## 1 Introduction
### Use on Bitumen Products in Construction Works  
Bitumen for waterproofing is a byproduct of oil distillation, specifically from vacuum distillation, where lighter fractions are separated [6]. In its raw form, this material is not suitable for roofing because it loses elasticity due to decomposition, evaporation, and the washing out of oils. This results in shrinking and brittle cracking. Nevertheless, it has been widely used due to its ready availability. Bitumen can also be derived from vegetable sources like tall oil [7]. It has a crystalline structure similar to salts. Air blowing modifies bitumen by increasing asphaltene content relative to aromatic oils and resins, creating a gel-like structure and appropriate viscosity. Bitumen can also be modified with polymer additives, causing a phase inversion where bitumen becomes the dispersed phase in a polymer matrix. This transformation imparts viscoelastic properties and enhances stability. Polymer-modified bitumen, commonly using SBS or APP, provides the flexibility and mechanical properties needed for waterproofing [8; 9; 10; 11]. In manufacturing waterproof membranes, reinforcing materials such as polyester fabric, glass cloth, or metal foils are coated with bitumen. The surface may be covered with sand, crushed stone, or foil. Historically, jute and asbestos fibers were used, but asbestos has been discontinued due to health risks. Bitumen membranes vary by source material, polymer matrix, and production method [12; 13]. While widely used in roofing, particularly in Estonia, recycling these materials is challenging. Reinforcing fibers degrade the melted bitumen's quality, limiting its reuse in new insulation materials. For improvement of the properties, bitumen modification of various polymer blends that improve specific properties of bitumen is widely used. Notable among these are the following:  
APP-Modified Bitumen: This blend uses atactic polypropylene (APP), a plastic that melts at approximately 160 \({}^{\circ}\)C, transforming into a liquid wax-like substance. This ease of melting makes APP-modified bitumen popular for residential and small commercial roofing applications, offering a user-friendly experience due to its high-temperature tolerance [12]. SBS-Modified Bitumen: SBS-modified bitumen incorporates styrene-butadiene-styrene (SBS), which provides a \"sticky\" melt rather than a free-flowing liquid. This type of bitumen requires less heat during installation, leading to faster application times. The synthetic rubber in SBS enhances the flexibility and stress recovery of the material, making it more resistant to environmental stressors like wind and temperature fluctuations [13]. Recycled rubber and PET can be used for modifying the properties of bitumen mixes. Theses combinations provide a material that maintains a balance between flexibility and durability, making it suitable for a variety of applications [13; 14]. Bitumen with Polyethylene: At elevated temperatures (around 50 \({}^{\circ}\)C), blends of bitumen with high-density polyethylene (HDPE) and linear low-density polyethylene (LLDPE) have demonstrated improved flow characteristics and mechanical stability. Increasing the proportion of HDPE has been shown to elevate the temperature of onset of flow from 80 \({}^{\circ}\)C to 120 \({}^{\circ}\)C. This demonstrates the ability of polyethylene to enhance the performance of bitumen under thermal stress [15; 16; 17; 18]. Bitumen modified with polymers is also used in road construction for the improvement of thermal and rheological parameters of asphalt mixtures. The rheological properties of polymer-modified bitumen (PMB) can be tailored using polyethylene (PE) of varying molecular weights, allowing for the development of binders suited to different climates [19; 20]. Recycled polyethylene (r-PE) shows considerable variability in thermal behavior, including melting temperature, crystallinity, and polydispersity. As a blend of HDPE, LLDPE, and LDPE, r-PE contains both linear and branched macromolecules, with type assessed by melting temperature.