Effects of Top Seal White on Performance of Road Wearing Course Materials; A Case Study of Lateritic Gravel

Abstract

It has proven possible to improve some soil qualities by stabilizing natural materials. Soils can be blended or mixed with commercial additives to alter the gradation, texture, or plasticity to attain the desired gradation. Additionally, the additives serve as binders to tie the soil together. Soils have been treated with bitumen, fly ash, Portland cement, and lime to improve their mechanical properties, including strength, texture, workability, and plasticity. This study evaluates how the top seal white additive affects lateritic gravel's performance as a material for road wearing courses. Most of the unpaved roads in the rural areas of Kenya have undergone much deterioration, characterized by many ruts, potholes and loose stones. Ruts and potholes have resulted in rough and uncomfortable driving surfaces, leading to high vehicle maintenance costs and low speeds and delays. The dust coming from the road surfaces reduces drivers' visibility at times, leading to loss of control and accidents. There is a need to develop innovative materials that can be used to improve the properties of the road wearing course either by full or partial replacement of the wearing course materials. These materials will enable the wearing course to be adequate and overcome the shortcomings it is currently experiencing. Through the road agencies, the Kenyan government has implemented several programs to aid in developing and maintaining rural roads. The Rural Access Roads Program (1974-1986), Minor Roads Program (1986-1996) and Roads 2000 and 10000 strategies (1996 onwards) have been implemented. However, the approaches have been capital intensive, and the government does not have the resources to match the demand. This has made it necessary for engineers to continuously look for alternative materials that can be used to develop new and maintain the existing Kenyan roads. The laterite gravel and the top seal white used in this study were subjected to physical and chemical tests to determine their properties. The top seal white was added to the laterite gravel, and tests were conducted to determine the influence of the top seal white on the laterite gravel's properties. Top seal white achieves optimum results with applications in soils containing at least 15% fines passing a 200 sieve, or in soils suitable for road wearing course construction. This study used 15, 20, 25 and 30 percent of fines passing a 200 sieve to determine the optimum acceptable content at which the compressive strength, atterberg limits and California bearing ratio are at their maximum. The concentration of the top seal white additive varied at ratios of 1:3, 1:5, 1:7, and 1:9. The assessment done in this research indicates that the higher the fines content, the better the performance of the lateritic gravel. This is attributed to the maximum dry density achieved with a higher percentage of fines involving a particle arrangement where smaller particles are packed between larger particles, thus reducing the void space between particles. This creates more particle to particle contact, increasing stability and reducing water infiltration. With the application of the top seal white, the properties of the soil sample were immensely improved. The plasticity index of the soil is reduced with the application of the additive, reducing the soil’s susceptibility to water content changes. The plasticity index upon treatment dropped from 24.99% for the untreated sample to 15.91%, 10.3%, 10.81% and 12.73% at top seal white concentrations of 1:3, 1:5, 1:7 and 1:9, respectively. The permeability of the soil was reduced, an indicator that the addition would increase strength. The maximum reduction in permeability was 93.38% at 1:7 top seal white concentration. Increasing the top seal white additive to the laterite soil improved the compressive strength and the California Bearing Ratio. The highest compressive strength improvement recorded was 136% at 25% fines passing the 200 sieve with 1:3 concentration of top seal white, while the lowest strength increase was at 54% with 1:9 concentration. The highest California Bearing Ratio of 32.66 was recorded, with 25% fines passing the 200 sieve at 1:3 top seal white concentration. This was a 25% increase in the California Bearing Ratio of the neat laterite gravel. Therefore, applying this additive will improve the properties of the pavement-wearing course and give it a long life. This is based on the improvement in the properties of the laterite gravel attained by the top seal white addition. Its application is therefore recommended whenever it is economically feasible. Top seal white should be tried in other soil types, too, as it will allow its use in soils that cannot support engineering structures.