Sign of a Broken Sidewalk

Construction

• Concrete sidewalks poured over dirt without any subsurface preparations seldom last long. Problems beneath the sidewalk account for most of the damage the sidewalk accumulates. Tree roots invading the soil under a walkway cause more than half the sidewalk damage in most U.S. cities, according to the Warnell School of Forest Resources. To prevent uplifting by frost heaves and growing roots, builders install a footing of gravel above compacted subsoil. Concrete slabs separated by expansion joints form the upper layer of the walkway. Water drains away from the walk and tree roots grow beneath the gravel layer.

Ice Damage

• When water collects under a walkway and freezes, frost heaves damage the walkway as the ground thaws. As ice warms, ice expands with enough force to shift sidewalk slabs out of position or shatter the concrete. When the ice melts, intact slabs don't completely settle back into place. The edges of a displaced slab can trip unwary pedestrians. Ice also damages the sidewalk from the top. Salt used to melt ice on walks penetrates into the concrete, drawing water with it. As temperatures fall, the water freezes and flakes the surface away. Years of gradual damage cause cracks that crumble the concrete.

Root Damage

• When roots first invade the ground under a sidewalk, the expanding root shifts gravel and soil instead of the walkway. As the root grows larger, sidewalk slabs tip out of the ground and can break into pieces. More than 90 percent of the sidewalk damage in Los Angeles involves invasive tree roots, according to chief forester George Gonzalez on the University of California, Berkeley, website. Temporary fixes include asphalt or concrete patches that ramp the mismatched concrete joints. Once the damage occurs, removing the tree allows a complete repair. Pruning roots can protect walks but also weakens the tree. Better planning avoids trouble by rerouting new walks or planting controllable trees farther away.

Repairs

• Filling small cracks in sidewalks can prevent the breakup of the walkway. Patches bond only to clean concrete in good condition. Preparation includes careful removal of the weakened concrete in the crack and cleaning with a wire brush. Mortar mix provides the basic patch, and adding a concrete epoxy to the mortar creates a fast setting, stronger repair. Homeowners can limit deicer damage to walks by sweeping away melted ice before it freezes again. Mixing 1 lb. of sidewalk salt with 50 lbs. of sand reduces the total deicer used and provides traction while the ice melts, according to Iowa State University Extension.