The company business is leasing trucks.  So the company did purchase and actually use them for their business.  Since they are not used by company as a vehicle, I would list them as equipment.  Thus you can depreciate or Sec. 179 the cement trucks as any other business asset.

However the only caveat in this type of business is terms of the lease.  If short term, temporary or operating lease then all is good to go for 179 deduction.  If the company leases the vehicles out in a capital type lease, it is really considered a sale by the company to the lessee.  Then 179 may be denied or required to be recaptured on the sale if it is a capital lease/sale.