Concrete is a commonly used construction material composed of cement, sand, aggregate, and water. The setting time of concrete is an important parameter that determines its workability and strength. The setting time can be divided into two types: initial setting time and final setting time.
The initial setting time of concrete is defined as the time period between the addition of water to cement and the point at which a 1 mm square section needle fails to penetrate the cement paste placed in the Vicat’s mould, 5mm to 7mm from the bottom of the mould. This is when the cement paste starts to harden and lose its plasticity, making it difficult to work with.
On the other hand, the final setting time of concrete is the time period between the addition of water to cement and the time at which a 1 mm needle makes an impression on the paste in the mould, but a 5 mm attachment does not make any impression. At this point, the cement paste has hardened sufficiently to support the weight of the structure without deformation.
Understanding the setting time of concrete is crucial for ensuring that the concrete is poured and molded in the desired shape and size. It is also important for determining the time available for finishing and curing the concrete before it reaches its final hardened state.
Technical Aspects of Concrete Setting Times
Cement setting is a crucial process that must occur at an appropriate pace to ensure optimal results. If cement sets too quickly, there may not be sufficient time for transportation and placement of the concrete before it becomes too rigid. Conversely, if it sets too slowly, it can significantly slow down work progress and may delay the use of the structure due to inadequate strength at the desired age.
It’s important to note that setting should not be confused with hardening, which refers to the mechanical strength gain after a specific degree of resistance to the penetration of a specialized attachment pressed into it. Setting time is the time required for cement paste to stiffen to a defined consistency. This process is indirectly related to the initial chemical reaction of cement with water to form aluminum-silicate compound.
The initial setting time is the duration during which the paste starts losing its plasticity. It’s essential to conduct an initial setting time test as it helps determine the appropriate transportation, placing, and compaction of cement concrete. The initial setting time duration is required to delay the process of hydration or hardening.
The final setting time is the point when the paste loses all its plasticity. It takes the cement paste or cement concrete sufficient time to harden and achieve the shape of the mold in which it is cast. The determination of the final setting time period is crucial as it enables the safe removal of scaffolding or form. This period marks the completion of the primary chemical reaction of cement with water.
Procedure to Find Setting Time of Cement
Apparatus Required
The list of equipment includes Vicat’s apparatus, a balance, a measuring cylinder, a stop watch, a glass plate, an enamel tray, and a trowel.
Test Procedure
Initial Preparation
Before starting the procedure to determine the amount of water required to achieve normal consistency of cement paste, a consistency test should be performed. To carry out this test, 400 grams of cement should be taken and mixed with water that weighs 0.85 times the weight of the cement required to achieve normal consistency. The mixture should be prepared until a neat cement paste is obtained. The gauge time should be between 3 to 5 minutes, and a stopwatch should be used to record the time (T1) starting from the moment when water is added to the cement.
To create a test block, the Vicat mould should be filled with the cement paste prepared above, and the surface of the paste should be made level with the top of the mould. This should be done while the mould is resting on a glass plate. The test block is then prepared and can be used for further testing.
Fig 1: Vicat’s Apparatus used for determination of setting time of cement
Test for Initial Setting Time
To begin the testing process, the test block should be placed inside the mould and rested on a non-porous plate. The next step is to lower the needle gently until it comes into contact with the surface of the test block. After making contact, the needle should be quickly released, allowing it to penetrate into the test block. Initially, the needle should completely pierce the test block. This process should be repeated, with the needle being quickly released every two minutes, until it fails to pierce the block for approximately 5 mm measured from the bottom of the mould. At this point, the time should be noted as T2.
Test for Final Setting Time
To determine the final setting time of cement, it is necessary to use a different needle on the Vicat’s apparatus. Instead of the standard needle, the needle with an annular attachment is used.
The process for determining the final setting time involves gently applying the final setting needle to the surface of a test block of cement. If the cement has reached its final set, the needle will make an impression on the surface of the cement. However, when using the needle with an annular attachment, it should fail to make an impression on the surface of the cement.
Once this occurs, the time at which the needle with the annular attachment fails to make an impression on the cement surface is recorded as the final setting time, denoted as T3. This measurement is an essential characteristic of the cement as it determines the duration required for the cement to develop the strength required to support loads.
Calculations
The setting time of cement is an important factor to consider when working with concrete. It is defined as the amount of time it takes for the cement to transition from a liquid state to a solid state. There are two types of setting times: initial setting time and final setting time.
The initial setting time is measured from the moment water is first added to the cement until the point at which a standard needle fails to penetrate the cement by 5 to 7 millimeters from the bottom of the mould. This signifies the point at which the cement begins to solidify and lose its fluidity.
The final setting time is measured from the moment water is first added to the cement until the point at which a standard needle makes an impression but fails to leave a visible attachment. This indicates that the cement has reached its fully solidified state and is ready for further processing.
Both the initial and final setting times of cement can vary depending on factors such as the type and quality of cement, the amount of water used, and the temperature and humidity of the surrounding environment. Accurately measuring these times is crucial for ensuring the proper performance and strength of concrete structures.
Standard Specification of Setting Time for Different Type of Cement
The setting time of cement can vary depending on the admixtures added during its manufacture. The use of different admixtures can result in different setting times for different types of cement. To standardize this, the Indian Standard Codes (IS Codes) have listed the standard setting times for various types of cement. These codes provide a guideline for the acceptable range of setting times for different types of cement, ensuring consistency and quality in the construction process.
Table-1: Setting Time for Different Type of Cement
| Cement Type | Initial Setting Time, min (min.) | Final Setting Time, min (max.) |
| OPC(33) | 30 | 600 |
| OPC(43) | 30 | 600 |
| OPC(53) | 30 | 600 |
| SRC | 30 | 600 |
| PPC | 30 | 600 |
| RHPC | 30 | 600 |
| PSC | 30 | 600 |
| High alumina | 30 | 600 |
| Super sulphated | 30 | 600 |
| Low heat | 60 | 600 |
| Masonry cement | 90 | 1440 |
| IRS-T-40 | 60 | 600 |
FAQs
What is initial setting time of cement?
Concrete is a widely used building material that consists of a mixture of cement, water, and aggregates such as sand and gravel. The initial setting time of concrete refers to the period of time between the addition of water to the cement and the point at which the cement paste begins to harden.
To measure the initial setting time of concrete, a test called the Vicat’s test is used. In this test, a small amount of cement paste is placed in a mold and a needle with a 1 mm square section is used to penetrate the paste. The test is performed by placing the needle 5mm to 7mm from the bottom of the mold and observing the time it takes for the needle to fail to penetrate the paste.
The initial setting time of concrete is an important factor to consider in construction projects because it affects the handling and placement of the concrete. If the initial setting time is too short, the concrete may not have enough time to be properly placed and compacted. On the other hand, if the initial setting time is too long, it can delay the construction process and result in additional costs.
What is final setting time of cement?
The final setting time of cement refers to the duration starting from the addition of water to the cement until a 1 mm needle creates an impression on the paste in the mould, while a 5 mm attachment fails to make any impression. This time period determines the point at which the cement paste reaches a hardened state, making it suitable for use in construction. The final setting time is an important factor to consider when working with cement as it affects the strength and durability of the final product. Therefore, it is crucial to accurately measure the final setting time of cement to ensure the structural integrity of any construction project.
What is the need for determining initial and final setting time of cement?
The initial setting time is a crucial test that determines when the paste loses its plasticity. This is significant for various aspects of cement concrete, including transportation, placing, and compaction. Additionally, it is necessary to delay the process of hydration or hardening. This test ensures that the cement paste is at the optimal consistency before it hardens.
The final setting time is the point at which the paste loses all its plasticity and has hardened sufficiently to take the shape of the mold. This is an essential test that enables the safe removal of scaffolding or form. During this period, the primary chemical reaction between the cement and water is almost complete. The duration of the final setting time facilitates the hardening process and ensures that the cement has attained the required strength and durability. This test is crucial for the quality and safety of cement concrete structures.