# Use of Lignin, Waste Tire Rubber, and Waste Glass for Soil Stabilization
## 4 Results and Discussion
### Results of the Resilient Modulus  
Data obtained from standard Proctor, CBR, and uniaxial compression tests for road subgrade do not provide information on the behavior of the material under dynamic loading. For this reason, resilient modulus tests were performed on the samples to determine the behavior of the prepared mixtures under cyclic loading. In the cyclic triaxial tests, the largest values are generally obtained for the smallest bulk stress under a 41.4 kPa confining pressure, while the smallest resilient modulus values are obtained for the largest bulk stress value under a 13.8 kPa confining pressure. For all mixtures of waste glass powder, lignin, and waste tire rubber, an increase in the resilient modulus was achieved with an increasing proportion of additives compared to the control sample. Among the samples with additive, the lowest value of the resilient modulus was obtained in the sample 5%GP + 0.5%RT (S4) under a 13.8 kPa confining pressure, while the highest value of the resilient modulus value was obtained in the sample 20%GP + 3%RT (S7). Compared to the control sample, the greatest increase in the samples made with waste glass powder and waste tires was achieved in the sample with 20%GP + 3%RT (S4) additive, where an improvement of 110% was achieved under a 13.8 kPa confining pressure. For the samples made from waste glass powder and lignin, the sample with 15%GP + 15%LG (S3) was the one with the highest improvement, achieving an increase of 85% (see Figure 8).  
Figure 8: Resilient modulus versus bulk stress relationships at a confining pressure of 13.8 kPa.  
Compared to the control sample, the greatest increase among the samples produced with waste glass powder and waste tires was achieved in the sample with 20%GP + 3%RT (S7) additive, where an improvement of 113% was achieved under a 27.6 kPa confining pressure. For the samples made with waste glass powder and lignin, the sample with 15%GP + 15%LG (S3) was the one with the highest improvement, achieving an increase of 97% (see Figure 9).  
Since the subgrade materials are located below the pavement layers, the resilient modulus value under a confining pressure of 41.4 kPa, which represents the stress in the deep layers, is of greater importance. Compared to the control sample, the greatest increase in the waste glass powder and waste tire samples was achieved in the sample with 20%GP + 3%RT (S7) additive, where an improvement of 178% was achieved under a 41.4 kPa confining pressure. For the waste glass powder and lignin samples, the sample with 15%GP + 15%LG (S3) was the one with the highest improvement, showing an increase of 147% (see Figure 10).  
As can be seen from Figures 8-10, the resilient modulus values generally decrease as expected as the bulk stress increases for each confining pressure. According to the results of the resilient modulus tests, the specimens made with waste glass powder and waste tires generally perform better than the specimens made with waste glass powder and lignin. In general, the void ratio can be significantly changed by adding recycled rubber and crushed glass to the soil or by applying pressure. This is due to the fact that the addition of rubber tires and glass powder changes the size, shape, and connection of the soil pores. It can, therefore, be concluded that the addition of waste tires and glass powder plays an important role in the pore size and strength parameters. When the addition of glass powder and waste tires began, large aggregate pores formed and caused the formation of smaller and more interconnected pores [63; 68; 69; 70].  
The evaluation of all resilient modulus test results taken together shows that the stabilization in this study makes a positive contribution to the resilient modulus of the soil. This means that under the actual loading conditions, the compressive strain effect on the  
Figure 9: Resilient modulus versus bulk stress relationships at a confining pressure of 27.6 kPa.  
stabilized subgrade is reduced and, thus, the rutting resistance of the stabilized subgrade is increased.