# Transition Effects in Bridge Structures and Their Possible Reduction Using Recycled Materials
## 5 Detailed Overview
### Properties and Use of Polymers in Bridge Structures
#### 5.4.2 Reducing the Transition Effect  
The primary requirement in constructing a bridge abutmen along with an embankment is to ensure smooth passage between these entities. Polymers that can be used to make ground reinforcements that reduce the pressure from the fill involve the occurrence of frictional forces between the ground and the reinforcement. Regardless of increasing the soil's shear strength and reducing the pressure on the abutment, reinforced ground provides a more even distribution of deformations. This is particularly crucial in the case of integral bridges, where, due to temperature changes, displacements of the ground behind the abutments alter the direction multiple times [62]. Polymers are actively utilized to reduce the transition effect. These are applied in engineering structures to reinforce the subgrade, increasing its stiffness (while decreasing its susceptibility) and reducing the transition effect, primarily through injection masses. An example is the use of polyurethane material as an adhesive that gradually stiffens the subgrade along the transition zone. Studies are being conducted on the use of polymer reinforcement in railway subgrades within transition zones at the approaches of engineering structures to mitigate the transition effect [246; 247]. The technology involves injecting a polyurethane polymer mass in order to gradually bind the ballast of the track bed along its length. In terms of the vertical displacement of the rail, typical reductions of 25%, 16%, and 3% can be achieved. After static and dynamic testing, we can conclude that performance of polyurethane polymer in the transition zones can achieve the transition of the ballast bed from low stiffness to high stiffness [246]. The maximum reduction occurred with polyurethane alone, and when adding assistant rails and compared to having no settlement, the vertical rail acceleration was reduced by 16.5% and 25.6%, respectively [247]. The research results demonstrated increased subgrade stiffness and a reduced transition effect. In this scheme, the bonding surface of the aggregate with the polyurethane determined the variation in the subgrade stiffness. This solution was adapted in China for the transition zone of a railway line at the entrance to a tunnel, where the ground changed from flexible to the rigid concrete at the entrance. Another example is the use of mats from used tires, which is a fully-fledged recycled polymer [248]. In this approach, after numerous analyses, engineers investigated a set of five-plate rubber mats placed under the rails in gradually increasing quantities. Based on the relationship between the rail deflection and rubber mat stiffness, the wheel-rail interaction force was significantly reduced from 120 kN to 85 kN. Rubber mats with different stiffnesses are designed to equalize rail deflection differences. With the proposed design, the smoothness of the transition zone can be significantly improved. Another solution being studied is the use of dispersed polymer reinforcement for concrete, which can also be recycled [249]. The main difference from standard solutions is the use of a mixture with a continuously changing content and type of reinforcement along the length of the track. It should be noted that changing the rail support in the transition sections, in order to eliminate the transition effect, had a positive effect on the total stiffness of the track system in the transition zone, estimated at up to 15%. Polymers are used as reinforcing materials in various construction projects, and there is substantial scientific research confirming their strength properties [161, 162, 198, 250]. The aforementioned literature demonstrates that polymers can have numerous applications in the construction of bridge abutments and embankments, both as structural and auxiliary materials. It is worth noting that there is not an abundance of scientific studies linking recycled polymers with bridge construction, particularly with abutments, embankments, and transition zones.