#civil stuff

[secondwhisper]

I'm currently attending a training on accommodating pedestrians in road work zones. It's really interesting to see how (ADA-compliant) accessible pedestrian infrastructure implementation is discussed in professional engineering spaces (as opposed to general disability spaces).

We have three groups of disabled road (+sidewalk) users that we must focus on design for: visually impaired & blind pedestrians, mobility impaired pedestrians, and cognitively impaired pedestrians. In this context, mobility impairments also include walking unsteadily, slowly, or with low endurance/stamina.

Generally, we must aim to provide the following accommodations for disabled pedestrians. For the visually impaired: high-contrast signage & markings, ground-level channelization as a "shoreline", a smooth and level walking surface, no protruding objects, smooth and stable hand guides / railings, and auditory and tactile guides at crossings or other complex maneuvers. For the mobility impaired: no protruding objects, no side barriers that could interfere with manual wheelchair or crutch use, a smooth level and grippy walking surface, smooth and stable hand guides / railings, and "refuges" on particularly long routes. For the cognitively impaired: high-contrast signage & markings that are clean and concise, arrows that point in exactly the correct direction, and channelization that reduces opportunities for someone to accidentally end up in a traffic lane.

We see some similarities across access needs: clear signage / guidance, barriers or other channelization to make wayfinding easier, no protruding objects, smooth and stable surfaces.

There's also one very glaring conflict in access needs: channelization. Barriers that reach the ground, and barriers with railings, help blind & visually impaired pedestrians move in the correct direction with confidence. Barriers to channelize the pedestrian detour path help cognitively impaired pedestrians keep within pedestrian zones and move confidently to the end of the detour. Barriers with railings can provide support for unsteady and fatigued pedestrians. But barriers at the edge of the pedestrian route give cane, crutch, and wheelchair users just one more thing to whack their knuckles, elbows, and devices on, and can reduce their ability to turn or recenter themselves, along with removing the ability of able-bodied pedestrians to get out of their way in narrow places.

I don't have some kind of big conclusion here, I just thought it was interesting to see that cognitively disabled pedestrians are included among those whom sidewalk closures can affect uniquely negatively, and to see a frank discussion of how not everyone with vision & mobility disabilities are helped by each other's accommodations. Within the broader context of "work zones are super inaccessible we have to start doing it right."

[secondwhisper]

Materials testing ASMR. Rolling a clay sample for a plastic limit test, HMA quartering, unmolding a compacted sample, rodding a concrete test cylinder. Proctor test if you're feeling silly

[secondwhisper]

My new (least) favorite (not actually fun at all) fun fact about roadways is that apparently in the 60s some real fucking geniuses (/s) built a bunch of pipes to carry roadway runoff directly into sinkholes.

So anyway now the sinkholes have grown, sections of our roads are sinking unexpectedly, mysterious karst cave ecosystems are probably dead of road salt and oil, and we don't even know where all these drains are because the construction plans were either lost or destroyed.

[secondwhisper]

My supervisor: The Ohio River is eating out the soil under our roadway again :(

Me:

[secondwhisper]

Idk since I'm bored at work & tired of seeing that post that claims "no one knows how Roman cement worked it's a big mystery and modern scientists/engineers are still stumped because the recipe was lost so modern concrete sucks, comparatively"

Roman concrete is .. actually not much of a mystery. I mean, first of all, it's got a pretty thorough Wikipedia page. Surviving sources written in the height of the Roman empire describe how to make concrete (and in the same section say not to use lead pipes for drinking water). There isn't a surviving exact recipe with ratios laid out, but we know Roman concrete had four components: lime (the mineral, not the fruit), volcanic ash (a pozzolan), rocks (aggregate), and water.

Lime is the main component of modern cement, but we've modernized how it's prepared from limestone. Modern cement concrete also has aggregate in it. Cool, we're 50% similar with Roman concrete! Today, we make concrete with fresh water - Romans may have used fresh water in some situations, salt water in some, maybe a mix, this part isn't super clear. But with 50-75% of modern concrete components being identical to Roman concrete, why is our concrete so much worse*?

That final component - the pozzolan - is really, really important. It reduces concrete's vulnerability to salt. The chemistry isn't totally clear, here. I'm not a concrete chemist, but from my understanding: salt makes lime concrete disintegrate, salt makes pozzolan concrete crystallize. This is the part that's still being studied. So, Roman engineers might have mixed some concrete with seawater, so that if the sea touches it, it still holds together for .. well, 2000 years and counting?

The obvious answer, here, is start putting pozzolana in modern concrete! In the past decade or two, pozzolan additives to concrete have gotten fairly common. It might have always been a component, but recall that Roman pozzolan was volcanic ash. Most the world (especially the Midwestern US, where I am) doesn't have volcanoes that explode all the time. So, we had to discover different pozzolana - it turns out that very fine ash from burnt coal, and byproducts of steel refining, are pozzolan materials. So now, we can put those in concrete and get better resistance to salt! (Environmentally-friendly concrete is .. a different conversation.)

So, that's the difference between modern and Roman concrete!

*Modern concrete isn't any worse than Roman concrete. I don't just mean that we're re-developing salt resistant concretes. I mean that Romans didn't have semi trucks, blizzards and ice storms, snow plows and salt trucks, or rapid freeze-thaw cycles getting ever more rapid as climate change progresses. Most of the American Midwest, where I live and work, has all of those things. Most non-tropical areas in the modern world have most of those things, too.

(For example, Rome today has no annual freeze-thaw cycles. It stays above 32°F year round. My town has 3 freeze-thaw cycles in a mild winter, and often is cold enough to freeze salt water. Roman concrete exposed to these conditions lasted less than 30 cycles - or the equivalent of 10 years - before just falling apart.)

So, our concrete isn't really that much worse than Roman concrete - we're just asking more of it.