Do you not find it strange to see how many concrete slabs have holes which haven't been filled to the fullest extent? If you look closer at the slabs, you'll see that these gaps are filled, but the entire surface hasn't been smoothed. This is intentional.
The gap you can see between the two slabs of concrete is actually an actual joint. It is most likely constructed to facilitate the expansion that takes place of the concrete when it is exposed to the heat. You can see these examples online by navigating to https://www.maxraft.co.nz/MAXRaft-Benefits/Homeowners/.
The material utilized in the joint absorbs the stress and stops the concrete from breaking. Its presence assures that it doesn't create a gap through which moisture and water can get in.
So, why is it that the joint isn't fully covered? It'll take at minimum one period of time before the cement can fully expand and contract, and for an expert to decide whether the joint is adequately filled. In this case covering the entire joints and filling them with concrete is likely to cause problems.
In the bigger scope of things, in which the concrete slab can last for 40 years at a time it is not wrong to wait for an entire year to complete the process of filling. In this case you must be prepared to wait.
This is crucial when you make use of this slab to serve a heavy-duty purpose. If you plan to put your car that weighs more than a couple of tonnes on the slab of concrete on your driveway, it's evident that the gap must not be filled in a hurry.
Be aware that concrete, despite its strength, is susceptible to damage If you begin breaking it up and pounding it to release the filler material. It is highly recommended to consult with experts prior to making any decisions.
There are many experts available online. They do not all cost a large sum of money. They do not all have any fees in any way.
You can join forums to learn more regarding joints and the way to be filled. This information is gathered from various individuals and experts. However, you should not apply this method to replicate the opinions of experts.