Application of Topsoil as a Construction Material in a Low Cost Pavements

This study was undertaken to find out the possibility of utilizing topsoil as a one of cheapest available construction materials. The study also believed to be more useful in developing countries where a road network suffer a lot of deterioration due to poor quality of materials. Kanto loam and Organic clay were selected to represent a group of weak materials commonly available at construction site. Both are well known to have higher ability to store moisture content and hence they have high-plasticity properties. Some of them become weaker and more unstable when disturbed (example Kanto Loam). These poor-quality materials typically have the potential to demonstrate undesirable engineering behavior, such as low bearing capacity, high shrink or swell potential, and others.

Several improvements have been thought and applied to weak materials and the confirmation of improvement in properties has been made through various tests, one of main test was the bearing capacity, CBR. The cost of additives in the remote areas (developing countries) leads the study to select method of improvements into two cases, first by blending materials (with locally available coarser grain materials) in appropriate percentages (improving particle interlocking) and then secondly was to apply traditional stabilizers (bonding improvement between particles).The study realized that the bearing capacity of the Kanto Loam was well improved approximately 5 to 8 times when 20% to 40% of blending material used. Also the CBR value of Kanto loam increased as higher as 74% when blended with 40% aggregate and then stabilized with 10% cement. The study also reveals that Kanto loam CBR value increases much higher when the blending techniques applied compared to when small amount of stabilizer used. However, the case was opposite in organic clay, where little improvement achieved through stabilization compare to blending. The study also realized that organic clay need high amount of stabilizing agent or nontraditional additives which are beyond to the scope of the study.

The results shows crushed aggregates improve Kanto loam CBR more than sand, however the range is not much significant (approximately 1 to 2%) and cannot have any big differences in designing. However in considering cost wise, natural occurrence sand is much cheaper than crushed aggregate. Under the study the blending percentage from 20 to 30 of sand or crushed aggregate was selected to be the optimum based on the improvement on the CBR values. However, still the blending composition can be altered to favor the appropriate specification and cost.

The laboratory testing also reveals poor results of Fly Ash and discarded from the beginning of the study. Cement and Lime shows good bonding improvement in blended mix. Lime reveals better results compare to Cement. Hence as a matter of concluding, lime is a better stabilizing agent for this type of material. This study selects 10% lime as an optimum additive mix; however, the room for further modification and selection to suite the requirement was allowed to materials engineer. The study also provides the improvement factor equations which will guide any materials Engineer in improving Kanto loam. It also provide a general flow-chart (protocol) for determination of mixing proportional for any type of weak materials. This protocol believed to guide engineer or technician in improving particle interlocking and bonding of topsoil (weak materials). Hence, provides a solution to the area where there is a deficiency of good materials or the cost of stabilizing agent is high.

Finally the cost analysis was performed based on Japan standard prices, the outcomes shows application of blending and then stabilization techniques reduces the cost by almost 10%. I believe the method will be cheaper in the developing countries since in Japan labor cost is higher than materials cost and also the level of economy determine the price of materials, hence the relative cost of construction in Japan is higher compared to other places. To support that a simple comparison on labor and material cost were done between Tanzania and Japan and the outcome shows in Tanzania’s labor and materials cost were cheaper by 12 and 7 times respectively.