runway pavement design

[danyul]

i am looking for suggestions on how to rehabilitate a runway.

the project has an existing runway which is in disrepair. meaning there are many potholes and drainage channels throughout due to the high level of rain. the current pavement is onsite crushed coral compacted and covered with a sprayed on soil cement. this cement spray does not last long and needs to be done too frequently.

the traffic would be 1-2 planes per month up to c-130 size.

the location is very remote. AC or concrete pavement is not an option.

we would like to use the onsite coral as base where the elevations are low. the subgrade is very dense coral.

the main problem is the wear and tear of the wearing surface. and maintenance of it.

any suggestions of a wearing surface that would be for long term use would be appreciated. tentatively we are planning a soil cement mixed with the onsite coral several inches. perhaps a cement treated base (CTB)as the surface?

thanks

 

[Ron]

I would go with a mix-in-place soil-cement. With the traffic you describe, make sure your mix depth is the maximum that you can achieve with the resources you have. The C-130 has contact stresses as low as practicable for the size of the aircraft.

Do a soil-cement mix design to get as much as you can out of the strength parameters....should be able to get in the 600psi range without too much difficulty. The coral is calcareous and will help the cement reactivity.

 

[motorbiketocrank]

From the conditions you describe, the surfacing is not necessary for "strength" purposes but merely to bind the surface material and protect the underlying aggregate and subgrade from precipitation, erosion, etc. I'd agree that cement modification of the coral "aggregate" would work but I'd also consider just a sprayed asphalt surface treatment. Also, proper grading of the runway and surrounding site will go a long way to prevent your current drainage related problems.....and pavement edge subdrains might also help.

 

[danyul]

thank you for the replies.

yes the bearing and strength of the soil is not really the issue. just the protection of the surface from loose gravels and erosion.

how long could we expect the sprayed asphalt to last under these conditions? right now the sprayed on product in use needs to be maintained every year. this is too often considering the location and difficulty of bringing in the product.

 

[Hoaokapohaku]

Re longevity of "sprayed asphalt" - There are many variables that will affect outcome such as grade of asphalt product used, application rate, degree of penetration. Can cutback asphalt products be used? Cutbacks generally work better than emulsions for this type of application but are used less and less often because of environmental concerns. However, cutbacks applied on a material that is conducive to penetration can last for many years. Circa 1996, I experimented (and succeeded) with formulating and manufacturing cutback grades MC-30, MC-70, MC-250, and SC-3000. The resulting experimental products, whether they met spec or not, were applied to an aggregate base haul road used primarily by large heavy off-road rock trucks. The material is still in place today and there are about 5 to 10 patched potholes along its 30' wide, 1.5 mile length, and this in a location known as the rainiest city in the USA. The particular base material on this road is very conducive to good penetration with an asphalt cutback.

The short answer - if an asphalt product will get good penetration in your coral base, you can expect that you can get years of use from a properly applied asphalt product. Cutbacks will work best, and if you can count on a good 24-48 hours rain-free, sunny days, for cure time, environmental risks are minimized.