16 Feb How Do You Prevent Creep In Concrete?
Concrete might be the most durable building material ever, but it’s not perfect. It’s vulnerable to a dangerous problem known as creep. If the concrete is not used properly, creep can set in and cause severe damage. This article contains practical ways to prevent creep in concrete and ensure your structures last long.
To prevent creep in concrete, you have to use a multi-faceted approach. First, the ingredients need to be of excellent quality. Secondly, optimize the concrete mix according to your project. Then, reinforce the structure and apply proper curing methods.
Keep reading for detailed methods and tips to make your concrete structures more resistant to creep.
What Is Creep in Concrete?
In essence, creep is the elastic deformation of concrete under constant pressure. The load gradually presses hardened concrete and changes its uniform shape over time.
Causes:
- The prime cause of creep in concrete is the load it has to sustain for longer periods. Most concrete structures are meant to support all kinds of pressure, but creep takes away that ability. It may creep in at a slow pace initially but is intensified by other factors.
- Environmental conditions like extreme humidity and fluctuating temperatures exacerbate creep. In these conditions, poor curing techniques result in structural flaws. Therefore, make sure to keep the concrete moist in hot and dry climates.
Effects:
- One of the worst effects of creep in concrete is how it challenges its durability. It forms cracks in load-bearing structures, significantly reducing their integrity.
- Creep can have devastating consequences if it affects buildings or bridges. The prestressed concrete in these structures supports the load of humans and machines all the time. If the creep sets in a deck of a bridge, the concrete will lose its prestress ability and crack halfway.
Factors Affecting Creep in Concrete
Creep affects different concrete structures in different ways. Its severity depends on the following factors:
Material Properties:
The properties of the concrete ingredients matter the most in dictating creep’s behavior. Water is the main component of concrete, but too much can make it its biggest enemy. A higher water-to-cement (w/c) ratio results in a more intense creep.
Similarly, for other materials, adjust the properties to prevent as much creep as possible. Cement is the backbone of concrete, but it’s weak on its own. Aggregates make cement stronger, so if they are soft and porous, creep can occur sooner than usual.
Mix Design:
After ensuring the quality of materials, it is vital to balance their proportions in the mix. For example, a ratio of 1:2:4 is commonly applied to the walls of a house. It creates denser concrete with fewer voids, making it less prone to creep. You have to design the exact ratio based on the requirements of your project.
For many applications, you may have to add various admixtures to the concrete mix to enhance its properties. Some are for increased workability and strength, while others reduce water content or control setting times. However, too much quantity of admixtures can decrease concrete’s performance in the long-run.
Environmental Conditions:
Finding an optimal environment during the construction is a complex process. Several conditions that help concrete can also harm it in the future. For example, hot temperatures are good for reducing moisture and speeding up hydration. However, they can also dry the concrete, resulting in creep early.
Only the proper curing methods can stop creep from occurring so quickly. Your goal during this phase is to strike a perfect balance between moisture and temperature.
Load Characteristics:
Concrete needs time to reach its full strength. If it constantly sustains heavy loads during that time, creep can decrease its reliability even after it is fully hardened.
Besides extensive pressure in the early stages, uneven load distribution speeds up creep. The structure starts deforming in areas where the stress is greater than others.
Methods to Prevent Creep in Concrete
There are several preventive methods to control how creep affects concrete in your construction.
1. Use High-Quality Materials
The first step is to ensure that the mix contains high-quality materials. It includes w/c ratio as well, which must be lower. For most constructions, the w/c ratio is ideally 0.4 or lower. It means for every kg of cement, 0.4 liters of water is added to the mix.
There are different grades of cement with varying degrees of strength. Higher grades resist creep more efficiently because of stronger bonds with the aggregates. This means that the choice of aggregates also matters. Granite, quartz, or limestone have a high modulus of elasticity that can lower creep.
Additionally, use admixtures that enhance concrete performance and prevent creep at the same time. A combination of silica fume and fly ash is mostly effective against creep. Silica fume hardens the concrete quickly, reducing creep in the initial phase. Whereas, fly ash focuses on fighting creep for years.
2. Optimize the Mix Design
The second step is to optimize the concrete mix with balanced proportions of cement and aggregates. If the volume of cement paste is greater than aggregates, concrete becomes jelly. Create less amount of paste and fortify it with coarse aggregates of varying sizes. This keeps the compound hard and protects constructions from creep for a long time.
To further optimize the concrete mix, avoid overloading it with water or additives. Excessive water increases the w/c ratio, resulting in a weaker cement paste. Also, add the recommended quantities of additives like superplasticizers. Overdosing can separate aggregates from the paste, making concrete more prone to creep.
To curb the chances of such mishaps, there are specialized design mixes for critical applications. They are engineered to achieve specific compressive strengths in each project.
3. Reinforce the Concrete
After optimizing the mix design, reinforce your concrete with steel bars, mesh, or fibers. This distributes loads evenly so the concrete structures can deal with creep easily.
Creep takes advantage of concrete’s weaker tensile strength. Use prestressed or post-tensioned concrete to counterattack creep with more compressive strength. This reinforcement responds with compressive force whenever the load exerts tensile strength.
4. Proper Curing
Curing is the most important step in preventing creep from damaging the final structure. Spray the concrete with water regularly to increase its initial strength gain. If it becomes stronger early on, concrete can resist damage from creep for years.
Also, make sure that the concrete doesn’t stay dry. Experts recommend keeping it damp for at least seven days. You may need to increase the frequency of spraying water in hot weather. On the other hand, use insulated blankets in cold weather to stop concrete from freezing and drying.
5. Control Environmental Factors
Finally, avoid exposing the newly placed concrete to extreme temperatures. Too much heat results in shrinkage, making concrete tensile from the inside. Cold temperatures, on the other hand, slow down hydration. If the concrete freezes before reaching its full strength, it is more likely to bend under pressure.
You can use different sealants or coatings to save concrete from these environmental effects. These protective layers shield the concrete from many external forces. Sealants help keep the concrete warm and moist simultaneously. And coatings protect it from freezing. Some coatings also prevent corrosion from chemical spills.
Additional Tips to Minimize Creep
Here are some additional tips to take into account to minimize creep.
Reduce Dead Loads:
One of the most practical methods to minimize creep is reducing the dead loads inside constructions. Dead loads permanently add stress to a building as long as it stands. Create lighter structures wherever possible, as creep grows more rapidly under high stress.
Uniform Load Distribution:
Another way to reduce creep is to distribute load evenly across the concrete structure. This ensures that no single area suffers extra stress. If each concrete slab shares the same thickness, the building is less likely to get warped by creep.
Regular Maintenance:
Look for signs of weakness and repair them right after placing the concrete. These issues enable creep to damage structures over time. Regular maintenance enables concrete to resist creep throughout its lifespan.
Use Creep-Resistant Materials:
Several advanced materials are inherently resistant to creep. By enhancing concrete’s power, they help distribute the load more efficiently. High-performance concrete (HPC) is known for keeping critical structures stable despite the load they bear all day.
Conclusion
It is impossible to completely prevent creep from attacking the concrete. It is a natural phenomenon that occurs even in the highest quality concrete. You can only take preventive measures like the ones suggested in this article to mitigate its effects.