WHY FINE M-SAND REQUIRED MORE WATER THAN COARSE SAND

 Introduction

Purpose : To explain why fine M-Sand has higher water demand.

• Impact of M-sand type on water demand and concrete quality.

• Relevance for mix design and site execution.


Core Statement

• Fine M-Sand requires more water due its larger surface area and tighter particle packing, which increases water absorption and reduces workability.


Surface area and Its role

• Fine M-Sand = smaller particles = more surface area.

• When particles are small, they have more total surface area compared to large particles(for the same volume or weight)

• When you mix sand with water in concrete, the water needs to wet or coat the surface pf every particle.

• Hence more surface = more water.

• Simple Example: Coating small marbles V/S large stones with paint, smaller ones need more paint due to large total surface area



Tighter Particle Packing

• Fine particles fit more closely together.

• Reduce voids less space for water to flow.

• Increase internal friction decreases workability.

• Requires extra water/Superplasticizers to loosen the mix.


Effect on Concrete...

• Fine M-Sand increases the surface area and reduces the void ratio in the mix, so it requires more water and admixture to maintain the same workability.

• When water or admixture is not adjusted properly the mix becomes less workable leading to poor compaction, reduce flow and cracks.

What happens if variation in M-Sand fineness during continuous concrete production ?

• During continuous concrete production, if one batch of concrete uses finer M-Sand and the next batch uses coarser M-Sand (eg. Zone II), the following issues arises.

1. Sudden Decrease in water Demand : Coarse M-Sand has lower surface area, so it doesn't need as much water or admixture. The pre-adjusted mix(for finer M-sand) becomes over dosed.

2. Concrete starts Bleeding & Segregation : Excess water and chemical admixture in the mix which was set for finer aggregates now cause bleeding (free water rises to the surface). Coarse particles may settle quickly leading to segregation (paste and aggregates separation)

3. Pumpability get affected : Segregated or bleeding concrete becomes difficult to pump. It causes pressure surges, pipeline blockages and pump breakdown.


Why Consistency in M-Sand Matters

Even if the same design mix is followed the performance will differ if material grading is inconsistent.

This directly impacts:

• Workability

• Finish Quality

• Strength

• Pumping operation


M-Sand Quality Control and Zone Classification

 We are conducting sieve analysis of M-sand as 

part of quality control measures.

 For concrete works, Zone II M-sand is considered suitable due its balanced fineness and workability.

 As per Is 386:2016, the M-sand is classified into 

four zones based on its particle size distribution, 

and their limits refer below snap.

 150 micron sieve limit for crushed sand: For 

crushed stone, permissible limit on 150 

micron sieve is increased to 20%

 This does not affect the usual 5% 

tolerance limit applied to other sieves.




Thanks for engagement

  -Farman K


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