Base Course for Asphalt Parking Lot 1

[mes11]

I have a client who is interested in using asphalt grindings as the base course material for a new asphalt paved parking lot. Lot size is a little over an acre. Wondering if anybody has done this before. My concerns are getting it compacted well enough and it's longevity/durability. Should typically see just passenger vehicle traffic and box delivery trucks occasionally. Very few if any semi-truck traffic is expected. Also, what thickness would you suggest?

 

[Ron]

If you are contemplating this, you need to get some information on the properties of the material that is to be used. You then have to decide on test methods to determine property achievement. That's not so easy with asphalt millings.

You cannot use typical moisture density relationships (Proctor), because you will not be able to accurately establish a moisture relationship. Determining the moisture content of the material is fleeting and somewhat irrelevant, unless it is mixed with soil. Even then it is difficult to get repeatability.

If you stabilize with asphalt emulsion, some soil and the millings, you will create an excellent base, but your whole criteria of acceptance will change from a soil based premise to one of asphalt.

Alone, the millings are not stable enough to use as a base material.

Do some analysis on your pavement loads to determine the proper thickness you will need.

 

[DDBPE]

Have the asphalt grindings been processed (crushed and screened) or is the material straight from the mill and stockpiled without being processed?

With the processed material, usually the top screen size is either 1/2" or most likely 3/8" and this does not make for a good base material, there is not enough larger aggregate in the composition.

If the material came straight from the mill, the material will be too inconsistent. You can get large chunks as well as the fines. Also, if the milled material was stockpiled, the heat can bind the millings back together and then you can get even larger chunks, that do not break down easily.

It sounds like your client is trying to save money, where I am from in the Eastern US, millings, when we do sell them (we typically use them for RAP in our asphalt plants), are half the price of a good base material. Trying to manipulate the material as Ron has stated may work, but it will be a lot of work and in the end would likely be more costly and as stated above, hard to get repeatability. Also, the reclaimer used to for this type of work really is not set up for a small lot.

As for thickness, again as Ron stated, you will need to do some analysis of the pavement loads and I might add you will also need to know the underlying material's CBR value.

 

[Phidelt218]

I have not heard of anyone use RAP for base but i know it is used in asphalt plants. You may talk you client into use the RAP in his asphalt mix and see what the requirements are with your DOT/City/Muni are for RAP since it varies from typical aggregate.

 

[mes11]

Phidelt218,

That's a good suggestion, I will check into that in the upcoming week. Thank you.

 

[eea]

You have a number of good suggestions already before you. As far as thickness, play with old basic AASHTO pavement design and see what your target SN shows. An actual Marshall would help, but you might ballpark the coefficient for the millings in at 0.10 to 0.15. A little more than a straight aggregate base at 0.1 just for a starting point. That is provided the millings have a good gradation with no chunks and the subgrade has a decent support value. My standard design in my local area usually finds us with a CBR=3 and a need for 6" of aggregate base and 3" of HMA (two lifts of 1.5" each). If the client is wanting to do this on the fly with no lab testing, I'd make no guarantees and suggest a 1:1 substitution of millings for aggregate.