Maybe remote sensing or hedonic mechanism

You might be interested in an observation I made last week.

The Project I am working on is removing a bridge with steel girders, and

a rebar reinforced concrete bridge deck. Because the bridge is over four sets of

railroad tracks, the bridge deck is being sawn into six foot wide strips, picked up

carefully, and placed into a haul truck to be hauled off. the concrete and steel over the two abutments and the three piers is in good shape both on the bottom and top mat of steel, but the concrete and steel are rotten over the centerline of the UPRR tracks, but only on the bottom mat, the top mat is still in good shape.

The Bridge is only 47 years old, and the columns and pier caps are spauling off

sheets of concrete, as is the bottom of the deck within 20 feet of the center line of the tracks. When picking up the slabs using a track hoe with a thumb, the entire lower two inches of concrete falls off in sheets, and the lower mat of steel dangles as it is

no longer attached to the concrete at all.

The effect is obvious as the delamination follows the skew angle of the bridge and is parallel to the axis of the tracks. The bottom of the concrete is black with white effervescent cracks over the entire surface above the tracks, but looks like normal concrete without cracks more than 20 feet away from centerline.

The other RR, the BNSF, does not show this effect, as it has about 1 train per day

passing under it, while the UPRR has up to 34 coal trains, and two Amtracks

passing under it where the delamination occurs.

Since the Bridge is only 47 years old, the fuel used has been Diesel Fuel, and it

was probably not low sulfur diesel. Apparently Carbon effects concrete, as does

sulfur. The effervescence should be the result of Calcuim Ions combining with the

Sulfur dioxide and moisture to create a dilute sulfuric acid, which combines with

the calcium to produce Gypsum. The carbon has something to do with the

reduction of the PH in concrete so that when it drops from 13 to below 11, then the

moisture can attack the rebar and create rust, which expands, fracturing the concrete

in sheets along the plane of the bottom mat of rebar. The cracking (random pattern cracking) on the bottom of the concrete allows gasses to enter the concrete allowing

an acceleration in the process of detrioration.

This same pattern should show up under bridges that have truck traffic, but it will

be more widely distibuted as truck locations and smoke stacks vary in location, while on trains, the alignment and the stacks are always in the same location.

This is a model of acidic attack on the infrastructure that can be compared to locations such as stream crossing bridges that do not have diesel fumes

attacking their under sides.

Thank you for sharing this interesting experience,,,