River sand is largely used in construction projects. At times along with river sand, filter sand will also be delivered to construction sites.
Without enough experience, many people in site will not be able to differentiate the Filter sand from river sand and they will use it in construction.
These filter sands have various disadvantages when we compare with natural sand.
First, let’s understand about what is Filter Sand:
River sand is taken from river beds where sand particles are pure. Filter sand is sourced from stagnated water beds where sand particles will have various impurities and lot of clay and silt mixed with it.
Why it is called as Filter sand:
These sands are taken from stagnated water beds with large amount of silt and clay. Then through the process of washing and filtering most of the silt and clay content would be removed and retained sand particles are separated.
These filtered materials will be supplied as Filtered sand.
What’s wrong with Filter Sand?
River sand is sourced from the beds of running water. So these sand particles will always be free from any chemical deposits. Hence these will not create unnecessary chemical reactions in the concrete mix.
Filtered sand is sourced from stagnated water bed. Since the water is stagnated for many years, whatever chemical impurities come to water will get deposited on the sand particles. Though washing and filtering process is administered, all the chemical deposits on the surface of sand particles cannot be removed. So this Filter sand can create unnecessary chemical reactions in mortar or concrete.
Practical issues of Filtered sand:
It is been observed that, usage of Filtered sand leads to any or many of the following issues,
Delayed setting time
Poor compressive strength
Higher percentage of Bulkage property
How to identify & avoid using the Filtered sand:
Identifying filtered sand is slightly critical. There is no immediate test or mechanism available as of now. With certain experience and considering following aspects, Filtered sand can be identified and eliminated,
Water retention in river sand is very less & in Filtered sand is slightly high
River sand is usually light in colour & Filtered sand will be slightly reddish in colour
When you hold & rub river sand in hand it will not leave much traces, but Filtered sand will leave large glittering silt particles in hand
River sand will not bind with each other when you try to make ball out of it, but Filtered sand relatively bind better than river sand
At some cases, smell and organic materials will be higher in Filtered sand
If the washing & filtering was inadequate, large percentage of silt will be found in silt test
By mistake if you have received Filtered sand, then the same can be used in following place:
As a filling material in soling
As a bed material for pavers and stones
As a bed material for underground plumbing lines
Can be used in landscape soil
Any other unimportant structures like soil leveling, back filling mixing, etc.,