Shear connectors, they allow for composite action between the steel girders and concrete slab, they are unrelated to expansion.The steel girders had what looked like rows of bolts on top (sorry forget their name) which are embedded in deck concrete slab.
It's unlikely to be that, any expansion of the bridge will cause the pavement to crack without expansion joints. From post #78 it looks like they have cast down into the earth at either end, which creates an integral abutment. This is where the bridge is designed to resist internal lateral stresses, and therefore does not expand. It is becoming increasingly common practice in the UK, as it greatly reduces maintenance requirements, as bearings and expansion joints are areas while are prone to failure.The road surface is not flat, road is on a slight hill. There is the a layer of stone between the two (the brown layer), which isn't the local stone, Oolitic limestone (Bath stone), or nearby Mendip stone, both of which are a creamy colour. With the brown stuff, when you watch the layers being compacted with a vibrator it appears to compress down like it is slightly spongy, presumably this allows for some movement.