Role of curing time and compactivite effort in stabilization of in-situ road gravel using lime and natural pozzolana
Bemba, Kafuko Kenneth
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Periodic mechanized maintenance of gravel roads is becoming increasingly difficult because of the dwindling stocks of fresh gravel materials required in this process. This study centered on determining the influence of curing of existing gravel during stabilization using Lime and Natural Pozzolana as a way of reducing the use of fresh gravels during periodic maintenance. The study was carried out on an existing gravel road of 30Km from Bukwiri to Kyankwanzi town. The objectives of this study were to characterize typical in-situ road gravels based on physical and mechanical properties, to develop an optimum dosage of Natural Pozzolana admixed with Lime suitable for stabilizing these gravels and lastly, to determine the effect of curing on this stabilization process. The materials used in this study were hydrated lime from Tororo cement factory, Natural Pozzolana from Kisoro hills and existing road gravel from Bukwiri-Kyankwanzi road. Three gravel samples were obtained from chainages 0+000 km, 15+000 km and 25+000 km respectively. These samples were subjected to British Standard tests to determine the soil index properties and California Bearing Ratio. The index properties and California Bearing Ratio of the gravels were evaluated with varying Pozzolana contents of 0, 2, 4, 6 and 8%. The results of the investigation showed that the gravels were classified as A-2-6(1), A-6(2) and A-2-6(0) for Ch. 0+000km, Ch. 15+000km and Ch. 25+000km respectively using the AASHTO classification system. It was found out that a 4% Pozzolana content is the optimum Popt. This optimum was then blended with varying lime contents of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5 and 4.0% respectively. The optimum Pozzolana content (Popt) of 4% with lime dosage of 2.0% was obtained as the most suitable combination of admixtures. The California Bearing Ratio of the three gravels blended with Pozzolana and lime showed 90, 130 and 190% increase at 10 blows, 44, 81 and 106% at 30 blows, and 48, 52 and 78% at 55 blows. The influence of curing was investigated basing on strength and the study showed that increasing curing time increased the efficiency of the lime added to optimum Pozzolana exhibited by the plots of California Bearing Ratio of Popt + 4% lime with curing periods of 7, 14 and 28 days, revealing 28days curing period as most effective period, while on the other hand increasing the compactive effort reduces the effectiveness of adding lime to optimum Pozzolana with respect to strength improvement. Infact the California Bearing Ratio versus Lime content plots became flatter as compactive effort increased. ANOVA indicates a significant influence of the main effects namely; curing period and Pozzolana-lime content on California Bearing Ratio. The study indicated that stabilization of existing gravels with 4% Pozzolana and 2% lime, cured for 7 days at a compactive effort of 30 blows provides the best combination for gravel road material. The study therefore recommended curing with an optimum blend of Pozzolana-lime mix of 4% and 2% to be tried on road section so as to assess suitability under typical field loading conditions, tropical weather, location, temperature and humidity.