When ACI 506.2-95, "Specifications for Materials, Proportioning, and Application of Shotcrete," was adopted in 1995, one of the most controversial sections required a visual core-grading system for evaluating reinforcement encasement. Five grades were established, with grade 1 indicating the highest quality and grade 5 the lowest.

The core-grading requirement is still a contentious issue because some industry experts question its reliability. Concrete Construction asked former ACI Committee 506 chairman, Steven Gebler, Construction Technology Laboratories, Skokie, Ill., and Leon Glassgold, current chairman of ASTM subcommittee C 09.46, Shotcrete, and chief engineer of Masonry Resurfacing and Construction Co., Baltimore, to discuss the issues involved.