Question. How can a diamond be used to cut concrete?

Answer. We asked Pat O'Brien, executive director of the Concrete Sawing & Drilling Association, to give us a primer on how diamonds cut:

A diamond saw blade is composed of a circular steel disk with segments containing the diamond that are attached to the outer perimeter of the blade. The diamonds are held in place by the segment, which is a specially formulated mixture of metal bond powders and diamond that have been pressed and heated in a sintering press by the manufacturer. The diamond and bond are tailor-made to the specific cutting application. The exposed diamonds on the surface of the segment do the cutting. A diamond blade cuts in a manner similar to how sandpaper cuts wood. As the blade cuts, bond tails are formed that trail behind each diamond. This bond tail provides mechanical support for the diamond crystal. As the blade rotates through the material, the diamonds chip away at the material being cut.

Contrary to a popular advertising campaign, a diamond is not forever. The exposed diamond cutting points eventually wear away, and if not for some provision to replace these cutting points, the blade or bit would soon be useless. This process is actually desirable since it provides a new layer of diamond crystals to continue the cutting action.

The ideal life of a diamond starts as a whole crystal that becomes exposed through the segment bond matrix. As the blade begins to cut, a small wear-flat develops and a bond tail develops behind the diamond. Eventually, small microfractures develop, but the diamond is still cutting well. Then the diamond begins to macrofracture, and eventually crushes. This is the last stage of a diamond before it experiences a popout, where the diamond quite literally pops out of the bond. The blade continues to work as its cutting action is taken over by the next layer of diamonds that are interspersed throughout the segment.