The improvement, reconstruction and repair of roads in recent years have increased the content of recycled asphalt in pavements. Using these materials in road construction projects because they reduce the costs, will also be of great help in improving environmental issues. In the present study, dune sand, which can be found in most desert area soil but does not have proper strength and loading capacity for a subgrade, was used. In order to increase the strength parameters of dune sand, various contents of cement and recycled asphalt were examined in California Bearing Ratio (CBR) and compressive strength tests. The results showed that the addition of cement and recycled asphalt can increase compressive strength and bearing capacity and reduce rupture deformations. In a stabilized sample with 27.5% recycled asphalt, increasing the cement from 7.5 to 12.5% increased the compressive strength by 1.045 times, which is the highest amount of change in the samples studied. The maximum CBR and minimum rupture deformations are related to 35% of the recycled asphalt and 12.5% of the cement. The predicted functions of the compressive strength, deformation and CBR depend on two variables of the cement content; the recycled asphalt was then calculated using the response surface method

No abstract

Improving the subgrade performance and increasing their efficiency can lead to improving the operation and increasing the life of the pavement. One of the common solutions to improve the resistance and engineering properties of the soils is using the stabilizing materials. Using the waste materials as a stabilizer in the soil can lead to a reduction in project costs and help the protection from the environment. In this study, emulsion bitumen and crushed waste tile are used to stabilize the sand dune which is soil with low bearing capacity and resistance properties. In the present study, the emulsion bitumen and crushed waste tile have been used. The effect of dimensions and percentage of crushed tile with different percentages of emulsion bitumen on the compressive pressure and bearing capacity as well as the compressive strength after applying freeze-thaw cycle. The results indicate that the addition of crushed waste tile increases the compression strength and bearing capacity and the tile with a higher dimension has shown more effectiveness. Applying the freeze-thaw cycle has reduced the compression strength and increasing the number of cycles has increased the resistance drop rate. Soil stabilized with coarse-grained tile has more resistance drop rate which increases by increasing the tile percentage. Then, the 3D graph and the recommended function related to each parameter investigated in the test were provided using the response surface analysis method.

One of the challenges of road construction is encountering soils with lack of required strength and durability. Nowadays, various stabilization techniques are applicable for improving the engineering properties of soils. In the present study, dune sand, as subgrade of pavements, was treated using various contents of fibrillating network (FN) fiber and cement. Dune sand has low bearing capacity that makes it unsuitable for construction activities such as pavement applications. The common solution is improving the strength properties of dune sand so that it can be used for civil engineering projects. Stability of subgrade is very important since the layer provides the stability for the whole pavement structure and the upper layers, namely subbase, base, and asphalt layers. In this regard, compression strength and California bearing ratio (CBR) tests were carried out. Freezing-thawing cycle is one of the most important factors affecting the mechanical properties of soils. Several researchers reported that freezing-thawing cycle could change the physical and mechanical behaviours of soils. The influence of freezing and thawing (up to 18 cycles) on the properties of samples was also studied. Based on the results, the inclusion of FN-fiber to the sand led to increasing the ductility and compressive strength. Also, the addition of cement reduced the ductility, and increased the compressive strength. By increasing the freezing-thawing cycles, the soil strength significantly decreased. Results showed that the stabilized sand soil as subgrade layer led to reducing the compressive strain under the applied wheel load, and therefore reduced the possibility of rutting failure of subgrade.