What is the difference between the apparent and true density of concrete?

The correct answer highlights that apparent density includes the volume of air voids, whereas true density considers only the solid material of the concrete.

To understand this distinction, it is essential to define what these two densities represent. True density is a measure of the mass of the solid particles in a given volume of concrete, excluding any voids that may exist within the concrete matrix. This means that true density provides a more accurate representation of the material itself, as it reflects the density of the concrete without the influence of air spaces.

On the other hand, apparent density incorporates the entire volume of the concrete sample, including both the solid particles and the voids (air pockets). This results in a higher value since the presence of air voids does not contribute to the mass while still occupying space within the concrete.

Understanding these definitions is critical for professionals in concrete testing, as they offer insights into the material's characteristics, performance, and durability. This distinction plays a vital role in the quality control and structural assessment of concrete materials, influencing factors like strength, thermal performance, and moisture retention.