Answer:
D. All the above
Step-by-step explanation:
A is correct. The theory of formation of concrete is based on this phenomenon of formation of voids because, a coarse aggregate aggregate on its own, contain voids. When a fine aggregate like sand is added, it occupies these voids. Further, when finely powdered cement is added to the mixture, it further occupies the voids between the sand particles.
B is correct. The bulking of sand should be taken into account when volumetric proportioning of the aggregates is adopted. Otherwise, less quantity of concrete per bag of cement will be produced, which naturally will increase the cost of concrete. This is because sand particles when left on their own, do not pack properly near each other due to sand buckling, leaving too many void spaces between the sand particles.
C is correct . The dry sand and the sand completely flooded with water have practically the same volume. This is due to the bulking of sand. When water is added to the sand, up to complete flooding, the sand particles pack near each other and the amount of bulking of sand is decreased. The addition of the volume of water, leads to a decrease in the volume of the sand due to the extra voids. These cancels out to practically leave the dry sand and the flooded sand with the same volume.