The sidewalk replacement criteria was developed by the engineering division with help from the city attorney and approved by the city commission.
The city deems that sidewalks which exhibit the following criteria will be removed and replaced:
1. Sidewalks that exhibit differential sidewalk elevations of one inch or greater
2. Cracked or broken sidewalk with any of the following:
Sidewalks broken into three or more pieces
Sidewalks where a crack is not tight and well seated
Severe crazing (alligator cracking)
Deteriorating joints (at least four inches long by one-inch wide at any point)
Spalled areas (at least three inches along any one side)
3. Other Surface condition issues:
Pitted sidewalks with any pit larger than one and a half inch and at least a half inch deep
Surface deterioration consisting of severe scaling or popping causing a safety issue
4. More than one issue listed above.
It should be noted that sidewalks may exhibit more than one type of deficiency. It should also be noted that the program not only addresses correcting identifiable sidewalk hazards, but includes defective sidewalks that may become hazardous before the next scheduled review and repair project occurs.
Pitting in sidewalk occurs over time as individual stones break up through the freeze/thaw cycle leaving a void in the sidewalk surface. This type of deterioration in small amounts may not necessarily constitute a hazardous walking surface. In large quantities, however, these defects diminish the smooth walking surface, compromise the sidewalk’s structural integrity, and contribute to poor drainage which propagates further pitting and surface defects.
Scaling is the general loss of surface mortar exposed to freezing and thawing. The aggregate is usually clearly exposed and often stands out from the concrete. Scaling is primarily a physical action caused by hydraulic pressure from water freezing within the concrete and not usually caused by chemical corrosive action. When pressure exceeds the tensile strength of concrete, scaling can result if entrained-air voids are not present to act as internal pressure relief valves.
Spalling is a deeper surface defect than scaling, often appearing as circular or oval depressions on surfaces or as elongated cavities along joints. Spalls may be 1 inch or more in depth and 6 inches or more in diameter, although smaller spalls also occur.
Spalls are caused by pressure or expansion within the concrete, bond failure in two-course construction, impact loads, fire, or weathering. Improperly constructed joints and corroded reinforcing steel are two common causes of spalls. If left unrepaired, spalls can accelerate pavement deterioration.
A pop-out is a conical fragment that breaks out of the surface of the concrete leaving a hole that may vary in size generally from 1/4 inch to 2 inches, but up to as much as 1 foot in diameter. Usually a fractured aggregate particle will be found at the bottom of the hole, with part of the aggregate still adhering to the point of the pop-out cone.
Most pop-outs appear within the first year after placement. Pop-outs caused by alkali-silica reactivity (ASR) may occur as early as a few hours to a few weeks, or even a year, after the concrete is placed. Pop-outs caused by moisture-induced swelling may occur shortly after placement due to the absorption of water from the plastic concrete, or they may not appear until after a season or year of high humidity or rainfall or after the concrete has been exposed to freezing temperatures. Pop-outs are considered a cosmetic detraction and generally do not affect the service life of the concrete.
Differentials typically occur at the joint between two sidewalk slabs. A differential consists of a lip or elevation difference at the joint and is measured along the vertical face of the joint. A differential sidewalk that exceeds one inch is a condition that warrants removal and replacement. The differential may have been caused by tree roots, trench settlements, or heavy weights placed on the sidewalks.