Are you in construction or work with concrete mix design? Then you understand the role of aggregate’s specific gravity. It’s key to the strength and durability of structures.
Specific gravity is critical to creating robust and dependable structures that stand the test of time. Higher specific gravity means higher strength, making it essential for structures and infrastructure that demand reliability.Â
Identifying aggregates with low specific gravity suggests weaker materials. These are prone to porosity, which can reduce your concrete’s overall performance.
This blog covers the specific gravity of aggregates, their types, and test procedures. It explains their importance in making strong concrete mixes.
Read on to discover the secrets to better construction.
What is the Specific Gravity of Aggregate?
Specific gravity, also known as relative density, is the ratio of the mass of aggregate to the mass of an equal volume of distilled water.
People also refer to it as the aggregate’s relative bulk density, which one should not confuse with the aggregate’s bulk density, that indicates the density of the pack of aggregates.
Aggregates with lower specific gravity are usually weaker. This makes specific gravity crucial for selecting construction materials. A higher specific gravity means harder, stronger aggregates. This leads to greater strength and less porosity.
Types of Specific Gravity
When it comes to aggregates, voids are generally present. This leads to the existence of two types of specific gravities measurements.
- Absolute Specific Gravity
- Bulk Specific Gravity (also known as Apparent Specific Gravity).
Methods used to measure the specific gravity of aggregates, such as IS: 2386 (Part III) – 1963, provide detailed standards for testing procedures, equipment, and calculations involved in determining both the specific gravity and water absorption of coarse aggregates.
Absolute Specific Gravity excludes voids in its calculation, while Bulk Specific Gravity considers both the volume of aggregates and voids, including impermeable voids.
These two types of specific gravities provide valuable insights into the strength and porosity of aggregates, ensuring optimal concrete mix proportions.
You may also like: Consistency of Concrete: Measure, Importance, and Workability.
How do you test the Specific Gravity of Aggregate?
Testing the specific gravity plays a vital role in ensuring the quality and strength of concrete. When the aggregate’s absorption reaches equilibrium, we use the term ‘saturated surface dry’ (SSD), crucial for accurate calculations in mixtures, including concrete. Formal procedures in the standard test method determine the relative density (specific gravity) and absorption of coarse aggregates, ensuring accuracy and consistency.
There are three main methods for conducting this test, each tailored to the size of the aggregates. They are:
Method I: Aggregates Larger than 10 mm
For coarse aggregates larger than 10 mm, the specific gravity is measured using a wire basket immersed in distilled water.
The process involves removing entrapped air, weighing the basket and aggregates in water, and then drying and weighing the aggregates to obtain absolute specific gravity. This method helps in evaluating the physical properties of aggregate particles, such as density, porosity, and absorption, by separating undesirable particles based on their specific gravity.
Method II: Aggregates Between 40 mm and 10 mm
Like method I, this test procedure involves immersing the aggregates in water, but performs the jolting process in two tanks. Heavy media liquid is used as a method for separating unwanted particles from aggregate materials based on specific gravity differences. The specific gravity is then calculated using the weight measurements.
Method III: Aggregates Smaller than 10 mm
For aggregates smaller than 10 mm, a pycnometer of 1000 ml is used to determine the specific gravity. The test method involves:
- Filling the pycnometer with aggregates and water.
- Removing entrapped air.
- Measure the weight of a given volume of aggregates. Compare it to the weight of an equivalent volume of water. This comparison is used to calculate the bulk-specific gravity.
Lightweight aggregates play a key role in construction materials. Proper handling and testing are crucial. This ensures their effect on concrete’s compressive strength is well understood.
You may also like: Materials Testing Experts Explain The Importance Of Concrete Testing.
Apparatus Required for Water Absorption and Specific Gravity Test on Aggregates
Certain instruments are essential to conducting the specific gravity and absorption test. These include:
BalanceÂ
A precise balance with a capacity of about 3 kg and accurate to 0.5 g is used to weigh the aggregates and other components.
Wire Basket (Density Basket)Â
A perforated container with not more than 6.3 mm mesh, suspended from the balance to hold the aggregates during the test.
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