It is often necessary to cut concrete for creating a channel, to install new pipework or conduits, or when you need to expand a sidewalk. If the concrete to be cut is about 4″, this is something that you can easily do with the right equipment. Thicknesses over 6″ are best left to professionals.
What you need basically, is an electric circular saw equipped with a diamond blade. You can always use abrasive blades to cut concrete, but these wear out so quickly, that for a single project you may need to replace several blades. Abrasive blades need greater force to be applied and this can often lead to loss of control over the equipment and lead to accidents. It is far better to make the larger investment in a diamond blade and do your work safely and far more easily.
Using a circular saw with a diamond blade will still require you to take all necessary steps for safety. This must include a mask over your face, as the cutting of concrete can create a lot of dust that can create unhealthy conditions. Besides this, use knee guards and shinpads to protect your legs from the uncomfortable position of your having to bend over while using the saw. Your equipment must also be properly grounded especially if you plan to use water to reduce the dust from the cutting of the concrete.
For a 4″ concrete slab your circular saw blade must be at least 7″. If you are using water, use a wet cutting diamond blade. The use of water reduces dust and also extends the life of the blade, as it will keep its temperature under control. Your seven-inch blade will cut to a depth of about 3 inches requiring you to chisel the rest. A 14-inch blade on the other hand will cut right through the 4-inch slab.
If you are using water, make sure you have a constant supply of water in a trickle over the cut. Also, make sure that the water can drain off easily so that things are less messy. If you are cutting a vertical wall, spraying water may be more of a problem and you may require someone to assist you. If you are using a dry process, allow the saw to cool down at intervals, while you also make sure that the dust that is raised does not become unmanageable.