During the winter, melted snow can seep into sidewalk cracks. The water can then refreeze and expand, which creates larger cracks and heaved concrete. On a dry fall day, sweep out all debris and crumbled concrete from the cracks, then fill them with a flexible concrete crack sealer to keep moisture out. For the best results, fill sidewalk cracks when the daytime temperature is above 50 degrees. If it’s too cold, the concrete sealant will not adhere properly, and water seepage can still occur.