Strength of Cement-Treated Aggregate 1

[stuus]

Hello everyone,

The use of cement-treated aggregate as base or sub-base layers in pavement sections varies across the country and so does the codes and strength requirements. There are different opinions as to what is strong enough and what is too strong.

I am involved in the construction of an airport runway, so the range I use is the 750-1000 psi specified by the FAA. However I do not have alot of experience with cement-treated aggregates and is curious about what experiences people have had with material outside of the 750-1000 psi range.

Have you had any success stories with pavements that had layers of stronger cement-treated aggregate? Have you experienced excessive pavement cracking even though the strength of the base layer was within the specified range.

Any feedback is appreciated and experiences from airport pavements are especially valuable.

Thanks

 

[ACtrafficengr]

For stabilized subbases under roads, 500 psi is more commonly used. We had shrinkage cracking on one of our roads. I hear this is common if you use too much cement in a stabilized subbase.

Then again, the thicker pavements in runway design may behave differently.

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[Ron]

The range you are discussing is sometimes called "Econocrete", "Controlled Low Strength Material (CLSM), and a few other monikers.

The greater the strength of the material, the greater the shrinkage potential will be, and thus the likelihood of cracking increases.

In most cases, for airfield pavements, the mass of the concrete surface pavement is not greatly affected by lateral shrinkage of the subbase. You should; however, investigate the pptential shrinkage of the subbase relative to the shrinkage of the surface pavement. They will both be shrinking in the same directions, and the subbase will have a headstart on the surface pavement, so it is usually not a problem. At least is there is a problem later on, you can say that you considered it and found it to be non-relevant (if that is the case) and thus you would meet your standard of care for that portion of the design consideration.

 

[stuus]

First of all I want to say that I appreciate the responses so far.

Ron's response made me realize that maybe some further explanation of my situation is necessary. The material I'm refering to is what the FAA calls P-304 Cement-Treated Base Course. Aggregate mixed with about 5% cement and has around 10% moisture. The surface pavement is AC.

Thanks

 

[cvg]

I have specified RCC up to 2000 psi at 7 days. This is somewhat different than CTB, but similar in that it was placed using a very dry, stiff mix and vibrated into place using a steel drum roller. It was not used for pavement base however, but for a drop structure in a river. I have observed only minor cracking - probably nothing that would reflect through an asphalt surface course.

 

[Ron]

stuus....what you have is a strong soil-cement. CTB will shrink. It will cause reflective cracks in the asphalt surface course. Unless you are prepared for a lot of crack maintenance, use a granular base under the asphalt with no cement.

 

[Fizzhead]

Stuus:

I worked building the new airport in Athens Greece in the late 1990s and we used a lot of CTB under concrete for aprons, taxiways and runways. In Athens, we have not observed any problems with differential shrinkage or cracking at all. Strength was roughly the same as you described. However, several road contractors who learned about CTB at the airport went on to build roads through the mountains north of Athens with CTB base courses in the 500-750 psi range and the shrinkage was sufficient that within two years we were seeing asphalt pavements disintegrating almost before our eyes. Major differences were the type and amount of deicers used, temperature extremes and the difference in subgrade strength and subsequent shrinkage.

 

[jimbo]

In one commmunity we designed about 21 miles of asphalt pavement, some of which was on cement treated natural gravel.

One interesting item we noted was that the cement treated base cracked at 15'-20' intervals longitudinally, the same as we would see in normal concrete pavement.

jimbo


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