Stalactite

This will take some explaining.

This is in Central Park. The main body of water is called Iroquois Lake. Iroquois Lake drains to the east via a small creek that, as far as I can tell, has no name. The main road into the park, Iroquois Way, passes over the creek via a concrete bridge.

It's been dry and hot lately, so the pond's water level is low. Low enough that the outlet has dried up and one can now walk on the creek bed. Under the bridge.

Someone who shall remain nameless was chasing the rumour of a 'giant frog' under there, so we had to go. The ground wasn't too muddy, even though the sun never reaches under there. While walking around, a drop of water went down my back. Which seemed curious, since above my head is an arched bridge - water can't exactly settle on it. The day was hot and dry; it seemed most unlikely that water was seeping UP the bridge from the ground only to leak down on me.

As I looked for the source of this mystery, I saw dozens of these stalactites. To me, they appear to be calcium carbonate but I'm no chemist. They are hollow tubes and each one has a drop of water on the end, slowly growing. The base, where they connect to the 'ceiling' is in the middle of a chalky white patch, and they all appear to be growing along the seams in the concrete.

It's still a mystery to me. Is the concrete still curing after all these years?