Specific Gravity represents the ratio of one material's density to that of another. However, water is nearly often used as the baseline reference in the ratio. Water has a density of 1000 kg/m3.
The term "relative density" is another name for "specific gravity,". It is the ratio of one substance's density of coarse aggregate to that of another. However, water is nearly often used in the ratio as the default comparison. Water has a 1000 kg/m3 density.
Specific Gravity of Coarse Aggregates
The specific gravity of coarse aggregates is defined as the weight of the aggregates dried to constant weight in an oven at 100°C splits by its absolute quantity such as the natural empty spaces within the aggregate particles, according to the "IS: 2386 (Part III)" - 1963" (Indian Standard- Methods of Test for Aggregates for Concrete - Specific Gravity, Density, Voids, Absorption and Bulking).
The specific gravity of coarse aggregates normally ranges from about 2.5 to 3.0.
Every rock or stone has a small number of gaps, and the specific gravity is an indirect indicator of the porosity of the aggregates. Low specific gravity could be an indication of high porosity, which would result in poor strength and durability. Some of the pores in the aggregates are permeable, while others are impervious.
Two types of specific gravities are defined:
One is the absolute specific gravity
Apparent specific gravity
Both the permeable and the impermeable spaces are disregarded when calculating the genuine or absolute specific gravity. However, it is not very useful because it is very difficult to estimate the number of interior pores that are impermeable.
On the other side, for the determination of the apparent specific gravity, the volume of the impermeable internal pore is added to the effective volume of the aggregates. It does not include permeable pores. The specific gravity will first depend upon the basic chemistry of rock and then on the number of pores or voids within it. If the basic rock is weak, then nothing will help.
Importance of Specific Gravity of Coarse Aggregates
It's crucial to specify gravity for a number of reasons:
The most crucial factor determining the strength or quality of aggregates is their specific gravity, which assesses their density of coarse aggregate indirectly. Strength increases as specific gravity increases.
Increased specific gravity would result in higher aggregate compressive strength, which would then transfer to the concrete.
High porosity is indicated by a lower specific gravity. Compared to aggregates with a higher specific gravity, these aggregates are weaker.
It is of important consideration when you deal with lightweight aggregates.
In aggregates, some detrimental particles are lighter than the beneficial ones. Therefore, by monitoring the specific gravity of aggregates, one can learn about material changes or potential contamination in them.
Applying a heavy media liquid, it is possible to separate dangerous particles from the commodities during the creation of aggregates by using the difference in specific gravity.
The specific gravity of cement concrete can be used to calculate the proportion of voids and the solid volume of particles.
In the field of concrete technology, the computation of compacting factors in relation to workability measures depends on the specific gravity of the aggregates.
Given the preceding significance, employing lightweight aggregates must be done with some degree of caution, and its effect on the compressive strength of concrete must be carefully considered.
How to Find Aggregate Crushing Value and Its Test Procedure?
According to "IS: 383 - 1970" (Specification for Coarse and Fine Aggregates from Natural Sources for Concrete), common rocks used for extracting aggregates include granite, basalt, sandstone, limestone, schist, granulite, gneiss, marble, gabbro, dolerite, and rhyolite.
The sorts of rocks, their specific gravities, and where they can be found in India are all listed here
Standard Procedures for Aggregate Specific Gravity Testing
Relative Density (Specific Gravity) and Absorption of Coarse Aggregates size Standard Test Method (ASTM C127-15)
Standard Test Procedure for Specific Gravity and Absorption of Coarse Aggregates size (AASHTO T 85)
Methods of Test for Aggregates for Concrete - Specific Gravity, Density, Voids, Absorption, and Bulking, IS 2386 (Part III) - 1963 Rocks Used as Concrete Aggregate Trade Groups.
Specific Gravity and Water Absorption Test of Coarse Aggregates
There are three primary methods used for measuring or determining the specific gravity of aggregates as per the size of aggregates, according:
IS: 2386 (Part III) - 1963," which is an Indian Standard- Methods of Test for Aggregates for Concrete - Specific Gravity, Density, Voids, Absorption, and Bulking.
Method I – Aggregates larger than 10 mm
Method II – Aggregates between 40 mm and 10 mm
Method III – Aggregates smaller than 10 mm
Both Method I & II can be utilised for aggregates with a size between 40 mm and 10 mm. Here, we'll go into more detail about the testing equipment, process, calculations, and results suggestion for the aggregates' specific gravity and water absorption according to Method.
This test covers the procedures for determining the specific gravity as well as apparent specific gravity and water absorption of aggregates.
Water Absorption of Aggregates: Aggregate water absorption is the amount of water that an air-dried aggregate absorbs after being submerged in water for 24 hours at 27°C. It is a crucial component of porosity.
It is regarded as a gauge of enduring weathering and resistance to frost action. The net water-cement ratio in the concrete mix is determined in part by the water absorption of the particles.
Test Apparatus- This test includes the methods for figuring out aggregates' apparent specific gravity, specific gravity, and water absorption.
Water Absorption of Aggregates: Aggregate water absorption is the amount of water that an air-dried aggregate absorbs after being submerged in water for 24 hours at 27°C.
It is a crucial component of porosity. It is regarded as a gauge of enduring weathering and resistance to frost action. The net water-cement ratio in the concrete mix is determined in part by the water absorption of the particles.
Followings apparatus are used to conduct the specific gravity test and water absorption test of aggregates:
Balance: A balance or scale that can weigh objects accurately to 0.5 g, has a capacity of roughly 3 kg, and has the proper size and shape to fit inside the basket containing the aggregates when they are hung in the water.
Oven: A properly ventilated oven with thermostatic control that maintains a temperature between 100 and 110 °C.
Wire Basket (Density Basket): A perforated container of a practical size with wire hangers for hanging it from the balance, or a wire basket or density of coarse aggregate basket with a mesh size of no greater than 6.3 mm.
A perforated container of a practical size with wire hangers for hanging it from the balance, or a wire basket or density of coarse aggregate basket with a mesh size of no greater than 6.3 mm.
The quality of the aggregates has a big impact on the concrete's workability, strength, weight, durability, and other qualities. The characteristics of aggregates, such as their size, shape, specific gravity, water absorption, flakiness, surface texture, abrasion resistance, and skid resistance, must all be understood before using them in any project.
In this article, the idea of specific gravity, its importance, and the recognised measurement techniques—like the water absorption test for coarse aggregates size—have all been discussed.