In New York City, urban high-rises with sidewalk frontage and outer-borough HOAs with walking paths, parking lots, and service roads are reliant on their paved surfaces and therefore need to regularly inspect and maintain their concrete.
While the terms cement and concrete are often thrown around as being interchangeable, cement is actually an ingredient of concrete.
“Concrete is a mixture of white sands, large aggregates and cements. All three of them comprised together make concrete,” says paving specialist Mario Sciacca of Etna Contracting in Red Hook, Brooklyn. “So when people refer to cement work, that’s wrong; it’s concrete work.”
Good concrete can be obtained by using a wide variety of mix proportions if proper mix design procedures are used. A good general rule to use is the rule of 6’s: A minimum cement content of 6 bags per cubic yard of concrete, a maximum water content of 6 gallons per bag of cement, a curing period (keeping concrete moist) a minimum of 6 days, and an air content of 6 percent (if concrete will be subject to freezing and thawing).“There is a wide variety of concrete mixes used throughout the New York City area,” says Sciacca. “But the New York City standard code is for 3,200 psi, which stands for pounds per square inch. But the industry normally uses 3,500 to 4,000 psi. The higher the psi, the better and the stronger the concrete would be but it also withstands the salts and the calcium chlorides much better than a lower psi concrete.”
To increase the strength and durability of heavily used surfaces additional thickness and reinforcement can be used. “The typical mix for house foundations and condo building foundations in Manhattan is 3,500 psi,” says Matthew Koerner, president of Manhattan Concrete Design in New York City.