The tensile strength may be determined by either Briquette test method or by split tensile strength test.In this section we willtalk about the Briquette Method.
Significance of Tensile Strength Test of Cement
Early Defect Indication: Tensile strength provides quicker insights into potential defects within cement compared to other testing methods.
Convenient Testing: Assessing tensile strength is more convenient than conducting tests for compressive strength.
Dual Strength Insights: As the flexural strength is closely linked to tensile strength, this test offers valuable information on both tensile and compressive strengths, especially useful when testing materials is constrained.
Apparatus Required
Testing Machine:
- This apparatus is pivotal in assessing the tensile strength of cement. It applies force to the cement sample until it breaks, measuring the maximum force required to fracture the specimen. The machine’s accuracy and calibration are crucial for precise test results.
Briquette Mould:
- The briquette mould is a specialized tool used to shape cement samples into standardized forms for the tensile strength test. It ensures uniformity in specimen size and shape, essential for accurate and comparable test results across different samples or batches of cement.
Spatula:
- A spatula is used for handling and preparing the cement mixture before it’s placed into the briquette mould. It aids in mixing the cement with water to achieve the desired consistency and assists in filling the mould evenly, minimizing air pockets that could affect the test results.
Materials Required for Tensile Strength test of Cement
- Cement – 600 g
- Sand
- Water that can be used for mixing
Test Procedure for Tensile Strength Test of Cement
A. Preparation of Sample
Mix Ratio:
- Combine cement and sand in a 1:3 ratio to create the cement mortar mix.
Water Quantity:
- Calculate the water quantity needed using the formula: Quantity of Water = (P/5) + 2.5 (P represents the percentage of water required for standard consistency, which is determined through the Standard Consistency Test of cement.)
Filling the Briquette Mould:
- Fill the briquette mould with the cement mortar mix, ensuring it’s evenly distributed.
Leveling and Smoothing:
- Add an extra heap of the cement mix on top and level it by applying pressure with a spatula until water appears, ensuring a flat surface. Repeat for the other side.
- Smooth the surface using a trowel blade to achieve a finished surface.
Mould Preparation:
- Prepare 12 moulds in total, maintaining the prescribed temperature and humidity conditions (27 ± 2 °C and 90% humidity) for 24 hours.
Curing Process:
- After 24 hours, remove the briquettes from the moulds and immerse them in clean water for further curing until testing.
B. Testing
Test Timing:
- Conduct tests on six briquettes at 3 days and another six at 7 days after preparation.
Using the Testing Machine:
- Position the cement specimen between the anvils of the testing machine.
Application of Load:
- Apply a load on the specimen gradually, starting from 0 and increasing at a rate of 0.7 N/mm² over 12 seconds.
Recording Failure Load:
- Note the load at which the cement specimen fractures or fails during the test.
Calculating Tensile Strength:
- Determine the tensile strength by dividing the failure load by the specimen’s surface area.
Observation of Tensile Strength Test of Cement
Observation Table for Tensile Strength Test
| Mould | Failure load P (N) | Mould Area A (mm²) | Tensile Strength P/A (N/mm²) at 3 days | Tensile Strength P/A (N/mm²) at 7 days |
|---|---|---|---|---|
| Mould 1 | ||||
| Mould 2 | ||||
| Mould 3 | ||||
| Mould 4 | ||||
| Mould 5 | ||||
| Mould 6 | ||||
| Average | – | – |
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Calculation of Tensile Strength Test of Cement
Where,
- is the failure load in Newtons (N) obtained from the test.
- is the fixed cross-sectional area of the least section of the cement sample, which remains constant at 645 mm².
The Tensile Strength of the given cement sample is calculated as the average of the results obtained from the six briquette samples tested. The average value of the Tensile Strength is derived from the individual Tensile Strength calculations of each sample using the formula
Result of Tensile Strength Test of Cement
The tensile strength of the given cement sample is ______ N/mm².
For Ordinary Portland Cement (OPC), the specified minimum requirements are:
- 3-days tensile strength should be greater than or equal to 2 N/mm².
- 7-days tensile strength should be greater than or equal to 2.5 N/mm².
Highlights of Tensile Strength Test Procedure
| Test Steps | Procedure Highlights |
|---|---|
| Prepare cement mortar mix of 1:3 | Add specified proportions of cement and sand to create the mix. |
| Add water of quantity (P/5) + 2.5 | Calculate and add the required water quantity to achieve the desired consistency. |
| Fill the mix in briquette moulds | Place the prepared cement mortar mix into the moulds evenly. |
| Level the top surface with a spatula | Ensure a flat surface by smoothing the top of the mixture. |
| Keep the mould in 90% humidity at room temperature for 24 hours | Provide the specified environmental conditions for curing the specimens. |
| Remove briquettes from the mould after 24 hours | Take out the specimens from the moulds after the specified curing time. |
| Keep the briquettes in clean water till they are taken out for testing | Continue the curing process by immersing the specimens in clean water until the test. |
| Test 6 briquettes at the end of 3 days while the remaining 6 at the end of 7 days | Conduct tests on specified samples at different intervals to assess tensile strength over time. |
| Apply a steady & uniform load from 0 at the rate of 0.7 N/mm² in 12 seconds | Gradually apply load to the specimens at a controlled rate for accurate testing. |
