J. Nig. Soc. Phys. Sci. 5 (2023) 1109 Journal of the Nigerian Society of Physical Sciences Effect of Pre-Test Drying Temperature on the Properties of Lateritic Soils L. O. Afolagboyea,∗, Z. O. Arijea, A. O. Talabia, O. O. Owoyemib aDepartment of Geology, Ekiti State University, Ado-Ekiti, Nigeria bDepartment of Geology, Kwara State University, Malete, Nigeria Abstract The properties of residual soils, according to literature, are sensitive to the pre-test drying method given to the sample prior to testing. Similarly, residual soils such as laterites/lateritic soils are formed under various climatic conditions; hence, they show different degrees of sensitivity to the pretest drying method. This work is therefore carried out to elucidate the influence of the pre-test drying temperature or method on the properties of three lateritic soils that developed over three different Pre-Cambrian basement complex rocks from Ado-Ekiti, SW, Nigeria. The soils were subjected to two pre-test drying temperatures before conducting laboratory tests. The pre-test drying temperatures considered in this study include air-drying, oven-drying at 60 ◦C, and oven-drying at 110 ◦C. Pre-test drying at 60◦ and 110 ◦C caused particle aggregation (which reduced the soil surface area) and loss of cohesion. Consequently, this reduced the specific gravity, optimum moisture content, clay content, consistency limits, and unconfined compressive strength of the lateritic soils. The maximum dry density and sand content increased as the pre-test drying temperature increased. The pre-test drying temperature did not significantly change the plasticity classification of the soils; however, at higher pre-test temperatures, the soils become less plastic. The free swell index of the lateritic soils increased with increasing pre-test drying temperatures (up to 60 ◦C) before decreasing when the temperature rose to 110 ◦C. This study has revealed the effect that pre-test drying temperatures may have on the properties of lateritic soils, and these may produce soil properties that do not likely indicate the actual field performance of the tested soils. DOI:10.46481/jnsps.2023.1109 Keywords: Lateritic soil, Pre-test drying temperature, Index properties, Oven drying, Soil classification. Article History : Received: 05 October 2022 Received in revised form: 21 January 2023 Accepted for publication: 27 January 2023 Published: 04 February 2023 c© 2023 The Author(s). Published by the Nigerian Society of Physical Sciences under the terms of the Creative Commons Attribution 4.0 International license (https://creativecommons.org/licenses/by/4.0). Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Communicated by: Oladiran Johnson Abimbola 1. Introduction Lateritic soils/laterites are residual soils that are highly weathered. They are usually low in silica but have sufficient concentrations of iron and aluminum sesquioxide to have been cemented to some degree. Lateritic soils are restricted to ∗Corresponding author tel. no: +2348037857241 Email address: afotayour@hotmail.co.uk; lekan.afolagboye@eksu.edu.ng (L. O. Afolagboye ) tropical and subtropical regions of the world and occur as the capping of hills; therefore, they provide excellent borrowing areas for extensive use in various construction activities [1]. The properties and behavior of lateritic soils vary because of differences in degree of weathering (laterization), parent rock, climate, position in the soil profile, and topography [2, 3]. In civil engineering, the determination of soil index and engineering properties is important and integral to any engineering construction and design. To determine these 1 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 2 properties, tests such as consistency limits, grain size distri- bution, compaction, and strength tests are carried out using or on disturbed samples, and the test procedures completely re-mould the samples. That is, the samples must be carefully prepared to the required standards. For instance, one of the general specifications of sample preparation for most of these standard laboratory tests requires either air-drying or drying in an oven at a temperature usually between 60 ◦C to 110 ◦C. This is required to obtain fully dried soil, with the assumption that water present in the soil pore spaces could be removed by heating without destroying or changing the soil composition/structure. However, previous works have shown that this assumption may not be true for all soils [4, 5]. Previous workers such as [6, 7, 8] reported that the method of drying and generally the method of sample preparation may significantly affect the index properties of some soils such as weathered, tropical/subtropical residual soils or soils that contain organic matter and halloysite or allophane. Terzagi et. al. [9] reported the Atterberg limits and grain size distribution of residual soils from Indonesia tested at Natural Moisture Content (NMC) and when air dried and oven dried. When tested at NMC, the soil had Liquid Limit (WL), Plasticity index (Ip) and amount of fine of 184%, 38%, and 95%, respectively. At NMC, the soil is classified as high plastic or organic silt. After air-drying, the amount of fines, WL and Ip decreased to 19 %, 79 %, and 6 %, respectively. When oven-dried, the amount of fines was 15 % and the soil became “non-plastic”. The soil classified as silty sand (SM) when air-dried and oven dried. Hence, the index and engineering tests may yield incon- sistent results or significantly different results as they are influenced by the degree of pre-test drying temperature (NMC, oven-dried or air-dried) used prior to testing. These changes are attributed to increased cementation due to oxidation of the iron and aluminum sesquioxides or dehydration of allophane and halloysite [10]. In addition, pre-test drying may alter the structure, physical behavior, and clay content of a residual soil by causing aggregation of fine particles. The resultant larger particles remain bonded together even on wetting or after dispersion by standard dispersion techniques [5, 11]. Previous studies have shown that lateritic soils are structured and contain significant concentration of iron and aluminum sesquioxides hence their properties are likely to be affected by the pre-test method of drying and generally the method of sample preparation [6, 7, 8]. In addition, the sensitiv- ity of different lateritic soils to pre-test drying, and sample manipulation is different depending on climatic conditions [12]. The present study is therefore aimed at further understand- ing the properties/behavior of the residual lateritic soil whose behaviors are termed problematic by investigating the effect of pre-test drying temperature on the geotechnical and index prop- erties of lateritic soils. These problematic behaviors can’t be explained by the accepted principles established for temperate soils [13]. In addition, to provide further insights as to why the plasticity classifications of the soil are sometimes not in agree- ment with the major component of the soil and in situ obser- vations. Three different genetically derived lateritic soils were selected for this study. 2. Geology of the Study Area Ado-Ekiti is one of the areas of southwestern Nigeria un- derlain by the Pre-Cambrian basement complex rocks. The rocks of the Pre-Cambrian basement complex are classified as “migmatite gneiss-quartzite complex,” “Schist Belts”, and “Pan-African Granites” [14]. Except for the schistose rocks, Ado-Ekiti contains most of the rock lithologies that comprise the Precambrian basement complex of southwestern Nigeria [15]. These rocks include charnockite, migmatite gneiss, gran- ite, and granite gneiss. Migmatite gneiss is characterized by a fine-grained texture and alternating bands of dark and light- colored minerals. Quartzites are ridge-shaped, non-foliated rocks. With only a trace amount of feldspar, quartz makes up the majority of the quartzite’s mineral composition. The con- stituent minerals in the granites do not exhibit any preferred ori- entation. They range from having a fine-grained to porphyritic texture. The granites also contain compact crystals that inter- lock with one another. Charnockite has a dark gray color and a texture that ranges from medium to coarse. Charnockite can be found along the edges of granites [16, 17]. 3. Methodology The lateritic soils used in this study developed over three different rock types. These rocks are granite, charnockite, and quartzite. The granite is made of quartz (66.3 %), biotite (12.2 %), albite (20.3 %), and opaque minerals [16]. Quartzite is mainly made up of quartz (about 95.1 %) and other minerals such as feldspar. The charnockite, on the other hand, is made up of quartz (21.3 %), microcline (16.7 %), plagioclase (36.8 %), biotite (16.5 %) and others [17]. Disturbed lateritic soil samples (that developed over quartzite and granite) were col- lected from active burrow pits where lateritic soil is presently being quarried for different construction purposes in Ado-Ekiti, Southwestern, Nigeria while samples of lateritic soil that devel- oped over charnockite were collected from a road cut exposure. The samples were collected from the laterite horizon because lateritic soil from this zone is the most preferred for most con- struction activities [3], [18]. The collected samples were stored in airtight sealed polythene bags to keep their water contents in- tact. In all, a total of five soil samples were taken from soils that developed over the three rock types. The lateritic soil samples were tested at their Natural Moisture Content (NMC) and three other states obtained through drying. These include air-dried soil, and soils oven dried at 60 ◦C and 110 ◦C. 3.1. Drying Process The soil samples that were not tested at their NMC were prepared under the following drying conditions: 2 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 3 i. Air Drying: the soil samples were spread on a clean wide pan and the spread samples were exposed to normal am- bient temperature (25 to 30 ◦C) for three — four weeks. During this period, we regularly turned the soil over to avoid local drying out. It is sufficing to say that it takes at least four weeks to reduce the moisture content of the air-dried samples to a relatively constant value. ii. Oven drying at 110 ◦C: This entails drying the soil sam- ples to a constant mass in an oven at a temperature of 110 ± 5 ◦C as stipulated by [19]. The period of heating is 24hrs. iii. Oven drying at 60 ◦C: This entails drying the soil samples to a constant mass in an oven at a temperature of 60 ± 5 ◦C. During heating, we constantly measured the weight of the samples and stopped the heating process when the weight of the samples became constant. 3.2. Index and Engineering Tests Procedure The index and engineering properties of these genetically different lateritic soil samples at their natural moisture content, air dried, and oven dried (60 ◦C and 110 ◦C oven drying) states were determined according to British Standard 1377 [19] with some modifications where necessary. The particle size analysis was carried out using British Standard 1377-2. To ensure proper segregation of the soil particles, we soaked the soil samples in Calgon solution for a day before wet sieving. We conducted the particle size analysis using sieve analyses and hydrometer test. Soil fractions retained on and passed through sieve No. 200 (75 µm), respectively, were used for sieve analyses and hydrometer test. The consistency limits were also determined using British Standard 1377-2 on soil fraction passing sieve size 425 µm. The determined consistency limits of the soils include liquid limits and plastic limits. Before the consistency limits tests, the sieved soil fractions were mixed with water and left to hydrate for 24 hrs. We determined the WL and Plastic Limit (WP) of the soils using the Casagrande percussion cup and thread rolling methods, respectively. For determining the moisture-density relationship of the soil samples, compaction test was carried out on fractions of the soils that passed through 425 µm sieve following the specification of British Standard 1377 – 4. We carried out the compaction test using the standard Proctor compaction efforts. The specimens for the moisture — density relationship test is about 10.2 cm and 11.2 cm in diameter and height, respectively. We performed the Unconfined Compression Test (UCT) on lateritic soil following the specification of British Standard 1377 – 7. The specimens were compacted at their Optimum Moisture Content (OMC) using the standard Proctor compaction effort. The specimens used for the test measured 5 cm and 10 cm in diameter and height, respectively. The compacted soil sample were loaded under a stress-strain controlled condition. The strain rate was set at 1.25 mm/min. We compressed the soil specimen till failure and monitored the deformation at each point of loading. The peak stress attained during loading correspond to the unconfined compressive strength. Free swell index (FSI) was carried out on fractions of lat- eritic soil that pass-through sieve size 0.425 mm. According to Rao et. al. [20], FSI can be considered as an index property of expansive soil, and it reflects the potential for expansion of the soil. Holtz and Gibbs [21] defined the FSI as the ratio of the difference in volumes of soil in water and kerosene to the volume of soil in kerosene. It is mathematically expressed as: FS I = Vd − Vk Vd × 100, (1) where Vd (ml) = final volume of soil in a graduated cylinder containing distilled water, Vk (ml) = final volume of soil in a graduated cylinder containing kerosene. Therefore, FSI is ex- pressed in (%). 4. Results and Discussion SG is an indicator for engineering behavior of lateritic soils in that, it’s the weighted average of the specific gravities of the minerals which comprise the soil. However, weathering and age of formation of parent rocks are fact factors to be considered while determining SG. Table 1 shows the specific gravity of the studied lateritic soils for all pre-test drying methods. At NMC, the table revealed that the average SG values of quartzite derived lateritic soil, charnockite derived lateritic soil and granite derived lateritic soil are 2.648, 2.686 and 2.670, respectively. The difference between the SG of the three lateritic soils may be due to the variation in texture and mineralogy of the parent rocks. Compared with lateritic soil tested at NMC, the SG of the three genetically different lateritic soils were lower and de- creased as the drying temperature increases from air to oven drying at 110 ◦C. The difference is, however, not significant. Sunil and Krishnappa [22] studied “the influence of drying on the properties of lateritic soils and observed that the SG of the air and oven dried lateritic soils did not vary significantly from each other. At NMC and all the pretest drying temperatures, the average SG of charnockite-derived lateritic soil is higher com- pared to the other lateritic soils. This could be attributed to the mineral constituent of the parent rock which contained more heavy and opaque minerals compared to granite and quartzite [16]. Generally, the high SG values of the soils are indicative of a high degree of laterization. 4.1. Particle Size Distribution Table 2 shows the results of particle size distribution of the lateritic soils as determined at their NMC, after air drying and oven-drying at 60 ◦C and 110 ◦C, respectively. The table reveals that the grain size distribution of the lateritic soils is affected by the parent rock factor. At NMC and all pre-test drying temperature, the lateritic soils are well-graded. The amount of sand size fractions in the lateritic soils are high. Quartzite derived-lateritic soils 3 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 4 Table 1: Effect of Pre-Test Drying Temperature on the Specific Gravity of the Lateritic Soil Parent Rock Drying Method SG Average Quartzite NMC 2.642 2.648 2.645 2.652 2.653 2.648 Air dried 2.643 2.644 2.643 2.643 2.643 2.643 Oven Dried at 60 ◦C 2.642 2.642 2.645 2.641 2.641 2.642 Oven Dried at 110 ◦C 2.634 2.634 2.636 2.636 2.631 2.634 Charnockite NMC 2.687 2.688 2.685 2.685 2.686 2.686 Air dried 2.688 2.687 2.685 2.686 2.684 2.686 Oven Dried at 60 ◦C 2.675 2.677 2.675 2.676 2.676 2.676 Oven Dried at 110 ◦C 2.661 2.661 2.664 2.665 2.663 2.663 Granite NMC 2.668 2.674 2.672 2.668 2.666 2.670 Air dried 2.667 2.668 2.67 2.662 2.664 2.666 Oven Dried at 60 ◦C 2.664 2.665 2.661 2.659 2.663 2.662 Oven Dried at 110 ◦C 2.654 2.655 2.654 2.655 2.653 2.654 Table 2: Grain Size Distribution of the Lateritic Soils at Different Pre-Drying Temperature Parent Rock NMC Air dried Oven Dried at 60 ◦C Oven Dried at 110 ◦C G (%) S (%) Si (%) C (%) G (%) S (%) Si (%) C (%) G (%) S (%) Si (%) C (%) G (%) S (%) Si (%) C (%) Quartzite 1.3 55.0 19.8 23.9 1.2 56.5 18.5 23.8 1.2 58.6 19.5 20.7 1.1 60.8 19.6 18.5 0.9 54.2 20.0 24.9 0.7 57.5 16.3 25.5 1.1 58.9 19.3 20.7 1.0 60.7 18.7 19.6 0.7 56.0 18.5 24.8 0.6 57.1 17.5 24.8 0.9 58.9 18.3 21.9 0.8 61.4 18.3 19.5 1.0 54.9 20.4 23.7 0.9 57.2 17.3 24.6 1.5 58.4 19.0 21.1 1.5 61.0 18.4 19.1 1.0 54.0 19.8 25.2 1.3 57.0 14.9 26.8 1.2 58.7 19.1 21.0 1.1 61.0 18.8 19.1 Average 1.0 54.8 19.7 24.5 0.9 57.1 16.9 25.1 1.2 58.7 19.0 21.1 1.1 61.0 18.8 19.2 Charnockite 0.7 46.7 20.7 31.9 0.6 49.2 20.4 29.8 0.6 51.0 20.7 27.7 0.6 53.3 20.5 25.6 0.9 46.1 20.0 33.0 0.8 48.9 19.7 30.6 0.8 50.8 19.9 28.5 0.8 53.2 19.6 26.4 0.5 46.0 20.4 33.1 0.4 49.0 19.7 30.9 0.4 51.1 20.5 28.0 1.1 52.6 20.3 26.0 0.5 45.0 21.8 32.7 0.5 48.8 22.4 28.3 0.5 51.3 21.0 27.2 1.2 52.4 20.9 25.5 0.6 45.0 21.0 33.4 0.8 48.2 21.6 29.4 0.6 51.0 20.6 27.8 0.9 52.9 20.4 25.8 Average 0.6 45.8 20.8 32.8 0.6 48.8 20.8 29.8 0.6 51.0 20.5 27.8 0.9 52.9 20.3 25.9 Granite 1.4 48.3 20.8 29.5 0.9 50.4 21.4 27.3 0.9 52.0 18.8 28.3 0.8 54.2 18.7 26.3 0.9 48.4 18.5 32.2 1.0 50.1 19.2 29.7 1.0 51.8 17.9 29.3 0.9 53.7 18.1 27.3 0.7 49.0 18.6 31.7 0.6 50.0 19.1 30.3 1.3 51.4 18.2 29.1 1.2 53.6 18.1 27.1 1.0 48.5 19.5 31.0 0.9 50.4 20.4 28.3 1.4 51.2 19.1 28.3 1.3 53.4 19.0 26.3 1.0 48.6 19.3 31.1 0.9 49.6 19.8 29.7 1.2 51.6 18.5 28.7 1.1 53.8 18.5 26.6 Average 1.0 48.6 19.3 31.1 0.9 50.1 20.0 29.1 1.2 51.6 18.5 28.7 1.1 53.7 18.5 26.7 NMC, Natural Moisture Content; G, Gravel; S, Sand; Si, Silt; C, Clay have more than 50% sand content at all the pre-test drying temperatures. From Table 2, it could be observed that the amount of clay and sand fractions are affected by method of drying that is the pre-test drying temperature. The percentage sand and clay fractions of the lateritic soils increased and reduced, respectively, with an increase in pre-test drying temperature. For instance, the average clay size fractions decreased from 24.5 to 19.2 %, 32.8 to 25.9 % and 31.1 to 26.7 % in quartzite, charnockite and granite derived lateritic soils respectively. Furthermore, it was also observed that the decrease and increase, respectively, in percentage clay and sand contents was mostly influenced by oven-drying at 110 ◦C than oven-drying at 60 ◦C and air drying when compared with NMC. The average percent increase in sand content for lateritic soil derived from quartzite was 4.2 %, 7.12 %, and 11.31 % at drying temperatures of air-drying, 60 ◦C, and 110 ◦C, respectively. The average percent reduction in clay content for soil derived from charnockite was 9.15 %, 15.24 %, and 21.04 % at pre-test drying temperatures of air-drying, 60 ◦C, and 110 ◦C, respectively. Basma et al. [6] made similar observation while studying the influence of drying methods on the properties of clays. The silt fractions of the soils, however, remain virtually constant at all the pre-test drying temperature. The decrease and increase in clay and sand fractions, re- spectively, of the lateritic soils may be attributed to particle ag- gregation as a result of drying (that is increase in temperature of pre-test drying). According to previous work, drying promotes loss of adsorbed and inter-particle water [23]. This mechanism leads to aggregation of smaller fine particles, inter-particle at- traction and separation of small particles [6]. This eventually produce an increase in capillary stress which allows close con- tact of particles in addition to development of strong Coulombic and Van der Waal bonds which are not easily reversible [5]. 4 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 5 4.2. Consistency Limits Table 3 shows the results of consistency limits of the lateritic soils as determined at their NMC, by air drying and oven-drying at 60 ◦C and 110 ◦C. The WL and IP of charnockite-derived lateritic soil were constantly higher than lateritic soils derived from granite and quartzite at all the pre-test drying temperatures used in this study. The WL and IP of the lateritic soils reduced with increase in pre-test drying temperature (Table 3). The significance of this effect is that NMC samples gave the highest WL and IP values while samples oven-dried at 110 ◦C gave the lowest values. In quartzite-, charnockite- and granite-derived lateritic soils, the averages IP decreased from 41.9 %, 56.7 % and 52.6 % when the samples were tested at their NMC to 37.6 %, 50.5 % and 48.0 % when the samples were tested after oven-dried at 110 ◦C, respectively. Increase in pre-test drying temperature, according to Sunil and Deepa [24], leads to aggregation and clustering of soil particles. The agglomeration of particles reduces the soils available surface area available for water interaction. This in turn will make the soil to absorb less water and consequently reduces the WL and IP. The results of particle size distribution also confirmed this observation. As earlier reported, the amount of clay and sand fractions in the lateritic soils are affected by the pre-test drying temperature. The percent clay and sand contents, respectively, decreased and increased as the pre-test drying temperature increases. Similar to the grain size distribution, it was also observed that the decrease in WL and IP for the three tested lateritic soils was mostly influenced by oven-drying at 110 ◦C more than oven-drying at 60 ◦C and air drying when compared with NMC. In charnockite-derived lateritic soil, the results in this research show a reduction in the IP when oven dried at 110 ◦C giving the highest reduction of 11.37 % while oven-dried at 60 ◦C and air- dried samples gave 8.57 % and 6.41 % reduction from NMC value. In granite-derived lateritic soil, a reduction of 6.16 % (oven-dried at 110 ◦C), 1.38 % (oven dried at 60 ◦C), and 0.22 % (air dried). The sensitivity of a soil, as revealed in the lit- erature, to pre-test drying depends on the type of clay mineral present and its state of hydration[6, 25]. It has been revealed that soils containing kaolinite are less sensitive to pre-test dry- ing [25]. 4.3. Plasticity Charts The decrease in consistency limits because of increase in pre-test drying temperature may become a significant factor as this may change the classification of the soil. To examine the effect of pretest drying temperature on the plasticity classifica- tion of the lateritic soils, the values of WL and IP in Table 3 were used to plot the points on Casagrande and Polidori [26] plasticity charts (Figures 1 and 2). It was observed that Poli- dori’s plasticity chart gives a fair classification of lateritic soils based on soil fractions [27]. On the Casagrande’s plasticity chart (Figure 1), the soils all plotted in the clay zones i.e., above the A-line. The soils are classified as either CI or CH. It was observed that even Figure 1: Casagrande Plasticity Classification of the lateritic Soil. a) Quartzite- derived lateritic soil b) Charnockite-derived lateritic soil c) Granite-derived la- teritic soil. CL: Inorganic clays of low plasticity; CI: Inorganic clays of inter- mediate plasticity, CH: Inorganic clays of high plasticity; ML: Inorganic silts of low compressibility; MI: Inorganic clays of intermediate plasticity; MH: In- organic silts of high compressibility 5 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 6 Table 3: Consistency Limits of NMC, Air Dried, and Oven Dried Lateritic Samples. Parent Rock NMC Air dried Oven Dried at 60 ◦C Oven Dried at 110 ◦C WL (%) WP (%) IP (%) WL (%) WP (%) IP (%) WL (%) WP (%) IP (%) WL (%) WP (%) IP (%) Quartzite 42.60 24.40 18.20 41.30 23.30 18.00 40.40 22.90 17.50 37.80 21.20 16.60 41.80 24.40 17.40 40.30 23.10 17.20 40.20 22.50 17.70 37.80 21.10 16.70 42.10 24.10 18.00 41.20 23.40 17.80 40.30 22.60 17.70 37.80 21.30 16.50 41.00 23.90 17.10 40.10 23.10 17.00 39.90 22.10 18.00 37.20 21.40 15.80 41.90 24.20 17.70 41.20 23.10 18.10 40.40 23.20 17.20 37.60 21.20 16.40 Average 41.88 24.20 17.68 40.82 23.20 17.62 40.24 22.66 17.58 37.64 21.24 16.41 Charnockite 56.30 22.20 34.10 54.30 22.20 32.10 52.70 21.40 31.30 53.50 21.20 32.30 57.10 22.60 34.50 55.20 22.60 32.60 53.70 21.30 32.40 50.10 19.80 30.30 56.80 22.40 34.40 54.60 22.40 32.20 52.40 21.70 30.70 49.40 19.40 30.00 56.50 22.30 34.20 54.70 22.30 32.40 52.20 21.20 31.00 49.20 20.20 29.00 56.70 22.40 34.30 54.30 23.20 31.10 52.80 21.40 31.40 50.50 20.10 30.40 Average 56.68 22.38 34.30 54.62 22.54 32.10 52.76 21.40 31.36 50.54 20.14 30.40 Granite 53.10 25.10 28.00 52.20 24.10 28.10 51.30 24.20 27.10 48.50 22.30 26.20 52.40 24.90 27.50 51.40 23.50 27.90 51.00 24.10 26.90 48.20 21.50 26.70 51.80 25.40 26.40 50.60 24.10 26.50 50.60 23.20 27.40 47.50 21.50 26.00 53.10 24.70 28.40 52.00 24.50 27.50 50.50 23.00 27.50 47.70 23.00 24.70 52.60 25.00 27.60 51.30 23.70 27.60 50.90 23.80 27.10 47.90 22.10 25.80 Average 52.60 25.02 27.58 51.50 23.98 27.52 50.86 23.66 27.20 47.96 22.08 25.88 NMC, Natural Moisture Content; WL, Liquid Limit; WP, Plastic Limit; Ip, Plasticity Index though the silt and sand fractions (combined) of the lateritic soils were more than the clay fractions, the lateritic soils are classified as CH or CI soils. The pre-test drying temperature does not change the classification of the quartzite-derived lateritic soil (Figure 1a) and charnockite-derived lateritic soil; except for two samples oven-dried at 110 ◦C. The classification of these samples changed from CH to CI (Figure 1b). In samples where the classification does not change, a closer look at relative shift in position of the points on the Casagrande’s chart distinctly shows that lateritic soils are becoming less plastic as the pre-test drying temperature increases. In granite derived lateritic soils, the pre-test dying temperature change the classification of the soil oven dried at 110 ◦C (Figure 1c). On the Polidori’s plasticity chart (Figure 2), the soils plot above the C-line (silt zones). The soils are classified as either ML or MH. The pre-test drying temperature does not change the classification of the quartzite-derived lateritic soil (Figure 2a) and charnockite-derived lateritic soil; except for two samples oven-dried at 110 ◦C. The classification of these samples changed from MH to ML (Figure 2b). In granite- derived lateritic soils, the pre-test drying temperatures change the classification of the soil oven dried at 110 ◦C (Figure 2c). 4.4. Compaction Parameters The moisture content-dry density relationships of the lateritic soils were obtained at their NMC, air-dried and oven- dried (60 ◦ and 110 ◦C) conditions. Table 4 shows the results of Optimum Moisture Content (OMC) and Maximum Dry Density (MDD) of the lateritic soils. The MDD of charnockite derived lateritic soil were constantly higher than lateritic soils derived from granite and quartzite at all the pre-test drying temperatures. The MDD and OMC increased and reduced, respectively, with increase in pre-test drying temperature (Table 4). The soil samples tested at their NMC gave the lowest MDD (high- est OMC) values while samples oven-dried at 110 ◦C gave the highest MDD (lowest OMC) values. In quartzite-, charnockite- and granite-derived lateritic soils, the average MDD increased from 1787 kg/m3 1858 kg/m3 and 1703 kg/m3 when the sam- ples were compacted at their NMC to 1926 kg/m3, 1954 kg/m3 and 1857 kg/m3 when the samples were compacted after oven- dried at 110 ◦C, respectively. On the other hand, the aver- age OMC of quartzite, charnockite and granite derived lateritic soils, respectively, decreased from 21.88 %, 21.68 % and 24.63 % (NMC) to 17.33 %, 18.2 % and 19.56 % when oven-dried at 110 ◦C. These results agree with the findings of previous re- searchers [11, 24]. The changes in the compaction parameters of the lateritic soils as a result of pre-test drying temperature may be attributed to the effect of particle aggregation and re- 6 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 7 Table 4: Compaction Parameters of the Lateritic Soils Parent Rock NMC Air dried Oven Dried at 60 ◦C Oven Dried at 110 ◦C OMC (%) MDD (kg/m3) OMC (%) MDD (kg/m3) OMC (%) MDD (kg/m3) OMC (%) MDD (kg/m3) Quartzite 22.40 1772 21.50 1797 19.00 1874 16.90 1940 21.60 1794 20.80 1819 19.30 1865 17.40 1924 22.10 1781 20.50 1828 19.50 1859 17.70 1915 21.40 1800 20.90 1815 19.20 1867 17.30 1928 21.90 1788 20.95 1811 19.30 1865 17.30 1923 Average 21.88 1787 20.93 1814 19.26 1866 17.33 1926 Charnockite 21.80 1856 21.20 1870 20.00 1904 18.40 1948 21.40 1864 20.80 1881 19.70 1912 18.20 1954 21.60 1859 20.40 1892 19.90 1906 18.00 1960 21.90 1853 20.80 1880 19.90 1910 18.20 1950 21.70 1857 20.80 1882 19.80 1903 18.10 1958 Average 21.68 1858 20.80 1881 19.86 1907 18.20 1954 Granite 24.60 1704 24.10 1719 22.80 1760 20.00 1843 24.40 1710 23.70 1732 22.30 1775 19.40 1862 25.00 1692 23.80 1729 23.00 1754 19.30 1865 24.50 1707 23.90 1723 22.70 1764 19.60 1857 24.60 1702 23.90 1728 22.80 1762 19.50 1858 Average 24.63 1703 23.87 1727 22.70 1763 19.56 1857 duction in micropores [28]. The reduction in OMC may be attributed to the decrease in specific area of the soils brought about by agglomeration of clay fractions to form silt/sand par- ticles. The increase and decrease, respectively, in MDD and OMC for the three tested lateritic soils were also mostly af- fected by oven-drying at 110 ◦C more than oven-drying at 60 ◦C and air drying when compared with NMC. For instance, in charnockite-derived lateritic soil, MDD increased by 5.17 % (oven dried at 110 ◦C), 2.64 % (oven dried at 60 ◦C) and 1.51 % (air dried) when compared to the value at NMC. 4.5. Unconfined Compressive Strength (UCS) The results of the UCT for the three genetically different lateritic soils as influenced by different pre-test drying temper- atures are shown in Table 5. As the pre-test drying temperature increases, the UCS decreased. For lateritic soil derived from quartzite, UCS (average) decreased from an average value of 229.80 kPa (NMC) to 220.18 kPa (oven-dried at 110 ◦C). In la- teritic soil derived from charnockite, UCS (average) decreased from 287.60 kPa to 270.68 kPa for NMC and oven-dried at 110 ◦C conditions, respectively. Although the MDD of the soils increased with increase in pretest drying temperature, the lateritic soils seemed to lose their strength as the temperature increases. Similar observa- tions have already been reported by various researchers [29], [30]. The reduction in strength may be attributed to the alter- ation/destruction of soil structure and loss of soil cohesion due to aggregation and clustering of the soil particles. Lateritic soils Table 5: Variation of UCS of the Lateritic Soils with Pre-test Drying Tempera- ture Parent rock NMC Air Dried UCS (kPa) Oven Dried at 60 ◦C Oven Dried at 110 ◦C Quartzite 229.40 218.81 223.40 218.80 228.40 222.90 221.40 217.90 230.50 229.42 225.90 228.30 230.90 223.40 220.80 215.70 229.80 223.60 222.90 220.20 Average 229.80 223.63 222.88 220.18 Charnockite 286.80 275.30 272.77 272.30 285.60 275.60 280.80 275.30 290.10 276.40 276.40 264.90 287.90 278.20 270.50 270.20 287.80 276.40 275.10 270.70 Average 287.60 276.38 275.12 270.68 Granite 263.80 252.40 253.80 252.40 265.90 250.20 252.90 241.80 261.70 253.40 251.40 249.40 264.90 257.10 250.30 245.30 264.10 253.10 252.20 247.30 Average 264.08 253.23 252.10 247.23 are known to partially derive their strength from cohesion, in- crease in particle aggregation due to increase drying tempera- 7 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 8 Figure 2: Polidori Plasticity Classification of the lateritic Soil. a) Quartzite- derived lateritic soil b) Charnockite-derived lateritic soil c) Granite-derived la- teritic soil. CL: Inorganic clays of low plasticity, CH: Inorganic clays of high plasticity; ML: Inorganic silts of low compressibility; MH: Inorganic silts of high compressibility ture will likely cause a loss in cohesion, hence a loss in UCS. Similar to other properties, oven drying at 110 ◦C produced the highest percentage reduction in UCS. In granite derived lateritic soil, for instance, the average UCS decreased by 6.27 % (oven dried at 110 ◦C), 4.49 % (oven dried at 60 ◦C) and 4.05 % (air- dried) when compared to the value at NMC. In quartzite derived lateritic soil, the average UCS decreased by 4.19 %, 3.01 % and 3.23 %, respectively, when oven dried at 110 ◦C, oven dried at 60 ◦C and air-dried. 4.6. Free Swell Index The free swell is a simple test used for estimating the swelling potential of a soil. The values of FSI for the three lateritic soils are shown in Table 6. It is observed that the maximum value of FSI for the lateritic soils was at 60 ◦C oven drying. This was followed by FSI of samples oven-dried at 110 ◦C and air-dried samples except in quartzite derived lateritic soil. Table 6: Free swell index of the lateritic soils Parent rock NMC Air Dried Oven Dried at 60 ◦C Oven Dried at 110 ◦C Quartzite 38.89 42.11 47.62 42.11 40.00 42.86 45.45 40.00 38.89 42.11 45.45 40.00 36.84 40.00 46.00 40.90 39.00 41.90 45.90 41.20 Average 38.72 41.79 46.09 40.84 Charnockite 42.11 45.00 52.38 47.37 42.11 45.00 54.55 50.00 44.44 50.00 52.38 47.37 42.11 42.11 53.70 48.30 42.80 46.00 52.50 49.00 Average 42.71 45.62 53.10 48.41 Granite 42.86 45.45 50.00 47.83 45.45 47.83 50.00 47.83 42.86 45.45 52.17 50.00 43.48 45.83 51.50 48.20 44.00 46.30 49.80 49.00 Average 43.73 46.17 50.69 48.57 The increase in FSI up 60 ◦C oven drying may be due to the clay minerals present in the soil developing a high repulsive force with increasing temperature. Consequently, according to Basma et. al. [6], “this caused the clay particles to separate more and developed a flocculated structure which led to more water being needed to make up for the deficiency upon wetting and hence more swelling”. The decrease in FSI when the pre- test temperature increased from 60 ◦C to 110 ◦C may be due to loss of plasticity and increasing aggregation of the soils. 5. Conclusions In this present study, the effect of pre-test drying tempera- ture on the properties of lateritic soils was examined. For this 8 L. O. Afolagboye et al. / J. Nig. Soc. Phys. Sci. 5 (2023) 1109 9 reason, three genetically unrelated lateritic soils were selected for this study. Three pre-test drying temperatures were used and this includes air-drying, and oven-drying at both 60 ◦C and 110 ◦C. Different tests were carried out on the three lateritic soils to study the influence of the aforesaid pre-test drying tempera- tures on particle size, specific gravity, consistency limits, free swell, compaction parameters, and strength properties. The in- dex and engineering properties at their NMC are influenced by the parent rock factors. Drying the lateritic soils to 110 ◦C re- duced the plasticity index, specific gravity, clay content, liquid limit, OMC, and unconfined compressive strength of the lat- eritic soils. The decrease in properties such as plasticity index, OMC and unconfined compressive strength may be attributed to particle aggregation (which reduced the soil surface are) and loss of cohesion. This study also revealed that lateritic soils dried at 110 ◦C may lead to underestimation of the UCS. The increased in pre-test drying temperature slightly reduced the silt content and plastic limit of the soils. The pre-test drying tem- perature did not significantly change the soils’ plasticity clas- sification, however, at higher pre-test temperature (namely 110 ◦C) the soils are generally less plastic. The MDD and sand content of the soils increased as the pre-test drying temperature increases. 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