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Geomechanical characterization of lateritic hardpans from Bamendjou (West-Cameroon)

Geomechanical characterization of lateritic hardpans from Bamendjou (West-Cameroon) vkatte@unam.na Department of Civil & This study reports on the physical, mechanical, mineralogical and geochemical analysis Environmental Engineering, carried out on four lateritic hardpan specimens from quarries in the Bamendjou area FEIT, University of Namibia, P.O Box 3624, Ongwediva, in the Western Region of Cameroon using common prescribed procedures. The results Namibia indicate that values of the bulk density, specific gravity, total and open porosities are Full list of author information very variable from one specimen to another. Meanwhile, the value of the compressive is available at the end of the article strengths of both the dry and immersed specimens were also very variable from one specimen to another, with the F2 and F1 specimens having higher values than the A1 and A2 specimens. All the specimens immersed in water recorded lower compressive strengths than the dry specimens. The flexural strengths also varied from one sample to another, with the F2 specimen having the highest resistance. The X-ray diffraction patterns reveal that the major peaks were assigned to gibbsite, goethite, and hematite, while the minor peaks were assigned to kaolinite and anatase. The mineralogy and geochemistry influenced the physical and mechanical properties, with the iron rich specimens having higher values in both the physical and mechanical properties than the alumina rich specimens. The results of the compressive strengths obtained were higher than (1–4) MPa obtained in Burkina Faso and India where they have been using latertic blocks for construction. Thus the hardpans of Bamendjou can also be exploited for building purposes conveniently. Keywords: Bamendjou, Building purposes, Lateritic hardpans, Physical, Mechanical mineralogical, Geochemical characteristics Introduction Lateritic hardpans are residual products of the laterization process from the parent rock developed in humid, tropical and subtropical regions of the world having good drainage. The combination of certain pedogenenic factors such as precipitation, temperature, sea - sonal variation and land morphology leads to the development of a weathering mantle which results in the formation of hardpan horizons within the soil profile. Buchanan [1] was the first to identify and name this soil laterite from the latin word ‘‘later’’ meaning brick. Since it can be cut into bricks, it is often utlised as building stones in some tropi- cal and subtropical regions of the world where it is readily available and it is economical compared to other natural stones [2]. In Cameroon, research on laterites and lateritic soil, started at the beginning of the twentieth century [3, 4] with many studies carried © The Author(s), 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the mate- rial. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 2 of 16 out on laterite for mining purposes [5, 6] while for road construction [7, 8] have carried out some useful studies. However, very little work has been done on the utilization of the lateritic hardpans in masonry, meanwhile, in India and Burkina Faso, a good number of studies where carried out with the development of specifications for the use of lateritic hardpans in masonry [9–11]. In spite of the existence of many works related to the utili- zation of laterite for building applications in others areas of the world, there are no avail- able information of similar utilization in Cameroon, in spite of its relative abundance in the country. Demographic pressure is now giving impetus to use non-conventional materials for building purposes and lateritic hardpans is among the plethora of these materials which can be utilized for sustainable construction practice. The Bamendjou vicinity contains one of the vast unexploited laterite deposits of Cameroon. It is there- fore exigent to have relevant scientific knowledge of the characteristics of these hard - pans if it is intended for building purposes. Materials and methods The site setting The study area is located between longitudes 10°10’ and 10°20’ East and latitudes 5°20’ and 5°30’ North (Fig.  1). It belongs to Bamendjou subdivision which is located in the Hauts Plateaux Division of the West Region and has a surface area of 45 k m . Geo- logically, Bamendjou falls within what is popularly referred to as the Bamiléké Plateau situated within the Western highlands of Cameroon and located in the central part of Cameroon Volcanic Line (CVL). In this region, the lateritic hardpans or duricrust were developed exclusively from the aphyric or porphyric basalts [12]. The vegetation is an anthropic savanna known as the Grassfield of Western Cameroon. The hydrography of the area shows a subparallel drainage pattern as shown in Fig. 2. Materials and methods Materials The lateritic hardpans were obtained from three quarries located in Bamendjou as shown in Fig.  2. The Nkong-Kang (NK) quarry is located at an elevation of 1628  m at a latitude of 05° 21′ 9’’North and longitude 10° 08′ 12’’East. At this position the lateritic hardpans outcrops to the surface. The Nkong Dang (ND) is at an elevation 1633  m at a latitude of 05° 23′ 22’’North and longitude 10° 20′ 14’’East. The Nkong-T’honta (NT) quarry is located at an elevation of 1566 m at a latitude of 05° 22′ 14’’North and longi- tude 10° 20′ 26’’East. The specimens of each of the various lateritic hardpans obtained from the quarries are shown in Fig.  3. The lateritic blocks were hewn out with a com - bination of rudimentary equipment such as pick axes, shovels and and an electric saw, after which they were then cut into blocks. Each of these blocks were rapped in cello- phane paper then wax sealed and then rapped again with another layer of cellophane paper for transportation to the laboratory. In all four samples were collected, comprising two from Nkong-Kang (NK) quarry (A1 and F2) and one sample sample from each of the other quarries, Nkong-Dang (ND) and Nkong-T’honta (NT) which were labelled as (A2 and F1) respectively. Each of these were shipped to the Faculty of Applied Sciences of the University of Liege in Belguim, where they were further cut to the required sizes with the aid of diamond tipped saw. Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 3 of 16 Fig. 1 Localization of Bamendjou on the Cameroon Map Physical analysis The following physical analysis were carried out on the specimens: water content, spe - cific gravity, bulk density, total porosity, open porosity and the degree of saturation using different but prescribed techniques. The water content test was performed in accord - ance with the French standards NF P94-050 [13]. The specific gravity (Gs) was deter - mined according to the standard NF EN ISO 8130-2 (2011) using the pycnometer with gas (Helium). The bulk density (ρ) and porosity (P ) were calculated using the hydro- static method in accordance with the EN 1936: [14] standard expressed as ρ = ρ g/m (m − m ) where ‘‘m ’’ is the dry weight of the specimen, ‘‘m ’’ is the saturation weight, ‘‘m ’’ is the 0 s h hydrostatic weight (immersed in water) and ‘‘ρ ’’ the density of water. ω Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 4 of 16 Fig. 2 Localization of different quarries Total porosity (N), open porosity (N ) and saturation ratio (S) were calculated as follows: (G − ρ) N = ∗ 100(%) (m − m ) s 0 N = ∗ 100(%) (m − m ) S = (%) Mechanical analysis Compressive strength testing was performed on six specimens of dimensions 5  cm × 5  cm × 5  cm while flexural strength testing was carried out on specimens of dimensions 5 cm × 2.5  cm × 15  cm. Figure  4(a) shows the experimental set-up of the compressive testing device while Fig.  4(b) shows the flexural strength testing device and Fig.  4c–e are the various specimens to be tested. The compressive strength was performed on specimens that were dry as well as specimens that were immersed in water. The immersed samples were in water for 192 h after which they were air dried Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 5 of 16 Fig. 3 Samples of lateritic hardpans from the various quarries A1 F1 A2 F2 F1 A1 A2 c de Fig. 4 a compressive strength device, b flexural strength device, c–e are the specimens for testing Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 6 of 16 for 48 ± 2  h (EN 13722 [15]) before testing, using a monoaxial compression method on an Instron 5585 universal testing machine, in accordance with the European norms EN 1926 [16]. The flexural strength was obtained using the same device as above, in accordance with the European norms EN 12372 [17]. Mineralogical and geochemical analyses The mineralogical analysis was carried out by X-ray diffraction using the Bruker D8 Advance diffractometer. The crushed samples were scanned using monochromatic Cu Ka radiation with 26 ranges of 2°–70° in steps of 0.020° operated at 40 kV and 25 mA using Cu-Kα1 radiation (I = 1.5406  A). The interpretation of the mineral phases was carried out in accordance with [18] with the aid of the EVA software which contains a Powder Diffraction File for mineral identification. Results and discussions Physical properties The results of the physical parameters determined in the laboratory comprising of the bulk density, specific gravity, natural water content, open and total porosity of the specimens are presented in Table  1. The values of the bulk density are very variable from one specimen to another ranging from 1.88 to 3.01  g/cm . The specific grav - ity are also very high and variable from one quarry to another ranging from a value of 2.8 to 3.84. It was observed that the natural water content was very low in all the specimens as shown in Table 1. The porosity of a material, is a measure of the void or empty spaces available in a material. Two porosity terms are often utilized which are the total porosity and open porosity. In this study the both open and total porosity parameters of the specimens varied from one specimen to the other within the same quarry. Similar results were observed by Lawane et  al. [19]; Vasquez et  al. [20] and Kasthurba et  al. [21] on blocks of laterites destined for construction purposes. The differences between values of total porosity may be due to differences in the porous system. The open porosity accounts for 30% to 63% of the total porosity resulting in the degree of saturation being much lower than 100%. This means that the material has a significant occluded porosity Brown [18]. Lawane et  al. [19], reported that in laterites, occluded porosity plays an important role in the resistance of rocks as well as of its degradation, depending if the voids are connected or continuous. Table 1 Mineralogical composition of the lateritic hardpans of Bamendjou Quarry Samples Minerals (%) Goethite Hematite Gibbsite Anatase Kaolinite Nkong-Thonta F1 60.96 6.90 16.66 1.94 13.54 Nkong-Kang F2 13.13 48.04 26.66 2.37 6.79 A1 10.45 1.53 81.58 3.69 2.58 Nkong-Ndang A2 20.59 6.79 66.39 3.33 2.91 Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 7 of 16 Table 2 Geochemical composition of the stone lateritic blocks of Bamendjou Quarry Samples Geochemical elements Total Al O Fe O SiO TiO MnO MgO CaO Na O K O P O SO LOI 2 3 2 3 2 2 2 2 2 5 3 Nkong-Thonta F1 14.30 58.88 6.30 1.53 0.08 0.39 0.03 0.00 0.02 1.45 0.00 16.13 99.11 Nkong-Kang F2 20.10 58.34 4.23 3.18 0.5 0.38 0.01 0.00 0.01 0.09 0.00 13.12 100.01 A1 51.63 12.93 1.44 3.70 0.11 0.02 0.00 0.00 0.00 0.28 0.00 29.35 99.49 Nkong-Ndang A2 43.85 23.43 2.44 4.00 0.04 0.16 0.02 0.00 0.01 0.50 0.00 25.58 100.03 Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 8 of 16 Mechanical properties The results obtained from the uniaxial compressive strength tests and the three point flexural strength tests are presented in Table  2. The samples were tested dry as well as immersed in water. The values of the compressive strength tested dry as well as immersed were very variable from one specimen to another. The values of samples F2 (75.97 and 75.7) MPa and F1 (32.18 and 23.15) MPa, were very high compared with those of the specimen A1 (22.73 and 8.79) MPa and A2 (13.89 and 5.51) MPa. However, we also note very significant variables within the same specimen (Fig.  5a; b). The resist - ance of the specimens that were immersed in water decreased considerably in all the specimens except for the F2 specimens.The compressive strength of lateritic stone blocks (LBS) obtained in Burkina Faso and India gave strength values between 1.5–4.0 MPa [11, 21]. Meanwhile the European standards EN 777-1 [22] precribes a minimum of 2.3 MPa for the compressive strength of bricks. Therefore all the specimens can be utilized safely for the construction of dwelling units since the minimum compressive strength of the hardpans tested dry was 13.89 MPa. The flexural strength also varied from one sample to another, with the F2 specimen having the highest resistance (15.51 MPa). The lowest value of flexural strength was observed in sample A1 (1.3 MPa). Moreover, we observe differences within the same specimen (Fig.  6). Both the results of the compressive and flexural strength showed some dispersion within the same quarry and from one speci - men to another with very high standard deviations. Similar results were found by [9] in Burkina Faso. The effect of immersion of the specimens in water on the durability of the material was evident when the compressive strength test was carried out. The results show that the compressive strength of specimens immersed in water decreased with the increase in water content. Similar results were reported by [9, 10, 23]. A negative, but very strong and signifi- cant correlation was recorded between the compressive strength of the immersed specimens and the degree of saturation (r = − 0.90). This means that when the degree of saturation increases, the compressive strength of the immersed specimens drops. In other words, the resistance decreases with the increase in the water content. The Number of samples Number of samples 1 2 3 4 5 6 7 8 Mean 1 2 3 4 5 6 Mean A1 A2 F1 F2 A1 A2 F1 F2 Different specimens Different specimens ab Fig. 5 a compressive strength of dry specimens according to different facies. b Compressive strength of water immersed specimens according to the different facies (Mpa) Compressive strength (un-I) σ (Mpa) Compressive strength (I) σ c Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 9 of 16 Number of samples 1 2 3 * Mean A1 A2 F1 F2 Different specimens Fig. 6 Flexural strength of dry specimens according to the different facies. Kaol: kaolinite; Boe: Boemite; Gib: Gibbsite; Goe: Goethite; Hem: Hematite; An: Anatase; Mag: Magnetite Fig. 7 XRD patterns of laterite hardpans only exception was with the F2 sample having a slight decrease,while the other sam- ples present a remarkable reduction of resistance after immersion. The samples with high alumina content showed a drop in the compressive strength after immersion in water of between 60 and 61%. This could be due to the fact that the aluminous min- erals are more hydrated than iron minerals [24] which would easily facilitate their hydration with water and subsequently decrease the material strength. Flexural strength (un-I) σ (MPa) c Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 10 of 16 Table 3 Physical properties of the stone lateritic blocks of Bamendjou Quarry samples Nbr Parameters Ρ (g/cm ) Gs W (%) S (%) N (%) N (%) ѡ 0 Nkong-Thonta F1 6 2.45 ± 0.01 3.69 1.17 54.16 ± 1.9 35.15 ± 1.11 19.04 ± 0.79 Nkong-Kang F2 6 3.01 ± 0.04 3.84 1.12 30.4 ± 2.11 21.47 ± 1.11 6.57 ± 0.63 A1 6 1.19 ± 0.02 2.8 0.4 52.08 ± 4.42 30.84 ± 0.7 16.06 ± 1.42 Nkong-Ndang A2 6 1.88 ± 0.05 3.16 0.6 63.75 ± 1.01 37.48 ± 1.73 23.89 ± 1.20 Number of samples (Nbr) Table 4 Mechanical properties of the lateritic hardpan specimens of Bamendjou Quarry Facies Mechanical properties State Compressive (MPa) Flexural (MPa) Nkong-Thonta F1 Un-Immersed 32.18 ± 9.20 04.33 ± 0.43 Immersed 23.15 ± 1.40 Nkong-Kang F2 Un-Immersed 75.97 ± 1.13 15.51 ± 1.52 Immersed 75.70 ± 1.35 A1 Un-Immersed 22.73 ± 4.96 01.30 ± 0.47 Immersed 08.79 ± 1.30 Nkong-Ndang A2 Un-Immersed 13.89 ± 2.76 02.50 ± 0.69 Immersed 05.51 ± 1.31 Mineralogical and geochemical composition The X-ray diffraction (XRD) patterns of the four lateritic hardpans from Bamendjou are presented in Fig.  7 while the mineralogical and geochemical characteristics are shown in Tables  3 and 4 respectively. It can be noted that all samples have their major peaks assigned to gibbsite (Gib), goethite (Goe), and hematite (Hem). The minor peaks were assigned to kaolinite (Kaol) and anatase (An). Goethite is the second most abundant mineral in these specimens, and represents 10.45 and 20.59% of minerals detected by X-ray. The results of the mineralogical analysis in Table  3 showed that lateritic hardpans exploited at three quarries in Bamendjou have significant proportions of iron oxide and hydroxide (goethite and hematite) and alumina (gibbsite). The A1 samples from the Nkong-Kang quarry and the A2 Nkong-Dang showed high levels of gibbsite (81.58% and 66.39% respectively), hence the high percentage of Al O (51.63% and 43.85% 2 3 respectively). On the other hand, F1 of the Nkong-T’honta quarry and F2 of Nkong- Kang have high Fe O contents, resulting in 60.96% goethite and 48.04% hematite for 2 3 the F1 and F2 samples, respectively. The high content in both the oxide and hydroxide is believed to be due to the humid tropical climate which occurs in the region which favors the allitization process. These hardpans have a different composition from the ones observed in Burkina Faso by Abhilash et  al. [9] and in India by Kasthurba et  al. [25]. The Al O and Fe O show opposing trends in the specimens while the SiO and 2 3 2 3 2 TiO are almost constant as it is expected in most lateritic hardpans [4]. Meanwhile the following oxides P O , MnO, MgO and CaO were present only in small amounts. It was 2 5 also observed that the geochemistry also influences the mechanical charatersitics of the hardpans. For example the density and specific gravity though variable from from one Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 11 of 16 quarry to another clearly indicates that the specimens F2 and F1 which are iron rich have higher values than specimens A1 and A2 which are alumina rich. From the geo- chemical composition of the quarry it was also found that laterites which are rich in iron oxide were also less porous, and are therefore more resistant. A positive, strong and significant correlation was recorded between dry compressive strength and the level of iron (r = + 0.72). The reverse was observed between dry compressive strength and total porosity (r = − 0.90). While within the same quarry, the geochemical composition and porosity vary considerably. This could also explain the variation of resistance in Nkong- Kang quarry. In addition to the iron content, the mineralogical composition associated with low porosity is a very important factor. This could also be the difference between F1 and F2 specimens, because both contain the same value of iron oxide (58%), but the difference in mineralogical composition (F1 is rich in goethite 60.96% and F2 in 48.04% hematite). The hardness of goethite (FeO(OH)) is 5–4.5, hematite (Fe O ) is 5.5–6.5, 2 3 gibbsite Al(OH) is 3.0 and kaolinite (Al [Si O ](OH) ) is 2–2.5 [21, 26]. Linear correla- 3 4 4 10 8 tions were established between natural compressive strength and hematite (R = 0.91). The variation in strength of Bamendjou laterite suggests the need for a development of a suitable classification system for building applications similar to that adopted in the case of lateritic stone blocks (LBS) based on the strength requirements as given in Burkina Faso by Lawane et al. [19]. Correlation between the various parameters The correlation between the mechanical and physical properties, then mineralogical and geochemical parameters is given by the Pearson coefficient shown in Table 5. It is deduced from this table that – A very negative correlation was found between the total porosity and the dry com- pressive strength (r = − 0.90) at a significant threshold of p < 0.05. Similarly, strong negative correlations were obtained for the water immersed compressive strength (r = − 0.89), and flexural strength (r = − 0.84). – A very negative correlation was found between the saturation ratio and the immersed compressive strength (r = − 0.94) at a significant threshold of p < 0.05. – A positive strong correlation was found between Fe O and the dry compressive 2 3 strength (r = + 0.72) at a significant threshold of p < 0.05. Similarly, strong positive correlations were obtained for the water immersed compressive strength (r = + 0.69), and flexural strength (r = + 0.70). – A negative strong correlation was found between Al O and the dry compressive 2 3 strength (r =− 0.64) at a significant threshold of p < 0.05. Similarly, strong positive cor- Table 5 Matrix of correlation between different parameters Parameters Total porosity Saturation ratio Fe O Al O Hematite 2 3 2 3 Mechanical properties b b b b Natural compressive strength r = (− 0.90 ) r = (+0.72 ) r = (− 0.64 ) r = (+0.94 ) b b b a b Saturated compressive strength r = (− 0.89 ) r = (− 0.94 ) r = (+0.69 ) r = (− 0.61 ) r = (+0.97 ) b b a b Flexural strength r = (− 0.84 ) r = (+0.70 ) r = (− 0.66 ) r = (+0.99 ) a b R, Coefficient of correlation; threshold of significance (p ˃ 0.01); threshold of significance (p ˃ 0.05) Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 12 of 16 y = -2.1931x + 138.16 70 70 R² = 0.9016 y = -3.5912x + 148.36 60 60 R² = 0.8487 50 50 30 30 20 20 010203040 02 04 06 08 0 Total Porosity Degree of saturation (%) ab Fig. 8 a Influence of porosity on compressive strength of dry specimens. b Influence of degree of saturation on of the compressive strength of water immersed specimens Immersed (MPa) Dry (MPa) y = 0.8279x + 4.4665 y = 1.001x -10.071 R² = 0.505 R² = 0.5297 02 04 06 08 0 F O content (%) 2 3 Fig. 9 Influence of F O content on dry and immersed compressive strength 2 3 relations were obtained for the water immersed compressive strength (r =− 0.61), and flexural strength (r =− 0.60) at a significant threshold of p < 0.01. And finally, a posi - tive strong correlation was found between Hematite and the dry compressive strength (r = + 0.94) at a significant threshold of p < 0.05. Also, strong positive correlations were obtained for the water immersed compressive strength (r = + 0.97), and flexural strength (r = + 0.99). Compressive strength (MPa) Compressive strength (MPa) Compressive strength (MPa) Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 13 of 16 Imnmersed (MPa) Dry(MPa) y = -1.1492x + 65.601 R² = 0.4077 y = -0.9501x + 67.042 R² = 0.3884 AL O content %) 2 3 Fig. 10 Influence of Al O content on dry and immersed compressive strength 2 3 Dry (MPa) Immersed(MPa) y = 1.2193x + 16.91 R² = 0.9163 y = 1.4662x + 5.0992 R² = 0.9508 01 02 03 04 05 06 0 Hematite content (%) Fig. 11 Influence of Hematite content on dry and immersed compressive strength The influence of the physical, mineralogical and geochemical properties on the mechanical properties The influence of the physical, geochemical and mineralogical properties on the mechanical properties are shown in Figs. 8, 9, 10 and 11. It comes out from these fig - ures that except for the lines from the Fig. 8 and 10, all the other figures present linear lines of average relationship with negative slope. Compressive strength (MPa) Compressive strength (MPa) Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 14 of 16 Table 6 Resistance of material lost after saturation and gibbsite content Characteristics (%) Specimens A1 A2 F1 F2 Loss in resistance after immersion 13.94 8.38 9.03 0.27 Percentage loss in resistance after immersion 61.32 60.00 28.60 0.35 (%) Total porosity 30.84 37.48 35.15 21.47 Open porosity 16.09 23.89 19.04 6.57 Hematite (%) 6.79 1.53 6.9 48.04 Gibbsite level (%) 81.58 66.39 16.63 26.66 A1 A2 y = 0.7868x -0.0518 R² = 0.71 F1 F2 Gibbsite Content (%) Fig. 12 Influence of gibbsite content on the resistance of material lost after saturation Influence of gibbsite content on the compressive strength of material lost after water immersion Table  6 presents the percentage of resistance in compression of material lost after immersion in water and the gibbsite content of material. It is deduced from this table that, the compressive strength of the A1 samples and A2 present a reduction of 61 and 60% respectively after immersion in water. The F2 sample is almost null because the load was not sufficient to cause the damage of material even after saturation. The A1 specimen presents a total porosity which is accessible to water and lower than F1 specimen, but which is more affected by water than F1 specimen (61.30% and 28.60%). The Influence of gibbsite content on the resistance of material lost after immersion in water is shown in Fig. 12. It comes out that, this figure present linear lines of average relationship with positive slope. Material Resistance loss after immersion (%) Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 15 of 16 Conclusion The aim of this study was to characterize four lateritic hardpan specimens coming from three quarries situated at Kong-Thonta; Kong-Kang and Kong Dang in Bamend - jou sub-division of the West Region of Cameroon. The values of the bulk density are very variable from one specimen to another ranging from 1.88 to 3.01 g/cm . The spe - cific gravity are also very high and variable from one quarry to another ranging from a value of 2.8 to 3.84. Both open and total porosity parameters of the specimen varied from one specimen to the other within the same quarry. The total porosity of the F2 specimen from Kong-Kang quarry is lower than that of the other quarries. The results of the mechanical properties of the compressive strength tested dry were all above that Lateritic Block Stones (LBS) found in Burkina Fasa and India with values ranging from 1 to 4 MPa. The minimum compressive strength of the hardpans was 13.89 MPa which is far superior to the ones found in Burkina Faso and India and therefore would be convenient for dwelling units. It is good to note that the European standard EN 777-1 [22] prescribes a minimum of 2.3  MPa for the compressive strength of bricks, while the French norms NFP 13-304  [27] prescribes values of  6–60  MPa for densely vibrated bricks and  1.5–7  MPa for lightly vibrated bricks. The flexural strengths of the specimens were different from each other with the minimum value of 1.3  MPa obtained for the A1 specimen. The F2 specimens gave the highest values of both the compressive and flexural strength followed by the F1 specimens. The predominant oxides in this laterite are Al O, Fe O and SiO , as well as other oxides such as SiO , 2 3 2 3 2 2 TiO P O , MnO, MgO and CaO in minor quantities. The major minerals found in the 2 2 5 hardpans were gibbsite, goethite and hematite. The mineralogical and geochemical composition are variable from one quarry to another and these both influenced the characteristics of the hardpans such as the physical and mechanical properties, with the iron rich hardpans giving better charateristics than the alumina rich hardpans. Acknowledgements We would like to thank the Académie de Recherche pour l’Enseignement Supérieure (ARES) for their partial support under the project : Stage en valorisation des ressources secondaires pour une construction durable. Authors’ contributions All authors read and approved the final manuscript. Declarations Competing interests The authors declare that there is no conflict of interest. Author details 1 2 Department of Earth Sciences, Faculty of Science, University of Dschang, P.O Box 67, Dschang, Cameroon. Depar t- ment of Civil & Environmental Engineering, FEIT, University of Namibia, P.O Box 3624, Ongwediva, Namibia. Depar t- ment of Civil Engineering, Fotso Victor University Institute of Technology Bandjoun, University of Dschang, Bandjoun, Cameroon. Received: 12 January 2021 Accepted: 31 August 2021 References 1. Buchanan F (1807) A journey from madras through the countries of Mysore, Canara and Malabar, 2nd edn. East Indian Company, London, pp 436–560 2. Fosso J, Ménard J, Bardintzeff JM, Wandji P, Bellon H (2000) Le stratovolcan de Bangou (Ouest Cameroun): une serie ème transitionnelle, dans la ligne du Cameroun in: 18 Réunion des sciences de la Terre, Paris. p. 133 Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 16 of 16 3. Edlinger W (1908). Contribution to geology and petrography of the German Adamawa (Doctoral dissertation, Ph. D. Thesis, Erlangen University, Erlangen) 4. Gidigasu M (ed) (2012) Laterite soil engineering : pedogenesis and engineering principles, vol 9. Amsterdam, Elsevier 5. Morin S (1987). Cuirasses et reliefs de l’ouest Cameroun. In Séminaire régional sur les latérites: sols, matériaux, min- erais (pp. 107–119). 6. Tchamba AB, Yongue R, Melo UC, Kamseu E, Njoya D (2008) Caractérisation de la bauxite de Haléo-Danielle (Minim- Martap, Cameroun) en vue de son utilisation industrielle dans les matériaux à haute teneur en alumine. Silic Indus 5–6:77–84 7. Nyemb BJF, Onana VL, Ntoh NG, Pianta Tadida C, Ekodeck GE (2013) Caractérisation minéralogique, chimique et géotechnique des graveleux latéritiques du tronçon routier Bahouan–Bamendjou–Batchum (Ouest Cameroun). Université de Douala, Cameroun, Colloque Géosciences et Appui au Développent 8. Sikali F, Emerati MD (1986) Utilisation des latérites en techniques routières au Cameroun. Acte du séminaire régional sur les latérites : Douala-Cameroun, pp. 277–288 9. Abhilash HN, McGregor F, Millogo Y, Fabbri A, Séré AD, Aubert JE, Morel JC (2016) Physical, mechanical and hygro- thermal properties of lateritic building stones (LBS) from Burkina Faso. Constr Build Mater 125:731–741. https:// doi. org/ 10. 1016/j. conbu ildmat. 08. 082 10. Gana LA (2014) Caractèrisation des matériaux latéritiques indurés pour une meilleure utilisation dans l’habitat en Afrique (Doctoral dissertation, Le Havre) 11. Lawane A, Pantet A, Vinai R, Thomassin JH (2011). Etude géologique et géomécanique des latérites de Dano (Bur- kina Faso) pour une utilisation dans l’habitat 12. Gribble CD (1988) The classification of minerals. In: Rutley’s elements of mineralogy. Springer, Dordrecht, pp. 147–149 13. NF P94-050 (1995) Soils: recognition and tests—determination of water content by weight—drying method 14. UNE-EN 1936 (2007) Standard Metodos de ensayo para piedra natural. Determinacion de la densidad real y aparente y de la porosidad abierta y total. AENOR, Madrid 15. EN 13722 (2001) Méthodes d’essai pour pierres naturelles—Détermination de la l’absorption d’eau a la pression atmospheric 16. EN 1926 (1999) Méthodes d’essai pour pierres naturelles—Détermination de la résistance en compression, Comité Européen de Normalisation. p. 16 17. EN 12372 (2007) Méthodes d’essai pour pierres naturelle - Détermination de la résistance en flexion sous charge centrée, Comité Européen de Normalisation. p. 19 18. Brown G (1982) Crystal structures of clay minerals and their X-ray identification, vol 5. The Mineralogical Society of Great Britain and Ireland 19. Lawane A, Vinai R, Pantet A, Thomassin JH, Messan A (2014) Hygrothermal features of laterite dimension stones for sub-Saharan residential building construction. J Mater Civ Eng 26(7):05014002 20. Vázquez P, Alonso FJ, Carrizo L, Molina E, Cultrone G, Blanco M, Zamora I (2013) Evaluation of the petrophysical properties of sedimentary building stones in order to establish quality criteria. Constr Build Mater 41:868–878 21. Kasthurba AK, Santhanam M, Achyuthan H (2008) Investigation of laterite stones for building purpose from Malabar region, Kerala, SW India-Chemical analysis and microstructure studies. Constr Build Mater 22(12):2400–2408 22. EN 777-1 (2003) AFNOR. Spécification des éléments en maçonnerie 23. Kasthurba AK (2006) Characterization and study of weathering mechanisms of malabar laterite for building pur- poses (Doctoral dissertation, PhD thesis, Indian Institute of Technology Madras, unpublished) 24. Momo MN, Tematio P, Yemefack M (2012) Multi-scale organization of the doumbouo-fokoué bauxites ore deposits ( West Cameroon): implication to the landscape lowering. Open J Geol 2:14–24 25. Kasthurba AK, Reddy KR, Venkat R (2014) Use of Laterite as a sustainable building material in developing countries 26. Reddy DV (1996). Decorative and dimensional stones of India. CBS Publishers & Distributors 27. NFP 13-304 (1983) Briques en terre cuite destinées à rester apparentes. NFP 13-304 Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png International Journal of Geo-Engineering Springer Journals

Geomechanical characterization of lateritic hardpans from Bamendjou (West-Cameroon)

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Abstract

vkatte@unam.na Department of Civil & This study reports on the physical, mechanical, mineralogical and geochemical analysis Environmental Engineering, carried out on four lateritic hardpan specimens from quarries in the Bamendjou area FEIT, University of Namibia, P.O Box 3624, Ongwediva, in the Western Region of Cameroon using common prescribed procedures. The results Namibia indicate that values of the bulk density, specific gravity, total and open porosities are Full list of author information very variable from one specimen to another. Meanwhile, the value of the compressive is available at the end of the article strengths of both the dry and immersed specimens were also very variable from one specimen to another, with the F2 and F1 specimens having higher values than the A1 and A2 specimens. All the specimens immersed in water recorded lower compressive strengths than the dry specimens. The flexural strengths also varied from one sample to another, with the F2 specimen having the highest resistance. The X-ray diffraction patterns reveal that the major peaks were assigned to gibbsite, goethite, and hematite, while the minor peaks were assigned to kaolinite and anatase. The mineralogy and geochemistry influenced the physical and mechanical properties, with the iron rich specimens having higher values in both the physical and mechanical properties than the alumina rich specimens. The results of the compressive strengths obtained were higher than (1–4) MPa obtained in Burkina Faso and India where they have been using latertic blocks for construction. Thus the hardpans of Bamendjou can also be exploited for building purposes conveniently. Keywords: Bamendjou, Building purposes, Lateritic hardpans, Physical, Mechanical mineralogical, Geochemical characteristics Introduction Lateritic hardpans are residual products of the laterization process from the parent rock developed in humid, tropical and subtropical regions of the world having good drainage. The combination of certain pedogenenic factors such as precipitation, temperature, sea - sonal variation and land morphology leads to the development of a weathering mantle which results in the formation of hardpan horizons within the soil profile. Buchanan [1] was the first to identify and name this soil laterite from the latin word ‘‘later’’ meaning brick. Since it can be cut into bricks, it is often utlised as building stones in some tropi- cal and subtropical regions of the world where it is readily available and it is economical compared to other natural stones [2]. In Cameroon, research on laterites and lateritic soil, started at the beginning of the twentieth century [3, 4] with many studies carried © The Author(s), 2021. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the mate- rial. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http:// creat iveco mmons. org/ licen ses/ by/4. 0/. Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 2 of 16 out on laterite for mining purposes [5, 6] while for road construction [7, 8] have carried out some useful studies. However, very little work has been done on the utilization of the lateritic hardpans in masonry, meanwhile, in India and Burkina Faso, a good number of studies where carried out with the development of specifications for the use of lateritic hardpans in masonry [9–11]. In spite of the existence of many works related to the utili- zation of laterite for building applications in others areas of the world, there are no avail- able information of similar utilization in Cameroon, in spite of its relative abundance in the country. Demographic pressure is now giving impetus to use non-conventional materials for building purposes and lateritic hardpans is among the plethora of these materials which can be utilized for sustainable construction practice. The Bamendjou vicinity contains one of the vast unexploited laterite deposits of Cameroon. It is there- fore exigent to have relevant scientific knowledge of the characteristics of these hard - pans if it is intended for building purposes. Materials and methods The site setting The study area is located between longitudes 10°10’ and 10°20’ East and latitudes 5°20’ and 5°30’ North (Fig.  1). It belongs to Bamendjou subdivision which is located in the Hauts Plateaux Division of the West Region and has a surface area of 45 k m . Geo- logically, Bamendjou falls within what is popularly referred to as the Bamiléké Plateau situated within the Western highlands of Cameroon and located in the central part of Cameroon Volcanic Line (CVL). In this region, the lateritic hardpans or duricrust were developed exclusively from the aphyric or porphyric basalts [12]. The vegetation is an anthropic savanna known as the Grassfield of Western Cameroon. The hydrography of the area shows a subparallel drainage pattern as shown in Fig. 2. Materials and methods Materials The lateritic hardpans were obtained from three quarries located in Bamendjou as shown in Fig.  2. The Nkong-Kang (NK) quarry is located at an elevation of 1628  m at a latitude of 05° 21′ 9’’North and longitude 10° 08′ 12’’East. At this position the lateritic hardpans outcrops to the surface. The Nkong Dang (ND) is at an elevation 1633  m at a latitude of 05° 23′ 22’’North and longitude 10° 20′ 14’’East. The Nkong-T’honta (NT) quarry is located at an elevation of 1566 m at a latitude of 05° 22′ 14’’North and longi- tude 10° 20′ 26’’East. The specimens of each of the various lateritic hardpans obtained from the quarries are shown in Fig.  3. The lateritic blocks were hewn out with a com - bination of rudimentary equipment such as pick axes, shovels and and an electric saw, after which they were then cut into blocks. Each of these blocks were rapped in cello- phane paper then wax sealed and then rapped again with another layer of cellophane paper for transportation to the laboratory. In all four samples were collected, comprising two from Nkong-Kang (NK) quarry (A1 and F2) and one sample sample from each of the other quarries, Nkong-Dang (ND) and Nkong-T’honta (NT) which were labelled as (A2 and F1) respectively. Each of these were shipped to the Faculty of Applied Sciences of the University of Liege in Belguim, where they were further cut to the required sizes with the aid of diamond tipped saw. Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 3 of 16 Fig. 1 Localization of Bamendjou on the Cameroon Map Physical analysis The following physical analysis were carried out on the specimens: water content, spe - cific gravity, bulk density, total porosity, open porosity and the degree of saturation using different but prescribed techniques. The water content test was performed in accord - ance with the French standards NF P94-050 [13]. The specific gravity (Gs) was deter - mined according to the standard NF EN ISO 8130-2 (2011) using the pycnometer with gas (Helium). The bulk density (ρ) and porosity (P ) were calculated using the hydro- static method in accordance with the EN 1936: [14] standard expressed as ρ = ρ g/m (m − m ) where ‘‘m ’’ is the dry weight of the specimen, ‘‘m ’’ is the saturation weight, ‘‘m ’’ is the 0 s h hydrostatic weight (immersed in water) and ‘‘ρ ’’ the density of water. ω Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 4 of 16 Fig. 2 Localization of different quarries Total porosity (N), open porosity (N ) and saturation ratio (S) were calculated as follows: (G − ρ) N = ∗ 100(%) (m − m ) s 0 N = ∗ 100(%) (m − m ) S = (%) Mechanical analysis Compressive strength testing was performed on six specimens of dimensions 5  cm × 5  cm × 5  cm while flexural strength testing was carried out on specimens of dimensions 5 cm × 2.5  cm × 15  cm. Figure  4(a) shows the experimental set-up of the compressive testing device while Fig.  4(b) shows the flexural strength testing device and Fig.  4c–e are the various specimens to be tested. The compressive strength was performed on specimens that were dry as well as specimens that were immersed in water. The immersed samples were in water for 192 h after which they were air dried Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 5 of 16 Fig. 3 Samples of lateritic hardpans from the various quarries A1 F1 A2 F2 F1 A1 A2 c de Fig. 4 a compressive strength device, b flexural strength device, c–e are the specimens for testing Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 6 of 16 for 48 ± 2  h (EN 13722 [15]) before testing, using a monoaxial compression method on an Instron 5585 universal testing machine, in accordance with the European norms EN 1926 [16]. The flexural strength was obtained using the same device as above, in accordance with the European norms EN 12372 [17]. Mineralogical and geochemical analyses The mineralogical analysis was carried out by X-ray diffraction using the Bruker D8 Advance diffractometer. The crushed samples were scanned using monochromatic Cu Ka radiation with 26 ranges of 2°–70° in steps of 0.020° operated at 40 kV and 25 mA using Cu-Kα1 radiation (I = 1.5406  A). The interpretation of the mineral phases was carried out in accordance with [18] with the aid of the EVA software which contains a Powder Diffraction File for mineral identification. Results and discussions Physical properties The results of the physical parameters determined in the laboratory comprising of the bulk density, specific gravity, natural water content, open and total porosity of the specimens are presented in Table  1. The values of the bulk density are very variable from one specimen to another ranging from 1.88 to 3.01  g/cm . The specific grav - ity are also very high and variable from one quarry to another ranging from a value of 2.8 to 3.84. It was observed that the natural water content was very low in all the specimens as shown in Table 1. The porosity of a material, is a measure of the void or empty spaces available in a material. Two porosity terms are often utilized which are the total porosity and open porosity. In this study the both open and total porosity parameters of the specimens varied from one specimen to the other within the same quarry. Similar results were observed by Lawane et  al. [19]; Vasquez et  al. [20] and Kasthurba et  al. [21] on blocks of laterites destined for construction purposes. The differences between values of total porosity may be due to differences in the porous system. The open porosity accounts for 30% to 63% of the total porosity resulting in the degree of saturation being much lower than 100%. This means that the material has a significant occluded porosity Brown [18]. Lawane et  al. [19], reported that in laterites, occluded porosity plays an important role in the resistance of rocks as well as of its degradation, depending if the voids are connected or continuous. Table 1 Mineralogical composition of the lateritic hardpans of Bamendjou Quarry Samples Minerals (%) Goethite Hematite Gibbsite Anatase Kaolinite Nkong-Thonta F1 60.96 6.90 16.66 1.94 13.54 Nkong-Kang F2 13.13 48.04 26.66 2.37 6.79 A1 10.45 1.53 81.58 3.69 2.58 Nkong-Ndang A2 20.59 6.79 66.39 3.33 2.91 Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 7 of 16 Table 2 Geochemical composition of the stone lateritic blocks of Bamendjou Quarry Samples Geochemical elements Total Al O Fe O SiO TiO MnO MgO CaO Na O K O P O SO LOI 2 3 2 3 2 2 2 2 2 5 3 Nkong-Thonta F1 14.30 58.88 6.30 1.53 0.08 0.39 0.03 0.00 0.02 1.45 0.00 16.13 99.11 Nkong-Kang F2 20.10 58.34 4.23 3.18 0.5 0.38 0.01 0.00 0.01 0.09 0.00 13.12 100.01 A1 51.63 12.93 1.44 3.70 0.11 0.02 0.00 0.00 0.00 0.28 0.00 29.35 99.49 Nkong-Ndang A2 43.85 23.43 2.44 4.00 0.04 0.16 0.02 0.00 0.01 0.50 0.00 25.58 100.03 Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 8 of 16 Mechanical properties The results obtained from the uniaxial compressive strength tests and the three point flexural strength tests are presented in Table  2. The samples were tested dry as well as immersed in water. The values of the compressive strength tested dry as well as immersed were very variable from one specimen to another. The values of samples F2 (75.97 and 75.7) MPa and F1 (32.18 and 23.15) MPa, were very high compared with those of the specimen A1 (22.73 and 8.79) MPa and A2 (13.89 and 5.51) MPa. However, we also note very significant variables within the same specimen (Fig.  5a; b). The resist - ance of the specimens that were immersed in water decreased considerably in all the specimens except for the F2 specimens.The compressive strength of lateritic stone blocks (LBS) obtained in Burkina Faso and India gave strength values between 1.5–4.0 MPa [11, 21]. Meanwhile the European standards EN 777-1 [22] precribes a minimum of 2.3 MPa for the compressive strength of bricks. Therefore all the specimens can be utilized safely for the construction of dwelling units since the minimum compressive strength of the hardpans tested dry was 13.89 MPa. The flexural strength also varied from one sample to another, with the F2 specimen having the highest resistance (15.51 MPa). The lowest value of flexural strength was observed in sample A1 (1.3 MPa). Moreover, we observe differences within the same specimen (Fig.  6). Both the results of the compressive and flexural strength showed some dispersion within the same quarry and from one speci - men to another with very high standard deviations. Similar results were found by [9] in Burkina Faso. The effect of immersion of the specimens in water on the durability of the material was evident when the compressive strength test was carried out. The results show that the compressive strength of specimens immersed in water decreased with the increase in water content. Similar results were reported by [9, 10, 23]. A negative, but very strong and signifi- cant correlation was recorded between the compressive strength of the immersed specimens and the degree of saturation (r = − 0.90). This means that when the degree of saturation increases, the compressive strength of the immersed specimens drops. In other words, the resistance decreases with the increase in the water content. The Number of samples Number of samples 1 2 3 4 5 6 7 8 Mean 1 2 3 4 5 6 Mean A1 A2 F1 F2 A1 A2 F1 F2 Different specimens Different specimens ab Fig. 5 a compressive strength of dry specimens according to different facies. b Compressive strength of water immersed specimens according to the different facies (Mpa) Compressive strength (un-I) σ (Mpa) Compressive strength (I) σ c Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 9 of 16 Number of samples 1 2 3 * Mean A1 A2 F1 F2 Different specimens Fig. 6 Flexural strength of dry specimens according to the different facies. Kaol: kaolinite; Boe: Boemite; Gib: Gibbsite; Goe: Goethite; Hem: Hematite; An: Anatase; Mag: Magnetite Fig. 7 XRD patterns of laterite hardpans only exception was with the F2 sample having a slight decrease,while the other sam- ples present a remarkable reduction of resistance after immersion. The samples with high alumina content showed a drop in the compressive strength after immersion in water of between 60 and 61%. This could be due to the fact that the aluminous min- erals are more hydrated than iron minerals [24] which would easily facilitate their hydration with water and subsequently decrease the material strength. Flexural strength (un-I) σ (MPa) c Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 10 of 16 Table 3 Physical properties of the stone lateritic blocks of Bamendjou Quarry samples Nbr Parameters Ρ (g/cm ) Gs W (%) S (%) N (%) N (%) ѡ 0 Nkong-Thonta F1 6 2.45 ± 0.01 3.69 1.17 54.16 ± 1.9 35.15 ± 1.11 19.04 ± 0.79 Nkong-Kang F2 6 3.01 ± 0.04 3.84 1.12 30.4 ± 2.11 21.47 ± 1.11 6.57 ± 0.63 A1 6 1.19 ± 0.02 2.8 0.4 52.08 ± 4.42 30.84 ± 0.7 16.06 ± 1.42 Nkong-Ndang A2 6 1.88 ± 0.05 3.16 0.6 63.75 ± 1.01 37.48 ± 1.73 23.89 ± 1.20 Number of samples (Nbr) Table 4 Mechanical properties of the lateritic hardpan specimens of Bamendjou Quarry Facies Mechanical properties State Compressive (MPa) Flexural (MPa) Nkong-Thonta F1 Un-Immersed 32.18 ± 9.20 04.33 ± 0.43 Immersed 23.15 ± 1.40 Nkong-Kang F2 Un-Immersed 75.97 ± 1.13 15.51 ± 1.52 Immersed 75.70 ± 1.35 A1 Un-Immersed 22.73 ± 4.96 01.30 ± 0.47 Immersed 08.79 ± 1.30 Nkong-Ndang A2 Un-Immersed 13.89 ± 2.76 02.50 ± 0.69 Immersed 05.51 ± 1.31 Mineralogical and geochemical composition The X-ray diffraction (XRD) patterns of the four lateritic hardpans from Bamendjou are presented in Fig.  7 while the mineralogical and geochemical characteristics are shown in Tables  3 and 4 respectively. It can be noted that all samples have their major peaks assigned to gibbsite (Gib), goethite (Goe), and hematite (Hem). The minor peaks were assigned to kaolinite (Kaol) and anatase (An). Goethite is the second most abundant mineral in these specimens, and represents 10.45 and 20.59% of minerals detected by X-ray. The results of the mineralogical analysis in Table  3 showed that lateritic hardpans exploited at three quarries in Bamendjou have significant proportions of iron oxide and hydroxide (goethite and hematite) and alumina (gibbsite). The A1 samples from the Nkong-Kang quarry and the A2 Nkong-Dang showed high levels of gibbsite (81.58% and 66.39% respectively), hence the high percentage of Al O (51.63% and 43.85% 2 3 respectively). On the other hand, F1 of the Nkong-T’honta quarry and F2 of Nkong- Kang have high Fe O contents, resulting in 60.96% goethite and 48.04% hematite for 2 3 the F1 and F2 samples, respectively. The high content in both the oxide and hydroxide is believed to be due to the humid tropical climate which occurs in the region which favors the allitization process. These hardpans have a different composition from the ones observed in Burkina Faso by Abhilash et  al. [9] and in India by Kasthurba et  al. [25]. The Al O and Fe O show opposing trends in the specimens while the SiO and 2 3 2 3 2 TiO are almost constant as it is expected in most lateritic hardpans [4]. Meanwhile the following oxides P O , MnO, MgO and CaO were present only in small amounts. It was 2 5 also observed that the geochemistry also influences the mechanical charatersitics of the hardpans. For example the density and specific gravity though variable from from one Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 11 of 16 quarry to another clearly indicates that the specimens F2 and F1 which are iron rich have higher values than specimens A1 and A2 which are alumina rich. From the geo- chemical composition of the quarry it was also found that laterites which are rich in iron oxide were also less porous, and are therefore more resistant. A positive, strong and significant correlation was recorded between dry compressive strength and the level of iron (r = + 0.72). The reverse was observed between dry compressive strength and total porosity (r = − 0.90). While within the same quarry, the geochemical composition and porosity vary considerably. This could also explain the variation of resistance in Nkong- Kang quarry. In addition to the iron content, the mineralogical composition associated with low porosity is a very important factor. This could also be the difference between F1 and F2 specimens, because both contain the same value of iron oxide (58%), but the difference in mineralogical composition (F1 is rich in goethite 60.96% and F2 in 48.04% hematite). The hardness of goethite (FeO(OH)) is 5–4.5, hematite (Fe O ) is 5.5–6.5, 2 3 gibbsite Al(OH) is 3.0 and kaolinite (Al [Si O ](OH) ) is 2–2.5 [21, 26]. Linear correla- 3 4 4 10 8 tions were established between natural compressive strength and hematite (R = 0.91). The variation in strength of Bamendjou laterite suggests the need for a development of a suitable classification system for building applications similar to that adopted in the case of lateritic stone blocks (LBS) based on the strength requirements as given in Burkina Faso by Lawane et al. [19]. Correlation between the various parameters The correlation between the mechanical and physical properties, then mineralogical and geochemical parameters is given by the Pearson coefficient shown in Table 5. It is deduced from this table that – A very negative correlation was found between the total porosity and the dry com- pressive strength (r = − 0.90) at a significant threshold of p < 0.05. Similarly, strong negative correlations were obtained for the water immersed compressive strength (r = − 0.89), and flexural strength (r = − 0.84). – A very negative correlation was found between the saturation ratio and the immersed compressive strength (r = − 0.94) at a significant threshold of p < 0.05. – A positive strong correlation was found between Fe O and the dry compressive 2 3 strength (r = + 0.72) at a significant threshold of p < 0.05. Similarly, strong positive correlations were obtained for the water immersed compressive strength (r = + 0.69), and flexural strength (r = + 0.70). – A negative strong correlation was found between Al O and the dry compressive 2 3 strength (r =− 0.64) at a significant threshold of p < 0.05. Similarly, strong positive cor- Table 5 Matrix of correlation between different parameters Parameters Total porosity Saturation ratio Fe O Al O Hematite 2 3 2 3 Mechanical properties b b b b Natural compressive strength r = (− 0.90 ) r = (+0.72 ) r = (− 0.64 ) r = (+0.94 ) b b b a b Saturated compressive strength r = (− 0.89 ) r = (− 0.94 ) r = (+0.69 ) r = (− 0.61 ) r = (+0.97 ) b b a b Flexural strength r = (− 0.84 ) r = (+0.70 ) r = (− 0.66 ) r = (+0.99 ) a b R, Coefficient of correlation; threshold of significance (p ˃ 0.01); threshold of significance (p ˃ 0.05) Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 12 of 16 y = -2.1931x + 138.16 70 70 R² = 0.9016 y = -3.5912x + 148.36 60 60 R² = 0.8487 50 50 30 30 20 20 010203040 02 04 06 08 0 Total Porosity Degree of saturation (%) ab Fig. 8 a Influence of porosity on compressive strength of dry specimens. b Influence of degree of saturation on of the compressive strength of water immersed specimens Immersed (MPa) Dry (MPa) y = 0.8279x + 4.4665 y = 1.001x -10.071 R² = 0.505 R² = 0.5297 02 04 06 08 0 F O content (%) 2 3 Fig. 9 Influence of F O content on dry and immersed compressive strength 2 3 relations were obtained for the water immersed compressive strength (r =− 0.61), and flexural strength (r =− 0.60) at a significant threshold of p < 0.01. And finally, a posi - tive strong correlation was found between Hematite and the dry compressive strength (r = + 0.94) at a significant threshold of p < 0.05. Also, strong positive correlations were obtained for the water immersed compressive strength (r = + 0.97), and flexural strength (r = + 0.99). Compressive strength (MPa) Compressive strength (MPa) Compressive strength (MPa) Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 13 of 16 Imnmersed (MPa) Dry(MPa) y = -1.1492x + 65.601 R² = 0.4077 y = -0.9501x + 67.042 R² = 0.3884 AL O content %) 2 3 Fig. 10 Influence of Al O content on dry and immersed compressive strength 2 3 Dry (MPa) Immersed(MPa) y = 1.2193x + 16.91 R² = 0.9163 y = 1.4662x + 5.0992 R² = 0.9508 01 02 03 04 05 06 0 Hematite content (%) Fig. 11 Influence of Hematite content on dry and immersed compressive strength The influence of the physical, mineralogical and geochemical properties on the mechanical properties The influence of the physical, geochemical and mineralogical properties on the mechanical properties are shown in Figs. 8, 9, 10 and 11. It comes out from these fig - ures that except for the lines from the Fig. 8 and 10, all the other figures present linear lines of average relationship with negative slope. Compressive strength (MPa) Compressive strength (MPa) Ngueumdjo et al. International Journal of Geo-Engineering (2022) 13:3 Page 14 of 16 Table 6 Resistance of material lost after saturation and gibbsite content Characteristics (%) Specimens A1 A2 F1 F2 Loss in resistance after immersion 13.94 8.38 9.03 0.27 Percentage loss in resistance after immersion 61.32 60.00 28.60 0.35 (%) Total porosity 30.84 37.48 35.15 21.47 Open porosity 16.09 23.89 19.04 6.57 Hematite (%) 6.79 1.53 6.9 48.04 Gibbsite level (%) 81.58 66.39 16.63 26.66 A1 A2 y = 0.7868x -0.0518 R² = 0.71 F1 F2 Gibbsite Content (%) Fig. 12 Influence of gibbsite content on the resistance of material lost after saturation Influence of gibbsite content on the compressive strength of material lost after water immersion Table  6 presents the percentage of resistance in compression of material lost after immersion in water and the gibbsite content of material. It is deduced from this table that, the compressive strength of the A1 samples and A2 present a reduction of 61 and 60% respectively after immersion in water. The F2 sample is almost null because the load was not sufficient to cause the damage of material even after saturation. The A1 specimen presents a total porosity which is accessible to water and lower than F1 specimen, but which is more affected by water than F1 specimen (61.30% and 28.60%). The Influence of gibbsite content on the resistance of material lost after immersion in water is shown in Fig. 12. It comes out that, this figure present linear lines of average relationship with positive slope. Material Resistance loss after immersion (%) Ngueumdjo  et al. International Journal of Geo-Engineering (2022) 13:3 Page 15 of 16 Conclusion The aim of this study was to characterize four lateritic hardpan specimens coming from three quarries situated at Kong-Thonta; Kong-Kang and Kong Dang in Bamend - jou sub-division of the West Region of Cameroon. The values of the bulk density are very variable from one specimen to another ranging from 1.88 to 3.01 g/cm . The spe - cific gravity are also very high and variable from one quarry to another ranging from a value of 2.8 to 3.84. Both open and total porosity parameters of the specimen varied from one specimen to the other within the same quarry. The total porosity of the F2 specimen from Kong-Kang quarry is lower than that of the other quarries. The results of the mechanical properties of the compressive strength tested dry were all above that Lateritic Block Stones (LBS) found in Burkina Fasa and India with values ranging from 1 to 4 MPa. The minimum compressive strength of the hardpans was 13.89 MPa which is far superior to the ones found in Burkina Faso and India and therefore would be convenient for dwelling units. It is good to note that the European standard EN 777-1 [22] prescribes a minimum of 2.3  MPa for the compressive strength of bricks, while the French norms NFP 13-304  [27] prescribes values of  6–60  MPa for densely vibrated bricks and  1.5–7  MPa for lightly vibrated bricks. The flexural strengths of the specimens were different from each other with the minimum value of 1.3  MPa obtained for the A1 specimen. The F2 specimens gave the highest values of both the compressive and flexural strength followed by the F1 specimens. The predominant oxides in this laterite are Al O, Fe O and SiO , as well as other oxides such as SiO , 2 3 2 3 2 2 TiO P O , MnO, MgO and CaO in minor quantities. The major minerals found in the 2 2 5 hardpans were gibbsite, goethite and hematite. The mineralogical and geochemical composition are variable from one quarry to another and these both influenced the characteristics of the hardpans such as the physical and mechanical properties, with the iron rich hardpans giving better charateristics than the alumina rich hardpans. Acknowledgements We would like to thank the Académie de Recherche pour l’Enseignement Supérieure (ARES) for their partial support under the project : Stage en valorisation des ressources secondaires pour une construction durable. Authors’ contributions All authors read and approved the final manuscript. Declarations Competing interests The authors declare that there is no conflict of interest. Author details 1 2 Department of Earth Sciences, Faculty of Science, University of Dschang, P.O Box 67, Dschang, Cameroon. Depar t- ment of Civil & Environmental Engineering, FEIT, University of Namibia, P.O Box 3624, Ongwediva, Namibia. 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NFP 13-304 Publisher’s Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Journal

International Journal of Geo-Engineering – Springer Journals

Published: Dec 1, 2022

Keywords: Bamendjou; Building purposes; Lateritic hardpans; Physical; Mechanical mineralogical; Geochemical characteristics

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