Which of the following proportion of cement and standard sand is used in cement mortar while testing the compressive and tensile strength of cement?
⚖️ Why a Standard Ratio is Crucial
To accurately determine the intrinsic strength of a cement sample, all other variables must be kept constant. The most significant variable in a mortar mix is the proportion of cement to sand. By fixing this ratio and using a "standard sand" (like Ennore sand in India), we ensure that the test results reflect the quality of the cement itself, not the quality or quantity of the sand used. This allows for a fair comparison between different cement brands and batches.
📝 Detailed Analysis of the Ratio
(a) 1 : 2
This is a richer mix (more cement). While used in some applications, it is not the standard for testing, as it would yield higher strength values that are not comparable to the standard benchmark.
(b) 1 : 3
This is the correct answer. Indian Standards (and most international standards) specify a mortar mix of 1 part cement to 3 parts standard sand by weight for both compressive and tensile strength tests. This ratio provides a consistent and reliable medium to evaluate the cement's binding properties.
(c) 1 : 4
This is a leaner mix. Using this ratio for testing would result in lower strength values and would not be a fair assessment against the established standards for cement quality.
(d) 1 : 6
This is a very lean mix, typically used for non-structural work like plastering. It is far too weak to be used as a standard for testing the inherent strength of cement.
📊 Standard Strength Test Details
| Property | Compressive Strength Test | Tensile Strength Test |
|---|---|---|
| Mortar Ratio | 1:3 (Cement : Standard Sand) | 1:3 (Cement : Standard Sand) |
| Test Specimen | Cube | Briquette |
| Specimen Size | 70.6 mm x 70.6 mm x 70.6 mm | 25.4 mm x 25.4 mm at throat |
| Apparatus | Compression Testing Machine (CTM) | Briquette Testing Machine |
💡 Study Tips
- The Rule of Three: For standard cement strength testing, the magic number is 3. Remember the 1:3 ratio.
- Consistency is Key: Understand that the goal of a standard test is to eliminate variables. The fixed 1:3 ratio is the most important part of this.
- Visualize the Shapes: Associate "compressive" with a solid, blocky Cube and "tensile" (pulling apart) with the figure-8 or hourglass shape of a Briquette.