Negative effects of high water to cement ratio
Negative effects of high water to cement ratio
(OP)
Other than reduction in strength, are there other negative effects to having a high water to cement ratio? Such as additional shrinkage, cracking, durability, etc.
The reason I ask is because in my experience, most of the issues I see with concrete is poor consolidation. Additionally, I have rarely seen low break strenght results. Based on this, I would rather see a higher ratio to achieve proper consolidation.
The reason I ask is because in my experience, most of the issues I see with concrete is poor consolidation. Additionally, I have rarely seen low break strenght results. Based on this, I would rather see a higher ratio to achieve proper consolidation.






RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
Higher w/c also increases the porosity of the concrete. That's why it doesn't perform well with melting compounds. They absorb into the concrete and the chlorides wreak havoc.
There's other ways to improve consolidation of concrete. Increasing w/c should be the last resort.
RE: Negative effects of high water to cement ratio
Increasing water above optimum does not help consolidation of aggregates; it increases paste volume so the mortar fills voids which encourages shrinkage. Use a water reducing admix and if you need really fluid concrete, also use a viscosity modifier to keep aggregates from segregating as readily.
RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
And by allowing a more workable concrete, I was just wondering what side effects it was inducing.
I feel there needs to be some flexability in the field. I don't want soup, but I also don't want a 1" slump.
RE: Negative effects of high water to cement ratio
Ease of placement can be designed into the mix while maintaining a low w-c ratio. This can be done with high range water reducing admixtures (plasticizers/super plasticizers).
Concrete placement and finishing crews typically know very little about the properties and effects of their work on the performance of concrete. They know their experience with placement, what makes it easier and faster for them, and little else.
Have the mix designed for the application, using the largest coarse aggregate practicable for the application and then don't let them screw it up in the field by their desire to make life easier for themselves.
RE: Negative effects of high water to cement ratio
So we're not only limiting the water to make the concrete hard to handle.
RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
Other then that the typical shrinkage as mentioned by others.
RE: Negative effects of high water to cement ratio
I was the one designing the mixes, paying for them, leading the crew to cast and finish, to ultimately control shrinkage cracking, and permeability...it wasn't an online masters degree.
It all boils down to the lack of knowledge at the concrete plant to stray outside typical mixtures and the obvious drive to keep the admixture and paste contents as low as possible.
RE: Negative effects of high water to cement ratio
Additionally, I am not blaming an engineer for anything. From my field experience I have seen some engineers push back on the construction company very hard when it comes to adding water to the mix in the field. And it was evident when the forms were stripped, a lot of honeycome was noticed.
I on the other hand would rather allow some water on site to prevent this from occuring.
The purpose of this post was to gain additional insite to know what negative effects are more likley to occur when water is added in the field.
RE: Negative effects of high water to cement ratio
And btw, they will usually try to cast cylinders before adding water, so if crushing is really that big of a concern to you, then you may want to consider when they pull from the truck.
RE: Negative effects of high water to cement ratio
I always require cylinder, air and slump be from the mix after everything is added.
RE: Negative effects of high water to cement ratio
You might be on to something big, but I would hesitate to say that the ready-mix plant (or engineers, or contractors) doesn't know what they're doing. They might simply be acting cautiously and prudently, which is good. Most ready-mix plants stay within known mix proportion bounds for obvious reasons.
I would agree that most ready-mix suppliers can provide w/cm < 0.45 that has both adequate workability and reliable durability and strength - you don't have to choose. Below 0.40, you're doing research.
RE: Negative effects of high water to cement ratio
Process control by the supplier is the only way to assure you get what you need, and sloppy control will get you wet and dry mixes with similar batch tickets.
RE: Negative effects of high water to cement ratio
A concrete mix is a pre-engineered product. If you change it, you take responsibility for it. Doesn't matter what your spec says, it's the mix design put together at the plant that holds any water in court. Since OP doesn't have a good handle on what adding water does, and probably doesn't know how to design mixes, I dont recommend taking the risk, but hey he can do what he likes.
RE: Negative effects of high water to cement ratio
Adding water should not be entertained unless there are specific instructions from the batch plant.
RE: Negative effects of high water to cement ratio
MainMan10....this is where we agree; however, most ready-mix suppliers know a lot more about mix designs than most engineers. They are the suppliers. They are supposed to deliver concrete to the site within the specifications....but they need to know the parameters at the site before they design the mixes. They are responsible for the mix design, characteristics at delivery, and performance, assuming no adulteration of the mix at the site. Water addition, if done by anyone other than the supplier's QC representative, is adulteration of the mix and relieves the supplier of his responsibility.
RE: Negative effects of high water to cement ratio
I assume that very high workability was due to admixtures rather than higher w/c ratio! Or maybe balancing between both.
RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
I have never changed the mix design, nor would I ever. What I have been saying is that I will not stop the contractor (QC representative) from adding water if they felt inclinded to do so. They are the ones taking responsibility for the mix, not myself.
You are getting off the point. The question was WHAT NEGATIVE EFFECTS", not who's fault, or who is going to take responsibility, or who's liability is absolved, etc.
RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
If you knowingly allow them add water and do nothing you can pretty easily be caught in the net should something go wrong. Many suppliers keep some of the batch water out of the mix for adding at the site if needed (essentially delivering a lower than designed w/c ratio to the site). The amount that may be added at the site is printed out on the ticket. I never let them add water beyond that amount. If the contractor has concerns about workability/placement I work with them and the supplier ahead of time to get a mix everybody is happy with before the truck gets on site.
RE: Negative effects of high water to cement ratio
I generally do not object to allowing the contractor to add water up to the amount allowed on the batch ticket or QC paperwork. I have seen others push back on the contractor preventing them from adding any of such water to the mix.
RE: Negative effects of high water to cement ratio
2) increases porosity/permeability
3) decreased resistance to chlorides and such
4) increased risk of shrinkage
5) increased surface defects, depends on finishing
6) decreased strength
Segregation can result in non-uniform strength and shrinkage.
The way to reduce shrinkage is to design a mix which, when placed, results in maximum rock-to-rock contact. In addition to other benefits like workability, small aggregate/sand acts as a filler to reduce paste. The paste will shrink as it cures and dries, so any excess paste can result in shrinkage. Adding water increases the amount of paste AND the the amount of excess water which will evaporate rather than react.
In the reaction/curing/drying process, wetter mixes end up with more and larger pores in the matrix. As the water fraction increases above optimum, the voids remain connected into pathways, rather than becoming individual pore. This is a reason for the increased permeability. The increased porosity can also mean less strength and durability since the optimum pores size for strength and durability is roughly 10 nm.
You might take a gander at:
http
for some more info. As the article says, it is difficult to related nano-scale reaction products with the mass of concrete in front of you when they represent nine orders of magnitude in size.
RE: Negative effects of high water to cement ratio
I only comment because you could actually have greater shrinkage if an excessive amount of water is held back and you dont allow them to add the remaining mix water. The mix could self desiccate early on and your capillary stresses would be huge causing a lot of shrinkage. This is a big problem with bridge decks and high performance mixes where they're using sub 0.39 w/c.
If you're really talking about letting them add water just to increase workability above and beyond the approved mix (like most contractors will do without even asking you), I would avoid doing that because of all the bad things listed above.
RE: Negative effects of high water to cement ratio
Concrete truck arrives on site, batch ticket/QC doc allows up to 4 gallon per yard to be allowed and still meet mix criteria. Concrete rolls out of truck stiff (1" - 2" slump).
What I have seen is some field engineers push back on the contractor telling them not to put any additional water in the mix. I on the other hand would not object to adding up to the 4 gallons per yard. Obviously, I would suggest adding 2 gal per yard and mix it up to see what that gives you.
I do not advocate adding more water than the mix design allows.
I was just trying to get a feeling why some want the mix as dry as possible - Even when the mix design allows more water to be added.
RE: Negative effects of high water to cement ratio
If you add water in the field, there are very specific requirements about how many rotations need to be done to get it to mix properly. As the old joke goes: "What is dumber than a concrete truck driver... 2 concrete truck drivers". I have little confidence that this will be mixed properly in the field.
By the way- adding 4 gallons per yard is a lot of water. You could easily lose a couple hundred psi based on that.
RE: Negative effects of high water to cement ratio
RE: Negative effects of high water to cement ratio
Aside from preventing a deviation from required slump, there should be no reason to withhold the allowed water. Drier concrete mix is not necessarily stronger or more durable. The supplier will have QA for a history of the mix, upon which we should rely, since we, as the engineer, really have no idea how that particular mix will look or behave.
Adding only the allowed 4 gallons of water is not a problem. The mix will almost always decrease slump between the plant and the job site, so some adjustment should be allowed using this water.
RE: Negative effects of high water to cement ratio