Pick up the correct statement from the following: A. The theory of formation of concrete is based on the phenomena of formation of voids B. The bulking of sand is taken into account while volumetric proportioning of the aggregates C. The dry sand and the sand completely flooded with water, have practically the same volume D. All the above

The correct answer is D. All the above.

The theory of formation of concrete is based on the phenomena of formation of voids. When cement and water are mixed, they form a paste that can fill the voids between the aggregates. The bulking of sand is taken into account while volumetric proportioning of the aggregates. This is because the volume of sand increases when it is mixed with water. The dry sand and the sand completely flooded with water, have practically the same volume. This is because the water fills the voids between the sand particles.

Here is a more detailed explanation of each option:

• Option A: The theory of formation of concrete is based on the phenomena of formation of voids. When cement and water are mixed, they form a paste that can fill the voids between the aggregates. The voids in concrete can be classified into three types: entrained air voids, capillary voids, and gel pores. Entrained air voids are intentionally introduced into the concrete to improve its durability. Capillary voids are formed due to the evaporation of water from the concrete. Gel pores are formed due to the hydration of cement.
• Option B: The bulking of sand is taken into account while volumetric proportioning of the aggregates. This is because the volume of sand increases when it is mixed with water. The bulking of sand is caused by the absorption of water by the sand particles and the expansion of the sand particles due to the formation of menisci at the surface of the sand particles.
• Option C: The dry sand and the sand completely flooded with water, have practically the same volume. This is because the water fills the voids between the sand particles. The volume of sand is equal to the sum of the volume of the sand particles and the volume of the voids between the sand particles. When water is added to the sand, the volume of the voids decreases and the volume of the sand increases. However, the volume of the sand particles does not change. Therefore, the dry sand and the sand completely flooded with water, have practically the same volume.