The compressive strength of mortar, as determined by utilizing 2-inch or 50mm cubes in accordance with ASTM C109 / C109M - Standard Test Method for Compressive Strength of Hydraulic Cement Mortars, serves as a crucial parameter in assessing the durability and load-bearing capacity of various masonry structures. Mortar, composed of a blend of cement, sand, and water, finds widespread application in masonry works such as bricklaying, stone masonry, and plastering of walls and columns. This article aims to delve into the significance of testing mortar compressive strength, the methods employed for its determination, and the calculation procedures involved.
Significance of Compressive Strength Test
Masonry structures, including load-bearing walls and columns, are integral components of residential and commercial buildings. The compressive strength of mortar plays a pivotal role in ensuring the structural integrity of these constructions, as it dictates their ability to withstand applied loads. Particularly in load-bearing masonry, where walls support vertical loads from upper floors, a requisite compressive strength is imperative to ensure structural stability and safety.
Procedure for Determination of Compressive Strength
To ascertain the compressive strength of standard cement-sand mortar cubes, a meticulous procedure is followed, employing specific apparatus and protocols.
Apparatus
The apparatus required for conducting the compressive strength test includes 7.06cm cube molds with a face area of 50cm², equipment for gauging and mixing mortar, a vibrator, and a compression testing machine.
Procedure for Compressive Strength of Mortar
- Measure 200g of cement and 600g of standard sand in a 1:3 ratio by weight.
- The sand utilized must conform to specified standards, exhibiting characteristics such as angular grains and passing through a 2mm IS sieve.
- Mix the dry cement and sand thoroughly for one minute, then gradually add water. The water quantity should be proportional to the combined weight of cement and sand, determined by a predefined formula based on the paste's standard consistency.
- Continue mixing until a uniform consistency is achieved, ensuring a mixing duration between 3 to 4 minutes.
- Transfer the mortar mixture into cube molds, compacting it by prodding the mixture 20 times within 8 seconds to eliminate entrapped air.
- If a vibrator is utilized, subject the cube molds to vibration for a duration of 2 minutes at a specified speed of 12000±400 vibrations per minute.
- Place the cube molds in an environment with a temperature of 27±2°C and 90% relative humidity for 24 hours.
- After 24 hours, remove the cubes from the molds and submerge them in clean water until testing. Testing should be conducted on their sides without any additional packing.
- Employ a uniform rate of loading, typically 350 kg/cm²/minute, for testing three cubes and report the average values as the compressive strength at both 7 and 28 days.
Result of Mortar Cube Test
The results of the mortar cube test are reported in terms of compressive strength at 7 and 28 days, expressed in N/mm². Additionally, calculations involve determining the breaking load, cross-sectional area, and ultimate compressive strength of the mortar samples.
In summary, the compressive strength of mortar serves as a fundamental parameter in assessing the structural robustness of masonry constructions. Through meticulous testing procedures and precise calculations, engineers and construction professionals can ensure the durability and safety of load-bearing structures, thereby contributing to the overall resilience of buildings and infrastructure.