Termite Mound Soils for Sustainable Production of Bricks

TMSs were used in this study. TMSs are widely available in the eastern parts of Africa in the rift valley region that covers a wider area. In Ethiopia, TMSs are abundantly available in different localities, including the main Ethiopian rift valley. Representative samples of TMSs were collected from Jawaj and Sene localities located in Kiramu District, East Wollega Zone of Oromiya National Regional State and Benishangul Gumuz Regional State, Ethiopia, respectively (Figure 1). In addition, conventional clay soils samples were collected from traditional local brick production site from Bada Buna, Jimma Zone, Oromia region. The TMSs have different colours based on the source materials depending on the geological history of the deposit in the locality (Figure 2).

Figure 1

Figure 2

The soils were crashed to obtain the desired particle size for laboratory investigation. Samples of TMSs from two localities were mixed in a 1:1 ratio thoroughly for characterisation. The chemical compositions of the TMSs samples were determined using X-ray fluorescence (XRF) spectrometry at laboratory of Geological Survey of Ethiopia, Addis Ababa.

Laboratory tests of the Atterberg limits were conducted at the laboratory of Jimma Institute of Technology, Jimma University according to testing procedures, ASTM D 4318 (Dewangan et al., 2016). The percentage of the soil samples that passed sieve 0.075 mm, No. 200 was conducted to determine the grain size of the soil as per the AASHTO Soil Classification System. The hydrometer analysis was conducted to determine the particle size distribution (percentage) of the samples and identify the silt, clay and colloids percentages in the TMSs samples.

The maximum dry density (MDD) and optimum moisture content (OMC) of TMSs were determined by the Standard Proctor Compaction Test following the test methods of ASTM D 698. The specific gravity of the soil was determined by following test procedure in ASTM D 854 (ASTM D 854, 2002).

Wooden moulds of dimensions 240 mm × 120 mm × 60 mm (L × W × H) were used to make the bricks from the soils. The moulded bricks were left in a shed to be dried with air. The time of drying was dependent on the moisture content of the green bricks and the humidity of the production area. The TMSs brick production process is given in Figure 3.

Figure 3

Firing of the air-dried bricks was done using furnace for 4 h in Burqa Gibe Metal and Metals Manufacturing Plc, Jimma, Oromia, Ethiopia. The firing temperatures were 500, 600, 700, 800, 900 and 1,000°C.

The compressive strength, σ, water absorption, efflorescence, linear shrinkage (LS) and saturation coefficient of the fired TMSs bricks were characterised according to the Ethiopian Standard Specification of Solid Clay Bricks (ES 86: 2001) and the American Society for Testing and Materials; Standard Specification for Building Bricks (ASTM C 67).

The LS of the TMSs bricks was determined using British Standard, BS 3921(1985) Test 5. The standard specifies that standardised mould takes the shape of half cylinder of 12.5 mm diameter and 140 mm length. The LS in percent was determined using Eq. (1): (1) LS(%)=100%⋆Ls/L {\rm{LS}}\left( \% \right) = 100\% ^\star{\rm{Ls}}/{\rm{L}} where L: initial length (the length of the mould); L_S: final length of the brick.

Then, the compressive strength, σ, of the bricks was calculated by dividing the maximum or failure load-by-load area of the sample bricks. The mean values of σ of the bricks under different firing temperature were determined using Eq. (2). (2) Compressive strength =Failure load (N)/Area(mm2) {\rm{Compressive}}\;{\rm{strength}}\; = {\rm{Failure}}\;{\rm{load}}\;\left( {\rm{N}} \right)/{\rm{Area}}\left( {{\rm{m}}{{\rm{m}}^2}} \right) The water absorption test was conducted as per ASTM C 67 using five bricks dried in an oven for 24 h and the weight (W₁) of the samples measured carefully using a digital balance. The bricks were cooled to room temperature and submerged in water for 24 h. Then, the bricks were taken out from the water and wiped by damp cloth and weighted (W₂). The water absorption of the bricks was then determined employing Eq. (3). (3) Water absorption(%)=(W2-W1)⋆100/W1 {\rm{Water}}\;{\rm{absorption}}\left( \% \right) = \left( {{{\rm{W}}_2}{\text{-}}{{\rm{W}}_1}} \right)^\star100/{{\rm{W}}_1} The dimension tolerance test was conducted taking ten bricks and measuring their dimensions following the procedures of ASTM C 216. All the bricks were considered as FBS (brick for general use in masonry). Ten bricks from each type were taken, and the test was conducted by measuring the length, width and height of each of the bricks, and the dimension was checked if it is within the ASTM C 216 standard limit. The inside dimension of the mould used was 240 mm × 120 mm × 60 mm. The dimensions were measured along the length, width and height of the bricks. The average dimension reduced was compared with the ASTM standard.

The efflorescence of bricks was tested as per ASTM C-67. The ten bricks analysed for the dimension tolerance test were considered to determine the presence of salt on the bricks. The bricks were immersed in water for 7 d, and the rating was done by observing the surface of the bricks if there are white dots on the bricks. The bricks were rated as ‘effloresced’, or ‘not effloresced’ as stated in the standard ASTM C 67.

The chemical compositions of the TMSs samples were given in (Table 1). Both Jawaj termite mound soils (JTMSs) and Sene termite mound soils (STMSs) had silica, SiO₂ > 60%. The alumina, Al₂O₃, contents for each of the TMSs from the two localities were > 17%. The sum of the percentage of SiO₂ and Al₂O₃ content are 80.59 and 79.86% for JTMSs and STMSs, respectively. According to the study conducted by Toure et al. (2017) on the mechanical and thermal characterisation of bricks, a combined percentage of SiO₂ and Al₂O₃ should be greater than 70% to be a good binder for the brick production. The combined percentage of SiO₂ and Al₂O₃ composition also meets the requirements of ASTM C-618 (ASTM C 618, 2010). Thus, TMSs can be considered as suitable raw materials for brick production. Alkali oxides (MgO, K₂O, Na₂O) compositions are 4.24 and 4.12 % for TMSs from Jawaj and Sene localities, respectively. The alkali content is > 3% for JTMSs and STMSs. The results of the investigation made by (Attah, 2008) on the composition and physical properties of some clays of Cross River State, Nigeria, support the finding of this study. Thus, the TMSs results in low temperature vitrification and increases the firing shrinkage.

The sieve analysis results show that the percentage of soil passing sieve No. 200 were 60 and 67% for TMSs from Jawaj and Sene localities, respectively (Figure 4). These values are greater than 35% passing for both localities, indicating that soils were fine-grained (silt or clay (A4–A7)) material according to AASHTO Soil Classification System. Soils containing clay and silt contents 40–65% are suitable for brick making.

Figure 4

The physical properties of the TMSs are presented in (Table 2). The liquid limits (LLs) were 38% for both JTMSs and STMSs. However, the LL for conventional clay soil was 34%. The plastic limits (PL) were 20, 23 and 19.27%, respectively, for JTMSs, STMSs and clay soil. The corresponding plasticity index (PI) values obtained were of 19, 16 and 14.7%, respectively, for JTMSs, STMSs and clay soils. The PI value greater than 17 for JTMSs is an indication that the TMSs from Jawaj were a highly plastic soil in character. The PI values for STMSs and clay soils ranged between 7 and 17%, indicating that the soils had a medium degree of plasticity property. Thus, the TMSs from both localities can be used as raw materials for brick production replacing clay soils.

The PI values for the TMSs from the two localities were 20 and 23%. According to the results of the percentage passing the No. 200 sieve and LL, the soil was either A4 or A6. The AASHTO Soil Classification PI for A4 is 10 max, and for A6, it is 11 min. The PI were 19 and 16 for JTMSs and STMSs, respectively. Hence, based on their respective PI values, both JTMSs and STMSs are categorised under A6, which are clay soils. Thus, TMSs can substitute clay soils as raw materials for brick production to deter environmental degradation due to excessive use of clay soils.

3.3.1

Liquid limit

The value at 25 blows from the LL flow curve for JTMSs and STMSs was 39% for both of them. Table 3 presents the AASHTO Soil Classification depending on LL. The soil type was categorised based on percentage pass by sieve number 200 (0.075 mm). The LL results of JTMSs and STMSs summarised in Table 3. As PI of JTMSs and STMSs was greater than 11 min, and they fall under A-6, clayey soil type. Figure 5 presents the LL of TMSs and clay soils.

Table 3

AASHTO classification for fine-grained soils (Brajam, 2002).

Soil type (1)	Passing No. 200 sieve (2)	Liquid limit (3)	Plastic index (4)	Material type (5)
A4	36 min	36 min	10 min	Silty soil
A5	36 min	41 min	10 min	Silty soil
A6	36 min	40 min	11 min	Clayey soil
A7	36 min	41 min	11 min & PI ≤ LL-30	Clayey soil
	36 min	41 min	11 min & PI > LL-30	Clayey soil

Figure 5

3.3.2

Linear shrinkage

Bricks will shrink when drying, so the mould size must be larger than the intended finished brick (Riza and Rahman, 2017). The LS results were 7.28 and 8.0% for JTMSs and STMSs bricks, respectively. According to Toure et al. (2017), clay soils with LS less than 5% are noncritical, 5 to 8% are marginal and LSs greater than 8% are critical. Higher LS is not desirable in brick making, as this may create cracks on final products. The TMSs used in this study were suitable for brick making as the LS values were, respectively, 7.28 and 8.0% for bricks made from JTMSs and STMSs. The value fall between 5 and 8%, which is the marginal range.

Figure 6

The graph of OMC and MDD is given in Figure 6. The pick point of the graph shows the MDD and the moisture content corresponding to the MDD, which is the OMC. Thus, the values of MDD for JTMSs and STMSs were 1,684 and 1,614 kg/m³, respectively. The OMC determined from the curve are 18 and 19% for JTMSs and STMSs, respectively. According to Arora (2019), the OMC of the TMSs from the two localities is between 14 and 20%, which is in the range of OMC for clay soils. The OMC for sand ranges from 6–10%, from 8–12% for silty sand, from 12–16% for silt and from 14–20% for clay soils.

The values of the specific gravity of the TMSs samples for Jawaj and Sene are 2.55 and 2.66, respectively (Table 4). The specific gravity of the JTMSs was between that of clay and organic soils. Whereas the specific gravity of the STMSs samples fell in the range of sand. The specific gravity of the clay soils from Jimma town was 2.68.

The mean compressive strengths, σ, of JTMSs bricks produced at different firing temperatures are presented in Figure 7. The σ of brick was remarkably improved by firing at higher temperature. With the increase in the firing temperature from 500 to 700°C, the σ increased from 11 to 18 MPa. The increase in the σ can be due to the decrease in porosity and increase in bulk density as the firing temperature increases (Tsega et al., 2017; Johari et al., 2010; Okunade, 2008; Glaydson et al., 2020; Karaman et al., 2006). As the firing temperature increased from 800 to 1,000°C, the σ of the brick decreased. The JTMSs bricks demonstrated a bit greater σ when compared with the σ of STMSs bricks (Figure 7). This could be because of the higher silica content of JTMSs.

Figure 7

Keeping the firing temperature in the range from 500 to 1,000 °C and increasing the firing time from 120 to 480 min resulted in a small increase in the σ. Therefore, increasing the firing time did not improve the quality of the bricks. So, prolongation of firing time is wasting of energy and time.

It was observed that the TMSs bricks demonstrated highest σ at about 700°C firing temperature, which was taken as the optimum firing temperature for brick production from JTMSs and STMSs. However, the σ of bricks produced from clay soils required greater than 700°C firing temperature. The finding of this study is in line with the observation made by Tsega et al. (2017). The σ of the bricks made from JTMSs, STMSs, the mixture of JTMSs and STMSs and the conventional clay soils were given in Table 5.

The physical property requirements of fired clay bricks are different in different standard specifications. Different countries have different physical property requirements of fired clay bricks in their specifications. For instance, lower values of water absorption are required in BS 3921(1985), Standard Specification for classifying clay bricks when compared with ASTM standard specifications.

The bricks produced from the JTMSs firing at 700°C are classified as class B, C and D based on their mean compressive strength, mean water absorption and mean saturation coefficient, respectively. This classification is according to the requirements of ES 86:2001 (Ethiopian Standards Agency, 2015). However, according to the ASTM standard, the bricks categorised as moderate weathering (MW) consider the σ, which was 18 MPa. The σ of the bricks is greater than 17.2 MPa, so JTMSs bricks produced at the firing temperature 700°C meet the ASTM standard specification. However, the σ of bricks produced from conventional clay soils increased as the temperature increased beyond 700°C. This shows bricks produced from TMSs demonstrated maximum σ strength at low temperature. According to Okunade (2008), σ of brick range between 15 and 18 MPa.

The water absorptions and saturation coefficient of the bricks made from for JTMSs and STMSs at different firing temperatures are given (Table 6). The observed mean water absorption values of bricks made from TMSs increased as the firing temperature increased by 100°C, whereas the saturation coefficients of the bricks reduced when the firing temperature increased. On the contrary, the water absorptions and saturation coefficients decreased for bricks produced from clay soils as the firing temperature increased. The findings of this study are consistent with the observations made by Matysek et al. (2016).

Based on the mean water absorption, clay bricks are classified as class A according to ES 86:2001 (Ethiopian Standards Agency, 2015), are also classified as MW according to the ASTM standard specification. This shows that classification of fired bricks is different based on different standards.

Figure 8 presents the dimension tolerance of fired TMSs bricks along the length of 240 mm. The dimension tolerance of the of TMSs bricks of the two localities did not fulfil the ASTM (ASTM C62/C62M-12, 2012) permissible dimension variation along the length. This was due to the shrinkage of TMSs bricks during sun drying and firing. The amount of water added during mixing of the TMSs for workability was lost during firing, causing reduction in the dimensions of the bricks. Firing temperature is one of the key factors to modulate the physical properties of bricks. The dimensions of the bricks decreased as the firing temperature increased. This finding was similar with the results of the study conducted by Karaman et al. (2006) on the clay bricks in Turkey.

Figure 8

The change in dimension along the width of the bricks produced at the firing temperature of 600°C fulfilled the ASTM requirements (ASTM C62/C62M-12, 2012). Size reductions of the bricks along the width are presented in Figure 9 (in this figure, a fourth-order polynomial was used to give better results than the tangent line approximation). The dimension reduction of JTMSs bricks did not fulfil the ASTM (ASTM C62/C62M-12, 2012) permissible dimension tolerance along the width. The findings of this study are different from the observations made by Kabtamu and Alemu, (2017) on the clay soils bricks quality and suitability. This could be because of the materials used from brick production are different in their composition and formation.

Figure 9

The average dimension reduction of TMSs bricks along the height is shown in Figure 10. TMSs bricks from Jawaj and Sene do not fulfil the ASTM C216 (ASTM-C216-16, 2013) maximum permissible variation. The reason of this phenomenon is high loss of ignition (LOI) in TMSs from Jawaj and Sene, which was about 8.38%-dimension tolerance along the length. According to ASTM C216 (ASTM-C216-16, 2013), the size variation occurred due to the production method of bricks. These size variations occurred due to the shrinkage during drying and firing of the bricks (Brick Development Association, 2006). Therefore, variations in dimensions are compensated by providing a mould size considering the expected change in the dimensions. For example, for JTMSs bricks, at firing temperature of 500°C reduced dimension along the length, width and height were, respectively, 18.5, 11 and 7.4 mm. As a result, to obtain brick the same as with 240 mm × 120 mm × 110 mm, the moulding box should have the internal dimension of 259 mm × 231 mm × 118 mm to get desired brick dimensions.

Figure 10

The efflorescence test for both JTMSs and a STMSs bricks was conducted according to ASTM C67 (ASTM C67-19, 2019). The test was followed after the dimension tolerance test was accomplished (Drive, 2007; Chin and Behie, 2010). The results of the efflorescence test on TMS bricks show that all the bricks were not effloresced.