If it's large enough for rail service, I can see a need for petroleum products in tank cars and aggregate in open hoppers. Other supplies could come by boxcar and machinery on flats.
Many asphalt plants are located near their supply of stone. A couple around here that I'm aware of are located on stone quarry property, and another dredges stone from the local river. It would have to be a really isolated plant with high volume to get the main ingredients by rail, but in our miniature worlds, we can do whatever we want.
Tank cars or tanker trucks with HOT tar and other petroleum products, aggregates in open hoppers, maybe a covered hopper of fly ash or soda ash, and covered hoppers of sand. Out bound could be anything from dump trucks of asphalt for roads, box cars of shingles. https://en.wikipedia.org/wiki/Asphalt_plant
Several near me used to have only the asphalt brought in by rail. Most everything else was brought in by trucks for many years. And now even the asphalt is brought in by truck. Of course the aggregate is near by so it's trucked and dumped in a pit. Front end loaders move it to elevators to make huge mounds. Some also have piles of reused material. For highway construction the equipment is mobile so that the ingredients are mixed on site as needed.
I know you asked about asphalt, but there was a large ready mix concrete operation in Wichita Kansas that brought in aggregates by rail. I would imagine they would also receive bulk cement that way as well. I don't know what source of supply there is close to Wichita, but I do know there are several cement manufacturing plants in eastern Kansas. You could do aggregates and asphalt tanks, if the plant mixes asphalt you would have dump trucks for hauling the mixed asphalt. If you have a asphalt paving company there as well you would need lowboy trailers, rollers, lay down equipment and distributor trucks. Also all the other associated construction equipment. You will also need tanks for bulk storege of oils and emulsions, and the equipment for unloading tank cars and hoppers, piping and conveyors. If I remember correctly, Walthers makes a asphalt plant. If you model one, please post up some pictures of it.
The OPs reference to dump trucks & front end loaders implies the road material, but another asphalt plant is the refinery that produces asphalt, the tar. Look at the Valero asphalt plant on bing maps and/or google maps. Address is 1651 Alameda St, Los Angeles, CA. It has a small cracking tower similar to the Walthers refinery, several storage tanks, a tank car loading rack, truck loading rack and office. It sits in between some large refineries, but is a relatively small industry itself.
I have a friend who owns a paving company and at the plant close to us, nothing comes in by rail. The plant is in a rock pit where they operate their own crushers to get the size aggregate they need. Front loaders do the all of work loading the proper size aggregate needed for the asphalt. The oil which has to be hot is trucked in from a refinery about 150 miles away. Even though the plant is right alongside the BNSF tracks, everything is done by truck.
