apodino From United States of America, joined Apr 2005, 3386 posts, RR: 7 Posted (4 months 6 days 23 hours ago) and read 3120 times:
One thing I have noticed in recent years is that almost all of the new runways being built in the US seem to be Concrete runways. This includes the rebuilt 7R-25L in LAS, the rebuilt 13R-31L at JFK, the new runways that have been built at CLT, CVG, and ORD to name a few. However I also notice BOS continues to use Asphalt to rebuild runways at BOS, even going as far as touting a warm mix asphalt that they use which is more enviornmentally friendly. My thing is, Concrete seems to be better for the environment than Asphalt from what I see. That aside, I notice that all the surface movement areas at BOS are asphalt and there is a lot of cracking that keeps having to be sealed, which I have not seen at airports with Concrete.
So my question is this, why is BOS using Asphalt instead of Concrete, when everyone else seems to be using Concrete, and is one really better than the other? Concrete seems better to me, but BOS still won't use it.
B6JFKH81 From United States of America, joined Mar 2006, 2406 posts, RR: 2 Reply 1, posted (4 months 6 days 22 hours ago) and read 3102 times:
The two points that immediately come to my mind are:
COST: Concrete is more expensive than asphalt.
TIME: It takes longer to do concrete than asphalt (unless you get pre-made slabs), which means longer down time for the runway, backed up operations at the airport, etc. A good example is the JFK Bay Runway which took months to do in multiple phases, and there were multiple times where JFK went down to SINGLE RUNWAY OPERATIONS. All 3 of the airlines shown in the picture below extended reduced/winter schedules to help reduce the backlog, but that hurt the airlines, and in some cases the reduced flying didn't help at all because you were dealing with only 1 runway.
Starlionblue From Greenland, joined Feb 2004, 15102 posts, RR: 69 Reply 3, posted (4 months 6 days 18 hours ago) and read 2957 times:
It depends on many factors:
- Climate, meaning prevailing temperature and humidity.
- Initial cost.
- Initial construction time.
- Maintenance cost.
- Expected lifetime.
Also, while we tend to think of asphalt and concrete as "static" technologies, they are still being developed, meaning new compounds and so forth. In other words, which one is correct for a certain application can change over time.
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Northwest727 From United States of America, joined Jul 2005, 475 posts, RR: 1 Reply 4, posted (4 months 6 days 5 hours ago) and read 2741 times:
Asphalt also degrades faster than concrete over time due to 1000ºF/538ºC jet exhaust being blasted over it constantly. I have personally seen the effect while interning at a major class B airport, the runway started having "ripples" all over the place that needed to be replaced, especially around the touchdown markers (where aircraft are flaring mostly).
JayinKitsap From United States of America, joined Nov 2005, 761 posts, RR: 1 Reply 5, posted (3 months 4 weeks 1 day 1 hour ago) and read 1879 times:
It's cost, local practice, and technology. Also, the economics of one v the other change with the market.
a) Asphalt pavements are more flexible, but the wheel load transmits to the native earth basically in a pyramid through the road base. A given amount of movement in the subgrade can be tolerated in asphalt that would crack concrete.
b) Asphalt pavements on typical city roadways is around 4 inches, main roads and highways are thicker, typically 6 to 8 inches. Taxiways are similar, major runways are 10 to 12 inches. As there is about 5% oil in asphalt, cost is significant.
c) Concrete has improved a lot over the last 40 years, reinforced concrete can spread the load out a significant distance to reduce the loads to the underlying soil. Also, less joints and better levelness.
d) An unseen thing is the addition of reinforced plastic grids in the gravel base below. These geogrids make the subgrade much stronger, allowing a thinner pavement, both concrete and asphalt.
Currently, concrete is probably the preferred material for runways, with a tossup for taxiways, and preferred for aprons. Both take a lot of energy to produce, with the cement making process using using coal vs oil.
NBGSkyGod From United States of America, joined May 2004, 499 posts, RR: 1 Reply 6, posted (3 months 3 weeks 3 days 22 hours ago) and read 1473 times:
It has a lot to do with the New England climate, there are very few runways up here that are completely concrete. There are a few that are mixed with concrete portions, but for the most part its all asphalt. The main reason for this is the fact that asphalt is more flexible in changing temperatures where concrete is much less.
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