Is this a proper concrete local road?

[JohnDavidHanna]

We have lime rock roads in my area and some of the homes are very expensive yet some of us can not afford the cost of new asphalt (about 75 bucks a foot here).

There is a cement factory with slag but they only seem to be interested in airport grade construction and ignore the roads that need to be paved in their own county (409 miles) because they need to be done economically.

A ten to 12 inch thick pour would be great, even a local road has the occasional concrete truck, and that could almost be done at the cost of asphalt BUT

The county pays a third of the cost so I am thinking that if county equipment is used to grade and roller the project the cost of materials might be brought within range IF

The sub base of 5 or 6 inches is crushed down from recycled concrete of no more than two inch jagged square.
The base is five inches of slag from the local cement furnace w/a bit of added cement and wet rolled into the sub base maybe 1000 psi
And finished with 3 inches of 4000 psi concrete w/added crumb rubber to help distribute the load lowering the psi to 3000

The sub base is obtained by the county from the land fill, crushed, at no additional cost to the county and the slag is at nominal cost and the surface at wholesale.

Am I on track here?
I am not a structural engineer (CE) but it seems doable in broad terms.
Any suggestions/ help?

PS there is nothing in this for me other than I am on these roads and do pay taxes.

 

[Ron]

JDH...you are sort of on the right track. Your pavement section thickness designs must be checked as they appear to be overly conservative. For residential traffic, the pavement thickness design for concrete will be on the order of 6 to 8 inches of 4000 psi concrete, using only a compacted sand subbase.

There are numerous options that would be even less expensive, such as a mix-in-place asphalt emulsion course.

Three inches of concrete would be insufficient for pavement purposes, even if on a competent subbase. Shrinkage, durability and cracking are important considerations.

For further assistance, please answer the following:

How much traffic is on the roads and what is the mix? Don't forget garbage trucks, UPS/Fedex, mail, general delivery, moving vans, construction trucks, concrete trucks etc. The cars make very little difference....the trucks have a tremendous impact on the pavement design.

What type of subgrade is below the existing limerock surfacing?

How thick is the current limerock surfacing?

 

[JohnDavidHanna]

thanks Ron,
There are roads with less traffic than mine but not many with more.
Per day there are fifty cars and one general delivery including Fedex and the mail is a car.
Garbage makes one pass twice a week, six wheels.
Construction is down but there are vacant lots so cement and construction trucks will happen again, residential construction.

The soil type is sugar sand below a thin sandy loam.
The lime rock slag mix may be compacted down to a foot in uneven patches but may have to be removed to recess the road pour to match driveway grades.

I read that recycled concrete has the same bearing potential as if it were new. What if the lower four inches was recycled slag and crushed concrete to 2inches compacted and then three of jagged recycled and the 4000psi pour to another inch but mixed in and around the crushed recycled to an effective four inches over the base?

and thanks again

 

[JohnDavidHanna]

Ahhh, check this out.
I checked the state DOT guidelines and I find that local concrete roads need to be 11 inches thick.
But, recycled concrete is graded PSI at the same value as before it was crunched and that recycled concrete and wet slag make an acceptable base.
Then I read the abstract of a Chinese article and they state that with the inclusion of crumb rubber that they got the pour down to 3 and one half inches and the test roads were holding up well.
??

The article from IEEE was in Chinese but the graphs are in cm from 14 to 20 so where is the three and one half inches?

So I think about it a little more and internet data gives some weak data about crumb rubber aggregates that weaken the strength but improve the flexibility and ride of the road. So what good is an additive that lowers the strength of the pour, how can that thin the depth and make it less expensive?

So I thinks about it some more and realize they are talking about a cap. A three and a half inch high strength cap with crumb rubber mix over the used concrete rubble underlay.

With a little thickening at the edge, maybe a bit of rebar at the edge and a jagged interface with the underlay (helping to distribute the load) you may be able to get a fifty year maintenance free road in rural roads while taking some pressure off of the land fill - cool.

Don't forget the sidewalk.
They provide community and decent backup if you ever run out of gas

What do you think?

 

[jgailla]

11 inches seems awfully thick for a local road.
Depending on conditions, you could get down to 6 inches.
Calculations sometimes indicate a 4 inch slab is sufficient, but the practice seems to be a 6 inch minimum.
I've never heard of crumb rubber.
Crushed concrete can make a good base material.

 

[Teguci]

Where do you live?

 

[JohnDavidHanna]

Here is the IEEE article link for crumb rubber cement

It is in Chinese but the abstract is English
and the best I can figure is that the addition of crumb rubber if used in a cap layer helps to distribute lateral stress to prevent cracking to an extent that the thickness can be reduced although reducing the overall strength so a good solid base is used.

Crumb rubber is shredded tires,
easily obtained and inexpensive as they heat the tires in an oxygen free room and the rubber maintains its flex yet crumbs off the steel wire and plate economically so it can be an inexpensive aggregate. Much better than chopping old tires.

For the crumb rubber article the name and link is below

Experimental research on thickness reduction of rubber modified concrete pavement surface

Electric Technology and Civil Engineering (ICETCE), 2011 International Conference

http://ieeexplore.ieee.org/xpl/logi...re.ieee.org/xpls/abs_all.jsp?arnumber=5776310

I am looking at the DOT Florida 2008 specs and we are in sugar sand here in Hernando County (Brooksville) so a base is required and the spec formula for hard surface local roads is clearly ten to eleven inches

but it also says that a base of recycled concrete can be used crushed to various ranges you know, quarter inch, half inch, two inch particles.

But a cap concrete road brings the cost to compatible with asphalt and of course there is a fifty year maintenance free (basically) surface and we have a lot of concrete here and asphalt is always on the rise.

When the government is always looking to raise revenue this seems like a good idea - my property taxes will go up as the homes - mini farms - sell to city folk that want a little more security - a bit closer to a food supply - for a minor cost.

I will not make anything in this. I only have one home and no plans to move so will be paying the tax and putting up with the influx of speeders that are slowed with the wash board surface I have now - not to mention the dangerous potholes on the edges where the lime rock has solidified and then crunched away.

People aren't looking to move to gated communities with expensive monthly fees but will bring their families and their incomes to larger lots where they can put in chickens, bees, crops and tilapia. It's win win win I think.

And for those few that can not afford the greater taxes they can move. That is better than not being able to sell while the taxes rise in any event eh?