A first-order reliability method (FORM)was employed to assess the compaction water content, CWC (i.e optimum moisture content) of residual lateritic soil mixed with plantain peel ash (PPA) and compacted with British Standard Light (BSL)and British Standard Heavy (BSH)energies, for flexible pavement applications. A Multi-linear regression model was generated from values obtained via laboratory tests using Mini-tab R15 software, which served as a performance function that was applied for the analysis. Using the regression models for CWC, established distributions for the relevant soil factors, safety index (SI) was computed using CWC as a dependent factor and the soil factors Plantain Peel Ash (PPA); Plasticity Index (PI); Percentage File (PF); Specific Gravity (Gs) and Compactive Effort (CE)as self-determining factors). The results revealed that the safety index is sensitive to changeability in the soil factors. Outcome from the analysis show that Gs and CE are greatly affected by alteration in the coefficient of variation (COV), and so it is essential to control Gs and CE in lateritic soil–PPA mixes in road pavements. From the safety index values it reveals that PPA content has a minimal consequence as its value virtually remained constant at all COV used. Stochastically, lateritic soil mixed with PPA produces an acceptable safety index value of 1.0, as mentioned by the Nordic Committee on Building Regulation (NCBR) at 10% COV for BSH of compaction water content only. Therefore a more effective additive such as cement, lime, or bitumen is recommended for modeling CWC of lateritic soil-PPA mixes for road pavement at 10–100% series of COV. Keywords: Coefficient of variation; compaction water content; lateritic soil; plantain peel ash; reliability index
The workability of any soil, when used as a construction material, is greatly affected by its plasticity and compaction characteristics. This research investigates the effect of iron ore tailings (IOT) on the plasticity and compaction properties of lateritic soil (LTS) and black cotton soil (BCS). Atterberg limit and compaction test using three energies, British standard Light, BSL, British standard Heavy, BSH, and West Africa standard, WAS were carried out. These tests were conducted on mixed ratios of 0, 2, 4, 6, 8, and 10 % of IOT mixed each with LTS and BCS separately. A Statistical conceptual model was developed using Minitab R15 to predict the values of the maximum dry density (MDD) and optimum moisture content (OMC) from the computed laboratory results. Analysis was then carried out on the predicted results using origin pro version 8 to test the efficacy of results obtained. The result of specific gravity test shows increase with IOT concentration. An improvement on the plasticity of the modified soil was noted. The liquid limit for both LTS and BCS decreased with increasing IOT concentration. Values drop from 43.4 to 42.7% for LTS and 56 to 52.6% for BCS at 0 and 10% of IOT content, respectively. Plastic limit increased with increasing IOT concentration for LTS and decreased for BCS. In the case of the Plasticity index, values decreased for LTS and marginally increased for BCS treated with IOT. MDD values increased and thereafter drop for LTS treated with IOT while for BCS values increased from natural up to 10% IOT content. OMC values increased for LTS treated with IOT and decreased for BCS treated with IOT. The effectiveness of the developed model was validated using the values of the correlation coefficient obtained from the statistical analysis, which showed a solid relationship between predicted and measured values. Plasticity index values obtained for IOT stabilized BCS did not meet up to the standard requirement when used as a sub-base and base course material respectively. However, the treatment of LTS and BCS with 8-10% IOT improved the soil properties and can be used for pedestrian walkways.
Poor geotechnical and mineralogical properties of soils used for road construction are a significant factor responsible for pavement failures. This is because most soils encountered at failed portions of some pavements do not meet the specifications according to relevant standards. It is with this in mind that this study carried out a systemic review on some residual soils in Nigeria, with a focus on their locations, geotechnical, and mineralogical properties in comparison to standards specified in the Nigerian specification for road and bridges. This study also reviewed how these properties have contributed to various road failures in different regions of the country. It was observed that the geotechnical and mineralogical properties of most residual soils in some regions of Nigeria did not meet up with the standards stipulated by the Nigerian Specification for road materials. Reviews carried out on the place of geotechnical and mineralogical characteristics on various road failures in Nigeria showed that a high volume of research works was carried out in the south-western and southeastern parts of the country compared to the Northern region.
The demand for access roads to vital services is on the high side in rural areas. This demand face much challenge due to the cost of construction. However, having the opportunity to use non-conventional materials that are naturally available in meeting this demand will ease people living in such environs. It is on this note that an investigation was carried out on an indigenous, naturally available sand popularly known as Sakasaka by Ilesha indigenes to ascertain its suitability for pavement construction. The Sakasaka collected from Ilesha borrow site, Ilesha West Local Government Area of Osun State, was used to produce concrete cubes that were tested after curing for 7, 14, 21, 28, 56, and 112 days respectively to know the strength of the material and compared to theoretical strength. Prior to the cubes production, some investigations such as chemical analysis, Sieve analysis, Specific gravity and so on were carried out on the sand. The study investigates the physical properties, chemical components of Sakasaka as well as the compressive strength properties of the concrete produced at ratio 1:2:4 using Cements A, B, and C 3x brand. The total numbers of cubes cast were 162 with a concrete cube size of 150x150x150mm. Sieve analysis, specific gravity, slump tests were also carried out for different water-cement ratios for the three cement. The concrete cubes were tested at the ages of 7, 14, 21, 28, 56, and 112 days. The effects of cements (A, B, and C) on the all-in-aggregate was investigated with respect to compressive strength at different curing age. From the results obtained, the compressive strengths of cubes were 17.76 N/mm2, 19.92 N/mm2 and 20.5N/mm2 which was in line with the standard compressive strength of concrete mix 1:2:4 at 28days.
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