[Fernando Veras]

Hello: First I apologize for my poor English cause I don´t live in the USA.

My question is for a good contractor. I have to repair my concrete slab on my garage. It was originally built as a 4 inches “raft” concrete slab over the ground(without rebars). The walls are supported for properly foundations. The garages floor is so damaged due to subsidences and differential settlements. So. I want to build another slab using concrete and steel reinforcement. I intend to do it as “ flouting slab. As I think the fill that supported the original slab is already compacted, due to the traffic and the natural settlements. I would like just to put that reinforced slab without sub-base( as crashed stone, etc) and without additional compaction. Just to make the job easier. I inform you that is not expected using so heavy vehicle as trucks, pick –ups,etc just popular cars. I will summarize bellow the information and how I am planning to do it.

PS: We use here metric units but I am going to convert is, as possible, at Imperial ones.

1)Milded climate( South Brazil): no freezing, thawing. Not too much hot climate the garage has a good roof. No ground water table.
2)Light vehicles, at maximum 2 tons.( The total vehicle´s weight)
3)The dimensions are : 4 X 9 meters(13’ X 29’ feet)
4)I will use a 13 mm slab(5” inches) with 25 Mpa concrete(3625 psi)
5)We don’t use welded meshs here( just on big enterprises) so I will use :

a)6, 3 mm rebar each 20 cm at the bottom on both directions( ¼” bar each 8 inches). Rebars tied with steel wire.
b)To stiffer it, I will use each 2 meters(6 feet) beams (inside the slab on the minor dimension) for 30 cm to 13 cm( 12 X 5 inches), having 3 bars top and bottom of 10 mm( 3/8 inches), tied with 6,3 mm stirrups, each 20 cm( ¼” stirrups each 8 inches), These beans inside the mesh I have already mentioned.
c)I will put proper covering: 30 mm at the bottom and 10 mm on the top( cause it will be covering by mortar and ceramics) ( 1 X 3/8 inches)
d)No joints are planned. Except for external wall perimeter when pile foundations are provided.

I thank you in advance.

Fernando

[21boat]

at the bottom on both directions( ¼” bar each 8 inches). To stiffer it, I will use each 2 meters(6 feet) beams (inside the slab on the minor dimension) for 30 cm to 13 cm( 12 X 5 inches), having 3 bars top and bottom of 10 mm( 3/8 inches), tied with 6,3 mm stirrups, each 20 cm( ¼” stirrups each 8 inches), These beans inside the mesh I have already mentioned.
c)I will put proper covering: 30 mm at the bottom and 10 mm on the top( cause it will be covering by mortar and ceramics) ( 1 X 3/8 inches)
d)No joints are planned. Except for external wall perimeter when pile foundations are provided.

I'm not sure what the beams are for?
By the way you did very well considering.
So far I think I got steel bars in a grid pattern. Is this single layer or double layers " matt" ?

What language do you speak there?
¿Qué idioma utiliza usted allí?

Hasta ahora suena bueno. Vivo en los estados y trabajo en Puerto Rico. Ellos también utilizan 1/4 barra para los caminos de entrada. Im que assume que usted sabe posiblemente español y si usted have trataba de mostrarle cortesía a usted y ver cómo mi español es.

The 8 inch by 8 inch grid steel rods sounds good so far as does the Psi.


Signed 21 Boat

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[Fernando Veras]

Thank you signed 21 boat

My native language is portuguese so, close to spanish. I am going to respond it in English(I hope it sounds understandable), so other mates can understand. My considerations are as follows.

- Is a one single layer rebar. ( but in both directions)
- Though the beams I proposed each 2 meters(6,5 feet), will have, of course top and bottom rebars( 3 top plus 3 bottom, 3/8 rebars)
- The goal I though to these beam is to increase stiffness in the slab. In fact I thought to use heavier beams. Say, the slab is 5 inches and the beams would be 15 inches, but I am thinking to make things easier. So, less digging( to set the beams), less reinforcements.
- According civil engineering pratices when you stiff a matt, a slab on the ground, you achieve more uniform pressure distribution under the slab. So less and more spread cracks.

Though my main doubt still remains:

I don't want to build a subbase .eg. Crushed stone as usually experts recommend. I don't want to compact the soil. Well, perhaps a little compaction by hitting the soil( no equipments).

The fact is. It´s a fill,under the original slab that has settled down. The bad thing is, underneath this fill there is a very soft soil layer. I say it cause, the main foundations of the house, are supported by driven concrete piles that reached 14 meters(46 feet).

I know it is impossible to predict exactly how this slab will behave. But if the subsidences will be the half I had, as well, differential settlements(as the civil engineers call it) are minimized I will consider I succeed.

So, my question still is. Do a subbase would influence so much the slab behavior. Feel free to answer it or not. I don't like to pestering you.

Muchas gracias por contestarme.

Best regards to all ladies and gentlemen who join this forum.

[21boat]

Though the beams I proposed each 2 meters(6,5 feet), will have, of course top and bottom rebars( 3 top plus 3 bottom, 3/8 rebars

Could you explain this a bit better please?
Don't worry about pestering anyone here. Your questions are what the site is all about.

The perimeters of the garage, Is it a block foundation? If so is there anyway of hammering drilling into the block to get side support?

Get back please, Its not a bother for me to continue to try and help you.

I'm a concrete contractor in the U.S.

Signed 21 Boat

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[Fernando Veras]

Dear 21 Boat,

In my last message I forgot to say that: Tu español es muy bueno. Lo he compreendido perfectamente,quizas es mejor que mi español. De hecho estoy cierto que tu eres uno muy bueno constructor. Ok, now answering in my (fake) English:

Yes, the perimeter of the garage lyes on beams supported in caps block that cover precast concrete piles. In fact, a civil engineer who I just had a contact by phone call, told me the same, you´re saying. The better is to drill the blocks, build another beams and so, put a slab on this new structure. But I´m hesitant about this idea. The pile caps are spaced some 3 meters and I will have to provide additional beams, forms ,etc. So( and may be I ´m too stubborn) I am thinking, as I told you, building an independent and "floating" slab. Less formwork, no drilling. There´s another problem. A lot of structural beam lyes on this floor. They receive some pilars that support the upper room I have over this garage structure. These beams lyes on that piles I mentioned. I though to reinforce these beams too and put the slab on it. But I am afraid to interfere on these existent structure. I know it will be not so reliable as a slab anchored on that piles, but I´m willing to take this risk. What I think is. This present slab( without steel reinforcement) took some 4 years to get totally damaged. If I be able to take half than the displacements I had and it tooks some 5 years I would be happy. If the settlements and displacements are small, the next repair I will do it just laying mortar. I read a lot about slabs on ground technical litterature, as well in "do it yourself" issues. One, very interesting, a standard specification from Texas, gave me some tips. Most of these litterature show you have to put gravel as subbase, not that Texan one.

Anyway, I am thinking to build the slab as I told you on actual soil just being compacted by hand. I think the reinforcement with a small displacement will start working. That´s what I am thinking.

In the other hand, if you think is a stupid idea, I will follow your advice.

Thank you very much again for being so nice and helpful. It´s amazing that good american contractors are willing to colaborate in sites as this.

Que seas feliz ahi en Puerto Rico. Muchas Gratias Y Hasta La Vista.

[21boat]

If you can tie into any pillars below slab or tie into the block then you have a good start. From the perimeters of any tie ins I would make the concrete thicker with 3/8 bars longways and cross tie those bars.

Basically what I'm trying to say is make some H patterns concrete beams that are approx 8 or 10 inches wide by 8 inches high or more. You can rough form this and pour it the same time as the floor. If the new formed beams are set up right its like I beams under the slab and yet doing it in concrete as a continuous pour. Now you have a slab supported by concrete beams that in turn are partially supported by the sides.. This way if the earth below keeps sinking it won't matter much because you have a bridge deck built at this point. If you are concerned with the added tie in weight punch a couple of holes through old concrete and pour some very short pillars where the H lines intersect and that can support the new concrete hand made beams that go through / under the whole floor.

I don't know if this will help you but a yard of concrete is about 4,000lb wet or dry its close either way. Also a yard is 46,656 square inches. Its takes about 7 days to get about 60 to 70% Psi in new concrete above 70 degrees. The wetter you keep it after you pour the better the PSi will be reached,


Signed 21 Boat

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[Fernando Veras]

If you can tie into any pillars below slab or tie into the block then you have a good start. From the perimeters of any tie ins I would make the concrete thicker with 3/8 bars longways and cross tie those bars.

Basically what I'm trying to say is make some H patterns concrete beams that are approx 8 or 10 inches wide by 8 inches high or more. You can rough form this and pour it the same time as the floor. If the new formed beams are set up right its like I beams under the slab and yet doing it in concrete as a continuous pour. Now you have a slab supported by concrete beams that in turn are partially supported by the sides.. This way if the earth below keeps sinking it wont matter much because you have a bridge deck built at this point. If you are concerned with the added tie in weight punch a couple of holes through old concrete and pour some very short pillars where the H lines intersect and that can support the new concrete hand made beams that go through / under the whole floor.

I don't know if this will help you but a yard of concrete is about 4,000lb wet or dry its close either way. Also a yard is 46,656 square inches. Its takes about 7 days to get about 60 to 70% Psi in new concrete above 70 degrees. The wetter you keep it after you pour the better the PSi will be reached,


Signed 21 Boat

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Thank you very much, my friend for your free consultancy. If you need something here in Brazil, you can count on me. My email is: [email protected]

[21boat]

Thank you for the invite. May visit some time and will look you up.

If there are any other questions you have especially in concrete post back. I can also help you to figure out yardage and slump in the concrete.

My project this week is sawing through concrete floors in rooms and going to pour new footers. Lay new bearing walls and concrete columns and concrete lintels. That supports the first floor. The second floor rebuilding new concrete archways and concrete railings and balusters. The I'm jack hammering 2 1/2 foot off the side of a 2 story concrete building and transferring the load of the building to the new walls etc.

A lot of vertical forming and concrete arches to build.


Concrete is second nature to me 30+ years.