Adding mixing water in the field 2

[legner]

I am wondering how to control the addition of water in the field. Contractors often want to add water to make a mix more workable, but doesn't this compromise the w/c ratio? Neither ACI 318 nor ACI 117 seem to indicate a tolerance for w/c ratio. Any comments?

 

[bb29510]

You hire an indepent testing lab to argue and fight for your cause while the placement is being done.

 

[Ginger]

Dear Legner<br>
<br>
this subject has been discussed under the "Admixtures" field so I suggest you look there for a good set of opinions and advice on this matter. Generally, the advice is DON'T DO IT.<br>
<br>
Regards<br>
<br>
Ginger

 

[JFCPEng]

Look at the delivery docket from the supplier, and if no record of addition of water is made, reject the batch, or the Supplier(Careful as you may or may not have that power). Often the first few trucks will arrive dry in order for the batch plant to get it right.In this case a tester should authorise it. This is normal and desirable. Have you ever noticed poor concrete supplier's trucks all seem to have broken water meters? If unauthorised water is added, reject just one truck at the Supplier's expense and it will never happen again, even though that truck's contents may still end up in the pour a half hour later on a new docket. A camera taking photos (or a video camera is excellent) of Contractors is amazing for lifting quality without a single word. Also, reject the concrete test samples if taken before water is added, as this is not a true representative sample, at the Contractor's expense. Request authority from the designer to use plasticiser and specify that on all concrete pours the Contractor must have adequate plasticiser on site to suit any approved concrete.<br>
The difficulty is rejecting the Product during construction.<br>
The QA ISO Standard has a)Acceptance, b)Acceptance with rework, c)Acceptance with concession, d)Rejection as the "power" you need. Prove it by video and recording "Indeterminate quantity of unauthorised water added" and use your own sample cylinder of concrete to reduce payment to contractor on c)Acceptance with concession of defective materials.<br>
Contractors (usually poor quality anyway) who rely on "add water" usually rush Engineers with an artificial urgency. Defective material may need removal from the work! At the Contractor's expense. Have you ever heard about jackhammering out the 13th floor? A good contractor soon wins a reputation.

 

[bb29510]

You will not be able to control water in the field nor will you be able to control supplier. You can reject a truck but in a couple hours you will be looking for a new job. the contractor owns the job till he sells to the client. If he wants to pour wet that his choice. How do you handle water, you learn the concrete track record and see what the mix will hold. You talk contractor into water reducer. You fight tooth and nail with finishers. It is a game to see what they can get away with. You have to find the happy media between too dry and too wet. Most mixes will handle 6 inch slumps with no problem. This is what I do for a living daily.

 

[JFCPEng]

The Client owns the job and has the right to reject accepting defective materials at the point of inspection. The cost of delay and material is Contractual and cost is not an Engineering term in design or Specified Quality.Try getting a truck driver to tell a Court the Engineer was wrong. You may well pour concrete like in Turkey, but try putting defective material in a bridge, in front of a good Engineer! You may value your paypacket. I have walked off three projects I was asked to sign for after a shoddy pour. The bridge will be around long after you get your last paypacket.You do it for a living daily. I do it for a Profession, always! How often have you built a bridge, a nuclear faility, the largest zinc or gold or copper mine in the world. How about 8.4 recorded on the Richter scale. A 6 storey retaining wall designed and constructed in 2 weeks! You earn a living, some people care what they are charged to provide. Ever poured concrete in 48dC or 0dC or ordered USD600,000 of plasticiser at 14000ft above sea level? Keep "earning a living"! Some Engineers know what unauthorised addition of water does!The Client owns the product and the materials used forever, and the "Engineer" holds himself out as an expert-refer ISO/QA, and has the Professional obligation to ensure the product complies, the intent of the design is maintained and a duty of care to the end user and Client. Rejection is easy. The vehicle from the QA ISO Acreditted Supplier does not have a calibration Certificate on the water meter, reject the product on this basis, due to faulty calibration. Tell me if you would sign for a Certified Structural weld by a trades assistant! Hope your Mum lived in Turkey during the earthquake, because anyone can sign a piece of paper for a living, just as anyone can turn a blind eye on duty!<br>
You can reject counterfeit reinforcement mesh or dirty reinforcement can't you! Oh you sign for a living!

 

[JFCPEng]

"Most mixes will handle 6" slump"! Fine! What if 3" was specified? Do you sign? Cracks, diminished durability, heat of hydration! Oh fine, another Korean shopping centre with 600 dead, or a Chernobyl on a fault line, Hong Kong rail failure. What a loose statement,6" is OK! The question was "doesn't this compromise w/c ratio"? No, "I sign for a living" does not fulfil the intent of the designers, nor does it alleviate the problem.!!You are unable to control addition of water in the field is not the correct answer. You have the obligation to ensure the Client obtains what he is paying for, or just sign for a living? I've poured at 14000ft, in 125deg F, at 32deg F, to tolerances allowing for shrinkage. Don't accept defective product or noncompliant Suppliers, ever! After all it is your signature!

 

[bb29510]

what bug got up yours. The question was How do you control water in the field. My reply was you have to play the game with the six grade drop out finisher in producing a good product with out them knowing. I reread my statement and did not see way I sign off anything. If I get a bad load i notify the general and 90 out of 100 he keeps pouring. I take samples and let the test speak for them selves. Here we ( the independent testing lab) do not own the concrete so if we reject a load without permission we get change ordered. here it is alwat the contractor duty to reject all I can do it bring it to attentions. Government jobs are different the tech has more power. Also the 6 was refering to the ability of the mix it did not say everything must be poured at six it meant if the spec calls for 3 and you know it will hold a six then a 4 1/2 is no problem, the finisher think they are winning. Oh I wish I had the power to hold to the spec but I been replace on too many projects. And I do not sign off anything if its bad my clyinders will reflect that its bad. I really do not care how many slab get jack hammer but the question was "How do you control water in the field" My answer was you fight tooth and nail you argue . Its not a pretty sight. And the question did not refer to the highly controlled projects like a nuclear plant or dam. I was refering to the everyday project where the contractor has undercut everything to make a profit. I stand by my answer Know your suppiler, your finishers,and your mixes. and fight.<br>
<br>
Johnnie Browne aci II brownbagg@hotmail.com

 

[JFCPEng]

Sorry if I rattled you, but I'm livid when I see on TV another concrete building collapse on sleeping men, women and children because someone signed without considering them. If a worker fell in the pour, you would save him even if you had to stop the pour. 50 years later when the concrete is structurally defective due to "turning a blind eye" to bad practices and a 1:500 earthquake squashes all the people asleep in the building, ask the Property Developer or the Contractor who signed? The duty is very very important and the practice whilst widespread could be readily avoided by<br>
a)all trucks have Certified calibrated water meters (ISO9000) and truck drivers were dismissed for adding water unauthorised. Otherwise reject the truck, before it discharges.<br>
b)water may only be added after a tester or Engineer authorise it on the delivery docket and record it, signed.<br>
c)Contractors supply their own plasticiser at their expense and obtain approval prior to pour, by submitting a Pour Procedure for approval with the tender document. This should state who authorises the addition of water and on what criteria, and makes a Contractor responsible. See how fast the practice disappears!!!!!!<br>
d) Only use competent Conractors and Suppliers.<br>
<br>
It is the Supplier and the Contractors' responsibility to verify that the finish product is as Specified, not the Client's or the testers or you, under ISO9000. You merely witness what happened, and by letting the practice occur, accept the defective material at who's liability?<br>
Government jobs are not really different. Concrete does not know whether it is in a bridge or in the bony base of a column under 40 storeys. Best Practises Supplier and Contractor is a cost worth paying for.<br>
Don't argue, have the power and the knowledge and the mechanism for acceptable practices only, in place always.<br>
A good Contractor does not fight, he complies with the intent of the Specification and Best practices, for his reputation for quality at a fair price is tomorrows work!<br>
Sorry if I upset you, but the original question has immense implications to the reputation of concrete as a preferred material in construction.<br>