Angular stone is one of the most important materials used in construction, particularly in roadworks, concrete mixes, and drainage systems. Its sharp edges and rough texture make it superior to rounded stones in providing better interlocking, strength, and stability. Understanding what angular stone is, how it’s produced, and where it’s used helps engineers and builders choose the right material for different structural and pavement applications.
What Is Angular Stone?
An angular stone refers to crushed rock fragments that have been mechanically broken from larger rocks to achieve a rough, sharp-edged shape. These stones are produced by crushing processes in quarries using crushers and screens to obtain the desired size and gradation. Unlike rounded stones found in rivers or natural deposits, angular stones have multiple sharp corners and flat faces, which help them lock tightly together when compacted.
Formation and Production of Angular Stone
Angular stones are obtained through the mechanical crushing of rocks such as granite, basalt, limestone, or trap rock. The process involves several stages of crushing and screening to achieve uniform sizes. The production steps generally include: quarry blasting to loosen large rock masses, primary crushing using jaw crushers, secondary and tertiary crushing for size reduction, screening to separate different grades, and washing to remove dust or clay. This method ensures that the resulting aggregate has sharp edges and consistent particle sizes suitable for civil works.
Properties of Angular Stone
Angular stones have specific properties that make them ideal for various construction applications. These include high compressive strength, rough surface texture, better interlocking characteristics, low water absorption, and good resistance to weathering. Their angular shape increases friction between particles, resulting in more stable and durable structures. The typical size range of angular stones varies from 4.75 mm to 63 mm, depending on usage.
Difference Between Angular Stone and Rounded Stone
Angular stones differ from rounded stones mainly in shape, strength, and performance. Rounded stones, often obtained from riverbeds, are smooth and have lower friction, making them less suitable for applications requiring strong interlocking. Angular stones, on the other hand, have rough, uneven surfaces that provide superior bonding and compaction. Rounded stones are used in aesthetic landscaping or decorative works, while angular stones are preferred for road construction, concrete aggregates, and drainage layers due to their strength and stability.
Uses of Angular Stone in Construction
1. Road Construction
In roadworks, angular stone is essential for constructing the base and sub-base layers of flexible pavements. The interlocking property helps distribute loads effectively and prevents surface deformation. Water-bound macadam (WBM) and wet-mix macadam (WMM) layers commonly use angular stones for superior compaction and load-bearing capacity.
2. Concrete Mixes
In reinforced and plain concrete, angular stone aggregates improve bond strength with cement paste. The rough surface increases the adhesion between cement and aggregate, resulting in higher compressive and tensile strength of concrete.
3. Railway Ballast
Angular stones are used as railway ballast, where they provide stability to the tracks and facilitate drainage. Their angularity ensures that the stones stay in position under the vibration and load of moving trains.
4. Drainage Layers
Due to their high permeability and void ratio, angular stones are used in drainage systems, retaining wall backfills, and filter layers. They allow easy passage of water while preventing soil clogging.
5. Foundations and Base Courses
Angular stones are commonly used in foundation fills, road base courses, and subgrade improvement to provide a stable and load-bearing surface for further construction layers.
6. Asphalt Pavement Construction
In asphalt mixes, angular aggregates are preferred because their shape enhances aggregate interlock and prevents rutting or deformation under heavy traffic loads. The angular structure provides better contact and stability within the mix.
Advantages of Using Angular Stone
The use of angular stone provides several construction advantages such as excellent interlocking and stability in compacted layers, better bonding in concrete and asphalt, improved load distribution in pavements, higher resistance to displacement and deformation, and enhanced durability and longevity of structures.
Disadvantages of Angular Stone
Despite its numerous advantages, angular stone also has some drawbacks. It can be difficult to work with due to its sharp edges, which may cause wear on construction equipment. Its irregular shape makes manual handling and compaction slightly more challenging compared to rounded aggregates. Additionally, producing angular stones requires crushing operations that consume more energy and can generate dust.
Specifications and Gradation of Angular Stone
The gradation of angular stone depends on its intended application. For instance, in road base construction, the stone sizes typically range from 40 mm to 63 mm. For concrete work, sizes between 10 mm and 20 mm are commonly used. Proper grading ensures that smaller particles fill the voids between larger ones, achieving better compaction and strength. The Indian Standards (IS: 383) specifies the grading requirements for coarse and fine aggregates used in construction.
Testing of Angular Stone
Several tests are conducted on angular stones to ensure quality and suitability, including:
- Aggregate Crushing Value (ACV) Test: Measures resistance to crushing under a gradually applied load.
- Los Angeles Abrasion Test: Evaluates hardness and resistance to wear.
- Impact Value Test: Assesses toughness and ability to resist sudden shocks.
- Flakiness and Elongation Index: Determines the shape characteristics of aggregates.
These tests ensure that the angular stone meets construction quality standards for strength, durability, and shape.
Environmental Impact of Angular Stone Production
The production of angular stone involves quarrying and crushing, which can impact the environment. Dust emissions, noise, and habitat disruption are common issues. However, using modern dust suppression systems, efficient crushers, and controlled blasting can minimize environmental damage. Recycled aggregates from construction waste are also becoming an eco-friendly alternative to freshly quarried angular stones.
Maintenance and Performance in Structures
Structures built using angular stone tend to perform better under load and exhibit longer service life. In pavements, the angularity of stones prevents displacement under traffic, while in concrete, it enhances mechanical bonding. Proper compaction, drainage design, and periodic maintenance further improve their performance.
Conclusion
In conclusion, angular stone is a critical material in civil engineering and construction due to its superior interlocking ability, strength, and stability. It is extensively used in roads, railways, drainage systems, and concrete works. Choosing the correct gradation, ensuring quality testing, and applying proper compaction techniques can significantly enhance the performance and longevity of structures built with angular stones. While the production process may have environmental challenges, modern sustainable practices and recycled alternatives make it a reliable and essential construction material for the future.
