ENHANCING PAVEMENT SUBGRADE BEARING CAPACITY THROUGH ROCK FLOUR ADDITION TO LATERITIC SOIL.
Abstract: This study aimed to enhance the bearing capacity of lateritic soil for pavement subgrade by incorporating rock flour stabilized at varying percentages of 0-12% by dry weight of soil in increments of 3%. Compaction was performed using three different compactive efforts, namely British Standard Light (BSL), West Africa Standard (WAS), and British Standard Heavy (BSH). The lateritic soil used in the study was classified as A-7-6 according to the American Association of State Highway and Transportation Officials (AASHTO).
The results demonstrated that the addition of rock flour led to an improvement in the index properties of the mixtures. As the rock flour content increased from 0% to 12%, the Liquid limit decreased from 42% to 32%, and the Plasticity index decreased from 29.30% to 13.48%. The plasticity indices of the A-7-6 soil mixed with rock flour also showed a significant reduction.
The maximum dry density (MDD) values for the natural soil were 1.802 g/cm³, 1.820 g/cm³, and 1.870 g/cm³ for BSL, WAS, and BSH compaction efforts, respectively. The optimum moisture content (OMC) values were 12.40%, 11.90%, and 11.60% for BSL, WAS, and BSH, respectively. The highest values were obtained with 9% rock flour addition. BSH exhibited the highest Unconfined Compressive Strength (UCS) value of 250.89 kN/m², while BSL and WAS had UCS values of 180.8 kN/m² and 218.12 kN/m², respectively.
A progressive improvement in soaked and unsoaked California Bearing Ratio (CBR) values was observed with increasing rock flour content. The lowest CBR values for soaked and unsoaked conditions were recorded with 3% rock flour addition. At 3% rock flour addition, the soaked CBR values for BSL, WAS, and BSH were 21.15%, 25.93%, and 28.21%, respectively, while the unsoaked CBR values were 37.88%, 41.74%, and 42.73%, respectively, for the same compactive efforts.
Regarding consistency limits, the mixtures did not meet the required threshold values for subgrade, which were LL < 35 and PI < 12% according to local codes. This suggests the need to increase the rock flour content to enhance these parameters.
In terms of soaked and unsoaked CBR values, the results from all three compactive efforts (BSL, WAS, and BSH) met the minimum requirement of 10% for flexible pavement subgrade, as specified by NGS (1997).
To optimize the structural strength for subgrade application, the mixtures should be compacted to 100% of the relative densities.
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