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+--- Thread: Diluting concrete with water to make it workable (/showthread.php?tid=13185)
Diluting concrete with water to make it workable - unknownjulie - 02-20-2014
Having conversation regarding concrete pour. Was told, "Oh not to worry, I'll just dilute it when it comes out of the truck to make it workable"... Now, I know you are not supposed to do this. What I am looking for is an actual math equation that tells exactly how much a given sq foot of concrete can be diluted by how much water- and what percentage decrease in strength would result from "said dilution". IN other words, "I am willing to pay 50% less for a job and have it not "done right" as long as the percentage strength decrease is reasonable and I can hopefully compensate in other ways. More rebar? More wire mesh? Thicker slab? Thanks.
RE: Diluting concrete with water to make it workable - Bullwinkle - 02-20-2014
do a search for "concrete slump" slump is what you get when you fill a small bucket like device and flip it over and lift it off the sample
its how the viscosity (and ultimate set strength) of concrete is measured
the more water - the weaker the mix there are standards and tables (astm) - residential slabs have a lot of tolerance ...
RE: Diluting concrete with water to make it workable - Rob Tucker - 02-20-2014
Bullwinkle is correct. Some water can be added for workability but too much will weaken the concrete.
There is some flexibility in the concrete design mix.
RE: Diluting concrete with water to make it workable - Haaheo okole puka - 02-20-2014
LMAO...
Typically what comes in on the truck is already "workable". There is a tool call a concrete "vibrator" that will settle the aggregates, work out the air and bring up the slurry while greatly leveling the surface to simplify screeding, etc. Without use of a concrete vibrator, the concrete will not attain its
If water is applied atop the surface after the pour, initial screed and float passes that will not effect the strength of the mix. In fact water should be applied to the surface for the first three to seven days to keep the overall hydration within the slab during the cure.
RE: Diluting concrete with water to make it workable - Rob Tucker - 02-20-2014
What comes out of the truck is what is ordered. The concrete can be wet (high slump) or dry (low slump). The desired workability and work time is a matter of the mix design (test strength) including the wetness (slump).
Vibrators are needed depending on the use. Vibrators minimize or eliminate voids. The potential for voids increases with the dryness of the mix (low slump). Vibrators do not add test strength per se.
Haaheo okole puka is very correct on keeping the concrete surfaces wet during it's cure.
RE: Diluting concrete with water to make it workable - Haaheo okole puka - 02-20-2014
8k-10k mix PT slab - Hydration %?
The amount of air within a site test specimen can indeed induce failure.
Here's a simplified version on the topic.
http://www.using-concrete.com/concrete-vibrating.htm
RE: Diluting concrete with water to make it workable - Seeb - 02-20-2014
If I remember right it's about 1000psi difference between a 3inch slump and soup .
RE: Diluting concrete with water to make it workable - Rob Tucker - 02-20-2014
The test strength at full cure will be determined by the design mix at the plant. Most concrete batch plants will supply a design mix above what is called for. If you order 2,500 psi concrete the design mix might be 2,800 psi or higher.
The batch plants do this to compensate for field conditions and placement irregularities. They assume that field curing and placement of concrete is not done in lab conditions. It minimizes their liability.
RE: Diluting concrete with water to make it workable - Haaheo okole puka - 02-20-2014
Concrete is actually a very in-depth topic including its sub topics such as cement types, aggregates and additives. With regard to slump - depending on the cement type, aggregate and fines sizes/types, it can vary. What may hold true here in Hawaii with regard to a particular cement type and its quarry supplier may not hold true on the mainland wherein we find a vast array of aggregates. Is the aggregate porous, smooth and round or jagged from being crushed? What sizes are the fines and what are they composed of? Are there any additional additives, detergents, etc? Aggregate types can even affect the actual hydration percentage necessary in a particular cement type as some aggregates absorb water. Air is another factor and becomes more prevalent in lower hydration mixes.
RE: Diluting concrete with water to make it workable - Haaheo okole puka - 02-20-2014
My initial point being that proper vibration will make most common mixes "workable". Any additional hydration should be done after the initial leveling and smoothing unless the truck has made a long journey from the batch plant. I don't believe this is an air entrained lightweight Ferro cement project or some other specialty application requiring air, it sounds to me as if this is a common home construction project and vibrating then becomes necessary be it a pad or form fill application.