Stabilization of heavily trafficked gravel roads using waste steel slag

Abstract

ABSTRACT Enormous quantities of waste materials, both domestic and industrial are generated every year in Uganda’s steel making factories which include among others Roofing Rolling Mills Ltd, Steel rolling Mills, Modern Steel International, Tian Tiang, Pramuk Steel and Tembo Steels. Many of these materials are non biodegradable; they remain and cause a waste disposal crisis. The increasing cost of road construction materials on the other hand calls for cheaper and alternative methods to put to use the waste materials to make roads durable in all seasons and all conditions including increase in traffic loads. In this research, index properties such as moisture content, Atterberg’s limit and particle size together with strength characteristics (Unconfined Compressive Strength, UCS, and California Bearing Ratio, CBR) of lateritic gravels from Mukono district stabilized using waste steel slag were investigated. Waste slag was first used in incremental dosages with reducing percentages of lateritic gravel. A general increase in CBR and UCS values was recorded with addition of waste slag, resulting into a significant reduction in the quantity of gravel materials. The UCS values were all within the range of 0.75–1.5, recommended by MoWT, (2005). A dosage combination of 90% gravel: 10% slag resulted into a CBR above 30%, recommended by MoWT, (2005) for gravel use on wearing courses. Also, there was a general reduction in plasticity index (PI) with Namanve borrow pit exhibiting a PI of 12.2% for a combination of 75% gravel: 25% steel slag which is within the range of 10 - 15% specified in guidelines by MoWT (2005).PI results for Mokono and Namugongo were all above the 10–15% recommended MoWT (2005).range hence the need to introduce lime. The above properties were also investigated when using a stabilizer combination of lime and steel slag. There was a general reduction in PI for all laterite sources with Mukono laterities showing the best response to additive formulations. Lime : Slag formulations of 5.40% / 5.11% for Namanve, 7.56%/5.53% for Mukono and 7.14%/4.16% for Namugongo were taken as optimum lime / slag combinations for enhancement of plasticity, since their PI values were within 10% - 15%, a range specified by MoWT (2005). Similarly, combinations of 3.85%/4.38% for Namanve, 5.40%/5.53% for Mukono and 5.10%/4.16% for Namugongo gave UCS values that were in the range (0.7 – 1.5MPa), hence identified as stabilizer combinations for optimization of UCS. A cost comparison was carried out and for every one ton of laterite, at least a saving of Uganda shillings 34,000/= and 20,000/= is realized if slag is used in combination with lime instead of lime only in the optimization of UCS and PI of laterites, respectively.