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]

RCC has no specified air content and is not delivered in transit mixers or generally using a chute. the book by the PCA is likely a very good resource, although I have not used it because I have been more involved with the dams. I have gotten good advice by talking with PCA engineers.

RCC can be batched on-site or done at a central plant and delivered to the site. It is generally handled as you would handle borrow material on an earthwork project and not unlike the process for soil cement. Dump trucks for delivery, graders and dozers to spread it, smooth vibratory rollers to compact. Place in 12-inch lifts and compact to the final thickness. No finishing, just 7 day cure like any other concrete.

My question is how will you get a smooth riding surface? RCC and soil cement are usually done for the base course with a riding course placed on top.

 

[Ron]

fattdad...I have designed several RCC pavements for industrial applications. We were not necessarily concerned with "ride quality" as in a surface tolerance comparable to conventional PCC; however, we did require at least a surface flatness as the industrial applications must have a relatively flat surface on which to work or dangerous conditions can result.

RCC is usually batched at the site or you might be able to convince a ready mix supplier to batch it at a nearby plant; however, with essentially no slump and no latent water, you can't have a long travel distance.

Otherwise, I agree with cvg's comments.

 

[concretemasonry]

Find a local RCC installation and show it to the client as a typical example and then explain the differences between that and what you may suggest. This should help to satisfy some of his early opinions and show that you are looking into his suggestions.

Dick

 

[Zambo]

Depending on the moisture content you may be able to deliver by truck mixers and discharge by chute. Another option would be to use a continuous mixer (pugmill) on site.

I also don't know anything about RCC but expect with the use of a grader you would get similar tolerances to CSM which is roadbase tolerance rather than concrete slab.

I think its the wrong spec for the job and PQ Concrete would be a better option.

 

[fattdad]

to put this matter into context: My client is a manufacturer of Portland cement and knows full-well what RCC looks like. They have likely seen it on other projects. This is a case where I may be less informed than my client.

I had never thought of finding a local batch plant and having the zero-slump RCC delivered in a dump truck. Believe it or not, that may actually work as I have a supplier close by the job.

cvg mentioned 12-in thick lifts. I like the sound of that, but it seems thick for an industrial pavement. Is 8 in an option for placing RCC (i.e., is 12 typical minimum)?

How do you manage air content? Is it a moot point owing to the fact that even with compaction, you'll end up with an air content that'll ultimatly work for freeze-thaw conditions?

Thank you all so much for your help!

¡papá gordo ain’t no madre flaca!

 

[cvg]

12 inch loose lifts, compact down to about 8". For most of my projects which are dams, levees etc. the finished thickness is much greater than 8" and the RCC would be similar to mass concrete, however there is no reason you can't place just one lift, compact it to 8" finished thickness and be done. If 8" is your final thickness, I would avoid trying to place it in more than 1 lift as the lift interface could become a cold joint if work does not progress quick enough. Durability tests can be run to determine the resistance to freeze thaw and erosion. The mix design should also include tests to determine the necessary cement content vs compressive strength. I would advise doing these tests before bidding the contract.

Regarding timing for transporting and placing the mixture, these are specs from my most recent project:

A. The CONTRACTOR shall minimize the total elapsed time between the addition of water to the mixture and the completion of compaction. Time limits for handling, transportation, and compaction of the RCC shall be as follows:
a. Maximum transportation time from mixing to the start of spreading shall be 30 minutes.
b. Compaction shall start within 15 minutes of spreading.
c. Maximum elapsed time between introduction of water to the mix to final compaction shall be 60 minutes.

 

[concretemasonry]

fatdad -

This is an opportunity to work with/for your client so he can use the project as a demonstration project and you can document the use and application for a non-mass installation. If the client is one of the large international cement producers that have more knowledge and technical support than an ordinary concrete engineer.

The specs you posted require nothing more than a stop-watch to insure quality, which is minimal.

Do not worry about air content since that is in realm of cast concrete and not zero-slump concrete. The vibration and compaction will change the air content of the placed concrete plus there is no guarantee that the air is too much more than the normal 1.5% generally in any concrete.

When you are dealing with zero-slump or very low slump concrete, the shape of the aggregate (rounded, spherical, etc., has is a very big factor in the performance. It is not that much different than the soil proctor tests commonly run using the locally available aggregates. It is good to have a supplier that is experienced with RCC concrete, but that could be controlled by your client, since concrete suppliers have their prime cement suppliers and cement producers also have their prime customers/producers. The best of both worlds would be a concrete supplier that is vertically integrated to the cement/aggregate supplier from a standpoint of technical assistance and future projects.

Dick

 

[fattdad]

Just to add some further insight. I learned today that my client wants RCC at their site to showcase an alternate and an effective use of this alternate in pavement construction. What better way to showcase a portland-cement bawed product in a non-typical setting then your own facility!

One item of note: We are somewhat concerned about how to handle contraction joints in RCC installation. Recognizing that all concrete cracks (and that RCC is concrete), and recognizing that the service load will be fully-loaded highway trucks that are moving portland cement cracks that loose aggregate interlock may lead to premature failure. In a slump concrete, we can use dowel baskets at the control joints as a backstop to aggregate interlock. In RCC I guess this is not an option. That said, I'm suspecting that RCC is less susceptable to slab curl and the like.

I really appreciate everybody's comments. My client has good relations with the Portland Cement Association and is working with their engineers to look at RCC design for the anticipated loading and site-specific CBR values. I'll give you all an update.

Have a great weekend!

f-d

¡papá gordo ain’t no madre flaca!

 

[hokie66]

fattdad, I would be in the same boat as you with RCC used in an industrial pavement application. Please keep us advised as to how this goes. But without knowing much, I would think that the RCC would be thicker than the normal concrete pavement. I normally start with 8" for industrial pavements, so 12" finished depth for a RCC pavement without all the jointing issues sounds attractive to me.

 

[Zambo]

Interesting thread. Based on fattdad's info about his client I withdraw my comment that PQ Concrete would be more suitable than RCC.

Having had a think about this and compared to the use of CSM (cement stabilised material) I would investigate using a paver (i.e the type used with bitumenous road surfacing). I think a good level control could be achieved and the augers tend to lay the material evenly prior to compaction. The semi-dry (or dry??) concrete could then be supplied by a pugmill at site, into trucks and then reversed up to the paver.

 

[concretemasonry]

fattdad

If the cement producer is really controlling things, they may have their mind on a certain type of application and want it done correctly, since it is critical for them to do it right.

Although concrete pavers use less cement they have been used successfully in international projects with heavy loads on marginal soils (heavy duty straddle loaders in ocean ports handling multiple containers or for airport taxiways). This could also be an attractive alternate, depending on the clients engineering/promotional interest.

If not, just rely on the technical support offered by the client and learn something with a different application. - you know this is not a project that the budget is not as important as the performance and educational/promotional value.

Dick

 

[DMcGrath]

fattad,

Any chance when the project goes to construction you could give us a heads up? I believe you and I are in the same vicinity, and if the project is nearby I would like to see the RCC placement process if possible.

Dan

 

[BigH]

For your work what is the difference between RCC and cement stabilized aggregate base? Not much - you can batch it in a batch plant or in a pug mill - moisture content needs to be controlled and you might need to be 1% or so above optimum for effects on drying. In our work in China - the cement treated aggregate base was placed using an asphalt paver in 12 inch lifts and compacted. Got good results on tolerances in placement - likely much better than using a grader or bulldozer. (Note, in Laos, we also placed the untreated base course with an asphalt paver).

 

[dicksewerrat]

For a parking lot, I'd use an concrete paving machine. then roll for compaction. The surface will be better than just dump out and push around with a grader.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[cvg]

Interesting article published by PCA today:

Diamond Ground RCC Replaces Failed Asphalt on US Highway 78

U.S. Highway 78 in Aiken, S.C., had deteriorated to the point where a thin resurface treatment was not a viable option. Looking for a solution to replace the failed asphalt roadway, the South Carolina Department of Transportation (SCDOT) explored multiple options, primarily focusing on minimizing traffic disruption, long-term durability, and cost of construction. The repair method chosen consisted of milling out the distressed asphalt and replacing it with 10 inches of roller-compacted concrete (RCC). To provide the desired ride quality for high speed traffic SCDOT chose to diamond grind the RCC surface rather than cover it with a thin asphalt or conventional concrete surface.

When it was successfully completed in August 2009, the diamond ground RCC pavement paved the way to add high-speed roads to the list of RCC pavement applications. For typical roads with speed limits of 45 mph or higher, a smooth road has an International Roughness Index (IRI) of 85 inches per mile or less. Approximately one week after placement, a milling machine was used to remove higher surface spots of RCC. This was followed by diamond grinding to provide the final smooth surface. After grinding, the pavement IRI was determined to be within the range of 50 to 60 inches per mile.

This project marks the first successful completion of diamond grinding RCC pavement for a major road in United States.

 

[fattdad]

CVG,

Thanks! I'll forward this to my colleagues and client. This project is moving forward and I'll followup when I have anything.

f-d

¡papá gordo ain’t no madre flaca!

 

[diggerman]

Air content is referring to entrained air within the concrete paste itself. You will never have 0% air in any concrete aas long as it has a paste (consisting of mortar)
Even though you are rolling the concrete and getting full compaction, you will still have air entrapped withing the paste. Don't think of it in terms of "air voids." Now I am no Dam Engineer by far, but I know concrete very well. It's probablly safer to batch a mix with minimum entrapped air. All entrapped air content is really good for is workability. I personally hate entrained air in any mix. However, you can't get rid of it even if you exclude air admixtures out of the mix design. It naturally is incorporated by the mixing action. PCA makes an excellent book on this. It's really an essential book if you are into concrete structures PERIOD. Every engineer needs to read it. Good Luck!

 

[fattdad]

o.k., but we use air entrainment to control freeze thaw damages - not just for workability.

f-d

¡papá gordo ain’t no madre flaca!

 

[diggerman]

...and freeze thawing.

Thnx