Concrete masonry units, also known as concrete blocks, are a common building material used in construction. These blocks are typically made from a mixture of cement, aggregate, and water, and come in both solid and hollow forms. They are rectangular in shape and are used in the construction of masonry structures.
Concrete masonry blocks can vary in size, with different nominal dimensions available. The length of the blocks can be 400mm, 500mm, or 600mm, while the width can be either 200mm or 100mm. The height or thickness of the block can vary from 50mm to 300mm, with several options available in between.
It is important to test the compressive strength of these blocks to determine their suitability for various construction purposes. This measurement provides valuable information about the block’s ability to withstand pressure and stress. Ultimately, understanding the compressive strength of concrete masonry units is crucial for ensuring the safety and stability of any building construction project.
Tests on Concrete Masonry Block Units
Concrete masonry units undergo several tests to ensure that they meet the required standards. In this discussion, we will focus on three specific tests that are conducted on concrete masonry blocks.
The first test is the dimension measurement, which is carried out on all blocks. This test involves measuring the dimensions of the blocks to ensure that they meet the required size specifications. Blocks of the same mix are taken, and their dimensions are measured to ensure that they are consistent.
The second test is the density test, which is carried out on three randomly selected blocks. This test is important because it helps determine the density of the blocks. The density of the blocks is crucial because it affects the overall strength and durability of the masonry structure.
The third test is the compressive strength test, which is carried out on eight randomly selected blocks. This test is essential because it helps determine the compressive strength of the blocks. Compressive strength is the ability of the block to withstand a compressive load without failing. This test ensures that the blocks are strong enough to withstand the expected load requirements in the masonry structure.
Overall, these tests are critical in ensuring that concrete masonry blocks are of the required quality and meet the necessary standards.
Dimension Measurement
In this step, it is necessary to check all blocks thoroughly. This includes measuring the length, width, and height of each block using a steel scale. For hollow blocks, it is also important to measure the web thickness and face shell using a caliper ruler. By doing so, the necessary information can be gathered to prepare a comprehensive report.
The report should include the average length, width, and height of the blocks, as well as the average minimum face shell and minimum web thickness. These measurements should be based on the recorded dimensions obtained during the checking process. By preparing this report, a clear picture of the quality and consistency of the blocks can be obtained, and any necessary adjustments or improvements can be made.
Density of Concrete Masonry Block
To determine the density of a block, three blocks need to be taken for testing. The testing process involves heating the block in an oven to a temperature of 100°C and then cooling it down to room temperature. Once the block has been cooled, its dimensions are measured to calculate its volume. The block is then weighed, and its mass is determined. Using the mass and volume values, the density of the block is calculated using the formula: density = mass/volume (kg/m³).
It is important to note that the density values for different grades of blocks should fall within certain ranges. The average density of the three blocks tested is used as the final density value for the particular type of block being tested.
| Type of unit | Grade | Density of block (kg/m2) |
| Hollow type unit | A(3.5) | >/= 1500 |
| A(4.5) | >/=1500 | |
| A(5.5) | >/=1500 | |
| A(7.0) | >/=1500 | |
| A(8.5) | >/=1500 | |
| A(10.0) | >/=1500 | |
| A(12.5) | >/=1500 | |
| A(15.0) | >/=1500 | |
| B(3.5) | 1100-1500 | |
| B(5.0) | 1100-1500 | |
| Solid type unit | C(5.0) | >/=1800 |
| C(4.0) | >/=1800 |
Compressive Strength Tests on Concrete Masonry Blocks
The compressive strength of concrete masonry blocks is determined using eight blocks that are collected and tested within three days of being brought to the lab. The age of each block should be 28 days. The compressive strength testing machine consists of two steel bearing blocks, one fixed in position on which the masonry unit is placed, and another movable block that applies the load to the masonry unit. If the bearing area of the masonry unit is larger than that of the steel blocks, separate steel plates are used. These plates are arranged on the steel blocks in a way that ensures the centroid of the masonry unit coincides with the center of thrust of the blocks.
To test the compressive strength of concrete masonry units, the bearing area of the units is capped with either a Sulphur and granular materials coating or gypsum plaster capping. The testing process involves applying one-half of the expected maximum load to the unit at a constant rate, and then applying the remaining load in not less than 2 minutes. The load at which the masonry unit fails is recorded, and the maximum load divided by the gross sectional area of the unit gives the compressive strength of the block. This process is repeated for 8 blocks in total, with the load and compressive strength recorded for each block. The average of the compressive strength of the 8 blocks is then calculated to determine the final compressive strength of the concrete masonry unit. The minimum average compressive strength of the individual units is represented in the table.
| Type of unit | Grade | Min average compressive strength of individual units (N/mm2) |
| Hollow type concrete masonry unit | A(3.5) | 2.8 |
| A(4.5) | 3.6 | |
| A(5.5) | 4.4 | |
| A(7.0) | 5.6 | |
| A(8.5) | 7.0 | |
| A(10.0) | 8.0 | |
| A(12.5) | 10.0 | |
| A(15.0) | 12.0 | |
| B(3.5) | 2.8 | |
| B(5.0) | 4.0 | |
| Solid type unit | C(5.0) | 4.0 |
| C(4.0) | 3.2 |