Asphalt Pavement-Prime Coat

[m8589]

I am writing specification for a small parking lot. When prime/tack coats are not required? What are advantages of applying prime coat. Please help?

 

[jimbo]

We quit using "prime coats" on aggregate a long time ago.

A tack coat (asphalt on asphalt) is needed. A tack coat which is too thin (sparse) is probably the greatest cause of delamination that I have seen.

jimbo

Buy a dictionary, keep it nearby and USE it. Webster's New World Dictionary of American English is recommended, and Webster's Collegiate Dictionary.

 

[ACtrafficengr]

The advantages are less delamination of the pavement. Tack coat helps the top stick to the binder, and the binder stick to the base. Primer helps the base course asphalt stick to the granular base. According to the Cornell Local Roads Program, tack coat adds ~$0.20 per sq yard, in exchange for three more years of pavement life. Not a bad deal at all!

I'd write the spec so that the contractor must use tack coat if they wait more than a few days between lifts. Also,primer coat helps if you are using thin pavements.

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[Ron]

A tack coat can serve both purposes. It is applied to the base or between asphalt lifts. It also protects the base somewhat prior to application of asphalt.

 

[BigH]

I suggest to use a prime coat on crushed stone base - why? For protection more than anything else. I've seen non-primed base go bad when local traffic pays no attention to the signs, etc. but it lasts okay if primed. You want about 5 to 7mm of penetration; make sure it dries before driving on it or paving on top. Tack coat - a bit ambivalent to it - it is usually specified if the new layer doesn't go on within a stipulated (2 or 3 days) time. Yet in China, we didn't use and and it was fine. Tack coat does add bitumen to the pavement structure and this may work its way up into the bitumen layers. We laid one wearing course at 4.8% bitumen, yet after secondary compaction, the % bitumen was over 5.3% - due also to fatty underlying bitumen base course - but tack coat if not properly done can add the bitumen. You should use emulsion and cut it 50%.

 

[m8589]

Thanks to everybody for responses. I will refer to state DOT standard specification and if,when and where DOT requires prime/tack coat contractor shall apply it.