Cutting joints in fresh concrete is accepting the inevitable. As the concrete hardens, it will crack. Adding joints is how a contractor controls where the concrete cracks. Although it is possible to put in control joints using a grooving tool, the best way is to use a saw.
Saws for this practice can be broken up into two main categories: early-entry saws and walk-behind saws. Early-entry saws are lighter weight and usually have smaller blade diameters. Ideal for short-run slab cutting, these machines are perfect for contraction joints and trenching. Walk-behind machines include the heavier saws for deeper cuts in concrete pavements, and smaller models for cutting joints in concrete flatwork.
Although there are contractors who specialize in cutting concrete, it is not uncommon for concrete contractors to do some of the work themselves. So when choosing a saw to fit your particular needs, there are several variables to consider including depth of cut, blade size, revolutions per minute (rpm), weight, propulsion, and power source.
Timing is critical when working with fresh concrete. If you wait too long, the cracks will have formed already, and if you get on the concrete too early, you could mar the surface finish.
When operating conventional walk-behind saws, ACI 302.1R-04 recommends that control joints be cut at least one fourth of the slab depth. Longitudinal cuts on concrete pavements need to be deeper, at least 1 inch, particularly when using early-entry saws.
Early-entry saws, invented in the late 1980s, address the longitudinal cut depth. They allow contractors to get on the concrete earlier, typically one to four hours after finishing depending on the ambient temperature, or as soon as the concrete can support the weight of the equipment. As a result these saws tend to be lighter weight.
One advantage of using an early-entry saw is that the sawcut does not need to be as deep. For that reason, early-entry saws don't frequently use large blade diameters. Sawing fresh concrete typically is faster than hardened concrete, and involves less wear on the blade.
Early-entry saws are a bit different than walk-behind models. Early-entry saws typically are “up-cut” saws with the rotation of the blade in the direction opposite of walk-behind saws. The up-cut helps push the debris out of the joint. Up-cut saws are used with crack repair and restoration projects.
These saws also are designed for use without water for cooling, often referred to as dry-cut saws. Some early-entry saws have skidplates that straddle the blade to minimize any crumbling of the joint edges, otherwise known as raveling.
Walk-behind saws for cutting joints in pavements weigh from 1300 to more than 2000 pounds, with higher horsepower engines (some as high as 85 hp). These machines run on gasoline or diesel. Because of their size, they are self propelled, usually capable of cutting up to 30 feet per minute, depending on the depth of the cut.
Cutting depths vary based on the diameter of the blade. When choosing a model, pay close attention to the blade capacity. Some machines allow a wide range of blade diameters for many different applications, making the equipment more versatile across jobs. This variety is perfect for contractors doing a lot of road repair, trenching, and joint or floor sawing.
Handles on walk-behinds should be well balanced and adjustable, if possible, because the range of motion on the unit can change over the course of the job. The feel of the machine can make the difference between fighting with the cut or moving smoothly.
Walk-behind saws for floors are smaller than their pavement counterparts, running up to 1000 pounds. Here the options include gas, electric, and even air power for enclosed spaces. Engine sizes are smaller, too, usually not much more than 30 hp. Again, because of their size, they feature hydrostatic drives, though smaller models (which are making shallower cuts) can go faster. Some smaller models require the operator to push the saw.
Smaller floor saws have engines from 13 hp down to 4 hp. With these machines, the speed of the blade can run to 3000 or 4000 rpm. This compensates for weights ranging from 300 pounds to as little as 100 pounds.
The compact, small floors saws are great for cleaning out joints in parking garages, work on airport runways, bridge decks, swimming pools, and other concrete surfaces.
Noise and vibration are two more issues to keep in mind when looking at saws. Government regulations are demanding quieter machines, as well as ones that won't cause long-term damage to the operator. The fewer vibrations the unit has means the longer the worker can be on that job.
Choosing the right saw can be difficult. There are many models, sizes, and options to choose from. Don't be afraid to rent a saw for a short period just to give it a try. Experience is the best method when choosing a saw.