Steel in RCC

i am not getting you when you say 'stone jelly'..before inserting you have to know the required size of cover on rebars (check the structural DDDs not just taking 1'' cover!!!!) ..and all materials inserted to provide cover have to be friendly with concrete(dont react with.. etc) and it should also offer structural strength,prefarably same strength and flexibility with concrete..and respond in the same way on weather with concrete...so at least you check it from there!

The 'stone jelly' implies crushed stones,used as aggregate for concrete.

thnks mate...it is a terminology rarely used in East Africanas!

Use either plastic chairs of continuous bolsters to support steel reinforcement in slabs. You can also use galvanized steel ones as well, but make sure that they have PVC caps on the bottom of the feet to eliminate rust.

Do not use concrete and cement block to support rebar as their presence induces a weak plane in the concrete section.

GA to Passington for excellent answer!

i prefer using precast concrete cover block it is concrete friendly and it dosnt effect the section of the element

Sorry to disagree with you, as any structural engineer or concrete contractor/subcontractor worth their salt knows that by supporting rebar with concrete block or stones actually diminishes the strength of concrete slab and introduces a weak plain throughout....you need a completely solid and homogeneous structural cross section derived from a monolithic concrete placement, with good solid concrete beneath the bottom bars as well as above them. You will not get that using blocks and stones as there is incomplete bonding of the concrete to them and to the underside portion of the rebar......you need complete concrete bottom cover of sufficient depth in order to form a true composite structural member.

Providing the prerequisite rebar chairs and bolsters to support the rebar atop the formwork and/or multiple layers of rebar is the only acceptable means of support in order to develop a transformed concrete section.

During my over 34 years of Structural Engineering I have found my fair share of failed structural floor slabs and beams. A vast majority of these were incorrectly constructed using your unacceptable method of supporting the rebar throughout the structural element.

The cost of these rebar chairs is at best roughly 0.5% of the total cost of the completed cost of the floor or roof slab.....that includes concrete costs, steel reinforcement costs, formwork costs, utility duct costs, and labor costs.

Concrete block covers seems to be the best choice, almost structurally monolithic.

Dear nvmani,

Your term "almost" is just that, and only counts in the game of "Horseshoes" and "Hand Grenades". Meaning that it is not good enough from a proper engineering and construction standpoint.

I cannot agree with your sentiment at all. If you choose to ignore the professional advice of several structural engineers in this thread, myself included (w/ nearly 34 years as an engineer, 16 years of which I have been a Licensed Professional Engineer), then the onus is upon you to assure that the concrete slab is structurally sufficient and safe. You came to us seeking advice and have chosen to disregard it. I tell you again that it will not be if you use tiny precast concrete blocks to support the slab reinforcement steel, especially for such a thin slab.

I wash my hands of this thread forever more....

It seems I did not communicate properly.

I entirely agree with you that a completely solid and homogeneous structural cross section derived from monolithic concrete placement with good solid concrete beneath the bottom bars as well as above them is needed.

Provision of the tiny precast concrete blocks under steel rods is just to ensure,while pouring the concrete mix while casting the slab that the concrete mix reaches below steel to provide sufficient depth of cover. This measure is just to make sure that required cover of solid concrete beneath the bottom bars is practically achieved after construction.

Kindly advise whether I am making my point clear.

Dear nvmani, you have been clear.

If you use the bar support chairs or bolsters you will not need to use the precast concrete blocks. In fact, you will end up with a superior floor slab.

Thank you.I will proceed with the bar support chairs.

Way to go nvmani! You'll be happy with the end result...