ConCretin
Well-known member
Kevin54 has it about right so I'll just add a couple thoughts. A solid sub base is extremely important but shrinkage is the most common cause of cracks in concrete. Rebar, mesh and fiber won't prevent shrinkage cracks. Control joints just hide your shrinkage cracks in the bottom of the groove or saw cut.
Controlling shrinkage and associated cracking is possible but it requires careful planning and execution and has little to do with reinforcing. Most of the time it's just cheaper to cut some control joints. The old chestnut that starts with "there are two kinds of concrete......" is BS. You can place crack free concrete if you're willing to put in the time and effort.
In long, narrow structures such as sidewalks you are usually better off allowing for shrinkage rather than trying to restrain it. Though they are often referred to as expansion joints, planned breaks in concrete are really contraction joints.
If you run rebar through these joints, you prevent vertical displacement, which is good but you also restrict lateral movement, making shrinkage cracks somewhere else more likely. A better approach is to use smooth or plate dowels. This will prevent vertical movement i.e. trip hazards but allow lateral movement.
The only place I'd take exception to K54's comments is the thought that concrete isn't what it used to be. Today's concrete is stronger and more durable than ever. When future generations start trying to demo the structures we are currently building, they'll have a lot more trouble than we do today. It's not even close.
Controlling shrinkage and associated cracking is possible but it requires careful planning and execution and has little to do with reinforcing. Most of the time it's just cheaper to cut some control joints. The old chestnut that starts with "there are two kinds of concrete......" is BS. You can place crack free concrete if you're willing to put in the time and effort.
In long, narrow structures such as sidewalks you are usually better off allowing for shrinkage rather than trying to restrain it. Though they are often referred to as expansion joints, planned breaks in concrete are really contraction joints.
If you run rebar through these joints, you prevent vertical displacement, which is good but you also restrict lateral movement, making shrinkage cracks somewhere else more likely. A better approach is to use smooth or plate dowels. This will prevent vertical movement i.e. trip hazards but allow lateral movement.
The only place I'd take exception to K54's comments is the thought that concrete isn't what it used to be. Today's concrete is stronger and more durable than ever. When future generations start trying to demo the structures we are currently building, they'll have a lot more trouble than we do today. It's not even close.
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