Tuesday, May 24, 2016

Construction Mystery Photo: Concretometer? iPod? Seismometer?

What on earth is going on in the photo above? Let's do some SAT-esque process of elimination! We know it can't be choice A, because this concrete is way too young to have any familiarity with the band Pavement and is really more of a Drake fan. B seems feasible, but we've seen enough earthquake news footage to know seismometers don't look like the device in the photo—they have a needle that draws wavy lines that tell us how much to panic. (Do not panic during earthquakes. Be prepared.) C can't be correct because the best way to test concrete "doneness" is to stick a toothpick in it and see if it comes out clean.* That leaves D as the correct answer.

The concrete and rebar in the photo is part of the structural support for the I-5 bridge over the Los Angeles River. Embedded in the concrete is a galvanic anode protection system, which helps minimize corrosion of the reinforcing steel. The system works by connecting the metal to be protected (the reinforcing steel) to a more easily corroded metal, aka a sacrificial metal. The sacrificial metal then corrodes instead of the protected metal, which helps reduce maintenance and repairs. The meter is the photo is measuring the electrical current to make sure the system embedded in the new concrete is working as intended.

The structures shown are part of the I-5 carpool lane project between SR-134 and Magnolia Boulevard. Learn more about the project here.

* The toothpick method doesn't actually work for concrete—unless you use chocolate chips and walnuts in place of aggregate.