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🔻The Use of Polymer-Modified Bitumen in Asphalt
Generally, the use of polymers in combination with bitumen aims to achieve the following two objectives:
1-Improving the existing performance properties and bringing them to the required quality.
2-Increasing the longevity and preserving the quality of bitumen in asphalt for consecutive years.
Although bitumen alone typically constitutes 4 to 5.5 percent of the total asphalt concrete, and it may seem that the role of bitumen in the behavior, durability, and performance of asphalt layers is not particularly significant, the truth is that bitumen and its physical and chemical properties have an important impact on the desirable performance, longevity, and stability of asphalt mixtures. Adding polymer to bitumen has positive effects on its properties and performance at high and low temperatures, altering all the characteristics of bitumen, which we will discuss further.
Today, a significant portion of government expenditures in various countries worldwide is allocated to asphalt pavement repairs, while these pavements deteriorate over time due to various factors such as loading and environmental variables, ultimately requiring substantial costs for repair, maintenance, or replacement of defective asphalt surfaces. Due to loading, asphalt pavements undergo deformation and experience stresses. Whenever the amount of horizontal tensile stresses in a pavement layer exceeds the tensile strength of its materials, it leads to cracking and breaking of that layer. Tensile strength is one of the most important parameters used to assess fatigue resulting from tensile stress in asphalt.
This parameter is calculated using appropriate laboratory methods and testing of suitable asphalt samples. As a result of studies conducted on the mixing of ordinary bitumen with Mamaton elastomeric polymer modifier which is produced in the form of filamentous polymer strands, all the performance parameters of bitumen have been enhanced, and in the asphalt mixture composition, it has successfully passed all laboratory tests formulated according to global standards.
Performance Grade (PG )(High-temperature range performance in summer and low-temperature range performance in winter): When asphalt is exposed to temperatures of 40 to 45 or -10 to -20 degrees Celsius, it undergoes significant degradation of its properties such as adhesion, softening point, ductility, and other characteristics, and it cracks due to shrinkage in freezing conditions (contraction cracks) and softens and flows at high temperatures in summer, raising the question of why, despite ideal grading, appropriate aggregate, optimal bitumen content according to the workshop formula and control, and monitoring of other specifications to an acceptable level, after one or two winters, asphalt deteriorates or, by retaining water for any reason, its surface becomes rough and uneven, and colloquially, the asphalt becomes naked.
Even a minor asphalt failure is like an open wound, and if not quickly repaired, with the penetration of water and air, especially water from the point of damage, asphalt degradation worsens and covers large areas, and under the influence of water, the fine particles of basic materials beneath the asphalt layer take on a fluid state and cause the asphalt to excessively flex, creating alligator cracks in it.
To achieve higher PG, polymers are used to produce highly resistant asphalts that can easily withstand a time span of 7 to 10 years and optimize expenditures in civil engineering.
Another important issue that justifies the use of polymer is the necessity of its use in asphalt with siliceous aggregates. As it is clear, if the aggregates used in asphalt are siliceous, the problem of bitumen separation from the aggregate arises over time. In other words, siliceous aggregates are bitumen repellent, meaning that good adhesion between them and bitumen does not occur, and with the presence of water in the asphalt body, which is inevitable due to rainfall, bitumen on the surface of the asphalt tends to separate from the aggregate and the phenomenon of aggregate stripping occurs, which is easily observable in asphalt pavements with a lifespan of several years, but with the emergence of polymer and its use in combination with bitumen, this problem is seriously addressed.
Next, we will discuss two other phenomena and problems in bitumens that affect the quality of asphalt.
As mentioned, with the passage of winter or excessive summer heat, many bitumen properties such as adhesion and ductility decrease, as well as its softening point. With the emergence of this problem, two other phenomena and crises arise, including aging of asphalt and early hardening of asphalt. Bitumen and asphalt hardening and aging are defined as follows:
Asphalt is always exposed to air, sunlight, environmental humidity, and ultimately oxidation. With the escalation of bitumen volatiles, asphalt experiences more oxidation and changes from dark to light colors, becoming harder and brittle over time. When the ductility and adhesion properties of bitumen decrease, the process of asphalt hardening and aging intensifies. Polymer materials maintain bitumen properties, delay hardening, and aging of bitumen, and increase the service life of asphalt.
The use of polymer materials in combination with bitumen improves all bitumen properties, prevents environmental factors from affecting it, and results in the following outcomes:
By using Filamentous Elastomeric Polymer, the following achievements are obtained:
-Prevention of aggregate stripping in asphalt mixtures. -Prevention of thermal contraction cracks.
-Reduction of deformation phenomena and bitumen bleeding on asphalt surfaces. -Prevention of asphalt cracks and the occurrence of reflective cracks.
-Reduction of hardening and aging of bitumen.
-Increase in fatigue resistance of asphalt mixtures.
-Increase in tensile strength of asphalt.
-Increase in bitumen softening point.
-Flexibility at low temperatures and no brittleness at the highest temperatures.
-Increase in compaction and reduction of air voids in asphalt.
For optimal utilization of polymer-modified bitumen in asphalt, a proper list of controls and inspections must be carried out. Failure to adhere to each of them will result in the asphalt not meeting the desired specifications, despite the use of polymer-modified bitumen.
The mentioned process is divided into 3 stages:
Stage One - Production of Materials and Storage at the Plant:
In the production of materials, adherence to the following parameters is essential:
1-Control of Los Angeles abrasion for coarse aggregate materials
2-Maximum weight loss with sodium sulfate (durability test) in coarse and fine aggregate materials
3-Maximum water absorption in coarse and fine aggregate materials
4-Maximum aggregate adhesion coefficient
5-Control of fracture percentage
6-Control of sand equivalent in the cold and hot intermediate stages
7-Quality control of filler (gradation - minimum binder content)
8-Gradation of coarse, intermediate, and fine aggregate materials
9-Control of proper stockpile formation at the asphalt plant site
10-Sampling of bitumen with supervision and conducting fivefold tests
11-Sampling of materials with supervision, conducting fivefold tests, and mixing design
12-Control of mixing design and its conversion into workshop formula