The most common concrete strength test measures the psi (pounds per square inch) of concrete to determine whether a particular concrete mixture meets the needs of a project. This is tested by breaking cylindrical concrete specimens in a special machine that is designed to measure this type of strength.
Another indirect measure of concrete strength is flexural strength, which measures the ability of concrete to resist bending or cracking under tension. This figure is generally 10 to 15% of the compressive strength, but it can vary depending on a specific concrete mixture.
The water-to-cement ratio of a concrete mixture is one of the most important factors when determining the strength of a concrete mix. Using too much water or too little cement paste can increase the amount of evaporation and cause the formation of fine particles in the mix, which reduces overall strength.
Optimal Mixing Time
It is essential to mix the right amount of water, air, and cement into a concrete mixture before pouring it. Adding too much water can make the concrete too soft and prone to cracking, while adding too little cement paste will create a rough, porous mix that is hard to work with and less strong.
Early Strength Gains
The psi level of a concrete is typically tested in seven days and again in 28 days to determine whether it has achieved the appropriate early strength gains for that specific application. In addition, concrete structures in colder climates may require a higher psi to withstand more freeze/thaw cycles.