Re bar again, is this any good?

[proton]

Never found out how much it costs but saw the sort the builder is using on another house doing the same job of re covering sunken driveway. This re bar looks more like chicken wire, it rolls up! Surely this is not as good as heavy rigid re bar I was thinking of?

 

 

 

 

[Lucky Bones]

Ask the uncle. He has all the money.????????

[Will B Good]

Never seen them use anything else for the likes of driveways........but then again I see a lot cracked, sunken driveways.

[brianthainess]

They use this even on major roads.

[Bill97]

Is there a question?

[OneMoreFarang]

Have you considered asking an engineer? 

[proton]

41 minutes ago, OneMoreFarang said:

Have you considered asking an engineer? 

I asked my brother in law in the UK a retired civil engineer, he just laughed, but he does that about almost any Thai construction topic

[Crossy]

Wait until you see them use bamboo

 

Seriously, for re-finishing a driveway on ground that's reasonably sound then the mesh is just fine, it's not like you are driving big trucks over it, are you?

 

 

[Lacessit]

Mesh pictured is fairly useless in preventing cracking. IMO the diameter should be 1.5 to 2 mm, that stuff looks like < 1 mm.

 

There are guides as to what to use in various applications.

 

https://www.ausreo.com.au/reinforcing-steel/

 

[steven100]

For a driveway ,  that mesh is fine,  it's used on many construction site pads etc .....   he's not going to use heavy duty re-bar for a damn driveway that's for sure . 

[DSBones]

It's ok for lightly trafficked driveways.  It's primary purpose is to stop cracking so should ideally be placed in the top of the slab within 40mm of the surface. 

I have a degree in civil/structural engineering but my specialism is not reinforced concrete design. I just know enough to be dangerous. Hope this helps. 

[steven100]

5 minutes ago, Lacessit said:

Mesh pictured is fairly useless in preventing cracking. IMO the diameter should be 1.5 to 2 mm, that stuff looks like < 1 mm.

 

There are guides as to what to use in various applications.

 

https://www.ausreo.com.au/reinforcing-steel/

 

that mesh is bigger than 1.0mm ....  I would say it's  1.5mm by the looks

[bunnydrops]

The real problem that I see is that it is not installed correctly. I see them just lay it on the sand. It should be up 1/3 the thickness of the slab. Sometimes I see them reach down and pull it up, but if they miss a spot, it is useless. Should be supported with little blocks before the pour.

[Bday Prang]

              It really depends on one main factor, that being the load bearing capacity of the ground beneath the concrete is it solid and stable , or spongy and soft. ?

              If as you say they are redoing an old existing driveway that's already cracked its likely that the ground is already well compacted from years of use and therefore further settlement is unlikely (its also advisable to break up the existing concrete in to even smaller sections prior to placing the new concrete to help  prevent any further movement and possible "shadow cracking") 

               This is really a classic Thai solution to a Thai problem in so much as its probably actually cheaper to do the job on the cheap twice  rather than pay a fortune doing it properly once.  The reason for this being the price of bringing in a machine to properly compact the original ground and the price and availability  of the "real" reinforcement that would be required 

                The steel mesh shown in the photo is a little on the "light" side but good enough for what it is probably actually being used for, I think it costs around 1500bt for a 50m x 2m roll so its quite cheap and can always be "doubled up " if required. I've seen heavier gauge mesh advertised at Thai Watsadu (at heavier prices) and it all comes in rolls

               Its quite difficult to get it really flat so there is no point in being too pedantic regarding at what level within the slab it is situated, the main concern (obviously) is that its not sticking out of the surface !

               If the ground is solid, the concrete is only  acting in compression, as it transmits any imposed loads straight to the ground below, concrete is very good a resisting compressive forces, actually no reinforcement would be required at all , and the concrete required for  parking an average car would only need to be about 50mm thick, proof of this being that many houses in the uk have their driveways constructed of 40 to 50mm thick unreinforced precast concrete paving flags although the fact that they may only be 60cm x 60 cm helps to mitigate any cracking from any slight settlement. and in the case of using an in situ slab I'd recommend  a minimum of 75mm (100mm would be better)

               If using in situ poured concrete on strong ground, the steel mesh is only really used to prevent any cracking which may occur as the concrete shrinks slightly whist curing, and to resist any later cracking due to expansion and contraction as a result in changes of temperature.

 

                 If the ground below is weak then different forces are acting on the concrete when weight is applied, primarily tensile forces, concrete is not too good at handling tension, as can be seen when a guy karate chops a (unreinforced) concrete slab in half He would not be able to do it if the concrete was reinforced, as steel handles tension very well,  

                  So in the case of weak ground, a minimum of 150mm thickness of concrete would be more usual and significantly more steel would be required and the cost would increase vastly,

A flat sheet of mesh with 10mm bars at 150mm centers each way would cost, I'm guessing, around 4000bt  for a standard 2.4 x 4.8m sheet with probably 2 layers required,  mesh like that might take a bit of finding too,   it wasn't readily available at homepro last time I looked

 

                   

                 

                 

[Bday Prang]

2 hours ago, steven100 said:

that mesh is bigger than 1.0mm ....  I would say it's  1.5mm by the looks

Its at least 2mm  less than 1mm would be akin to piano wire or a guitar string would it not?

I bought some identical stuff recently and it was sold as 2.5mm but my vernier gauge says between 1.9mm to 2.1mm for the bits I could be bothered checking out of interest.

 

[Lacessit]

2 hours ago, steven100 said:

that mesh is bigger than 1.0mm ....  I would say it's  1.5mm by the looks

You may be right; however, it still looks too flimsy to me.

[Cake Monster]

2 hours ago, steven100 said:

that mesh is bigger than 1.0mm ....  I would say it's  1.5mm by the looks

Thais use 2 gauges of this stuff ( or should )

3 mm Dia and 4 MM Dia

[Tropposurfer]

That photo you show us is NOT re-bar ... You're correct.

 

That is non-galvanised, what we in Oz call 'dog-fence' wire.

 

It's completely inadequate for any sort of laod bearing concrete slabbing.

 

I would not recommend a mesh diameter of less than 7.6 mm for any type of high load bearing  slab e.g. a normal car carrying driveway.

 

The larger the surface area the greater the mesh diameter needs to be.

 

If the driveway is to take high loads e.g. trucks, then I would recommend 10 mm bar.

 

*** Don't forget to make expansion cuts, or insert expansion jointing foam in between the slab sections e.g. at say every 2 to 3 metres intervals.

 

If you want the slab to stay n ice n dry lay builders plastic throughout underneath (this will also slow the curing and help avoid cracking).  

 

For a footpath with normal foot-traffic you could go as low as 4.6 mm diameter mesh - don't forget your expansion cuts.

No offence to Thais but their structural building knowledge and application generally sucks.

[unheard]

24 minutes ago, Tropposurfer said:

If you want the slab to stay n ice n dry lay builders plastic throughout underneath (this will also slow the curing and help avoid cracking). 

A layer of striped-blue plastic sheets? Instead of sand?

[Tropposurfer]

8 minutes ago, unheard said:

A layer of striped-blue plastic sheets? Instead of sand?

Sand? No. Serves ZERO purpose.

Just make sure the ground is evenly screeded shovel levelled fairly evenly (no big rocks or rises throughout the area) before laying forms, plastic, rebar chairs, then the mesh.

 

Slab at no less depth than 125 mm for a cars. Again, if for heavy loads then 150 mm thickness.

Some might say 100 mmm is fine but better to add the 25 mm and know it will take almost any load you might put on it without cracking.

 

*** If the temperature is hot like it is now, or the pour is in direct sunlight, I would fine spray the slab with the hose nozzle to dampen it lightly and do it with a gentle spray so as not to mess up the textured (broom) finish. Say; gently every half hour or so for the rest of the day till night falls. This will help slow the sure further and deter cracking. 

 

The reaction of the lime in the cement and the other additives they put in modern crete creates some exothermic reaction (heat) and this will accelerate the curing somewhat, especially in hot climates.

The dampening with a fine mist spray of H2O helps correct this.

 

I wouldn't use the slab for a few weeks if it were my place. Walking across it fine after a day or so but driving no. Better to be safe and let the slab 'settle' and cure., 

 

Plastic: Just builders plastic. It usually comes in plain black, or orange here (same colour in Aussie). Comes in a roll, thick and tough. Folds out to a 2 meter wide strip.

Overlap  @ about 150 mm to 200 mm.

 

Make sure the concreter uses concrete chairs too, simply pulling the mesh up by hand, or putting rocks under the mesh during the pour is useless and the mesh will sink to the bottom, and from the concreter walking on it while screeding.

This sinking weakens and affect the structural integrity of the slab.

[NanLaew]

8 hours ago, Crossy said:

Wait until you see them use bamboo

 

Seriously, for re-finishing a driveway on ground that's reasonably sound then the mesh is just fine, it's not like you are driving big trucks over it, are you?

 

 

If in doubt, make a second layer that's offset from (or orthogonal to) the original so the 'grid' is tighter.

 

Now waiting for the Australian civil engineers to spit the dummy.

[unheard]

1 hour ago, Tropposurfer said:

Sand? No. Serves ZERO purpose.

Slab at no less depth than 125 mm for a cars. Again, if for heavy loads then 150 mm thickness.

Some might say 100 mmm is fine but better to add the 25 mm and know it will take almost any load you might put on it without cracking.

 

Plastic: Just builders plastic. It usually comes in plain black, or orange here (same colour in Aussie). Comes in a roll, thick and tough. Folds out to a 2 meter wide strip.

Overlap  @ about 150 mm to 200 mm.

Thank you for the info.

Will ask my builder to follow your advice.

[bangkok19]

Most definitely using a reinforcing of that gauge would contribute to cracking.. especially if heavy vehicles or even a car use it.

The other common problem that causes cracking and subsidence is they don't compress the base material whether it be clay, roadbase, sandy soil etc.  Also the lack of separate slabbing with expansion joints in between...  the crack can increase instead of being confined to the 1 slab section.

On our farm, the concrete pathway between house and side wall (8ft wide) sunk at a 10 degree angle because the base was never compressed...  and being very high in clay, it contracts (shrinks) during the dry/cool season.  Luckily it's sloping now towards the wall, and not the house. 

[Andycoops]

Standard stuff here for paths and drives.

Mine has been fine for 14 years.

[Srikcir]

I agree to use of proper mesh thickness and subsurface compaction, ie., 110%. Depending on the total surface area, grooves should be made in the surface to assist in minimizing any crack propagation caused by expansion and contraction of the concrete to prevent an uneven surface and minimize area to be repaired.

[unheard]

14 hours ago, Tropposurfer said:

Plastic: Just builders plastic. It usually comes in plain black, or orange here (same colour in Aussie). Comes in a roll, thick and tough. Folds out to a 2 meter wide strip.

Can you (or anyone else) please post a link to this product?

I was searching around Lazada and HomePro but coudn't locate anything similar.

All my searches have returned thin wrapping plastic, masking films or greenhouse covers.

The greenhouse/shed cover is being the closest match.

[unheard]

3 hours ago, unheard said:

Can you (or anyone else) please post a link to this product?

Never mind.

Greenhouse cover plastic is thick enough to use in place of builders plastic - not as thick but should suffice.

[Kalasin Jo]

Our driveway was concreted using this kind of mesh that came in rolls. I'd hardly call it re- bar! The mesh was laid on sand over the ground which itself was imported fill material, then concrete pour from a mixer truck and levelled with  lengths of wood planking by men in wellies. There were 3 pours with a waiting time of about 30 minutes between each for the mixer to return to base and refill. I've watched this process so many times here from house builds like ours to highish condo construction. Now In it's 8th year the driveway has done well, except for cracking which directly follows the unfortunate irregular line between one pour and the next, mesh notwithstanding. I guess caused by the set time of the concrete in this heat and the interval between pours creating a weakness. There is no discernible difference in levels so it's not a settlement issue. I think each pour should have been straight lined and expansion joints inserted between each pour would have avoided this. Now these cracks are degrading and getting wider and anticipate will need cutting out and refilling which will be a tedious long winded job and may not last long either. Helpful advice would be appreciated.