Fibers vs mesh

[Captain Concrete]

I've been asked to do large haul road and yard area, the formation has been down for years and is solid were going to do 175mm on the haul road and 200mm on the bow mouth and turning area, with expansion/contraction joint every 5 m. The customer has asked for fibres which Iam not keen on, I have advised 252 mesh, they tell me the amount of fibres needed to get it up to 252 standard is 2.5kgs per m3. We have made some large concrete blocks with this amount of fibres and Iam not convinced. the fibres we been recommend are call Forta and the 54mm in length. Anyone have any views or experience on this? Thanks in Advance

[Brucieboy]

When you say asked for, do you mean "recommended" or "specified"?

Who has determined that 2.5 kg/m3 of Forta macrofibres is equivalent to A252 mesh (one layer or two)?

Being an external road (presumably to take hgv's or similar), what about air entrainment? BS 8500 recommends a PAV2 (C32/40, 340 mcc, 0.45 w/c ratio, S3 slump, plus air entrainment) for external paved areas subjected to heavy use by rubber tyred vehicles.

Are you going to use a volumetric mixer or traditional ready mix drum mixer and who is responsible for adding the fibres?

[Captain Concrete]

The Farmer/customer has asked for the fibres instead of mesh, the fibre people say 2.5 kg per m3 is equivalent to one layer of A252 mesh, having just chatted on the phone and explained what its is going to be for they are going to revaluate it. Think were going with the mesh its tried and tested over many years, just wonder if anyone has used fibres in such a situation.

[lutonlagerlout]

you 2 are the concrete experts but I would always favour mesh over fibres
farmers in my experience are always trying to save pennies

I reckon the fibres are a good addition to floor screeds and maybe a good idea in addition to mesh but I always go with the tried and tested

cheers LLL

[Brucieboy]

Fibres versus mesh is mostly dependent upon personal choice / application.

Macro plastic fibres (or steel fibre alternatives) for use in commercial type ground floor slabs, e.g. DIY stores, distribution warehouses etc are becoming more popular primarily due to speed of installation - time is money. Just prepare the base, add the fibres at the mixing plant or on site (generally with a dosh of superplasticiser) then place the concrete.

The quantity of fibres added per m3 should be determined by the manufacturer (this service is normally free of charge) based on loading requirements, ground conditions, grade of concrete etc. Care needs to be taken if the slab is subjected to any point loads.

Correct addition of fibres to the concrete mixer is also critical to success. In most cases this task is undertaken by the concrete supplier (unless something out of the ordinary). Bag / box sizes do not always correspond to the dosage per m3 so care must be taken to ensure the correct quantity is dispensed for each load.

Mesh is fine as long as it is placed in the correct position. All too often it's just trampled in under foot without any care generally ending up where it serves no purpose and the integrity of the concrete suffers.

Do not confuse macro fibres with the normal monofilament ones - they have different uses. The latter are usually added to the concrete at a dosage of 0.9 kg/m3.

[Captain Concrete]

Thanks Brucie, LLL right the Farmer wants to save a few pennies, but has the belief that fibre would be as strong, while also being more convenient and I can see it would be easier to lay no sheets of mesh, no chairs, no cutting but will it really give the same amount of reinforcement as 252 mesh? Iam with LLL statement "I reckon the fibres are a good addition to floor screeds and maybe a good idea in addition to mesh but I always go with the tried and tested"

cheers AC

[GB_Groundworks]

factory we are in recently has a 150mm floor no mesh but metal fibres like 60mm long x 3mm with an m shape on each end

id always go mesh for this spec as its bound to get some serious loads on it

if it goes wrong he's going to be blaming you, no engineer involved?

i just priced 270m2 yard patch up for big steel fabricators yard for 40ton hgv and 12 ton forklifts spec from engineer was 200mm c35 with 1 layer a142 for crack control on 200mm consolidated type 1



Edited By GB_Groundworks on 1417654201

[lutonlagerlout]

the bow/bell mouth to my mind is the area where most loading will occur
big lorries and turning forces

maybe steel in this area and fibres in the rest?

I can emphasise a little as most farm haul roads are long we dug a water main beside one in soulbury that was .7miles long

imagine the amount of concrete in that

LLL

[Captain Concrete]

Cheers Guys going to go with 252 mesh I will get some photos up when we start, in the new year.