"When is the right time to cut a saw joint in concrete, and what is the proper blade to be used for cutting?" Ask 10 different concrete contractors these questions and chances are good that you may receive 10 different answers depending on the project, ambient conditions, the aggregates used in the mix, and whether the concrete is recently finished or has been in place for a number of years.

In order to address such questions, Concrete Construction published this special issue to examine a plethora of concrete joint cutting and sawing-related technical topics. In addition, we've opted to address a subject related to a final phase in the preparation of floors: diamond polishing.

As many of you know, the cutting or sawing of joints in freshly finished concrete should be done as soon as the concrete has hardened enough to prevent aggregates from being dislodged by a saw blade and the concrete edges from raveling. Of course, determining exactly when the concrete is ready to be cut is a concern that has long plagued concrete contractors, primarily because the proper time to cut or saw joints depends on the variables I mentioned earlier. As a general rule, concrete joints should be cut 4 to 12 hours after the concrete hardens. The thinking behind this guideline is that the concrete has developed enough strength to prevent raveling as the saw is cutting. However, partly due to experimentation and partly due to necessity, concrete engineers discovered that it is possible to begin joint cutting concrete even sooner in some instances.

This option is ultra-early entry joint sawcutting, which allows a contractor to cut contraction and control joints one to four hours after the final finish. With ultra-early entry sawcutting, joint installation can begin when the concrete has a compressive strength of 150 to 500 psi, perhaps even as low as 25 to 50 psi.

When it comes to the physical act of cutting joints into concrete, diamond sawing is the preferred cutting technology for concrete contractors. However, selecting a blade is not as simple as you may think. For example, blade operating speeds, tensioning, and the type and size of aggregate used are some of the measures to consider when selecting the proper blade to ensure effective concrete cutting.

Both ultra-early entry and diamond blade selection are two of the topics examined in this special issue, sponsored by Husqvarna, a manufacturer of a wide variety of equipment used by concrete contractors including concrete cutting saws and diamond polishing tools. Only the top experts per the specific technical features were considered as authors.

Additional topics covered in this special issue are the methods of properly choosing and using diamond polishers to ensure a high-quality polished floor. We examine the basics of floor cutting and warehouse control joints in order to minimize random cracking as well. Finally, this special issue includes three projects that incorporated saws used to cut concrete in a vast array of projects.

We hope you enjoy this special issue, and feel free to send us any feedback.