Why do sidewalks have bumps on them?
Those blister-like bumps, also known as “truncated domes and detectible warning pavers,” are a part of “tactile paving” (meaning: paving that can be felt). It helps the visually impaired detect when they are about to leave the sidewalk and enter the street.
The yellow bumps that you refer to are called truncated domes and fall under code requirements for "detectable warnings." They are state regulatory requirements found in Chapter 11 of the California Building Code to inform a blind person that they are entering a hazardous area (i.e. area of vehicular travel).
The sidewalk, parkway strip, and curb & gutter are typically made of concrete and located next to the street on the front and/or side portion of your property. The curb and gutter are located at the edge of the street pavement.
A rumble strip is applied along the direction of travel following an edge line or centerline, to alert drivers when they drift from their lane.
Rumble strips (also known as sleeper lines or alert strips) are a road safety feature to alert inattentive drivers of potential danger, by causing a tactile vibration and audible rumbling transmitted through the wheels into the vehicle interior.
Sidewalks have operated for at least 4000 years. The Greek city of Corinth had sidewalks by the 4th-century BC, and the Romans built sidewalks – they called them sēmitae.
These little peel-and-stick bumps can be used on any clean, dry, flat surface to identify everyday items. Conveniently sold on strips of waxed paper, these tactile dots are a breeze to peel off and stick on. You can mark various objects in the kitchen, keys on a piano, or the volume button on the TV remote.
These Bump Dots allow a variety of uses from tactile marking of everyday items such as computer keyboards, telephone keypads, and multiple switches to adding feet to vases and ceramic pieces. In homes or offices with both blind and sighted people, use the clear dots so the view of keypad displays aren't obscured.
And the correct answer is: gumballs, bubble gum, stick gum. In other words, Rolf, your friend is correct: chewing gum makes those black dots that mar white concrete.
Contraction/Control Joints. Contraction/control joints are placed in concrete slabs to control random cracking.
What is grinding on a sidewalk?
SIDEWALK REPAIR METHOD - GRIND
Grind. Concrete grinding, or horizontal saw cutting, is a method typically used to remove “stub toes” that are 1 inch (1”) high or less, perpendicular to the flow of pedestrian traffic.