Yes, in about a month, fine cracks should disappear. While shrinkage cracks can appear on the surface within hours of pouring concrete, it takes a full month for new concrete to fully settle. Don't be surprised if the cracks that seemed visible at first are almost impossible to see after a month of settlement. Concrete cracking can appear at any time, even on a year-old slab like yours.
The base under the driveway may not have been compacted properly, and that may have caused the concrete to sag or settle slightly and therefore crack. Or, some water may have flowed under the slab and eroded or consolidated the base to the point where the concrete was not supported. Concrete may not have been properly formulated, placed, or finished and cured for strength either, so the weight of car traffic could have contributed to cracking. Cracks in concrete are extremely common, but are often misunderstood.
When a homeowner sees a crack in their slab or wall, especially if the concrete is relatively new, they automatically assume something is wrong. This is not always the case. Some types of cracks are unavoidable. The best thing a contractor can do is try to control cracking.
This is done by properly preparing the subbase, ensuring that the concrete is not too wet, using reinforcement where needed, and properly placing and spacing the crack control joints and expansion joints. However, cracks sometimes occur despite the precautions taken. You can cut them into the concrete slab the day after pouring them with a circular saw equipped with a concrete blade. In theory, concrete that is properly formulated for use and is placed on a well-compacted, well-designed base, and with a perfect finish, should never crack.
Since concrete cannot shrink around a corner, stress will cause the concrete to crack from the point of that corner. The key point to understand in relation to cracking is that water is a certain percentage of the concrete mix. There is a constant battle between the supplier who has promised that the concrete will achieve a certain strength or hardness, and the laying contractor whose job it is to pull the wet gray material to the center of a slab and make it flat. Since these occurred shortly after the slab was poured, they were most likely due to concrete shrinkage.
One of the most common mistakes made by DIYers who are new to concrete is adding too much water to the dry concrete mix to make mixing easier, which leads to the concrete weakening and a high risk of cracking. Engineers spend their entire lives trying to make concrete slabs and walls crack where they want. Because the flexural strength of concrete is lower than its compressive strength, concrete bends to its breaking point. If the spacing between these control joints is larger, even though the concrete follows the control joint pattern, extremely wide joints will be obtained that become more difficult to fill and maintain.
However, proper site preparation and good concrete finishing practices can go a long way in minimizing the occurrence of cracks and producing a more aesthetically pleasing project. They are simply grooves that are machined into fresh concrete or cut into the slab shortly after the concrete reaches its initial set. They often use wire mesh as reinforcement, which keeps the concrete pieces together but does not prevent cracking. Feel free to place them closer together for greater protection against cracking, and consider breaking large concrete slabs with joints that are also perpendicular.
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