Itc on works contract

Could someone please provide the clarification for the following

1. As per the notification 20 of CGST act, the work contract tax has reduced to 12% from 18% with full ITC. My doubt is that my client purchasing materials and consumables at the rate of 28% and 18%. So the GST rate on materials procured for works contract execution which is more than the works contract rate. This lead to an additional benefit work contract supplier. Is it correct, can we claim the ITC more than the works contract rate? Please clarify with applicable provisions.