We have already learned that volumetric batching is not frequently used in concrete industry because of its incorrect measuring of ingredients of concrete mix. With this problem, in Indian subcontinent this method of batching is used even in important projects. Due to improper batching it is often allowed in small or less important construction project. Now we will learn the evil of such batching method.
If the granular portions of concrete mix are measured by volume, the resulting concrete may have different properties for a same ratio of batching when other conditions are considered same (placing handling, compaction, finishing etc). This is due to measuring error of materials, as same volume of granular part may have different weight depending on water content and voids in particles.
Consider two same volume of sand, one in moist condition and other in dry condition. A certain volume of dry compacted sand has much weight than same volume of moist loose sand. So when we measure one cubic meter of granular materials, we actually measure an indefinite quantity. For this reason concrete batching on the basis of weight is the only method for accurate proportion of a mix.
In the previous post we have learned about way of measuring cement. So we are not discussing this term here. There has no problem with water. Water can be measured by kg or liters as 1 kg of water have volume of 1 liter. Water measured in term of water/ cement ratio. Definitely the measuring criterion of cement is its weight.
But when volumetric batching cannot be avoided, we will use certain techniques to minimize errors and taking assumption. Here gauge boxes are introduced having different designed volume depending on volume of cement per bag. Dear reader we will discuss this elaborately in the next post.