EFFECT OF DRYING TEMPERATURES ON THE ENGINEERING PROPERTIES OF LATERITE SOILS IN AKURE, SOUTH-WESTERN NIGERIA

Abstract

Laterite is one of the most important natural soil types used as material for different construction purposes worldwide, its engineering behavior is very sensitive to drying conditions. In this study, the effects of drying temperature on laterite properties were determined on samples from Akure metropolis, Southwestern Nigeria, where laterite soils are the main soil cover. Fifty four (54) laterite soil samples were collected from 18 locations from the three classical layers of laterite soil profiles (viz. top accumulation, middle accumulation and mottled zone). The samples were taken from soils derived from four different types of rocks. Four (4) samples each were obtained from Charnockite and Porphyritic granite-derived soils while three (3) and seven (7) samples were obtained from quartzite and Granite gneiss-derived soils respectively. The soils samples were characterized using standard tests of engineering soil classification i.e. natural moisture content, grain size analysis, atterberg limits and compaction tests. The sensitivity to increasing temperature was assessed using the three (3) modes of drying (i.e. air-drying, oven-drying at 105oC for 24 hours and oven-drying at 105oC for 48 hours). The variation in the values of specific gravity, atterberg limits (LL and PL), linear shrinkage, and free swell were used to understand the behavior of these soils. Particle (grain) size analysis results showed that 79.6% of the laterite soils obtained are well graded while the remaining 20.4% are poorly graded. The average values of liquid limit range between 27.7% and 57.2% for air drying. The sensitivity values obtained ranged from 23.2% to 52.3% and 22.4% to 52.3% for oven-drying at 24 hours and 48 hours respectively. The plasticity index values range from 7.3% to 31.8% for air dried soil, 7.4% to 32.2% and 3.4% to 32.7% for oven dried soils for 24 hours and 48 hours respectively. The free swell index values range from 11.1% to 44.4% for air dried soil, and oven dried soil at 1050C for 24 hours and 48hours respectively. The average specific gravity values ranged from 2.58 on granite gneiss to 2.80 on granite gneiss for air dried soils and from 2.59 on Porphyritic granite to 2.84 on granite gneiss and from 2.65 on Porphyritic granite to 2.84 on Granite gneiss for 24 hours and 48 hours oven drying respectively. The maximum dry density (MDD) for soils range from 1429 kg/m3 on Charnockite rock to 2241 kg/m3 on Porphyritic granite and the optimum moisture contents range from 13.0% to 24.1% for the laterite soil samples tested. Based on AASHTO system of classification, 33.3% (18 samples) of the sampled soils were classified as A-7-6 soils, 5.6% (3 soil samples) were classified as A-7-5 soils. 5.6% (3 vi samples) were classified as A-4 and 14.8% (8 samples) as A-6 soils, while 18.5% (10 samples) were classified as A-2-7 soils, 14.8% (8 samples) were classified as A-2-6 soils and the remaining 7.4% (4 samples) of the sampled soils were classified as A-2-4 soils. It implies that only A-2-7(18.5% of the samples), A-2-6 (14.8% of the samples) and A-2-4 (7.4% of the samples) soil types are good foundation materials. All these test results adequately show that Porphyritic granite and Quartzite derived lateritic soils possess the highest strength. Granite gneiss-derived soils possess moderate strength, while those derived from Charnockitic rocks possess the lower strength for foundation and construction purposes. There exist weak positive correlations between fine contents with MDD for top and middle accumulation zones. There is a strong positive correlation between fine content and MDD for the mottled zone. Also, there exists weak positive correlation between Clay content and MDD for all the layered zones. The research shows that the temperature and length of drying time have effects on some of the engineering properties of the laterite soils studied. In addition, although geology has some effect on these engineering properties, it is not significant enough to provide a discriminant for the choice of the soils used as engineering materials.