Of the many challenges facing roofing systems, hail is the most destructive, as storms bring cold rain and the resulting hail can slam against the tiles.
The National Weather Service's annual severe weather report records where hailstones are ≥2.54 cm in diameter, and the property damage caused by hail in the United States is about $1.25 billion each year. The impact of hail can damage roof cladding. For asphalt shingle roofs, there are 3 main failure modes: shingle cracking, asphalt damage and mineral aggregate shedding.
The impact force brought by the hail hitting the tile surface will cause the asphalt shingle to bend downward, the upper surface of the tile is subjected to vertical compressive stress, and the lower surface of the tile is subjected to horizontal tensile stress. In order to absorb the above-mentioned stresses, the bottom of the tile will expand, and this expansion will lead to cracks, i.e. chipping of the tile surface.
If the crack does not extend to the entire tile, it is called "asphalt damage", and asphalt damage is still considered functional damage because it makes the tile brittle. Impact can also dislodge mineral pellets from the surface of the asphalt shingle, making it easier for asphalt exposed to UV light to age.
Research by the Insurance Institute for Business and Residential Safety found that homes with roof coverings, which are considered impact-resistant, are 40 percent less likely than homes without roof coverings.
Although many asphalt shingles pass the UL 2218 standard 4 impact test, they still perform differently. Independent testing by the insurance research center also showed that in the impact resistance test, the impact resistance of polymer-modified asphalt shingles was 20% to 50% better than that of traditional oxidized asphalt shingles for all four steel ball impact grade tests. %. This is also proved by the actual use situation. The roof covering materials of two adjacent buildings in the same area are SBS modified asphalt shingles and oxidized asphalt shingles respectively.
All roofing materials are a system of components that work together to form a protective barrier, and so are tiles. Asphalt shingles are mainly composed of carcass, asphalt, fillers and mineral aggregates, each of which has its own function. In the quest for innovation, modified bitumen ushered in a new era of resilient bitumen applications.
In the traditional asphalt shingle production process, asphalt is used as the covering material. The raw bitumen is generally called raw bitumen, which is the base material of roof covering materials, and has a softening point of 27-49 °C. And the test temperature of asphalt shingle roof exceeds 82 ℃, in order to exert the function of roof covering material, the asphalt needs to be hardened so that it can withstand the normal working temperature of the roof. The traditional process is asphalt thermo-oxidative aging or oxidation reaction. The usual practice is to oxidize the liquid asphalt by blowing air at 260 °C for 1-10 h. Once the raw pitch is oxidized, its softening point will rise to 93-107 °C.
The natural aging process of asphalt is affected by 3 factors: heat, oxygen and UV light. The natural aging process can be artificially catalyzed by heat and oxygen to chemically change the raw bitumen to form long-chain asphaltenes from low-molecular-weight compounds. As a result of asphalt hardening, the ability of oxidized asphalt to respond to stress is limited. Therefore, in order to resist the stress caused by hail impact, conventional asphalt must have a sufficiently large molecular weight.
Another way to tune the physical properties of asphalt is polymer modification. Polymer materials are generally composed of macromolecules of similar chemical composition, and their molecular weights do not change with ambient temperature. Different from polymer materials, bitumen is composed of a complex mixture of small molecules. The binding force of these small molecules is highly dependent on temperature. The mixture of polymer and bitumen can make the binding force more stable. less dependent.
Polymer modification can not only control the softening point temperature, but also improve the adhesive quality. Adding SBS to bitumen can increase the softening point without changing the chemical composition of the bitumen and better maintain flexibility that may be lost during oxidation. The use of this modified polymer in the asphalt oxidation process changes the strain properties of the asphalt, allowing it to function under greater stresses, such as those caused by hail hitting the shingles.
The introduction and application of modified polymers in the production process will also affect the durability of asphalt shingles. There are generally 3 methods for introducing modified polymers during the production of asphalt shingles.
The first method is to fully impregnate the carcass with polymer-modified asphalt. This method reduces throughput because the addition of polymer-modified asphalt increases viscosity and requires more time to fully impregnate the carcass. Asphalt shingles fully impregnated with SBS modified asphalt have excellent flexibility and resistance to deformation of SBS.
The second method is to impregnate the matrix with oxidized asphalt, and then coat the upper surface with a layer of polymer-modified asphalt. Due to the low viscosity of the oxidized asphalt, this method can maintain a fast production speed, but compared with the first method, the flexibility and other properties are relatively poor.
The third method is to add polymer blend oil, rosin or resin additives to the oxidized asphalt. This method can only soften the oxidized asphalt slightly, but because of the introduction of artificially catalyzed oxidized asphalt instead of raw asphalt, this method cannot fully exert the modification effect of polymer on asphalt.
We cannot change the weather, but we can strengthen the roofing system so that it can better adapt to the increasing functional demands. In order to improve roofing solutions, the Commercial and Residential Security Insurance Institute has established independent testing guidelines for strengthening roofing system projects, aiming to reduce potential property damage due to natural disasters; at the same time, it is also seeking new solutions and continues to study how asphalt can be combined with The blend of polymers creates a more resilient roofing material.