Buildup in the Silo is an Indication of Ratholing
No matter the design or the materials stored, silos are susceptible to material flow issues caused by blockages. Buildup in the silo is an indication of ratholing and potentially asymmetric flow, which can increase pressure loads inside silo walls. When you have buildup in the silo, the loads associated with asymmetric flow can be detrimental to the structural integrity of the silo as they can lead to wall failure and total silo failure.
Material flow that is unimpeded by blockages is essential for smooth operations and the continued functionality of your silo. Blockages not only promote bad flow characteristics, but also lead to a reduced storage capacity.
You can help reduce the likelihood of material buildup through a number of ways. Depending on how easily stored material compacts or hydrates, your silo may need to be completely emptied on a regular schedule as often as once a month or as little as every year.
To prevent stored cement from setting inside the silo, the structure must be completely watertight. Even pinhole leaks in silo roofs and walls damage your stored materials and can result in blockages and material flow issues. Ambient humidity levels can also cause some materials to set. If you do aerate stored materials, it is important to use air dryer systems to help lower the ambient humidity level in the silo. You should also avoid over aerating stored materials. Excess aeration can pump unneeded moist air into the silo which may lead to hydration of the cement.
Essential maintenance includes exterior waterproof coating(s) and keeping your air pad and air stones in good operating condition. Completely emptying your silo frequently is also important as it helps prevent compaction of stored materials.
Fly Ash Silos
It is important to keep the fly ash cool as it is loaded into the silo. Make sure your ash does not include unburnt carbon material as this can lead to material buildup along the silo walls. Chemicals from pollution control chemicals can cause your ash to become cementitious, or sticky. Coal from the Wyoming Powder River Basin is also inherently cementitious in nature. Cementitious material leads to asymmetric flow. Learn more about Fly Ash Silos.
It’s essential to have a proactive silo maintenance schedule, ensuring continued, safe operation.
While professional inspections are recommended every two to five years, unless there are structural or operational concerns that would necessitate more frequent inspections, frequent in-house inspections will verify that preventive maintenance measures are being followed. Silo maintenance should include regular checks of airflow units, a routine professional cleaning, and regular, complete silo emptying. Of these measures, one of the most important is the regular emptying of silos.
Silos that are regularly emptied and refilled are less likely to experience buildup issues seen in those kept topped off. Regularly emptied silos need professional cleaning less frequently in comparison. They are also less likely to experience issues like compacting and hydrating. Hydration occurs when moisture mixes with stored materials and causes them to solidify within the silo. When this happens, materials can expand and cause added wall pressure which increases the likelihood of structural failure.
The routine examination of your silo is only effective in increasing facility safety and ensuring smooth operations when it is conducted in conjunction with professional inspections (and cleaning services) as part of a regular preventive maintenance schedule. A recent case study provides an example of how asymmetric flow can cause silo failure.
To learn more, be sure to check out our full library of silo inspection videos on silo maintenance, inspection and repair on
Like all structures, silos degrade over time. This natural and inevitable deterioration can lead to safety hazards such as falling debris, leaks, wall failure, roof failure, and/or structural failure.
When it comes to the silo structure, the roof and its design is a crucial component. In addition to this, proper maintenance of the silo roof is a requirement but may pose a significant challenge. Many areas that may require repair are not readily visible and often structural damage is not noticed until a significant failure has occurred, the roof has settled, or the risk of impending total failure has been reached.
Leaking roofs can lead to contamination of stored materials which impact product quality. Water penetration also leads to corrosion of metal silo components like roof beams – an issue that can lead to total roof failure if not addressed. Roof beams are a frequent area of corrosion, or concrete deterioration often due to roof leaks. Spalling of concrete roof beam pockets can further expose beams and lead to eventual roof failure or collapse.
Signs of ponding water on the silo roof (as well as signs of cracking or peeling in the roof-top coating) are indicators that your roof structure is at risk. Regular ponding on the silo roof lowers the lifespan of coating membranes and can lead to deterioration and leaks. More seriously, ponding water is usually caused by issues with the supporting roof beam, potentially indicating severe underlying structural problems. Left unaddressed these problems become costlier to correct and increase liabilities.
Problems with silo roof slabs are mostly related to critical structural conditions such as material buildup, the addition of heavy equipment to the original design or flaws with the original design. The roof beam supports should have been designed to accommodate for thermal expansion and vibration from equipment and cycling of the silo by filling and discharging. This is accomplished by allowing the roof beam base plates to freely slide in the longitudinal direction over an embedded steel plate on the wall beam pocket.
The embedded plates that support the roof beams are usually involved in the failure process. Weather and temperature changes, vibration, and movement of beams cause the concrete walls to deteriorate faster around the beam pockets than the rest of the silo walls. Such deterioration leads to spalling and loosening of the bond between the embedded steel anchors and the concrete walls. When such conditions occur, the roof supporting steel beam will eventually rest on unprotected concrete. The constant thermal expansion and contraction of the beam, combined with the dead and live loads applied to it, creates a grinding force between the beam’s base plate and the silo wall. Often times this will lead to breakage of part of the silo wall immediately under the beam. When this happens, the beam shifts downward until it rests again on a solid portion of the silo wall.
Silo Repair Case Study
Beam pockets are a critical point on the silo as these roof beams hold up the roof slab and all the necessary equipment to operate the bulk storage system. One of our recent case histories examine a silo roof beam bearing repair.
Regular inspections of the underside of the silo roof along with all equipment are imperative to eliminate potential failures in any production system, including silos. Proper silo roof design is critical. While roofs are designed to hold equipment, they are not designed for excessive amounts of material. If a loading system fails or a silo is overfilled, creating bulk material on the roof, unseen damage can result and compromise the entire structure.
To learn more, be sure to check out our full library of silo construction videos on silo maintenance, repair and inspection on
Early storage silos, primarily used by farmers for the bulk storage of corn, were built using wood, brick, stone or galvanized steel throughout the late 19th century. The use of concrete for the construction of storage silos revolutionized the industry in the early 20th century and expanded the use of storage silos beyond the farm. Today, both steel and concrete silos are commonly used in industry for the storage of ash, coal, lime, aggregate and more.
Concrete Silo vs. Steel Silo, Which One is Better?
Concrete silos are favored over steel silos because they are a superior cost savings solution that can be designed to resist internal abrasive wear, while withstanding pressures that would cause steel silos to buckle.
Over time, concrete storage silos are less costly to maintain – lifetime savings can reach 50-70% over steel construction. As steel structures battle costly corrosion issues – especially when contents have moisture or are corrosive – regular repair of rust areas as well as exterior cleaning and painting is required. In addition, steel silos often need internal repairs requiring the silo to be emptied, creating costly downtime and inconvenience.
Cement silos cannot rust and require no exterior painting or cleaning. Additionally, repairs are usually made to the outside of concrete silos without disturbing the inside contents.
Advantages of Concrete Silos
- Concrete silos are typically lower in cost than metal silos.
- Concrete silos have good resistance to corrosion, including both corrosion of internal walls due to the stored bulk solid and external corrosion caused by moisture. Metal corrosion is a well-known problem.
- No need for expensive painting of silos due to corrosion thus lowering operational cost.
- There is no concern about electrolytic effects at welds or liner connections.
- Careless detailing of metal walls may leave inward facing ledges or welds, which can obstruct flow and increase wall pressures. This is avoided with concrete.
- Concrete is better able to resist abrasive wear than most metals.
- Concrete is more robust and thus better able to withstand internal pressure loads and impact loads.
- Concrete has higher wall friction angles with most bulk solids than most metals. This results in higher frictional drag down the cylinder walls and hence lower pressures acting normal (i.e. perpendicular) to cylinder and hopper walls.
- There is no concern about weld quality or stress risers, such as bolted connections.
- There is no concern about leakage to the environment.
To learn more about the advantages of concrete silos over steel silos, read our concrete vs. steel safety bulletin.
What’s the Difference Between a Jumpform Silo and a Slipform Silo?
Jumpform construction is an economical construction choice as the form can be set up and ready to make the first pour of concrete within a week. Due to an incremental schedule rather than the continuous schedule, costs are reduced approximately 20% over Slipform construction. Concrete storage silos from 10' to 65' in diameter can be built using this technique.
The Jumpform silo framework is reusable and takes just a few days to set up after delivery to the job site. Once set up, the form provides a safe, circular deck used to access and erect the concrete silo from the interior, allowing a smaller job site. When construction is finished, the form is quickly removed from the job site.
Since Jumpform silos are poured in a slow controlled process it allows additional time to complete a thorough quality control inspection of the form, steel reinforcements and embedments before concrete is poured.
Marietta Silos’ standard horizontal construction joint detail creates a leak-proof joint system. Jumpform construction is the best choice for concrete storage silos less than 65’ in diameter. Marietta Silos is the only Jumpform manufacturer in the country that complies with OSHA 125' scaffolding requirements.
Slipform silos are best for construction projects over 65’ in diameter. They are formed from a continuous, monolithic pour of the concrete walls, which creates a smooth, continuous outer appearance. The need for a continuous pour necessitates a 24 hours per day schedule, including nights and weekends, until the silo is completed. This contributes to a possible 20% increase in overall costs over Jumpform construction techniques under 65' in diameter.
The walls of Slipform silos are faster to pour than Jumpform silos. However, the time savings is offset by the time required to construct a custom-built form system for both the interior and exterior of the silo wall. Construction of the Slipform system takes approximately two months to create. Overall, the construction time is equal to the Jumpform.
Slipform silo forms are an integrated form and work deck system that includes an interior work deck and interior and exterior finishing scaffolding. The form is also supported by jack rods that are attached to the hydraulic jacks to slowly raise the forms during construction. The forms raise continually, about one foot per hour, with crews working both above and below the rising forms at the same time. Workers on the interior work deck continue to pour new concrete and steel reinforcement along with embedment as the form raises, while workers on the interior and exterior scaffolding hand finish the silo walls as they are exposed by the rising form.
Slipform construction is typically the best choice for more than 65’ diameter silo construction or if multiple concrete silos need to be created at one time.