We saw how the specimen cubes were cast and tested on 7th & 28th days from the date of casting.
We also spoke about the characteristic strength of concrete.
We also saw 4 different cases of multidisciplinary coordination.[Read post: Progress continued ..upwards ]
Now let’s go ahead and focus on the next activity ..the columns beams slab.
Basement roof slab has been cast.
Dowel bars are left protruding from the columns .
Further activities shall be undertaken as follows:
1.Dowel bars shall be lapped with new bars of the same diameter so that the bars reach above the proposed slab .The dowel bars shall extend at least 45 times the bar diameter above the slab.
( If the bar diameter is 12 mm then we must verify that these extend for a minimum of 45 x 12 = 540 mm above the slab level.Some situations may require that this lapping distance be maintained as 52 times bar diameter. This detail shall be provided in the RCC drawings.
The lapping between the bars shall be tied together with the binding wire .
Binding wire is mild steel wire of 1.6 mm diameter . Some builders use galvanized binding wire which is resistant to rusting and hence improves the durability of concrete.
Hand held portable machines are also available for tying the bars with binding wire .
2.Stirrups shall be inserted in the main bars of the column and shall be fixed at the spacing specified in the drawing.
Usually the doughnut shaped cover blocks are fixed in the stirrups so that the cover to the reinforcements is maintained.
3.Form work for the column shall now be fixed on the starter.
Starter is a small piece of column which is cast before the main column is cast.
A wooden box of internal size exactly matching with column size is placed in position. The center lines are checked.and concrete of the specified grade is poured in this mould .
The advantages of having a starter are:
a.It is easier to establish & verify the center line of the starter than of that of the column.
b.It is sturdier to fix the column shuttering if the starter is already in place.
c.The chances of column form work becoming skew are eliminated.
5. The column shall be cast after all checks are completed with the approved concrete mix.
6.the column shuttering shall be removed next day and the curing shall be taken up. depending on the climate ( temperature and humidity ), the curing can be done either by spraying water at intermediate intervals or by wrapping column with hessian clothe and keeping it wet.
Author’s note :
Thank you for reading so far with total attention.
In the next article we shall speak about the entire process involved in the casting of the roof slab.
Till then , bye bye