On most repair projects, we find that delaminated and deteriorated concrete often extends beyond the boundaries determined by chain dragging. For this reason, we usually prefer to chip out the deteriorated concrete first, then sawcut around the perimeter. But some owners and engineers object to this, saying that we should make the sawcuts first so our workers have a definitive point at which to stop chipping. Which method is correct?
This subject is often a source of great debate between owners, engineers, and contractors. The answer depends on which you believe to be a more accurate tool for identifying deteriorated concrete the chain drag or chipping. Neither method is very scientific. The chain drag relies on the operator detecting differences in the tone produced by the chain dragging across the surface. A hollow sound indicates a delamination; a ringing sound indicates good concrete. Some operators may not be able to hear the often subtle difference between the hollow and ringing sound. To differentiate good concrete from bad when chipping, one rule of thumb is that aggregate particles in sound concrete will fracture when hit with a chipping hammer. In deteriorated concrete, they will simply separate from the cement matrix. However, in some lower-strength concrete, the aggregate may not fracture even though the concrete is sound. Once again, the method is subjective. It's in the best interest of all parties to have all deteriorated concrete removed. Meet with the owner and engineer and point out areas where deterioration extends beyond the boundaries outlined in the condition survey. Then remove the remainder of the damaged concrete. If you can gain the trust of the owner and engineer, you may be able to get payment for additional work.