In Chicago, urban high-rises with sidewalk frontage and suburban HOAs containing walking paths, parking lots, and service roads are reliant on their paved surfaces for conducting their everyday business. Therefore, it's crucial that buildings and associations regularly inspect and maintain their concrete.
The first step to healthy, functional paved surfaces is understanding some basic terms. While the terms cement and concrete are often thrown around interchangeably, they're not the same thing; cement is actually an ingredient of concrete.
“Concrete is basically a mixture of aggregates and paste,” says Tim Zera of Zera Construction Inc. in Niles. “The aggregates are sand and gravel or crushed stone; the paste is water and Portland cement.”
A wide variety of mix proportions can be used to make good concrete, as long as proper mix design procedures are used. A good general rule to use is what industry pros call the rule of 6’s: A minimum cement content of six bags per cubic yard of concrete, a maximum water content of six gallons per bag of cement, a curing period (keeping concrete moist) a minimum of six days, and an air content of six percent (if concrete will be subject to freezing and thawing).
There is a wide variety of concrete mixes used throughout the Chicagoland area,” says Matt Serna, a paving expert with Dubois Paving in Wheeling. “The most typical mix is a 6-bag (4000 psi) air-entrained, low-chert ready mix. These are mostly used for sidewalks, stoops and residential driveways.” To increase the strength and durability of heavily used surfaces additional thickness and reinforcement can be used.