Adding mixing water in the field
Adding mixing water in the field
(OP)
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?





RE: Adding mixing water in the field
ACI does not have a tolerance on water-cement ratio because acceptance is based on the 28 day strength, not the water cement ratio. As long as the concrete meets the performance criteria (in this case strength), it is acceptable.
Workability should be considered in the mix design. If workability is a concern, the ready mix supplier may well need to add mid or high range water reducing admixtures to meet the contractor's workability needs while maintaing the w/c ratio to meet your strength needs.
RE: Adding mixing water in the field
RE: Adding mixing water in the field
RE: Adding mixing water in the field
We are typically geared to look for high slumps as rejects, but dry mix can be problematic also. In formed walls, voids are likely due to inadaquate consolidation or perhaps segregation due to over vibrating the dry mix into place. In pavements or other flat work, a dry mix usually finishes poorly.
RE: Adding mixing water in the field
my background 17 years indepent testing lab field technician. concrete,soils, asphalt
with the high price of fossill fuels,cement ,labor, equipment concrete producer are doing everything to cut cost. while two producer in the same town are turning out a good product there is alway a third producer that is cutting back on cement and over doing he fly ash and forgetting about the admixture. so he is producing a 3000 that will barely hold a 4 slump. then the unskill, uneducated, uncontrolled concrete finisher start dumping the water to it. contractor will not argue because afrraid they will walk. producer are scare stiff. cold joint are more problem than returning loads. so i must step in and argue and look like an ass. must fight with drivers, then finisher, then contractor just to turn a good product. if the sample do not break its alway the lab. never the stupid un skilled i do not give a damn finisher. think about it the total srength of that skyscaper is in the hands of a six grade dropout finisher.
RE: Adding mixing water in the field
RE: Adding mixing water in the field
1. Our specification requires that the builder must provide the mix design to us for our approval. We then get to see who the supplier is. If there is any doubts as to the suppliers credibility and expersience then it is rejected and another supplier/mix design is requested. You get to know the names of the shonky suppliers in town and hence steer clear of them.
2. For most large construction jobs, it is a QA requirement (in Australia) that the builder holds what is called "toolbox meetings" whereby all the sub-contrcators for a particular aspect of the job are put in the one room and the construction process discussed in detail. These are veryuseful meetings and I normally try to get one of my engineers to attend this. It gives us a good chance to table our expectations for things like reo, PT and concrete supply.
3. For the larger concrete pours we would normally have at least two engineers on site on the day. One checking the reo (and any changes you requested) and keeping an eye on the laying and compacting techniques and the other keeping an eye on the concerete supply. As one is linked to the other I have both engineers communicate with each other via two way radio.
4. If there are any doubts as to the concerete supply then it is rejected and the truck sent away. A good tip is to note the rego of the truck as they have been known to switch drivers and simply drive around the block.
RE: Adding mixing water in the field
Tom Bryan
bryantc@mail.icongrp.com