Flaky and elongated aggregates are becoming a growing focus in today’s construction industry. These shape-based aggregates have a considerable impact on structural integrity. It’s usually not prioritised as much as other aggregates. Rather, it has numerous other implications that cannot be ignored completely. Its irregular shape often adds benefits to construction materials.
Modern construction projects usually limit the use of flaky aggregates, ensuring the standards. The industry’s shifts in trends to focus more on material characteristics, enhancing the construction outcome, and keeping the use of these aggregates minimal.
What is Flaky Aggregate?
Aggregates are classified as flaky when their particle thickness is less than 60% of the mean dimension of the particle.
Also, the particle thickness should be smaller than both the length and width. Generally, the flaky aggregates are thin and flat with a higher surface area, which impacts the workability of the concrete.
Flaky aggregates negatively impact the strength and durability of construction materials due to their inadequate interlocking capacity. They require fewer binding substances because of the tighter packing of particles, resulting in fewer voids. However, they can break down more easily as they have poor load-bearing capacity along their thin axis.
Causes of Flaky Aggregate in Construction
Source: Since they are obtained from weak or laminated rocks by improper crushing techniques. The flaky aggregates are usually considered poor quality.
Natural Rock Type: The flaky aggregates can be naturally produced in rocks such as schist and slate. The weathered rocks are more likely to break and form this type of aggregate.
Shape and Size: The aggregates are of various shapes. Those that are smaller with irregular shapes are classified as flaky aggregates. The major sources include river beds and quarries. However, when compared to quarries, river beds contain fewer flaky aggregates.
Climatic Influence: Geological conditions can cause flaky aggregates to form due to thin layers or planes of weakness. Additionally, poor extraction methods can contribute to their production.
Processing: Higher moisture content during crushing results in the production of flaky aggregates. Also, soft aggregates break down into flaky particles.
Properties of Flaky Aggregate
Thickness: Flaky aggregates have a very small thickness, which is less than 0.6 times the mean size.
Shape Index: a shape index defines flakiness. Flakiness is defined by a shape index. It measures the aggregate’s thickness relative to its length.
Workability: Flaky aggregates increase water demand. It results in providing poor bonding with the cement paste.
Strength and Durability: Bonding affects the concrete. Due to poor bonding, structures with flaky aggregates have lower overall strength. This also causes reduced durability.
Void Amount: The flaky aggregate increases the void content within the concrete. This results in higher water and cement demand.
Interlocking Property: Flaky aggregates reduce the interlocking of particles, weakening the material.
Load Bearing: It causes reduced load-bearing capacity and creates poor stability. Makes compaction harder with concrete when the flaky aggregates are used.
Flaky and Elongated Aggregate
Flaky and elongated aggregates negatively affect the strength of concrete. When combined, they significantly reduce the concrete’s overall strength and durability.
The permissible percentage of flaky and elongated aggregates is typically limited to 15-30%, depending on the specific application. Crossing this limit can affect and lead to rejection.
Difference Between Flaky and Elongated Aggregate
| Aspect | Flaky Aggregates | Elongated Aggregates |
| Criteria | The thickness should be less than 0.6 times the mean dimension. | The length should be greater than 1.8 times the dimension of the mean value. |
| Shape and size | Flat and thin | Long and Narrow |
| Index Measurement | Flakiness Index | Elongation Index |
| Concrete | Reduces concrete workability and strength | Increases the water demand and reduces workability |
| Compaction | Difficult to compact; results in higher void content | Hard to compact due to particle interlocking |
| Angular Nature | Less angular, more prone to breakage | More elongated, affecting angularity |
How to Measure Flakiness and Elongation Index
Flakiness Index: The Flakiness Index measures the proportion of flaky aggregates in a material sample. It is known as the “Shape Index.” It determines the aggregate thickness relative to its length. It should be less than 60% of its mean size. A thickness gauge is used to determine the percentage of the flaky particles in the aggregates. It is calculated by dividing the mass of the flaky particles by the total mass of the aggregate sample.
Elongation Index: The Elongation Index measures the percentage of elongated particles in the aggregate sample. It determines the aggregate length with a greater dimension. Its length should be 1.8 times more than the mean value. A length gauge is used to determine the percentage of the particles in the aggregates that are elongated. It is calculated by dividing the weight of the elongated particles by the weight of the entire sample.
Effects of Flaky and Elongated Aggregate on Construction Materials
- The flaky and elongated aggregate requires more water. This results in reduced workability of the concrete. The increased water requirement can decrease the strength and durability of the concrete.
- These types of aggregate have poor compaction. Therefore, it leads to poor density and stability of the concrete.
- Flaky aggregate has a high possibility of breaking down during construction. Concrete with flaky and elongated aggregate tends to have decreased durability.
- The concrete particles produce internal resistance. It is highly influenced by the shape of these aggregates. With the decreasing index value of these aggregates, the stability of the concrete reduces.
- Flaky aggregate creates more voids in the concrete. This leads to less density and requires more binding material.
Impact of Flaky Aggregate in Concrete Mixes
Workability Issues
Flaky aggregates significantly affect the concrete’s workability. Workability is defined as how easily the concrete can be mixed and handled.
These aggregates, relative to the volume, have a larger surface area. This increases the friction between the concrete particles. As a result, more water is often required, making it difficult to handle. Achieving the desired cement-water ratio causes other issues, such as segregation and bleeding.
Reduction in Strength
Flaky aggregates compromise concrete strength. Increased water demand causes a higher water-cement ratio, which creates more voids and decreases the density of the concrete.
Additionally, flaky aggregates under pressure tend to break. This reduces the overall construction strength. Therefore, this aggregate usage is critical in the application of high-rise buildings.
Poor Bond with Cement Paste
The bond between cement paste and aggregate is crucial for developing structural integrity. This determines the durability and the compressive strength of the concrete. The irregular shape of the flaky aggregate with a larger surface area makes adherence difficult.
This creates more voids within the concrete. It weakens the bond and thus decreases the overall workability. This causes poor bonds of aggregate particles in creating the cement paste.
Methods to Minimize Flaky Aggregate in Construction
The flaky and elongated aggregates can create a negative impact on the concrete. It affects the concrete’s strength, durability, and workability. It can affect the compactness and bonding of the concrete particles. Lesser use of flaky aggregates is important. Here is a detailed explanation of methods to minimise the flaky aggregates:
Proper Selection of Materials
- The source of material selection can significantly affect the shape of the aggregate. This greatly influences the concrete quality. Prefer choosing aggregates from reputed queries.
- Avoid using aggregates with high flakiness and elongation index. Always ensure the aggregates are well-graded. This means that the particles must be adequately distributed. It helps in achieving stability and density.
Use of Crushing Equipment to Reduce Flakiness
Crushing tools play a significant role in reducing the flakiness of aggregates. The following methods can be used for crushing:
- Jaw Crushers: For primary crushing, use Jaw Crushers. It can produce more cubical aggregates good for construction.
- Cone Crushers: These are effective for secondary crushing. This tool can produce aggregates with better shape and texture.
- Vertical Shaft Impact (VSI) Crushers: This tool forms cubical aggregates. It is done by using high-speed impact to break down the particles.
Quality Control Measures
Implementing quality control measures is essential. It ensures that the aggregates used in construction meet the required standards. Key measures include:
- Regular testing on aggregate samples is crucial. It can monitor their shape, size, and quality. Tests include the flakiness index, elongation index, and sieve analysis.
- Inspection and monitoring of the aggregate production process ensure consistency in quality.
- Maintaining detailed records of aggregate performance is needed. The tests, inspections, and quality control data are secured. It measures to track performance and identify areas for improvement.
Conclusion
In conclusion, flaky aggregates present significant challenges in modern construction. Their flat and thin nature affects the construction process, particularly in high-stress environments. It includes application in roads and load-bearing concrete structures.
The main concern with flaky particles is their inherent weakness, which result in reduced compaction and bonding strength of concrete. This leads to durability issues over time. While flaky aggregates remain available in the market, their use is increasingly restricted. It is due to the negative impacts on material performance. Construction standards evolve to focus on sustainability, strength, and longevity. Therefore, minimizing flaky aggregates has become a critical part. Mainly, it helps ensure the quality of concrete structures.