Answered Concrete Deterioration Slurry problem

Dnyan Deshmukh

Staff member
In General Columns are of 2.4 meter + height, the concreting is done by directly pouring from top of shutter by fixing some plywood in slope to pour the concrete.

Poured concrete then hit the shutter and rebar and finally goes down at the base of column.

During this process the segregation by separation of aggregates happens, slurry goes on one side and aggregates goes on other side.

To avoid this, you can pour the some amount of rich cement mortar say 2 ghamela before pouring the concrete in column, this ensure the aggregates gets less segregated and also reduce the voids in concrete.

At the Top of column

When over vibration is done at top, the fine particles get accumulated and forms a weak layer of concrete at top, which is most dangerous from structural stability point of view. Many building collapse due to weak layer of concrete at column top just below beam.

How to avoid fines coming at top of column portion.

Last layer in the concrete, should be compacted manually by using bamboos, this will ensure the required compaction efforts and no fines accumulation at top.

Further to this
Best construction practice
Make a construction joint at the top of concrete by any following method;

Insert 20mm aggregates half way in concrete to form a key.

Make shear keys in column by penetrating square / round any means till 2 inches to form a key.

Remove laitance from top surface of concrete with wire brush, water jet.

The issue shown by you can also happen due to less or almost no cover to column reinforcement.
 
In General Columns are of 2.4 meter + height, the concreting is done by directly pouring from top of shutter by fixing some plywood in slope to pour the concrete.

Poured concrete then hit the shutter and rebar and finally goes down at the base of column.

During this process the segregation by separation of aggregates happens, slurry goes on one side and aggregates goes on other side.

To avoid this, you can pour the some amount of rich cement mortar say 2 ghamela before pouring the concrete in column, this ensure the aggregates gets less segregated and also reduce the voids in concrete.

At the Top of column

When over vibration is done at top, the fine particles get accumulated and forms a weak layer of concrete at top, which is most dangerous from structural stability point of view. Many building collapse due to weak layer of concrete at column top just below beam.

How to avoid fines coming at top of column portion.

Last layer in the concrete, should be compacted manually by using bamboos, this will ensure the required compaction efforts and no fines accumulation at top.

Further to this
Best construction practice
Make a construction joint at the top of concrete by any following method;

Insert 20mm aggregates half way in concrete to form a key.

Make shear keys in column by penetrating square / round any means till 2 inches to form a key.

Remove laitance from top surface of concrete with wire brush, water jet.

The issue shown by you can also happen due to less or almost no cover to column reinforcement.
2 ghamela rich mortar,in the column or in the concrete?and if in concrete then in 1m3 concrete 2 ghamela mortar is required?
 

Dnyan Deshmukh

Staff member
Should be poured in the column before starting concrete.

You need to decide on how much you should put in, by doing experiments at site.

Normally 2 ghamela rich mortar with adequate workability can help to avoid segregated concrete and help in building sound concrete.
 

ceteja

Newbie
I completely agree with Mr. [B]Dnyan Deshmukh[/B] . In my opinion the condition is due unsound segregated concrete placed in the form work. The concrete placing prior to the placement already segregated. Its just that the condition become much worse due to bad placement. I feel Check concrete for segregation is much more important.
 

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