What is the point of inserting new concrete rectangles into a concrete freeway?

Here in Hillsborough County, Florida the highway authorities have been doing a reconstruction project on Interstate 275 and Interstate 4 that’s likely to be going on for a couple of years yet. Some of this is widening, adding another lane, and some of it is adding extra on-ramps, which are urgently needed where the two highways meet at the downtown “malfunction junctions.” But recently, one thing they’ve done is dig rectangular sections out of I-275 – sometimes covering one lane, sometimes two – and then fill them up with fresh white concrete. In some stretches they’ve dug and filled a whole series of these holes, one after the other, so surface looks like gray-and-white stripes and the drive is a bit bumpy. I can’t understand why. They’re not patching or repairing anything; the concrete surface was just fine before they dug the holes. Does anyone understand the purpose of this?

They could be testing different candidate materials for wear/durability properties.

Or it could be that, although no visible defects were present, a survey vehicle had detected problems within the material of the road surface.

Or that they’re installing some kind of sensor below the road surface, to monitor traffic flow/weight, or to control the implants in the base of your skull.

How many? It could be that they are installing traffic sensors to measure traffic flow, especially if the highways are as crowded as you indicate.

My father is a retired roadways civil engineer, so I think there’s a good chance he’ll be able to answer this.

I’ve emailed the link for this thread to him. He and my stepmother check email rather infrequently, so I’m thinking if I haven’t seen a response from him by late afternoon tomorrow, I’ll give him a call and ask him to check the email I sent.

Most likely there were defects in the original slabs. These could include differential settlement, i.e., one end sags or rises below or above the edge of an adjacent slab, causing a noticeable bump. There could be hairline cracks, visible only to close inspection, that could lead to future larger cracks. There could be spalling, or flaking off, of parts of the surface, though this is more common in northern states where snow-melting chemicals can more quickly deteriorate Portland cement concrete pavements. There could be settlement of the foundation material under the slab, due to sinkholes or inadequate drainage. This can be found by rolling densometers that measure the density of the underlying strata. Also, the slabs are usually “connected” to adjacent slabs with dowels that bridge the narrow gaps and these may have deteriorated, leading to settlement. Or, they could have been installing expansion joint material between slabs to prevent blowup of slabs after extended periods of very hot weather. When this happens, two adjacent slabs expand longitudinally against each other and if the expansion joints are too narrow or nonexistent, the common ends of both slabs, or maybe just one end, can pop up explosively way above the end of the next one, causing the road or the lane(s) to be shut down until repaired.

A whole lotta many. Dozens.

Yow. In the 60’s and 70’s there was speculation about whether a politician had “presidential timber.” Now, they become one with the highway if they’re “candidate material.” It’s a rough business. :rolleyes:

I’ve wondered too.

My father, the retired civil engineer I mentioned earlier, replied with a point about the bumpy drive that BrainGlutton had mentioned. He wrote: