The front sidewalk at the Habitat site. One of the construction management instructors from the local junior college (red jacket upper-right) brought his construction management students for the pours of the front and back sidewalks.
From Wonderopolis: “To prevent sidewalks from cracking in random spots and breaking apart, builders make lines in sidewalks. … The technical term for sidewalk lines is contraction joints.
“Contraction joints are placed in fresh concrete before the concrete dries and has a chance to create its own joints, which we call cracks. As the concrete dries and shrinks, any cracks that form should follow the path of the contraction joints, since that's where the concrete is thinnest.
“If the cracks follow the contraction joints, the sidewalks won't look as bad. They also won't tend to form further cracks and break apart like they might if allowed to crack at random places.
“Builders place contraction joints in fresh concrete with saws, special grooving tools or plastic strips called zip-strips. They have to make sure that the joints are deep enough and made before the concrete begins to dry, so that cracks won't appear in the wrong places.”
What about where the wet concrete meets the city sidewalk (over the white hoodie in the photo)? A concrete expansion joint has been placed there. That is, from Everything About Concrete, “a material placed … to allow for expansion and contraction of the concrete due to changes in temperature and moisture levels.”
Retired economics professor (“dismal scientist”). Married 40+ years to the love of my life; we have two grown daughters, both married, two granddaughters and a...
