modified bitumen with polymer
It is common practice to modify bitumen with polymer in order to reduce the sensitivity of bitumen and asphalt to high and low temperatures. This reduces the occurrence of common failure mechanisms including rutting and cracking. Traditionally, thermoplastic or elastomeric polymers have been included in the bitumen modification process.
The name "polymer" is derived from a phrase that means "composed of several parts." You might think of polymers as long chemical threads composed of numerous smaller molecules (monomers) joined end-to-end.
The polymers are composed of these monomers. Consequently, polymers can be composed of a variety of different numbers of monomers and have a range of different chain lengths. When it comes to the use of a specific type of polymer in bitumen, certain chain lengths are preferred over others.
For instance, the polymer known as "polystyrene" is composed of many styrene molecules that are sequentially connected to one another. In the process of modifying bitumen for use in road applications, two basic classes of polymers are employed: Bitumen is found in nature, although it is typically produced as a byproduct of the oil refining process.
Despite this, bitumen's thermoplastic qualities make its usage in road building troublesome. It has been discovered that the temperature at which bitumen undergoes a transition to an apparent glass state is quite near 0 degrees Celsius.
Bitumen is a viscoelastic substance, which means that, depending on temperature and time, it can display either elastic or viscous behavior or a combination of the two. Due to its viscoelastic qualities, bitumen can display either elastic or viscous behavior. When subjected to sufficiently frigid temperatures and high strain rates, bitumen behaves virtually identically to an elastic solid.
As a result, asphalt concretes are susceptible to low-temperature cracking, which may lead to fracture. Moreover, when the asphalt is exposed to high summer temperatures, it undergoes a process called flow or creep. For asphalt paving surfaces to maintain their level of stability, they must resist the impulse to flow or creep when subjected to heavy loads.
Elastomers and Plastomers
In a polymer's structure, an elastomer is distinguished by its flexible "rubber" backbone and its large side chains. Styrene butadiene styrene is an example of a product in this category (SBS).
A polymer is a plastomer if it can be deformed into a plastic or viscous condition at melting temperatures and then harden and become rigid at low temperatures. This indicates that the structure can be irreversibly destroyed by applying heat.
In this procedure, both elastomeric materials and thermoplastic modifiers are utilized. There are four types of thermoplastics: alpha-polyolefins (APO), atactic polypropylene (APP), isotactic polypropylene (IPP), and ethylene-vinyl acetate (EVA) (EVA). Elastomerics include styrene-butadiene-styrene (SBS), and styrene-butadiene rubber (SBR) (SBR).
The choice of polymer modifier affects the method in which the polymer is administered. Since the melting point of thermoplastic sheets (APP types) is too high to properly bind with hot asphalt, the sheets are often heat-fused to the substrate prior to being put to the surface.
The SBS-treated sheets may be either burned or mopped. Because APP sheets have a higher temperature at which they begin to soften, they are sometimes chosen for usage in highly hot environments. In contrast, SBS sheets are preferred in cold climates due to their increased flexibility at low temperatures.
In high-stress parts of the roof, such as flashings, modified bitumen systems offer substantial advantages over conventional BUR. They have contributed to the continued existence of the BUR market.
In contrast to bituminous underlayment rolls (BURs), polymer-modified bituminous sheets (MB) utilize reinforcement sheets that have been factory coated with rubberized bitumen. MB employs reinforcement sheets. The sheets have a natural resistance to water on their own.
When polymers are mixed with bitumen as a coating, the coating's flexibility, durability, and performance at low temperatures are enhanced. The fact that MB systems require, on average, fewer layers and are, as a result, less labor- and material-intensive than BUR systems is a significant advantage of MB systems.
The following are examples of unique MB system types:
- Using a propane torch or a hot-air welder, the factory-applied bitumen is remelted so that it can be used as an adhesive in the heat-fused process.
- Using typical hot BUR cleaning techniques, the floor is mopped in place.
- Adhesives consist of liquid solvents.
Internally adhesive (peel and stick)
Almost typically, two layers of reinforcing sheets are required when constructing a membrane. There are several alternatives for the base layer, including a modified sheet, a standard asphaltic base sheet, or multiple layers of BUR ply sheets embedded in hot asphalt. In some circles, this latter technique is also known as a hybrid system.
Reinforcement
Glass fiber, polyester, and composites two are common construction materials. Plastic core materials have also been utilized in a variety of waterproofing and roofing underlayment applications.
During the production process, reinforcements are utilized to support the sheet, and the finished membrane benefits from both its tensile strength and stability.
Surfacing
As a top surface, a number of BUR systems utilize a flood-coat composed of hot bitumen and aggregate. In addition to being labor- and material-intensive, the surface is also heavy (four to six pounds per square foot), durable, water- and fire-resistant.
Because MB sheets are factory-coated, the vast majority of roofing granules and metallic foils are likewise coated at the factory. To achieve the recently sought-after goal of highly reflective roof surfacing, a white coating can be applied in the factory over the granules or even the polymeric sheet itself.
In other instances, the cap sheet is either installed unsurfaced, in which case the internal reinforcement of the glass mat provides the weather resistance, or it is coated in the field with a colored or asphalt-aluminum coating. Rarely, if ever, flood coat and gravel are used in MB systems.
Climate or Weather
Before coated MB sheets may be unrolled, they must be stored at temperatures above freezing for a minimum of 24 hours. In some solvent-adhesive systems, the body of the sheet may be embedded in the glue to obtain a quick and reliable seal, but the side laps and end laps may need to be burned.
Self-adhering sheets sometimes require temperatures above 50 degrees Fahrenheit to create adhesion. In addition, several systems use mastic adhesive at T-joints to reinforce the self-adhesion at those spots.
Employing a Propane-Powered Torch
The heat from the torch makes the MB sheets more conformable, which is one of the intriguing aspects of torch application. Since heat is only required at the spot where it is being applied, the kettle, lugers, and mops are no longer practicable. In addition, the heat contributes to the substrate's moisture evaporation, hence reducing the risk of blistering.
On the other side, new safety-related concerns emerge. When propane is used, fire districts may require daily reporting and prohibit the use of torches in occupied buildings outright.
A fire watch should be established for at least one hour following the extinguishment of the last torch. Additionally, a qualified torch applicator should be required. The National Roofing Contractors Association (NRCA) and the Midwest Roofing Contractors Association (MRCA) both offer training for those who wish to become Certified Torch Applicators (CERTA) (MRCA).
Adhesives manufactured from Ice
In some situations, both polymer-modified and untreated bituminous adhesives have been utilized. As a reaction to concerns over volatile organic chemicals, some low-volatility adhesives with high solids content have been created (VOCs). Because MB sheets are impermeable, it is impossible to employ water-based adhesives, as the water would be unable to evaporate.
Particularly with new construction, where it might be difficult to manage the flow of traffic from the various crafts, a sluggish setting may be counterproductive. Before the adhesive has the opportunity to set, the side and end laps may curl. Certain systems can eliminate the curling issue by torching or heat-sealing the side and end laps.
Roof Terraces and Smoke Control Systems
The criteria are comparable to those for BUR systems, with the difference that torching must be avoided over the majority of combustible decking and insulation boards.
As a cover board, a variety of fire-resistant underlayment, such as gypsum board, can be placed on top of cellular insulations. Also recommended while applying hot mopping to foam insulations is the use of the cover board.
Flashings
In the majority of MB systems, cant strips are necessary for vertical flashings in order to lower the angle at the base of the wall or curb. (Fire-resistant canisters are necessary for torch systems.) Since MB flashing materials have proved so good, it is tempting to eliminate the requirement for a backer sheet; but, for the best waterproofing and durability, a backer sheet is still recommended.
The quality of the MB flashing materials has been so high that it is tempting to eliminate the requirement for a backer sheet.
To maximize the performance of your bituminous roofing systems, you must buy bitumen of the greatest possible grade. We are here to ensure that you receive the highest quality bitumen available on the market. Getting in touch with us is the only requirement. Our qualified and seasoned sales representatives will guide you through each stage of the process and give you all the information you want.
How useful is this article to you?
Average Score
5
/
Number of votes:
1
