I'm currently supervising a road designed to a bitumen standard-surfacedressing.The pavement layers composes of stabilised subbase,crushed stone base(CRR)and surfacing.Now I'm at base course stage and in principle Ihave already analysing the most important tests required for the assessment of the rock to be used as stone base.The tests already conducted are grading analysis,P.I,ACV,LAAV,SSS(5cycles)and TFV dry/TFVsoaked.Is pertographic analysis important in this case?and what else important tests to be conducted?
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Wich important tests are required on crushed stone base course?
- Thread starter defg
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Drumchaser
Civil/Environmental
Depending on your answer to cvg's first question, we require a minimum compressive strength.
Triaxial Compression for Base Materials
Not sure what the ASTM no. on this would be.
Triaxial Compression for Base Materials
Not sure what the ASTM no. on this would be.
Drumchaser....triaxial compressive strength is not a test typically run on base materials, particularly crushed stone base (crusher run), as the material is not cohesive and would not hold together for such a test unless it was tested in a triaxial chamber with a membrane and confining pressure....which would have no interpretive relevance to base testing.
Generally, we require stability testing (CBR or similar), in-place density checked against AASHTO T180 (modified Proctor) with a requirement for 98 to 100 percent compaction. If it is a graded aggregate base (which I assume this to be) we would require a gradation to check against specifications (usually state Departments of Transportation provide requirements for gradation on such materials).
As cvg noted petrography would not be indicated unless you suspect a reactivity or other problem with the parent rock material.
Even though the graded aggregate base is not directly exposed to traffic abrasion, you might consider abrasion testing on the aggregate as it is a good indicator of overall durability of the aggregate (absent reactivity).
I assume from your posting you are either from the UK, Australia or S. Africa. I'm not sure what your acronyms refer to, so you might give us a bit more information on those.
Generally, we require stability testing (CBR or similar), in-place density checked against AASHTO T180 (modified Proctor) with a requirement for 98 to 100 percent compaction. If it is a graded aggregate base (which I assume this to be) we would require a gradation to check against specifications (usually state Departments of Transportation provide requirements for gradation on such materials).
As cvg noted petrography would not be indicated unless you suspect a reactivity or other problem with the parent rock material.
Even though the graded aggregate base is not directly exposed to traffic abrasion, you might consider abrasion testing on the aggregate as it is a good indicator of overall durability of the aggregate (absent reactivity).
I assume from your posting you are either from the UK, Australia or S. Africa. I'm not sure what your acronyms refer to, so you might give us a bit more information on those.
After running the typical DOT required tests, then you need to establish what limits you will accept. For instance,in frost country you might want to limit P-200 to 8 percent or lower. I'd typically say "the material must meet the DOT requirements for base curse".
Drumchaser
Civil/Environmental
Ron....while the triaxial may not be required in other areas, we require it on all flexible base. The majority of our base is limestone which is produced and graded from oversize quarried aggregate that originates from a single naturally occurring source.
min. comp. strength, psi Gr1 Gr2
lateral pressure 0 psi 45 35
lateral pressure 15 psi 175 175
Included in the Test Method is the use of a triaxial chamber, membrane, confining pressure, capillary wetting, axial load measuring device, etc.
THE TRIAXIAL-COMPRESSION TEST IS USED TO DETERMINE THE FUNDAMENTAL STRENGTH CHARACTERISTICS OF MATERIALS USED IN THE CONSTRUCTION OF FLEXIBLE PAVEMENTS.
This requirement along with P.I., L.L., gradation, wet ball, and a minimum 98% compaction has yielded some very good base courses over the years.
min. comp. strength, psi Gr1 Gr2
lateral pressure 0 psi 45 35
lateral pressure 15 psi 175 175
Included in the Test Method is the use of a triaxial chamber, membrane, confining pressure, capillary wetting, axial load measuring device, etc.
THE TRIAXIAL-COMPRESSION TEST IS USED TO DETERMINE THE FUNDAMENTAL STRENGTH CHARACTERISTICS OF MATERIALS USED IN THE CONSTRUCTION OF FLEXIBLE PAVEMENTS.
This requirement along with P.I., L.L., gradation, wet ball, and a minimum 98% compaction has yielded some very good base courses over the years.
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Drumchaser...thanks, that's interesting. How does it correlate with any of the empirical or elastic layer criteria?
You're close to a resilient modulus approach, but the analytical techniques generally do not use your results directly.
Since your triaxial criteria are closely intertwined with other strength criteria (higher compressive strength generally yields higher stability), I suspect you are getting good results by default, as your specifications are likely tight and require good field control.
Stability can be directly related to a compaction curve as in the CBR. The same is not necessarily true of compressive strength.
Most construction materials testing laboratories do not necessarily have the capability to perform triaxial testing. Further, the cost and time required for the process is more expensive than stability and density testing.
Thanks for a different perspective, though.
You're close to a resilient modulus approach, but the analytical techniques generally do not use your results directly.
Since your triaxial criteria are closely intertwined with other strength criteria (higher compressive strength generally yields higher stability), I suspect you are getting good results by default, as your specifications are likely tight and require good field control.
Stability can be directly related to a compaction curve as in the CBR. The same is not necessarily true of compressive strength.
Most construction materials testing laboratories do not necessarily have the capability to perform triaxial testing. Further, the cost and time required for the process is more expensive than stability and density testing.
Thanks for a different perspective, though.
I find the use of triaxial compression test rather interesting; have not run into its use before as a specified test. Resilient modulus I have seen but not specified during construction. Normally we haven't even done CBRs on crushed stone - other than maybe one or two at the very beginning to "prove" that the crush stone when compacted to a specified level of compaction will achieve greater than 80 CBR (or "so"). It seems that many are still hoping that "super-strong" base courses will overcome the negative effects of poor drainage within the base course - a problem noted many years ago by Cedergren.
Drumchaser
Civil/Environmental
Ron & BigH
The axial loading combined with the criteria mentioned above (mainly P. I., gradation and wetball) restrict the material significantly. This provides a high quality base that is easy to work, and the finish (if done correctly) is slick and smooth. This material (when processed correctly) sets up like concrete.
I am familiar with the CBR test method, but only with regard to soils. Also have had some experience with Mr, but only in Research Project form.
The axial loading combined with the criteria mentioned above (mainly P. I., gradation and wetball) restrict the material significantly. This provides a high quality base that is easy to work, and the finish (if done correctly) is slick and smooth. This material (when processed correctly) sets up like concrete.
I am familiar with the CBR test method, but only with regard to soils. Also have had some experience with Mr, but only in Research Project form.
Drumchaser - agreed that material is restricted - Of course we always have a gradation spec and as well the PI is specified - usually to be less than 6 although in Ontario, it is to be non-plastic. With these limits, limits on durability (whether Los Angeles Abrasion or the newer method Micro-Deval), Aggregate Impact Value, Soundness, etc. seems that the triaxial wouldn't be needed. Ah, learn something new every day. BTW - what is your general geographic area of work? (I've worked Canada, China, Laos, India and Indonesia).
Drumchaser
Civil/Environmental
sorry to hijack your post defg
![[pirate]](/data/assets/smilies/pirate.gif "[pirate] [pirate]")
BigH
Obviously, here in the states, agencies spec. matl.s based on availability and locally available resources. I beleive this to be responsible for some of the rather punitive requirements in place. Just because a material is readily available does not necessarily mean it is of minimum quality, as you well know.
Of course, I prefer rigid pavements to flexible: 13" to 15" CRCP is my favorite cherry on top.
My general geographic work area(s) would be the southwest and southeast.
BigH
Obviously, here in the states, agencies spec. matl.s based on availability and locally available resources. I beleive this to be responsible for some of the rather punitive requirements in place. Just because a material is readily available does not necessarily mean it is of minimum quality, as you well know.
Of course, I prefer rigid pavements to flexible: 13" to 15" CRCP is my favorite cherry on top.
My general geographic work area(s) would be the southwest and southeast.
South Florida roads use crushed limestone base. A typical section is 1 inch bituminous, 6 to 8 inches limerock, and 12 inch 'stabilized subgrade' i.e., the native sand with enough limerock mixed in to stabilize it to LBR 40.
In this case, LBR = Limerock Bearing Ratio, which is equivalent to about 80% CBR.
For DOT work, the minimum carbonate content is 60 to 70 percent- this allows the base layer to 'set.'
In this case, LBR = Limerock Bearing Ratio, which is equivalent to about 80% CBR.
For DOT work, the minimum carbonate content is 60 to 70 percent- this allows the base layer to 'set.'
to follow escrowe; the stabilization of the native material under the base course can also be acheived (and frequently is) with a combination of clay, rock and or shell fragments. watch out for too much clay stabilization, this will significantly reduce bearing capactiy in saturated (wet-season) conditions, particular if drainage is less than ideal.
Drumchaser
Civil/Environmental
escrowe
You lucky so and so. S. Florida...now that that sounds like a winner.
I like the limestone.....have had considerable experience with it. If set-up correctly, it is tough to beat.
You lucky so and so. S. Florida...now that that sounds like a winner.
I like the limestone.....have had considerable experience with it. If set-up correctly, it is tough to beat.
escrowe...if you are recommending 1 inch of asphalt in your geotech reports, you might want to re-think that one. The pavement section you gave is a good one, except the asphalt thickness. If you do that with Type S1, you'll get extensive raveling. If you do that with Type S3, you have better success, but still too thin, as S3 has 3/8 to 1/2 inch top size aggregate and there's not enough room with a 1-inch layer to bond and encapsulate it well.
I would recommend 1-1/2 inches of Type S3....no S1 except on moderate to heavily traveled roadways, and NEVER for a parking lot.
I would recommend 1-1/2 inches of Type S3....no S1 except on moderate to heavily traveled roadways, and NEVER for a parking lot.
Ron, for example, 1 inch is the minimum thickness for Palm Beach County road sections. When I relocated here from Maryland and saw that 1" thickness-- well, the shock took a while to wear off. : )
We usually spec 1.5 inches bituminous for low volume road sections such as parking lots. The quality of the ubiquitous sand and limerock material lets you get away with that, but poor drainage can still kill the road.
We usually spec 1.5 inches bituminous for low volume road sections such as parking lots. The quality of the ubiquitous sand and limerock material lets you get away with that, but poor drainage can still kill the road.
Ron, I am with the local (Palm Beach) office of a regional, but good-sized outfit (+/- 500 employees). The company primarily serves Florida, Metro Atlanta, Gulf coast areas outside of Florida, the Bahamas, etc... It's Hellish, I tell you... 
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