Dear Reader ,

In our journey into the mystery of a construction , we have so far covered concrete in the non-numerical aspects. Right ?

**Now let us also understand the mathematics involved .**This shall need a dedicated reading of this post.

For a new reader , it is suggested to please first read the following posts for general understanding of the subject and then return to this page .

**Remember :**

**To supervise the manpower at site certainly requires skills but if you can do quantity estimation, bills verification etc and also control manpower , your compensation shall rise in steep curve.**

**So, please don’t ever skip the calculations part while learning the construction.**

**Volumetric batching of the concrete.**

**There are two distinct methods of proportioning the ingredients for concrete :**

**1. By the measuring box ( Hindi : Farma ):**

**2.By the buckets ( Hindi : Ghamela ,Tagari & Marathi :**

**Pati,)**

**Both methods are in actual use at the construction sites**

**where volumetric batching is followed.**

**Remember :**

**1.The RMC plants , however, do the batching of concrete based on the design mix and hence weigh batching is practiced.**

**2.Certain sites also practice the design mix at site and use**

**weigh batching .**

**The discussion on S.nos 1 & 2 is excluded from the present post.**

**We are talking about only those construction sites which manufacture the concrete at the site**

**( In short : Nominal mix , Mixed at site & cast in situ concrete ) .**

**1. By the measuring box ( Hindi : Farma ):**

**the dimensions of A Standard measuring box : 12″ X 12″ x 15 “**

**You must be thinking :Is there is any significance of keeping this size of the measuring box ?**

**Right ?**

**So**

**first**

**let us see the importance of this size.**

**The cement bag has a standard weight of 50 Kg.**

**Cement has a bulk density of :**

**1429**

**Kg/CuM.**

**Hence the**

**volume of 1 bag of cement shall be**

**= 50/1429 =0.03499 CuM.**

**Since 1 CuM = 1000 Litres**

**therefore, the volume of 1 bag of cement shall be**

**0.03499 CuM.X 1000 Litres**

**= 34.99**

**Litre.**

**For practical purposes, we can consider this volume to be 35**

**Litre.**

**How do we use the**

**measuring box for batching different grades of concrete ?**

**1.Let us say we want to mix a**

**concrete of**

**grade**

**M20 .**

**We know that the Nominal mix for M20 grade is : 1 :1.5 :3**

**since we are doing volumetric mix, this means that :**

**If we take**

**1 part of cement by volume,**

**we shall have to take 1.5 parts of sand measured in the same units and**

**3 parts of aggregate again**

**measured in the same units .**

**So now , the same proportion**

**1 :1.5 :3**

**can also be written as :**

**1x 35**

**Litres : 1.5 x 35**

**Litres :3 x 35**

**Litres**

**or this can be further converted into :**

**1 bag of cement : 1.5**

**measuring boxes of sand : 3**

**measuring boxes of coarse aggregate.**

**Assuming that we have to maintain a water cement ration of 0.5 ,**

**we shall need 0.5 x 50 kg = 25 Kg or 25**

**Litres of water for one batch of concrete.**

**Now the steps are quite clear . Right ?**

**We start rotating the drum , pour about 10**

**Litres of water into the drum ,**

**Place**

**3**

**measuring boxes of coarse aggregate in the mixer drum ,**

**Followed by**

**1.5**

**measuring boxes of sand ,**

**Add remaining water ,**

**and then finally place 1 bag of cement in the drum .**

**One batch of concrete is ready to pour after rotating drum for**

**about 1 to 3 minutes.**

**This concrete can now be transported to the actual location either through trolleys or hoist and trolleys.**

**Advantages of this method :**

**There is no variation in the proportioning of ingredients and hence concrete produced has a consistent quality.**

**Disadvantage :**

**Local changes are not possible.**

**Like if we see that the aggregates are not properly blended, little sand is usually added to the mix.**

**This extra quantity of sand cannot be measured by the standard box.**

**2.By the buckets ( Hindi : Ghamela ,Tagari & Marathi :**

**Pati,):**

**This method is followed at many sites.**

**First step in using the buckets is to know exactly how many buckets are filled up in one bag of cement ?**

**This check is essential s**

**ince**

**buckets are produced in**

**various sizes ( 12″ ,15″ and 18 ” diameter ) .**

**Suppose the buckets which we are using on the site are such that**

**exactly 4 buckets are filled up with one cement bag.**

**Now , the same proportion of**

**1 :1.5 :3 can be written as :**

**4 buckets of cement : 1.5 x 4**

**buckets**

**of sand : 3 x 4**

**buckets**

**of aggregate**

**or ,**

**1 bag of cement : 6**

**buckets**

**of sand : 12**

**buckets**

**of aggregate**

**Now see the mixing sequence :**

**We start rotating the drum , pour about 10**

**Litres of water into the drum ,**

**Place**

**12**

**buckets**

**of coarse aggregate in the mixer drum ,**

**Followed by**

**6**

**buckets**

**of sand**

**,**

**Add remaining water ,**

**and then finally place 1 bag of cement in the drum .**

**Advantages of this method :**

**It is possible to add an extra bucket of sand in this method for achieving a dense concrete.**

**Shifting the sand & aggregate in buckets is easier due to light weight .**

**Lifting & dropping material from buckets to the drum is convenient.**

**Disadvantage :**

**There is lot of variation in the proportioning of ingredients since each bucket can be filled up at different levels**

**and hence concrete produced may not be consistent .**

**There is always a possibility that one or two buckets are missed or added extra since individual labour carries one bucket full of material at a time.**

**Keeping a track of material actually placed in the drum is difficult for the novice on the site.**

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