The compressive strength of mortar, which is a mixture of cement, sand, and water, is determined using 2 inch or 50mm cubes according to the ASTM C109/C109M standard test method. Mortar finds its application in masonry works such as brick and stone masonry and for plastering walls, columns, etc. The strength of the mortar is dependent on the ratio of cement to sand used in the mixture. The common mix ratios for mortar used in masonry works are 1:3, 1:4, and 1:6 of cement to sand ratio. For masonry structures that are deemed important, such as brick walls, a 1:3 ratio of cement to sand is commonly used.
Why Compressive Strength Test of Mortar is Important?
Load bearing masonry structures, such as walls and columns, are commonly used in the construction of residential and other buildings. Brick masonry is often used for building foundations in masonry construction. To ensure that a load bearing masonry structure can withstand the weight placed upon it, it is crucial to determine the necessary compressive strength of the masonry.
A masonry wall, for example, must be able to bear the compressive loads exerted by the floors located above it. This requires that the masonry used to construct the wall possess adequate compressive strength to support the weight placed upon it. Without sufficient compressive strength, the masonry would be unable to withstand the load, potentially resulting in structural failure.
Therefore, the compressive strength of masonry used in load bearing structures must be carefully considered and evaluated in order to ensure the safety and stability of the building. By ensuring that the masonry has the necessary strength to withstand the loads placed upon it, builders can ensure the longevity and durability of the structure.
Determination of Compressive Strength of Mortar
The compressive strength of standard cement sand mortar cubes can be determined by using certain apparatus and following a specific testing procedure. This test requires the use of cubes made from cement sand mortar, which will be subjected to compression in order to measure their strength.
The apparatus required for this test include a compression testing machine, a cube mould of standard size, a weighing balance, and sieves. The compression testing machine is used to apply a compressive load to the cube mould containing the cement sand mortar cube. The cube mould is a standard size that has been previously established for this test. A weighing balance is used to measure the weight of the cube before and after the test. Sieves are used to separate the sand and cement particles to ensure that only the correct proportion of each is used in the mixture.
The testing procedure involves preparing the cement sand mortar cubes by using a mixture of cement, sand, and water in a predetermined ratio. The cubes are then left to set for a specific period of time, typically 24 hours. After the cubes have set, they are removed from the mould and placed into the compression testing machine. The machine applies a load to the cube until it fails, and the maximum load that the cube can withstand is recorded. The weight of the cube before and after the test is also recorded to calculate the compressive strength of the cement sand mortar.
Overall, the compressive strength of standard cement sand mortar cubes can be accurately determined by following this specific testing procedure and using the necessary apparatus.
Apparatus
The equipment required for this task includes 7.06cm cubes moulds, which have a face area of 50cm². In addition, an apparatus for gauging and mixing mortar will be necessary to ensure the correct consistency and strength of the material. A vibrator will also be needed to ensure that the mortar is evenly distributed within the moulds. Finally, a compression testing machine will be used to determine the compressive strength of the cubes once they have hardened. All of these tools are essential to ensure accurate and reliable results in the testing process.
Procedure for Compressive Strength of Mortar
In order to prepare a mix of cement and sand, a pan is required with a total weight of 800 grams. The mix ratio of cement to standard sand is 1:3 by weight. The standard sand used in this mixture must be of the quartz variety and should be either light gray or whitish in color. Additionally, it must be free from any silt. The sand grains must be angular in shape, with their approximate shape resembling that of a sphere. Any elongated or flattened grains should only be present in small quantities.
The standard sand must also pass through a 2 mm IS sieve and be retained on a 90 microns IS sieve. The sand must have a particle size distribution that meets the following requirements.
To make mortar, the first step is to mix the cement and sand together in a dry condition using a trowel for at least one minute. Then, water needs to be added to the mixture, and the amount of water should be (p/4+3)% of the combined weight of cement and sand. Here, p represents the percentage of water required to make a paste of standard consistency, which has been determined beforehand. After adding the water, the mixture needs to be continuously mixed until it turns into a uniform color. The mixing process should take no less than three minutes and no more than four minutes.
Once the mortar is mixed, it should be immediately placed in a cube mold and prodded with a rod 20 times in about eight seconds to remove any entrained air. If a vibrator is used, it should vibrate for two minutes at a specified speed of 12000±400 vibrations/minute. After this, the cube molds should be placed in an environment with a temperature of 27±2o C and 90% relative humidity for 24 hours.
After 24 hours, the cubes need to be removed from the molds and submerged in clean water until testing. Just before testing, the cubes should be taken out of the water. The cubes should be tested on their sides without any packing, and the rate of loading should be 350 kg/cm2/minute, and it should be uniform. The test needs to be conducted for three cubes, and the average value of the test results for both the 7-day and 28-day compressive strength should be reported.
Result of Mortar Cube Test
Compressive strength at 7 days =……….N/mm2 Compressive strength at 28 days =……….N/mm2
Calculations of Compressive Strength of Mortar
The given problem involves calculating the range of selection for compressive strength of a material based on certain parameters. The allowable compressive stress is provided as well as the area of cross section of cubes, which is 50cm2. Using these values, the expected load can be calculated by multiplying the stress by the area and a factor of safety. The range of selection for compressive strength can then be determined based on this expected load.
Additionally, the problem also involves calculating the breaking load, area of cross section, and compressive strength of a mortar. These values are not directly related to the range calculation mentioned earlier, but are still relevant to the overall problem. The breaking load and area of cross section can be used to determine the compressive strength of the mortar, which is another important parameter in material selection.