It's not clear why you are compelled to do this, or what benefit for either party would be achieved by doing it.
What do you hope will happen by telling your "day job" about your "concrete company"?
What do you hope will happen by telling your "day job" about your "concrete company"?
Otherwise it's not dishonest. There's nothing unethical about earning money while also delivering on the promises made as a contractor for someone else.
In case that's not obvious enough, consider this scenario:
You're an actual employee at the day job, not a contractor. On the weekends you like hitting up thrift shops looking for antiques which you then sell on eBay.
Is it dishonest not to talk about that to your employer?
Not talking about something doesn't mean automatically mean it's dishonest. Just like I'm not talking about what I just ate for dinner, not talking about additional ways you make money doesn't mean you're being unethical, immoral, unkind, or dishonest.