The tests conducted on aggregates, namely the specific gravity test and water absorption test, serve different purposes. The specific gravity test is performed to assess the strength or quality of the material. On the other hand, the water absorption test is carried out to determine the water holding capacity of both coarse and fine aggregates.
The primary aim of conducting these tests is to obtain relevant information about the characteristics of the aggregates. The specific gravity test helps in evaluating the overall strength and durability of the material, while the water absorption test provides insight into the amount of water that the aggregates can hold.
By obtaining this information, engineers and construction professionals can make informed decisions regarding the selection and use of aggregates in construction projects. This knowledge can also help in ensuring that the aggregates used in construction meet the necessary standards and requirements.
Aggregate Sample
Specific gravity is a measure of the strength or quality of a given material. It is defined as the ratio of the weight of a certain volume of aggregate to the weight of an equal volume of water. In the case of aggregates, the specific gravity value can provide valuable information about their properties.
Aggregate materials with a low specific gravity value are generally considered to be weaker than those with higher specific gravity values. This is because the low specific gravity value indicates that the aggregate is less dense than water, which can lead to a decrease in its overall strength. On the other hand, aggregates with higher specific gravity values are denser than water and are typically stronger.
In summary, specific gravity is an important measure for determining the strength and quality of a material. For aggregates, a higher specific gravity value generally indicates greater strength, while a lower value may suggest weaker properties.
Procedure of Water Absorption and Specific Gravity Test on Aggregates
To determine the specific gravity of aggregates, there are three testing methods available based on the size of the aggregates. For samples larger than 10 mm and 40 mm, a specific test method is used. However, for samples smaller than 10 mm, a different test called the Pycnometer test is carried out.
The method used for aggregates larger than 10 mm and 40 mm is not specified, but it is different from the Pycnometer test used for smaller samples. These methods are used to accurately determine the specific gravity of the aggregates, which is a measure of their density compared to water. The specific gravity is an important factor to consider in the construction industry, as it can affect the strength and durability of structures made with the aggregates.
Apparatus for testing Specific Gravity and Water Absorption of Aggregates
Apparatus Required
The equipment required for this task includes a precision balance with a capacity of 3kg and an accuracy of 0.5g. The balance should be designed in such a way that it allows the sample container to be weighed while suspended in water.
A thermostatically controlled oven capable of maintaining a temperature range of 100-110° C is also necessary.
To suspend the sample container in water, a wire basket with a mesh size of no more than 6.3mm can be used. Alternatively, a perforated container with thin wire hangers may also be used, as long as it is of a convenient size.
A container for filling water and suspending the basket is required to carry out the weighing process accurately. An airtight container with a capacity similar to that of the basket is also needed to store the samples after weighing.
Finally, a shallow tray and two absorbent clothes, each measuring not less than 75x45cm, will be necessary to ensure a clean and dry work surface.
Procedure
The process begins with taking a 2 kg sample of aggregate, which is then washed thoroughly to eliminate any fines. The sample is then drained and placed in a wire basket. The basket is submerged in distilled water with a depth of at least 5 cm above the top of the basket. The water temperature should be between 22-32°C.
To eliminate any entrapped air, the basket containing the sample is lifted 25 mm above the base of the tank and dropped at a rate of about one drop per second. The sample should remain immersed in water for the next 24 hours.
After 24 hours, the basket and the sample are weighed while still suspended in water at a temperature between 22-32°C. This weight is recorded as W1g. The basket and aggregates are then removed from the water and allowed to drain for a few minutes.
The aggregates are then transferred to dry absorbent clothes, and the empty basket is returned to the tank of water. The basket is jolted 25 times and weighed again in water, and this weight is noted as W2g. The aggregates placed on the absorbent clothes are surface-dried until no further moisture can be removed.
The aggregates are then transferred to a second dry cloth, spread in a single layer, and left to dry for at least 10 minutes until they are completely surface-dry. The weight of the surface-dried aggregate is recorded as W3g.
Finally, the aggregate is placed in a shallow tray and kept in an oven maintained at a temperature of 110°C for 24 hours. It is then removed from the oven, cooled in an air-tight container, and weighed. This weight is recorded as W4g.
Observations of Test
The given context describes a weighing process for aggregates using a basket suspended in water. The weight of the saturated aggregate suspended in water with the basket is represented as W1 in grams. The weight of the basket alone when suspended in water is represented as W2 in grams.
The weight of the saturated surface dry aggregate in air is represented as W3 in grams. Additionally, the weight of the oven dry aggregate is represented as W4 in grams.
By subtracting the weight of the basket alone from the weight of the saturated aggregate suspended in water, the weight of the saturated aggregate in water can be determined as (W1 – W2) grams.
Finally, the weight of water equal to the volume of the aggregate can be determined by subtracting the weight of the saturated aggregate in water (W1 – W2) from the weight of the saturated surface dry aggregate in air (W3) resulting in a weight in grams represented as (W3 – (W1 – W2)).
Formulas:
The properties of aggregates used in construction can be determined through various tests, such as specific gravity, apparent specific gravity, and water absorption. The specific gravity of an aggregate is calculated by dividing its weight in air by the weight of an equal volume of water. The formula used for this calculation is W3 divided by (W3 minus the difference between W1 and W2). The apparent specific gravity, on the other hand, is calculated by dividing the weight of an equal volume of water by the difference between the weight of the aggregate in air and the weight of an equal volume of water displaced by the aggregate. This is expressed as W4 divided by (W4 minus the difference between W11 and W2).
Water absorption is calculated as the percentage of the weight of water absorbed by the aggregate when immersed in water for a specified duration. The formula used for this calculation is ((W3 minus W4) divided by W4) multiplied by 100. It is important to note the size of the aggregate and whether it has been artificially heated when conducting these tests.
Although a high specific gravity is often associated with high strength, it is not sufficient to judge the suitability of an aggregate sample. To fully assess the quality of the aggregate, it is necessary to evaluate its mechanical properties, such as aggregate crushing, impact, and abrasion values. These tests provide a more comprehensive understanding of the aggregate’s performance under various conditions, allowing for better decision-making in construction projects.
Recommended Values of Specific Gravity and Water Absorption for Aggregates
Aggregates are an important material used in the construction of roads. Typically, the specific gravity of these aggregates falls within a range of 2.5 to 3.0, with an average of around 2.68. It is crucial for these materials to meet certain specifications to ensure their effectiveness in road construction. Specifically, their water absorption should not exceed 0.6 per unit by weight, which helps maintain their structural integrity over time. Adhering to these guidelines helps ensure the quality and durability of roadways.