# How to determine the strength of a concrete block

The strength of a concrete block, also known as a Concrete Masonry Unit (CMU), is primarily determined by its compressive strength. This is the maximum amount of pressure the block can withstand before it breaks. Here’s a step-by-step guide on how to determine the strength of a concrete block:

Understanding Compressive Strength: Compressive strength refers to the maximum crushing stress that a concrete block can take. It’s calculated using the formula: Compressive Strength = Applied Maximum Load / Surface Area of the Specimen. For concrete blocks, the compressive strength is typically around 17.5 N/mm² or 2500 psi.

Testing Compressive Strength: The compressive strength of a concrete block is determined by dividing the maximum load for a given masonry unit by the unit’s total cross-sectional area.. Eight blocks are taken to determine the average compressive strength. The blocks should be tested within 3 days after collection in the lab. The age of each block should be 28 days.

Dimension Measurement: All blocks should be checked for their length, width, and height with a steel scale. If it’s a hollow block, then the web thickness and face shell are measured with a caliper ruler. An average of the recorded dimensions is prepared.

Density Measurement: Three blocks are taken to determine the density of the block. First, heat the block in the oven to 100°C and then cool it to room temperature. Now take the dimensions of the block to find out the volume and weigh the block. The density of the block is determined from the relation: Density of block = mass/volume (kg/m³).

Factors Affecting Compressive Strength: Several factors can affect the compressive strength of concrete blocks. These include the quality of raw materials, the water/cement ratio, the quantitative relation between aggregates, the aggregate to cement ratio, entrapped air, concrete compaction, the age of concrete, curing time, temperature, and relative humidity.

Remember, safety should always be your priority when conducting these tests. Always wear appropriate personal protective equipment and follow the guidelines and standards for testing concrete blocks.