Effect of curing time and amount of Corncob ash on mechanical properties of swelling soil in forest road

  Swelling soil such as clay soil is known as unsuitable material for forest transportation due to the high volume change and mechanical defects. So, it is necessary to improve the mechanical properties of clay soil by silica content biologic stabilizers such as ash. The aim of this study was to investigate the capability of corncob ash for enhancing the mechanical strength of soil in recommended forest roads of district two in Bahramnia forestry plan in Golestan province. In this study the waste of corncob plant was collected from farmlands of province. The nodes of stem which have higher content of Silica were separated and then grind and heated in furnace at 580°C for 2 hours. Produced ash didn’t have plastic properties and most of the particles had the size of smaller than 0.075 mm. In addition the swelling soil samples were brought from the recommended roads to the soil mechanic laboratory. Samples were treated by 5%, 10%, 15% and 20% corncob ash and in curing times of 7, 14 and 28 days the tests of Atterberg limits (Plastic and liquid limits), standard proctor or maximum dry density and unconfined compressive strength were done with three replications. Findings showed that plastic index decreased by increasing of corncob ash. With increasing the amount of ash content in the mixture, the maximum dry density of the mixture decreased and optimum moisture content increased. Proctor curves of the treatments of 10% and 5% were similar from curing time of 14 days and had significant distance from the curves of the treatments of 15% and 20%. This issue shows that the use of ash more than 10% couldn’t change the dry density and optimum moisture content. Unconfined compressive strength of the mixture increased until adding 10% of ash, and then the trend didn’t change significantly. Increasing the curing time causes that the maximum dry density and unconfined compressive strength to increase, whereas plastic index of soil decreased. In most of cases there wasn’t significant difference between the curing times of 14 and 28 days, in terms of unconfined compressive strength, maximum dry density and optimum moisture content. Findings indicated that because of the pozzolonic properties of corncob ash, it is enough to use the optimum amount of 5% and curing time of 14 days for improving the mechanical properties of swelling clay soil of forest road bed