How the hell did we ever make the gigantic, interconnected system of roads we now have? The sheer scale of it boggles the mind, and while pondering it, I realized I didn’t even know how a single local road is built, much less the entire amazing interstate system.
I mean, you have this random mountain somewhere with hostile terrain, loads and loads of giant trees, random rocks, etc., and all of a sudden there’d be a paved road running through it. How do they remove everything that’s there, make it all flat, get the necessary raw materials (gravel? asphalt?), transport it all there, lay it all down, paint miles and miles of lane dividers, lay down perfectly-placed reflectors, etc.?
Just driving through some of these mountain paths makes me uneasy; I can’t imagine what it’s like having to work to build them before infrastructure was available. How long does the average road (if such a thing even exists) take to build?
I’m a curious person and I’m sympathetic to the desire to want to know about specific things but asking for the A-Z of modern road building to be delivered to you without your even **trying to look anything up before asking the question is kind of weak.
With all due respect, astro, I’m as curious as Reply and the links you provided (helpful as they were) leave a huge gap between the design and earthworks/construction phases.
I understand house plans. I can’t figure out what kind of plan a road construction crew works from when faced with a mountain the designers have determined the road should go through.
They would have an overhead topological map indicating the existing terrain, planned future terrain, the road right of way, areas that need to be cut and backfilled. They would probably also have elevation drawings.
The others have provided good info on the overall process but I think you might be wanting more specifics. I work in a lab testing roadworks (Austrailan tests are based mostly on US models so it should be applicable) so here are some details from the actual building. Should answer about 25% of your question.
The material used for the road construction is tested to make sure it near enough to ‘optimum moisture content’ for maximum compaction. In the lab we take a sample dug from the roadwork and compact it with hammers (the weight and number of blows determined by national standards),measure density, mix in or dry out a bit of water, repeat some more, and work out at what moisture content does the material achieve maximum dry compaction. Depending on what layer studied (fill, subgrade, subbase, base) the density of the material measured on the field must lie within a certain percentage of the optimum value from tests (around 90% for fill I think, but gets higher for the uppermost layers of the road). To put a number on this, in my local area this test must be performed at intervals of 50m along any roadwork being constructed. Considering there are 4 layers at each point, this amounts to a lot of testing for a length of road. As a rough guess about 5% fail and need to be relaid/wetted up.
Additionally, raw materials from the quarries are graded before distribution. For certain types of construction there are particular particle size distributions allowed. So raw materials are seived and the size ratio of the stock is determined to see if it is suitable for a particular use. This test fails about a quarter the time at first when sourcing new material and devising a new blend, so the quarries put a lot of work into making their mix work.There’s also other aggregate tests relating to rock shape and linear dimension performed less frequently which goes along with this.
There are also less frequent test that are done on soils, not always for just road work, but these include soil type classifisation (mostly about dispersion properties) and measuring the liquid and plastic limits (look up wiki atterberg limits and emerson class for good explanations on these). I also haven’t described the other test that are done on drainage materials along the sides of the road. These are density tests for non-binding materials.
As an endnote, and Im willing to submit to anyone who has a cite to the contrary, I’ve heard that regular asphalt road have a typical lifetime of 5 years and concrete about 25. So hopefully I don’t have to worry about any recessions taking my job any time soon
Asphalt roads are a type of flexible pavement road. Most of their strength comes from the compacted material below the asphalt, consisting of a well-graded mixture of processed aggregate. (“Well-graded” means that there is a uniform distribution of aggregate size, ranging from 1-inch to fine particles that can lock together.) The thickness of this compacted material ranges from 6 inches thick (for driveways) to as much as 24 inches thick (for highways).
There are also different grades of asphalt. More durable asphalt contains larger pieces of aggregate (i.e. rock), but has a less smooth surface. Asphalt with smaller aggregate is less durable, but has a smoother driving surface. Most roads are made up of layers of more durable asphalt on the bottom, and smoother asphalt on top.
The top layer of asphalt is sometimes referred to as the “wear course,” as it wears out fairly quickly. However, this layer is easily milled off and replaced. This is referred to as “road resurfacing.” Depending on traffic, a road may require road resurfacing every 5-10 years.
Asphalt roads should last 20-30 years before complete road reconstruction is needed, meaning removing and replacing all of the layers of the road, including the compacted subgrade beneath the asphalt.
Concrete roads do tend to last longer, but are much more expensive to build in the first place, and if the subgrade is not properly installed, they can crack. (Concrete is not flexible like asphalt.) Any settlement or subsidence that occurs will also cause them to crack. Around here, most of the concrete roads that were built in decades past have since been overlaid with asphalt.
