I think it’s going to depends if you cross state lines . If you cross state lines you most likely need one . If not , you need a STATE DOT number which is different from the federal DOT number .
Do you know anyone who’s running a similar business ? if so just call them , take em to Lunch and ask
If its an exempt product you don't need an MC, even if crossing state lines. But I think asphalt and rock are NOT exempt.
I used to think that if you are staying in state all you need is a DOT number, but according to the FMCSA (https://www.fmcsa.dot.gov/faq/what-operating-authority-mc-number-and-who-needs-it) anyone operating as for-hire carriers (for a fee or other compensation) needs an MC as well. But I have heard they are getting rid of the MC number.