In older neighborhoods around Frederick, Gaithersburg, Rockville and Silver Spring, the front walks went in decades ago and the street trees have had all that time to work on them. Add Maryland's freeze-and-thaw winters and almost every walk of that age has at least one bad section. The question is which ones actually need to come out.
Start with the trip hazard test, because it is the one that matters legally and practically. Run your foot across each joint. If one slab sits more than about half an inch above the next, that is a trip hazard — it catches a toe, and it is the single most common cause of a fall on residential property. In many jurisdictions the homeowner carries responsibility for the walk fronting their property, so this is not only a cosmetic question.
Next, look at what kind of crack you have. A hairline crack running across a slab, with both sides still level and tight together, is doing no harm. Concrete cracks; that one is cosmetic and can be left alone or sealed. A crack that has opened wide enough to put a coin into, or where one side has dropped below the other, is a different thing — the slab has broken into two pieces that are now moving independently, and it will keep getting worse.
Then check whether it rocks. Step on each side of a suspect slab and watch the joint. Movement means there is a void underneath, usually washed out by water tracking along the base. A slab with nothing under part of it will break, if it hasn't already.
Finally, look for the root. If a slab has been tented up into a peak, there is a root under the middle of it. This is the case where patching is genuinely pointless — grind the high edge down or fill alongside it and the root keeps growing, and you are back within a season or two. The section has to come out so the root can be dealt with properly and the base rebuilt before a new pour goes down.
So, roughly: hairline cracks with everything still level, leave them. Surface spalling and flaking, usually from de-icing salt, can often be resurfaced. Anything that has lifted, dropped, rocks underfoot, or is being pushed by a root should be cut out and replaced as a full section between joints.
One thing worth knowing: replacing a section is not much more disruptive than a serious patch, and it looks dramatically better. We saw cleanly on the existing joints, take the failed run out, deal with roots and rebuild the compacted base, then repour to match the level and the finish of what's around it. Done that way the repair reads as part of the walk rather than as a patch.
A word on de-icing salt while we're here, because it shortens the life of every walk in this region: rock salt is hard on concrete, and it is especially hard on concrete under a year old. If you have new work, get through the first winter with sand for traction instead. After that, use de-icer sparingly and shovel first — most of the damage happens when melt water refreezes in the surface.
Call VERAMD LLC at (301) 712-0717 for a free walkway assessment across Frederick and Montgomery County. We'll tell you honestly which sections need replacing and which ones you can leave alone.