]. Increasing the temperature forms denser CCB.  also showed Si and Al as the major constituents in clay with a trace of Fe. The minor constituent elements present, including Fe, Mg, and K, were more than 10% (

Plasticity Analysis of Bricks
Brick samples dried at room temperature for 21 days had no observable defects, such as bloating or cracks. After fracturing samples heat-treated to 900 °C, there was no observed dark coloration on the fracture surface, suggesting that any organic residues were  Figure 5 illustrates SEM micrographs of brick materials that have been heat-treated at 100 • C, 300 • C, 600 • C, and 900 • C. It can be seen from this figure that the ceramic bricks became denser as temperature increased from 100 • C to 900 • C; Figure 5. The irregular crystalline particles of bone ash bonded and fused eventually with the irregular sphere particles of clay, decreasing the apparent porosity as the temperature increased. Generally, bone ash addition increased the quantity of hydroxyapatite and, therefore, increased the cementitious reaction as the temperature became higher [35]. The surface of the ceramic brick produced at 100 • C became smoother owing to an improved cementation reaction within the clay ceramic brick ( Figure 5) [35]. Dense crystalline phases on CCB at 600 • C and 900 • C were due to sintering clay bone ash composite, as observed by Johari et al. (2010) [27]. Increasing the temperature forms denser CCB.
Similar to the work of Ifka et al. (2012) [44], the EDX analysis showed calcium and phosphorus as the major constituents in bone ash, with some traces of Si (Figure 6a). EDX also showed Si and Al as the major constituents in clay with a trace of Fe. The minor constituent elements present, including Fe, Mg, and K, were more than 10% (Table 2). No surface cracks were observed on CCB for bricks fired up to 900 • C. Obianoyo et al. (2020) have shown that hydroxyapatite in bone ash and Si in laterite soil improve the cementitious property and compressive strength of bricks. In our results, the presence of hydroxyapatite, as evidenced by X-ray and EDX with Ca and Si, helped improve the cementitious property of the CCB and resulted in higher compressive strengths.

Plasticity Analysis of Bricks
Brick samples dried at room temperature for 21 days had no observable defects, such as bloating or cracks. After fracturing samples heat-treated to 900 • C, there was no observed dark coloration on the fracture surface, suggesting that any organic residues were completely burned out after the 900 • C heat treatment. The physical properties of raw materials analyzed before the production of the clay ceramic bricks indicated that bricks fired above 1200 • C will crack and effloresce owing to the over 10% minor chemical constituents in clay ( Table 2). The Atterberg Limits according to BS1377 standard [45] were used to characterize the physical properties of clay. An amount of 400 g of clay was mixed with distilled water for 10 min in a glass plate. Using a Palette knife, the paste was transferred in a brass cup while tapping gently to avoid air trap, and excess clay was removed. The penetration cone was placed at the surface of paste and the dial gauge was lowered to touch the cone shaft, and the first reading was recorded. The cone was released for a period of 5 s and the dial gauge was released to touch the cone shaft. The second reading was taken and the difference between readings was recorded during penetration. The process was repeated until the overall range was not more than 1 mm. The process was repeated five times. A graph of moisture content versus penetration of cone was plotted and the moisture content corresponding to 20 mm is the liquid limit. The clay sample retained material on a 425 µm sieve was removed and 40 g of sieved clay mixed with distilled water was placed in a glass plate. The paste was allowed to dry partially and became plastic to roll. The clay was rolled into a ball with fingers until slight cracks due to drying were noticed. The rolled clay was divided into two halves of 20 g each and each half was further divided into four parts. The different parts were rolled into threads until reaching a 3 mm diameter and the first crumbling point was taken as the plastic limit. The plastic limit, liquid limit, and moisture content are important parameters in forming clay bricks ( Table 3). The plasticity of clay is given by its plasticity index. The plasticity index of clay was measured by calculating the difference between the liquid limit and plastic limit. The plasticity index for kaolin clay is usually between 30% and 35% [46]. A reddish brown coloration of clay observed as spherical particles (Figure 4b) is due to the presence of iron oxides [47]. The presence of iron oxide in clay gives clay a low plasticity. The presence of Fe in the clay was confirmed by the EDX analysis ( Figure 6). Therefore, the reddish brown clay used in this work had a low plasticity index of~15.32%. Consequently, the plasticity of the clay material was improved by soaking in water for a month prior to being used. The clay liquid limit of 41.8% was good enough for handling and molding.

Bulk Density
The bulk densities of clay ceramic bricks are presented in Figure 7. Clay ceramic bricks samples at 100 • C and 300 • C were not verified for bulk density, apparent density, and apparent porosity owing to the high water absorption of the bricks and the samples' dissolution in water. The bulk density of clay ceramic bricks (CCB) was between 1.59 g/cm 3 and 1.81 g/cm 3 . Generally, the bulk density increased with the percentage of bone ash added. This could result from the increase in the reactive silica from 5BAC to 20BAC reacted with CaO, hence forming C-S-H, which caused an increase in the bulk density. The materials became denser and the pores reduced as the molecules take the place of the interstice, hence increasing the packing factor, which results in a dense material. The sample 5BAC showed a moderate bulk density of 1.59 g/cm 3 and 1.62 g/cm 3 at 600 • C and 900 • C, respectively. It is also suggested that the presence of a fluxing agent (K 2 O, MgO, Fe 2 O 3 , and CaO) >10% forms liquid phase molten materials during firing at 900 • C compared with CCB fired at 600 • C, which led to increased bulk density [48]. Thus, we assume that the required minimum of hydroxyapatite in bone ash to improve the cementitious property with a moderate bulk density is~5% and the maximum is 15%.

Apparent Porosity
The apparent porosity of a clay ceramic brick is a very important parameter in bu ing materials. Figure 8 presents the apparent porosity of clay ceramic bricks (CCB) at t peratures of 600 °C and 900 °C [34]. Apparent porosity increased from 600 °C to 90 and decreased from sample 100C to 20BAC. The evolution and coalescence of pores higher temperature might be attributed to the increase in apparent porosity at 900 However, the decrease in apparent porosity from sample 100C to 20BAC is due to

Apparent Porosity
The apparent porosity of a clay ceramic brick is a very important parameter in building materials. Figure 8 presents the apparent porosity of clay ceramic bricks (CCB) at temperatures of 600 • C and 900 • C [34]. Apparent porosity increased from 600 • C to 900 • C and decreased from sample 100C to 20BAC. The evolution and coalescence of pores at a higher temperature might be attributed to the increase in apparent porosity at 900 • C. However, the decrease in apparent porosity from sample 100C to 20BAC is due to the decrease in the evolution of pores as the interstice is occupied, the packing fraction of bricks increases, and thus the porosity reduces. The 100C, 5BAC, and 10BAC samples heat-treated at 900 • C had porosities of 35%, 33%, and 31%, respectively, which was congenial to clay bricks [49]. The slight increase in apparent porosity from samples 15BAC to 20BAC might be a result of the increase in pozzolanic and cementitious reaction in 20BAC at 600 • C. The apparent porosity increased with the increase in heat treatment temperature from 600 • C to 900 • C. This might have been a result of the loss of organic compounds at higher heat-treated samples at 900 • C in the brick material that caused extra pores, leading to a higher porosity.
ing materials. Figure 8 presents the apparent porosity of clay ceramic bricks (CCB) at t peratures of 600 °C and 900 °C [34]. Apparent porosity increased from 600 °C to 900 and decreased from sample 100C to 20BAC. The evolution and coalescence of pores higher temperature might be attributed to the increase in apparent porosity at 900 However, the decrease in apparent porosity from sample 100C to 20BAC is due to decrease in the evolution of pores as the interstice is occupied, the packing fractio bricks increases, and thus the porosity reduces. The 100C, 5BAC, and 10BAC sam heat-treated at 900 °C had porosities of 35%, 33%, and 31%, respectively, which was c genial to clay bricks [49]. The slight increase in apparent porosity from samples 15BA 20BAC might be a result of the increase in pozzolanic and cementitious reaction in 20B at 600 °C . The apparent porosity increased with the increase in heat treatment tempera from 600 °C to 900 °C . This might have been a result of the loss of organic compound higher heat-treated samples at 900 °C in the brick material that caused extra pores, lead to a higher porosity.

Water Absorption
The effect of water absorption on clay ceramic bricks (CCB) is essential to validate their durability. The water absorption of CCB is inversely proportional to its durability. The higher the water absorption, the lower the degradation and the durability of the CCB [31]. Figure 9 shows the water absorption of clay ceramic bricks versus percentage addition of bone ash (BA) in clay at 600 • C and 900 • C. Water absorption decreased with increased BA addition, which resulted in densification from 100C to 20BAC. The increase in bulk density decreased with water absorption. This may due to the formation of a calcium silicate hydrate (C-S-H) thin layer and calcium hydroxide (portlandite) at high temperatures, which reduce water adsorption at higher temperatures [3]. Owing to incomplete dehydration of water molecules from CCB heat-treated at 100 • C and 300 • C, the bricks collapsed totally during the water absorption test. A complete dehydration of water molecules in the consolidated CCB body and the closing of interstices at 600 • C and 900 • C prevented the CCB from completely absorbing water. A temperature as low as 600 • C is recommended to achieve low water absorption and high compressive strength to fabricate low energy cost CCB. This result agrees with the study of red brick ceramics sintered at 600 • C conducted by Monteiro et al. (2003) [29].
collapsed totally during the water absorption test. A complete dehydration of water m ecules in the consolidated CCB body and the closing of interstices at 600 °C and 900 prevented the CCB from completely absorbing water. A temperature as low as 600 ° recommended to achieve low water absorption and high compressive strength to fabric low energy cost CCB. This result agrees with the study of red brick ceramics sintered 600 °C conducted by Monteiro et al. (2003) [29].

Percent Weight Loss (%) of Clay Ceramic Bricks
The percent weight loss ( Figure 10) of clay ceramic bricks (CCB) was measured weighing the bricks after drying (Wb) in the oven and after heat treatment at temperatu of 100 °C , 300 °C , 600 °C , and 900 °C for an hour (Wa) (Equation (8)). The weight los CCB increased with the increasing temperature. Moreover, the weight loss increased w bone ash addition in clay. The increase in weight loss is due to the removal of water m ecules and organic compounds during heat treatment at the given temperature. This related with the increase in apparent porosity ( Figure 8) as temperature increased. CC 100 °C and 300 °C showed very low weight percent loss, attributed to water retent thanks to the hydrophilic nature of the samples.
Percent weight loss (%) = w a − w b w b X 100 Figure 9. Water absorption of clay ceramic bricks at 600 • C and 900 • C.

Percent Weight Loss (%) of Clay Ceramic Bricks
The percent weight loss ( Figure 10) of clay ceramic bricks (CCB) was measured by weighing the bricks after drying (W b ) in the oven and after heat treatment at temperatures of 100 • C, 300 • C, 600 • C, and 900 • C for an hour (W a ) (Equation (8)). The weight loss of CCB increased with the increasing temperature. Moreover, the weight loss increased with bone ash addition in clay. The increase in weight loss is due to the removal of water molecules and organic compounds during heat treatment at the given temperature. This correlated with the increase in apparent porosity ( Figure 8) as temperature increased. CCB at 100 • C and 300 • C showed very low weight percent loss, attributed to water retention thanks to the hydrophilic nature of the samples. The effect of bone ash addition to the compressive strength is presented in Figure 11.

The Effect of Bone Ash Addition and Temperature on the Compressive Strength of Clay Ceramic Bricks
The effect of bone ash addition to the compressive strength is presented in Figure 11. The bone ash addition to the clay matrix for the production of clay ceramic bricks (CCB) increased the compressive strength. Further, the compressive strength was found to increase at higher temperatures. The addition of 10% and 15% bone ash showed the highest compressive strength at all temperatures. The strength increase was highest for CCB samples processed at 600 • C and 900 • C, suggesting that the cementitious properties of bone ash are effective at higher temperatures. Figure 10. Percent weight loss of clay ceramic bricks after drying at 100 °C , 300 °C , 600 °C , and 900 °C .

The Effect of Bone Ash Addition and Temperature on the Compressive Strength of Clay Ceramic Bricks
The effect of bone ash addition to the compressive strength is presented in Figure 11. The bone ash addition to the clay matrix for the production of clay ceramic bricks (CCB) increased the compressive strength. Further, the compressive strength was found to increase at higher temperatures. The addition of 10% and 15% bone ash showed the highest compressive strength at all temperatures. The strength increase was highest for CCB samples processed at 600 °C and 900 °C, suggesting that the cementitious properties of bone ash are effective at higher temperatures. The addition of bone ash at different percentage levels, that is, 5%, 10%, 15%, and 20%, increased the bulk density and decreased the apparent porosity, resulting in improved compressive strength (Figures 7-9 and 11). The pozzolanic and cementitious reactions that prevent pore growth lead to an increase in the bulk density, decrease in porosity, Figure 11. Compressive strength of CCB after drying at 100 • C, 300 • C, 600 • C, and 900 • C.
The addition of bone ash at different percentage levels, that is, 5%, 10%, 15%, and 20%, increased the bulk density and decreased the apparent porosity, resulting in improved compressive strength (Figures 7-9 and Figure 11). The pozzolanic and cementitious reactions that prevent pore growth lead to an increase in the bulk density, decrease in porosity, and increase in the compressive strength. Effective cementitious properties may be due to the presence of Ca and P in bone ash for CCB composite, which are absent in the control sample (100C), leading to improved compressive strength. This agrees with the XRD results indicating the presence of hydroxyapatite in 20BAC and its absence in 100C (Figure 2).

Conclusions
The effect of bone ash addition to a clay matrix and the effect of temperature on clay ceramic bricks (CCB) material was investigated. Bone ash addition to clay slightly improved the compressive strength for samples heat-treated at 100 • C and 300 • C, but significantly increased the compressive strength at temperatures of 600 • C and 900 • C. Therefore, the addition of bone ash helps the cementitious reaction at elevated temperatures to increase the compressive strength of CCB. The bone ash containing hydroxyapatite addition to kaolin (alumino-silicate) clay for clay composite mimics the cementitious reaction in Portland cement bricks as a construction material. Compared with bricks manufactured with clay as a control (strength of 20 MPa), bricks formed with 5%, 10%, and 15% bone ash had strengths of~41.6 MPa,~49.3 MPa, and 46.1 MPa, respectively. Though the compressive strengths of samples 10BAC and 15BAC showed the highest, the bulk densities were also higher than that of sample 5BAC. In addition, these samples had less water adsorption of 20% owing to decreased porosity. At a temperature of 600 • C, the compressive strength of CCB is improved and water absorption is decreased. It is suggested that, depending on the purpose of building material, the amount of bone ash added and firing temperature should be considered. A high temperature is required to improve the durability of the bricks to avoid high water absorption. The reduction in environment pollution, both landfill and carbon dioxide reduction, through the usage of bone ash will sustain climate change reduction, affording low-cost building materials with high compressive strengths.  Institutional Review Board Statement: Humans and animals were not involved in this study.

Informed Consent Statement:
This is not applicable in this study with no human involved.

Data Availability Statement:
The data presented is available on request from the corresponding author after obtaining permission of authorized person. The authors adhere to the MDPI Research Data Policies.