Pavement design using roller-compacted concrete 7

[fattdad]

O.K. for starters, I know nothing about RCC (roller-compacted concrete). What I know is they use it for gravity dams, it has about a zero slump, and it's compacted using a roller (duh). I'm assuming that it's batched on site, as a concrete delivery truck needs some slump to mix and chute from the back side of the truck. Then again. . .

Here's a few of my questions: If you design an 8-in thick industrial pavement using 4-in slump, 4,000 psi, 6 percent air content concrete, how would you design an alternate for RCC? How do you get air content into the RCC?

Of what possible benefit would you get from a program such as this:

http://www.cement.org/bookstore/profile.asp?id=2309

Thanks in advance for any/all assistance. We have a client that wants us to specify RCC for his developemnt and we are talking about a 1,100 cy pavement job. I think the scale of the job sounds too small for this design change. Then again. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[cvg]

unless you are using conventional slump concrete - which you aren't, you will not have a significant amount of entrained air. You will have some entrapped air and you might assume 1.5 percent, but that is not the same thing as entrained air. RCC mixes are not designed for air entrainment.

 

[fattdad]

So, how do you make RCC durable for freeze-thaw conditions? I'd think the face of an RCC dam would undergo such cycles and the consequence would be unfavorable. Are there admixtures for RCC that provide entrained air?

Be nice to me, as I'm really not that familiar with RCC, but do understand nobody wants a road that busts all up after the first really cold winter - ha.

f-d

¡papá gordo ain’t no madre flaca!

 

[diggerman]

I know here in Florida, almost every concrete plant batches concrete with liquid admixtures. Typically a bread and butter mix has 5 to 6 ounces per cubic yard. Rule of thumb is 1 ounce/yd^3 gives you 1% air....8 ounces/yd^3 gives you 8% air. Its not exact, but a rule of thumb in the business.

There are a few manufacture's who produce good quality liquid admixtures....

Darex is a brand I'm more familiar with.
Masterbuilders INC.
Boral INC.

Anyways, yes air admixtures are quite common!

 

[fattdad]

Oh my (we seem to be going around in circles). Yes, air admixtures are quite common in ready-mixed concrete. I want to know how is RCC prepared to protect it from freeze thaw. Then again, maybe it's not prepared that way. I don't know. Do you know whether RCC uses admistures to provide entrained air? Then again, in Florida maybe it's not to common. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[diggerman]

Sorry fatt dad, I'm a concrete guy not a dam man.

Digger

 

[fattdad]

Yeah, this is not a dam project. You can read the entire thread above and get the overall idea of what I'm working on if you want to. . .

f-d

¡papá gordo ain’t no madre flaca!

 

[SirAl]

I have been involved on a number of RCC pavements, primarily for industrial plants in the northeastern BC /northwestern Alberta Area. The mixing process that I am most familiar with, the aggregates are fed continuously from a surge bin (or a series of bins) via conveyor to a continuous pug mill. Cement is applied continuous from a vane onto the aggregate stream prior to entering the pug mill. Mixing water is applied to aggregate and cement in the pug mill. The end product is a zero slump material, truck hauled to the paving location. I am not aware of any air entrainment ever having been added to the mixing water on the projects that I've been involved with. I'm not sure on how air could be tested accurately in the final mixed product, short of coring and running a linear traverse on the hardened concrete. With that stated, I am not aware of any serious durability issues with the RCC that we have tested in our frigid neck of the woods.

 

[cntw1953]

No knowledge on RCC, just guessing.
Would that the type of aggregates, percentage of fines, level of compaction have something to do with its duribility?

 

[diggerman]

Sounds like a fairly simple operatiion.

 

[cntw1953]

diggerman:

You shall be able to answer my question in general sense. Appreciate your comments.

 

[SirAl]

The RCC can be paver placed as BigH mentioned. The placed RCC is compacted like Asphaltic Concrete using pneumatic (rubber tire) rollers and steel vibratory rollers. We test it in the field for density and moisture, referenced to a modified proctor. We also form cylinder specimens in steel moulds for compressive strength and beam specimens for flexural strength. As for durability, we may assess the aggregates for L.A. Abrasion. Desired gradation characteristics would correspond with a good crushed granular base course product, perhaps cleaner on the bottom end.

 

[BigH]

SirAl - sounds exacting like the CTAB (cement treated aggregate base) that we used in China - and it was placed with paver.

 

[cntw1953]

A few seem good abstracts/papers on "durability of RCC dam/pavements. The PDF seems in line with the first. The second is quite general.



1. China Experience (DAM - Freeze & Thorw Resistance Study):

http://www.sciencedirect.com/scienc...serid=10&md5=b0e46c27cfd6fa18243aa03d5c641e4b

2. PCA Article (RCC Pavements):

http://www.cement.org/pavements/pv_rcc.asp

3. Abstract from University of Wisconsin Milwaukee (PDF)

 

[SirAl]

BigH - Agreed, the mix, delivery, and placing of RCC are very much the same as CSBC, more powder though. Other than that, not a whole lot different. CSBC was used here for years as the base structure (or component thereof) for road pavements. The main draw back has been seasonal movements in our road beds from frost penetration. The CSBC readily cracks under flexture, the cracks of which reflect through an ACP pavement, increasing maintenance costs, decreasing rideability, etc. As such, there has been a move away from CSBC in recent years.

 

[cvg]

CSBC has a much lower compressive strength than RCC without the forming or shrinkage issues. RCC is generally designed with strengths similar to conventional formed concrete and higher. You will get the same or better performance than conventional PCCP.

 

[BigH]

cvg - not necessarily true. The RCC on two dams of which I am aware had 365 day compressive strength requirements of between 12 and 14 MPa (1700 to 2000 psi) - total cementitious (cement and fly ash) of 130 kg/m3 (220 lb/ye3). The real consideration is the weight (mass) and achieved compaction level.

 

[cvg]

that may be true but seems low. I'm sure performance is fine for mass concrete dam. must have been poor quality aggregate or very little cement or both. we can get over 2,000 psi in 7 days around here using river bottom sand and gravel with no processing (except to remove the 2 inch and larger rocks) and only 6 percent cement (including fly ash). last project I worked on had two mixes with the higher strength mix being 5,000 psi at 28 days.

 

[BigH]

The dams I noted are judged low-paste RCC (different from high-paste) with 60:40 cement-fly ash ratio. What was the maximum size of your agg?

 

[cvg]

material was screened for 2 inch maximum size

 

[BigH]

Thought that is what appears to be happening in RCC in the States. Some are using 40mm minus. The ones I am talking about use up to 63 mm with 10% larger than 40 mm.