Plasticity and stiffness of aged road gravel stabilized with Acrylic polymers
Gabula, Edward Kitamirike
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World over, the increasing need to reduce costs, conserve materials and use of marginal soils have resulted in the use of soil stabilizers in increasing quantities in the construction of roads. As such, this research study sought to assess the use of Geogrit (BP2G) as a suitable stabilization agent. Geogrit contains two components which are commercially available namely BP2G and BP3G. BP2G hardens the soil by stabilization and this was tried in Malaysia on weak silty sands and their performance greatly improved. Normally, there is need to import gravel from approved borrow pits for construction of roads. However, due to increasing depletion of quality gravel material, there is need to develop technologies that can be used to stabilize aged gravels. This therefore prompted the use of acrylic polymers (Geogrit) to stabilize aged gravels. The physic - chemical properties of the BP2G Geogrit sample were analyzed and observed to meet and comply with Regulation 3 of the National Environment (Standards for discharge of effluent into water or on land) regulations, S.I. No.5/1999, Section 26 and 107 of the NEMA act. Soil samples were obtained every 200m from ch. 0+000 km to ch. 1+200 km along Lubowa – Ndejje road (Ch. 0+000km -1+300 km). The seven test soil samples obtained were generally classified as clays of intermediate plasticity and A-7-6 soils according to the Unified Soil Classification System and American Association of State Highways and Transportation Officials soil systems respectively. The test soils were stabilized with Geogrit (BP2G) in variations of 0, 2, 4, 6 and 8%. Laboratory tests that include Atterberg’s Limits, California Bearing Ratio (at 10, 30 and 65 blows) and Unconfined Compressive Strength test were carried out. Results obtained from laboratory experiments were analyzed using statistical tools and regression analysis to obtain the optimum amounts of Geogrit for suitable stabilization. Limiting values from the Ministry of Works and Transport General Specifications and Road Design Manual (2010) were used for Atterberg’s Limits, California Bearing Ratio and the Unconfined Compressive Strength respectively. Results from this study indicated that the sampled soils are fine grained clays with a minimum of 25% passing the 0.075mm and a plasticity index greater than 24. The addition of Geogrit reduce the plasticity index by an average of 6.5%. The optimal dosage for application of Geogrit in silty clay soils was found to be 4.5% on application of a maximum dosage of 8%. Normally stabilization is carried out on imported gravel material meeting stated specifications. However, this research attempted to carry out stabilization on aged road gravels due to the scarcity of gravel material arising out of urbanization and land values. By eliminating importation of gravel material, the cost of road construction is expected to reduce. This is eliminate the high and unpredictable material transport costs, differences in sources of construction materials and plant. Additionally, gravel and sand have been declared as minerals by Government, therefore their excavation will require a license and this will definitely increase on the cost of gravel. Stabilization of existing road material using Geogrit provides a layer of sealant to the soil particles hence impairing water absorption which improves compactibility and therefore CBR and strength. The sealant eliminates gravel loss, dustiness and reduces on the likelihood of occurrence of other distresses on the road. The obtained soil mixes demonstrated improvements from their control samples. Basing on all the investigated soil properties, Geogrit has demonstrated utilization in stabilization of unpaved roads. Therefore, the use of Geogrit to stabilize marginal soils can thus provide sustainability to the local road construction industry.