A lot of time customers will call us with failed concrete wondering if there is a solution that doesn't involve re-doing the entire thing. The answer unfortunately is a grey area. From a more permanent and warrantied standpoint- your most fruitful action that is long lasting is to have the existing concrete demolished and removed, the area excavated, built up again using concrete block and a new pad poured (if we are talking porches). In this scenario we would assume that there is more than a hair line crack and that the porch is unsightly.
Another option, less expensive that can actually ad value to your home, is to clad the porch or area in stone (if the concrete is in good shape). Properly laid stone not only is completely aesthetic, but also long lasting.
A product we sometimes use but that is more of a short term solution, is Concrete Renew. While the product tends to give a new finish on old failing concrete, the problem itself is likely to reoccur. If the originally poured concrete failed due to heaving and shifting (as does occur in Canada when the ground freezes and thaws) and the bedding was insufficient- it is almost guaranteed to reoccur . You can imagine that putting a thin layer (more concrete) over this is not really a permanent solution.
Therefore it is recommended, if you can, to halt putting a small amount of money (which is wasted in the long term), into your porch project and instead wait until you have the right budget to get your porch done right, to last,
with Otto's Masonry.