It seems that you, "has been advised as 3.6 kg/ cubic mtr or 6 lb/cubic yard" already. Presumably by someone who knows the materials and local conditions.

I agree with CaptMoosie, don't try to do it on the cheap.

I agree with you ..that seems way high usually fiber comes in prepack bags of about one liter volume ---fairly highly compressed--- and you put one or two per cubic meter --bounce that quantity off your material and see how that stacks up-- whatever you do be sure it is polyester fiber not glass fiber you are putting in a shop floor as the mechs will die a thousand deaths on the bed of nails if you use glass.

Soy Cowboy

somewhere in the Balkans

Thank for ur reply

It is polypropylene fibers.

I felt it high dose as we got difficulties while leveling the surface with a straight bar.

Power tools were created to either improve hands on methods or do work that was difficult to impossible with out them. If you are having problems placing and finishing said concrete, you should bring the matter up with the Engineer. All too often Engineers look only toward the end results, like strength, flexibility, etc. and refer to the known specifications published in manuals. Many times they actually don't have any experience with the difficulties in constructing that which they have engineered. That being said, the Engineer must be notified of your difficulties and provide a solution to resolve your problems. If you cannot place this cement satisfactorily with the proper tools and labor, then the Engineer is responsible to instruct you in just how he wanted it done. Issues such as this and the methods for resolving them should be spelled out in the specifications created especially for this project. If it cannot be reasonably accomplished, this is a problem for the Engineer, not the placement contractor to resolve.

I would expect that you are not using a vibrating power screed to settle and level the mix. Another issue that comes to mind is that Engineers are responsible to determine the length of time that the mix can be mixed before it can be placed, EX: time and number of revolutions of the mixing drum. Clearly there is an optimum amount of both for the product to perform as designed.

Having water available to keep the hydrating mix moist is a good thing, but adding water beyond the design parameters will weaken the strength or shorten the life of the finished product though a little more water will help make the mix more workable it may not be permissible..

"IF YOU CHANGE ANYTHING, YOU JUST BECAME THE ENGINEER OF YOUR OWN PRODUCT AND ARE RESPONSIBLE [LIABLE] FOR THE RESULTS."

TMF

If you are having a workability's problem with the specified concrete mix, then discuss the matter with the Design Engineer together with possibly using a mid-range to high-range plasticizer admixture. Be sure to file a RFP with the engineer as well receive his/her written approval to change the mix design. You may have to submit for approval test results of a proposed mixture pursuant to applicable sections of Contract Documents.

Hope that helps....

Hi Allsai,

The figures you quote do seem a little high, but, it may need the extra strength and flexibility this dura-fiber will give, and the constituents of the concrete pavement will also be designed for the use of aircraft and to minimise any damage to any part of the aircraft.

If I was you I would query the figure, at least then they can double check and be sure the figure is way too much or correct. A simple phone call could take all your worries away, OK?

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I looked at the Dura-fiber Inc site and they recommend ¾ Lb to 1.5 Lbs per yard³, but this was for a 'Dwelling' not for the use of aircraft

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Please see the site below which should help as it describes in detail how an aircraft bay should be paved.

The search field:

http://www.google.co.uk/search?hl=en&client=firefox-a&rls=org.mozilla%3Aen-GB%3Aofficial&hs=aNp&q=Ratio+of+Dura+Fiber+in+Concrete+Mix+for+aircraft+bays&btnG=Search&meta=&aq=f&oq=

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http://onlinepubs.trb.org/onlinepubs/acrp/acrp_syn_006.pdf

Take care.

Hello Babybear,

I was a project manager on an air field demo and repair about 10 yrs ago. The consulting engineering firm was PBS&J. The Engineer for the project provided specifications for the concrete that were almost impossible to live with. The base materials and compaction requirements were met with out too much adoo!

However the concrete, though designed just for modern airfields, was to be placed with a one inch slump. The ready mix was so stiff that it could not be rotated out of the truck fast enough to place it. Even with only one short shute in place, the crew had to rake it from the truck. Two trucks standing by had to be sent back to the batch plant as the concrete was already too "HOT" before the mix could be unloaded.

I suggested that the Engineer, who was on site for this pour, increase the slump requirements to 3" or add a plastisizer to the mix. He agreed to the additional water. This was good and it worked well. Then the subcontractor who was placing the concrete asked for an additional inch of slump and the representative from the testing Lab. concurred. I objected. The additional inch of slump was added and the mix became so fluid that that the crew placing the concrete was cause to work even harder to prevent the concrete from running away from the power screed. The next truck load and all there after was placed with a 3" slump.

This Subcontractor never again questioned my judgment for the placement of concrete or any other work he did for the company I was working for. The bad part about this experience is that the area where the truck that was unloaded with the 4" slump mix now collects a water puddle when it rains.

TMF

Hi Toomuchfun,

I have worked with the total incompetence of a 19 year old 'in charge' of making engineering decisions for a 500 home complex. He could not even work out the corner Axis' which were all pre-cast anyway!

I am not decrying all Engineers, just some who are thrown in the deep end with a pad and calculator and told to "learn", you know? He was not aware of different brick bonds and ways of laying drains. Had never worked with concrete and certainly had not come close to an "A" in geometry. He spent about 6 hours a day asking for verification of 'details' which any 'bricky' knew off by heart. I know this sounds OTT but he did not understand the water table on the site and, in one classic screw-up misread the plans and told the bloke in the JCB to dig to 27 meters, instead of 2.7 meters. The JCB driver said, tell you what, get your tape and we will measure the length of my backhoe. Then you can explain how I can dig drainage channels (for salt-glazed pipe), and why your instructions are to fit all drainage about 24 M (~60') below the 'WT'. This baby Engineer said whats "WT", and the digger driver told him Water Table. The reply was brilliant........ The Engineer said, "well, that is what I have worked out so can you please do it"? By this time most of the 50 odd people on site were listening on scaffold, and anywhere else they could perch. The digger driver said " do you have any knowledge of building underwater", because if I do as you say......... (I can't say the next few words, but they mostly began and ended in "F") we wont need waders, we will need scuba gear!

This meant nothing to the Engineer. So a bricky shouted "can you find a supplier of 30M (~90') scaffold poles and breathing gear please"? The Engineer went back in his cabin for half an hour. Then he went over to the bricky and asked him why he wanted breathing gear for laying bricks..................... etc etc..........

The whole point of all this chat above, is, ask the man at the sharp end of running the site, IE the Site Agent, before any baby Engineer starts to give orders. The Engineer stayed on site, but, (after a rollickin' from the site agent and his boss) the Engineer always started any future discussion with a very quiet _{"do you think this would work".......?}

Memories............................................................

Take care

Hello TMF et All,

Been there, done it too, when I was an Engineering Officer with the USACE involved with the rehabbing of concrete ramps and tarmacs at numerous military airfields. It's too bad that the Engineer of Record didn't specify the use of Mid-Range to High-Range plasticizer admixture for inclusion in the ready mix design from the get-go! Also, very surprised that the GC, the concrete Subcontractor, and the ready-mix concrete supplier didn't catch this omission in the submission of the shop drawings. Looks like a ton of balls were driopped on that project!!!! Do you remember offhand if test specimens where ever made of the proposed concrete mix prior to the shop drawing submissions? Any RFI's too???? If they had, the problems associated with specifying the use of a very low slump and resulant W/C Ratio that you encountered would have been most likely caught before actual construction began. Good thing you had the good sense to say no to the higher slump called for by the Sub!!!!

Typically, whenever I was on the jobsite and a contractor asked for addition of more water my answer was usually NO WAY, because it would result in a weaker concrete. If they wanted workability and high slump I'd agree to the addition of an already reviewed and approved plastizer only added at the ready-mix plant pursuant to the specifications and approved submissions. Many a time I had to turn around a ready mix truck when filed test results show an inferior product....and I made lots of GC's and Subcobtractor equally pissed and stark-raving mad at me in the process. My attitude was to them, well too freaking bad....follow the specs and we won't have any troubles now will we??? Let's work on this together and have a meeting of the minds before we proceed.....it'll save us lots of headaches and possibly save you money in the long run. OKAY????? HMM????? *LMAO*

Unfortunately, it would appear that the area of concrete where the extra water was added in the field which resulted in a 4-inch watery slump will most likely fail before the surrounding areas do. Equally surprised that this didn't catch the eye of the independent testing agency on hand (and red-flagged ) or the EOR, otherwise that section would most likely have been removed and replaced as deficient. If it was my neck on the line on that project and I was the EOR, I most likely would have taken a keen look at the concrete testing results for that area, including the matching 14-day and 28-day concrete cylinder breaks for compressive strength as well as Petrographic Analysis. If the break results show ant anomaly I would have ordered further testing be done such as Windsor Testing, and if need be, core samples taken and compression testing and analysis undertaken.

Just my 3 Cents, for what it's worth.....

Why 12'x12'x1' tiles? Why not a continuously poured slab? I should feel very uncomfortable handling an aircraft over these 1 Sq ft tiles. Understandbly the hangar being 'relocatable', the tiles are intended to be re-used. But could'nt you go up in size to at least one Sq meter / yard improving load distribution? You may have to improve thickness as well. What does your consultant say about that?

Dear Lodhi,

If you go back and re-read the original post made by Alisai, please note that the concrete pads being placed are 12 Feet wide by 12 Feet long by 1 foot thick (12' x 12' x 1'), not as 12 inches sqaure. You must have have misread the dimensional "tick marks". In a sense you are correct about load distribution in regard to the size of the pads (they are not tiles) if they had been constructed that small.

In regards to the correctly mentionad 12 foot square pads:

I seriously doubt that the aircraft hanger, if it would be removed in the future some time from now, with the existing concrete pads be utilized in a new future runway. Any decent airport engineer would notice right away on an airport rehabilitation project that the 12 inch thick concrete pads that were once in a hanger would be typically too thin to be reused for a runway pavement. The thickness of a rigid pavement such as a concrete one would have to be much thicker in a runway. Same goes for the subbase material in order to provide an adequate and stable foundation not only for load resistance, but also necessary for proper conveyance of sub-surface drainage away from underneath the pavement.

Getting back to the size of the pads placed in the hanger bays. It is not uncommon to construct such sized concrete pads for use in hangers, aprons (ie, tarmac), and in some cases in taxiways because the impact force due to rolling aircraft landing gear in those pavement locations is much less greater than what would be found in an active runway where you have much greater applied main landing gear loads at touch-down plus the impact forces due to aircraft landing velocity. In the case of the hanger floor pads, the loads imparted by the aircraft can pretty much be considered static because the rolling speed in very small, hence the impact factor is equally small.

Please note that not all airports are designed equally either, and especially in respect to acceptance of the largest aircraft flying today or into the near term future, such as the Boeing 747, Boeing 777, Boeing C-17, Rockwell B-1B, Boeing B-52G/H, the McD widebody such as the KC-10 tanker, one of the new Boeing and Airbus jumbo-monsters, a C-5B Galaxy, and the Russian AN-224, etc.. Those super heavies are in a class all their own. It should be noted here that a majority of airports are built only as Regional Airports and cannot usually accept the super-heavies, where the entire design is based on the acceptance and handling of lesser-sized aircraft, hence lesser aircraft landing gear loads. At these airports you'll notice that the runways widths and lengths are much smaller than say an International Airport or a major military airfield, such as a former USAF SAC base or some of the larger current USAF bases servicing large transports and strategic bombers.

Just my 3 Cents added for what it's worth....

Dear CaptMoosie

My apologies. I did misread the dimensional "tick marks". 12 feet is more or less the standard practice inside hangars and helipens. Thanks for additional info on RWYs.

Dear Lohdi,

You are very welcome. Please have a great day!

Signed,

CaptMoosie