How come some concrete is pitted from winter salt and some isn't?

[orezok]

There is very little concrete placed that meets the specifications of the mix when it left the plant.

You are probably correct for non critical concrete, but let me add my $0.02.

Attached is a copy of the design mix for this project. The concrete specified was 4,500 PSI mix with a W/C ratio of point 44. The in-truck slump is 6", but by the time it leaves the 30 meter pump it will drop to 3 1/2" to 4".

In order to be an approved mix, the concrete plant must submit no less than 10 test breaks from different batches by a certified testing lab indicating that it meets the design strength. This mix had 18 breaks averaging 4,800 PSI. The cylinders broken from my pour all averaged 5,500 to 6,500 PSI. We allow a maximum of one hour batch to place on public works projects.

The difference is probably that we require a full time batch plant inspector who sits in the weigh room with the weigh master to assure that the exact design mix is supplied.

I suspect that the home and garden contractors receive a mix that may not meet the design criteria.

 

[JeffinIA]

I don't know much about it. I only made 115 ACI certified test cylinders last year that averaged over 6000 psi. Every one of those had either fly ash or ground mill slag in the mix. You can use what ever you want.

And Your right on !!!

Concrete with (type C) Flyash,What I have experience with , Will continue to gain strength literally Forever, Concrete with out gets to a give PSI and pretty much peters out. There is nothing wrong with Flyash.

 

[Gary Fowler]

We hand rod them

That is the only way to meet ACI specs for making a test cylinder. Rod diameter has to be per ACI with a round point and smooth surface, exactly the same number of rods per layer(30 IIRC), minimum of 3 layers and rodding penetrants at least halfway into previous layer. I did ACI certification test about 30 years ago, but have had test lab technicians on the job to do it for me for over 2.5 decades and my memory isn't always accurate(been a Quality Manager for 25 years so I had technicians and inspectors to do the actual work)

 

[Gary Fowler]

You are probably correct for non critical concrete, but let me add my $0.02.

Attached is a copy of the design mix for this project. The concrete specified was 4,500 PSI mix with a W/C ratio of point 44. The in-truck slump is 6", but by the time it leaves the 30 meter pump it will drop to 3 1/2" to 4".

Should note that the W/C ratio is .44 by weight not 44. Most of the mix designs I have been associated with require max of .41 W/C ratio (higher means more water in the mix ) with a maximum slump of 6" and prefer a 4" slump. FOR the not so concrete wise amoung the crowd, slump is tested using a standard slump cone that is 12" tall. The concrete is placed in the cone in 3 equal volumetric layers and rodded 30 times for each layer to consolidate the aggregate, then the cone is slowing and continuously raised to release the concrete onto a dampened plate. the cone is reversed and the rod used as a straight edge across the top and a measurement taken to the high point of the concrete pile. So if the pile measures 8" then you have a 4" slump (measure of how much the cone of concrete "slumped" or fell from original height of 12". This is just an indicator of placement abilities and though it is indicative of more water= higher slump, that may not be the case in all mixes and aggregates. I have seen crushed limestone that you could take a hose and wash out all the cement and it would stand in a pile 10-12" high because all the aggregate locked together like a stack of bricks.
A proprietary mix design I have used call "Aguilar" is considered to be 12" slump as it flows like water but has a less than .41 W/C ratio and lots of something (secret mix design) to make it flow. I witnessed a test with a T shaped form that was 10 feet from the bottom of the T to the top with clear plexwindows around a square embed which is the hardest to get concrete to flow around. The concrete was poured from the truck into the bottom of the T end and filled the 6" wide form with no vibration (vibration is not allowed) level within 1" at the far ends of the top of the T with no voids anywhere. It also hardens up in same time as normal concrete, but about double the cost of normal concrete. We used it (only with client approval due to excessive cost)on a TarSands project in Fort McMurray Canada when the pours had lots of embeds or tight clearances on the rebar. Compressive strength was always above 35Mpa (5000 PSI)

 

[/pine]

Six or seven years ago (maybe longer) I was reading about a new mix/process that was supposed to take the concrete world by storm but I guess it must have proven to be cost prohibitive because I have not heard anything about it since...

The "new" concrete allowed them to pour slabs that could be built on within hours after finishing...and even more astounding was runways could be poured and landed on (large military planes) in the same day...anyone know anything about this?

 

[orezok]

Six or seven years ago (maybe longer) I was reading about a new mix/process that was supposed to take the concrete world by storm but I guess it must have proven to be cost prohibitive because I have not heard anything about it since...

The "new" concrete allowed them to pour slabs that could be built on within hours after finishing...and even more astounding was runways could be poured and landed on (large military planes) in the same day...anyone know anything about this?

They use a similar mix on freeway repairs in CA where they have to remove complete blocks of paving. Cures for traffic use in a couple of hours.

 

[orezok]

Should note that the W/C ratio is .44 by weight not 44.

As stated in my post point 44 (.44).

 

[vtsnowedin]

They use a similar mix on freeway repairs in CA where they have to remove complete blocks of paving. Cures for traffic use in a couple of hours.

I've worked a project twenty years ago using something on this line call latex modified concrete. All the parts had to be mixed as it came down the chute which had an auger built into it to do the mixing. Time to first set was about fifteen minutes and you could open it to traffic in five hours if needed. It worked but was very expensive and the custom built truck was over weight before you filled any of its aggregate bins.

 

[forgeblast]

Just wondering then, if you were going to pour a driveway in a frost freeze area what type of mix would you ask for? Or if/when contractors come to bid the job what would you as a professional look for. Would you require the contractor to do a slump test?
In a few years we would like to get our driveway done, along with the pad for a garage. I would much rather have concrete over blacktop. I worry about the salt and freeze/thaw though. Thanks.

 

[Piperflyer]

Just wondering then, if you were going to pour a driveway in a frost freeze area what type of mix would you ask for? Or if/when contractors come to bid the job what would you as a professional look for. Would you require the contractor to do a slump test?
In a few years we would like to get our driveway done, along with the pad for a garage. I would much rather have concrete over blacktop. I worry about the salt and freeze/thaw though. Thanks.

good compacted gravel base, 4500# fibermesh concrete, cure it, cut it and you will never have a problem