Concrete will expand and contract with moisture and climate changes. The change in volume of the concrete will cause concrete to crack. Control joints are either tooled or most often machined sawed to give the newly poured concrete a designated weakened place to crack during curing time shrinkage and later once hardened due to curing and climate changes, as it takes 28 days for concrete to cure to 90% of its hardness.
Control joints are placed strategically to give the concrete a place to move, and in essence crack. Please note that it is not a guarantee however that it will not crack in another area.
Control relief joints can also be achieved by using expansion joint material approximately ¼” to ½” in thickness. It is either sponge rubber, plastic or other material highly weather resilient. Expansion joint is usually used when concrete is poured to join or abut an existing slab or structure of any type. It can also be used in place of hand tooled joints and sawed joints as well.
All concrete cracks. If your control joints has done its job in designating where that crack will be, it will leave your concrete looking its best.