1. So, first you need to slightly enlarge the crack using chisel and hammer, slowly and carefully cutting the edges for the formation of shallow hollows.
2. Before applying the cement mortar it is necessary to purify the resulting hollow with a stiff brush, for example, of steel wire.
3. Prepare solution (1 part cement to 2 parts sand), thoroughly moistened with water groove and fill it with a solution as tightly as possible.
4. Carefully smooth the solution and wetting the trowel with water, smooth out the seam. While the cement cures (3-7 days), the former crack better cover the Board that the work was not in vain.
5. If the crack time has not “healed” and a concrete strip crumbled, nothing to do, you will have to restore it. But first you need to cut with a chisel the damaged area.
6. To indicate the edge of the track, we need to sit to it wooden plank, a metal strip or Board and fasten it by two or three pegs, not to depart.
7. A shovel lay in the niche of sand-cement mortar (1 part cement to 2.5 parts gravel), compacted, for example, Poleshko, if necessary adding a solution.
8. Final step: carefully restored, smooth place grout from sheet metal or plywood. Now it is desirable to shield or cover a restored section of the track.
According to the magazine “Earmaster” (Hungary)
Recommend to read “SHERMAN” in the MIDDLE EAST After the Second world war, the army of the victorious countries have experienced a surplus of armored vehicles. Most directly it was the most massive tank of the Western allies,... TO NOT UNSCREW THE SCREW To nut the connections didn't loosen during operation of the device, usually put the second (jam nut) or enclose the washer Grover. If such is not at hand or you need to fix the little... 
Wow, what a shame — cracked and crumbled concrete path on your country station! To talk about the fact that slim was a layer of mortar or the soil slipped, too late… But you shouldn’t be upset— your track is easily “cured”. But this must be done as quickly as possible, while the crack is small.