I was recently on a bridge deck pour and the pump boom was set up for the placement so the concrete did a free fall through about half the length of the boom and dropped onto the deck.  This of course drastically reduced the measured entrained air content when sampled on the deck, and caused 60 cubic yards of pricey DOT type concrete to be rejected.  I suggested using two 90's to form a "knuckle" on the end of the discharge to prevent the concrete from free falling through the line (a technique I have seen used many times before).  The pump operator told me that OSHA had banned that practice recently.  Can you confirm this?  Do you have any other suggestions?  Thanks!

Pump faster so the boom pipe are full of mud and the end hose , if the 5" not get full (it should be) put a 4" endhose on . Call the RM-plant to put more air in the mud , if he lose 2% put atleast 2% more in the mud from the RM-plant . The operator , didn't he know how much air he lose ? I dont lose more than 0.5% on My Putz M46-5 when it is A-frame , in Z I lose les than 0.5% . My old Schwing M42SX 2525 longrock was the same not more than 0.5 , often les than 0.5% . I alway talk to the testingguy so I know how much I air I lose . From every plant I get mud . My 2 cent....

First idea-use a telebelt if access permtis it.  air loss on my belt is 0% on my belt at hose.  if belt is not a viable option, could you configure boom in such a way that tip section is pumping up and take sample while pumping as opposed to swinging to test area and dripping into wheelbarrow..  i have even laid tip 90 on ground and picked the tip hose up and pumped into wheelbarrow to help reduce freefall.    ive never seen this done but would a rams horn at top of tip hose be effective?

Simple - The test man took the sample wrong.  You probably swung off to the side and stopped pumping and waited for him to put a little in the wheel barrow.  Of course when it splased into the wheel barrow all the air bubbles burst.  You have to have the test man standing by the pour location and when there is a steady stream of concrete swing it over to the wheel barrow.   If the test man was not aware of how to properly take a test then the test lab should pay for the concrete

Sometimes they require you to boom down off the bridge to them or back to the edge - when that happens you have to tell the super that you need to pump out half a yard so the test won't be tainted.  Once again it is the test people who are screwing up.  

If you have to pour slow and cannot keep a steady stream of concrete and it is falling then just boom down and put the hose on the deck and let the hose man pick up the end - keep the hose in a u shape and there will be no air loss.

I agree with Biloxi, that it's not a represenative test! It should be done with an airpot midstream, and a Chace from the deck! Do your own calculations, test with a Chace at the mixer, then on the deck! Double 90's ARE illegal, as per OSHA! And use a 5" to 4" reducer, or a reducing hose! But what I'm really hoping, though, is that you are not trying to use this forum to throw the pump company or operator under the bus!

PS an A-Framed boom cannot freefall through 1/2 the boom as the elbows between the sections prevent this!

It's always a contentious issue, where to test for air, and the method.  One construction company I worked with a lot said that entrained air was merely a 'specification test' and had little to do with material as placed.  Think of how test cylinders and how differently they are made compared to concrete in place in a wall, and the evironment in which they are cured compared to insitu conditions.  They felt entrained air was part of the material specs and it should be taken at the end of the mixer's chute, as that was where the material supplier's responsibility ends. How can you hokld the RM supplier responsible for loss of air due to the placing method?  And have them pay for the admix and eat the time to re-mix all the time?  If you want an as-placed test, then shovel it out of the wall or slab after vibration.  And handle it with kid gloves....  

The engineering firm couldn't argue with thet logic, the spcs have been written as material supply, not in place.  The rookies that they send out usually had no or very little real-world experience in sampling.  The site super would video just how badly then mis-handled sampling, testing and cylinder preparation.....Nerves were frayed, threats of shutting the job down made, but nothing ever made it out on paper, the job went on.  Everybody wants to throw their (percieved) weight around, but nobody wants to put it in writing, that's what holds up in court.  Can't deny the letter, or memo with a signature to the Judge.  And the owner just wants his building on time and on budget.

Ever heard of someting called reducer?

Not sure about the crete over there, but the Vic roads mix here in Melbourne is sticky enough to fill the hose even at idle so a double 90 would be no advantage anyway!

Contactor should challenge the qualifications of who is doing the testing, demand to know how long they have tested and who trained them to test and why they test the

way they did.   On private jobs it is usually a minimum wage tester.  On public jobs like bridges some states use an independent firm and others use their own personnel.  Usually the state inspectors have at least one (I have seen up to 7 on one bridge pour) that has real expierence - the rest are engineers right out of school and have no real life expierence.

Not one single person addressed the question. The answer is YES, OSHA has banned the used of metal ends on boom hoses. Now, tell him how to reduce air loss.

The ACPA has two great reports on the topics here, one Air Entrainment report, only cost you $50.00 if you want to read it or you can join the ACPA and its free.

http://www.concretepumpers.com/content/air-entrainment-report

The Second ACPA report you should get is the Double S-Bend elbow or Rams horn report. it will only ocst you $2.50

http://www.concretepumpers.com/content/double-s-bend-elbow-or-rams-horn-can-be-deadly

Personally i would let you have them but I guess you have to pay Caesar what is due Caesar’s

The NRMCA put this out for free, might also help you a bit, good read anyway, I dont know how up to date it is but its free.

http://www.nrmca.org/aboutconcrete/cips/21p.pdf

Here is other information

http://ndconcrete.com/Downloads/2011TechDay/Air%20Entrainment%20Issues%20of%20Pumped%20Concrete.pdf

Out here we had meetings with CDOT and came up with either using a 25' 4" hose strapped to create an S-Bend " not a very feasable way" or to use a 5" to 4" self reducing hose to allow for greater reduction length. You need to make sure you get at least a yard out of the boom so that all of the prime water is gone and at the very least have a full stream of concrete when the sample is taken. The best way is to lay the hose on the deck, pump until you have a full boom and smooth flow out of the hose then take the sample. We do a lot of bridge decks with different suppliers and I would say that I generally see an air loss of 2 to 3% if done right.

Doug - here is the quote from the OSHA web site in regards to the use of double ended elbows.

"This section does not explicitly prohibit the use of a double S-bend elbow shut-off valve at the end of a delivery hose."

In face it you search the OSHA web site looking for anything about concrete pumping safety this is the only part there is a reference and it is from a 2010 Question posed to OSHA.

Here is the entire OSHA mention of double ended elbow use - Why they even mention air hose couplings is beyond me.

Question: Does OSHA prohibit the use of a Double S-bend Elbow (a/k/a "Rams Horn") shut-off valve at the end of a concrete pumping hose?¹

Answer:Title 29 CFR 1926, Subpart Q, addresses concrete pumping. Section 1926.702(e) provides the requirements for concrete pumping systems as follows:

1. Concrete pumping systems using discharge pipes shall be provided with pipe supports designed for 100 percent overload.
2. Compressed air hoses used on concrete pumping system shall be provided with positive fail-safe joint connectors to prevent separation of sections when pressurized.

This section does not explicitly prohibit the use of a double S-bend elbow shut-off valve at the end of a delivery hose.

However, § 5(a)(1) of the OSH Act requires employers to "furnish to each of his employees employment and a place of employment which are free from recognized hazards ...." Construction work-practices that are prohibited by a consensus standard typically provide evidence of a recognized hazard. Notably, neither ASME B30.27-2009 § 27-1.10² or ACI 304.2R-96, chapter 3.6³, prohibit the use of a double S-bend elbow shut-off valve at the end of a delivery hose.

Your incoming letter attached an opinion from the American Concrete Pumping Association (ACPA), which stated, "the ACPA does NOT recommend the use of either [a double "S-bend" elbow] or a double-ended discharge hose." According to the ACPA, a double S-bend elbow is unsafe because, in the event of hose-whipping, the shear weight and mass of this shut-off valve can cause serious harm if it strikes a person. Although hose-whipping is a hazard associated with concrete pumping, there are recognized safe work practices that protect employees from this hazard. These recognized work practices are unrelated to the type of shut-off valve used. For example, § 27-1.9 of ASME B30.27-2009 provides that "[t]he horizontal slewing speed at the end of the boom shall not exceed 5 ft/sec (1.5 m/s)." Operating a concrete pump in accordance with § 27-1.9 of ASME B30.27-2009 is just one example of a recognized work practice that protects employees from hose-whipping.

Nevertheless, even where the safe work practices described above are used by employees, there may be scenarios where employees may still be exposed to the hazard of hose-whipping as a result of a concrete pump's design or configuration. In these cases, OSHA will examine how the concrete pump is configured to determine whether the use of a double S-bend elbow creates a recognized hazard to employees. Employers may, for example, mitigate the hazard of hose-whipping from a double S-bend elbow by keeping the double S-bend elbow shut-off valve elevated above employees' heads and attaching a single-ended discharge hose for employees to handle, while pouring concrete as suggested by ACPA.⁴

Sincerely,



Ben Bare, Acting Director
Directorate of Construction

One more mention of air loss - I have asked test people to let concrete sit for a while and then retest the same concrete for air loss again.  The air went up from the first test - This brings into question if the pressure of pumping the concrete forces the air into the aggregate?  I don't know but food for thought.

I looked it up and stand corrected. I attended several meetings years ago when the standard was being written. At that time, the language was not going to allow for anything on the end of a discharge hose other than a shotcrete nozzle.

That being said regardless of what OSHA says we will not use anything other than a shotcrete nozzle on the end of any hose. I would tell the contractor it is unsafe in our expert opinion therefore we would not use one.

We take the same stand on soft tremmees. Others use them for congested walls - we don't.

why not just use a 3 foot 5-4 reducer and a 10 ft 4" single end hose ? we have used these for years on jobs where loss of air was a problem, operate z boom in z configuration also helps.

Doug - I admire your company stand - Its great to hear - However do not discard the mud snake as a soft tremmie hose - It has been rated for burst pressure and if used and taken care of properly will solve some of your weight problems when hanging anything from the boom.  Try it out and I am sure you will like it.

The problem is people use them where they shouldn't Mike. So we chose not to use them here. We live in earthquake country so there's lots of reinforcement. Plenty of others will use them though. The operators who come to work for us after working at companys who use them thank us though. That speaks volumes to me.

Doug

All comes back to training - when, where and how you doing everything when it comes to concete pumping.  Training training and mor training with backup followup and documentation of that training.   If your people are not trained in the proper use of a layflat hose then by all means they should not use it.  Good for you guys.

From experience, I would rather use a tremmie hose made out of water discharge hose with a lower burst strength than a mud snake!  Absolutely no question there.