Have questions about concrete? We have answers.
As concrete experts, we get asked a lot of questions. Here are the most popular inquires along with our answers.
What is the difference between cement and concrete?
Cement is an ingredient in concrete, much like flour is an ingredient in cake mix. Dry, powdered (Portland) cement is blended with sand, crushed stone, and water to produce concrete. Gerken is a producer of ready-mixed concrete.
What is ready-mixed concrete?
Ready-mixed concrete comes batched for delivery from a production plant rather than undergoing mixing at the job site. Each ready-mixed concrete batch is made following contractor specifics and delivered in a pourable condition via cylindrical trucks called “cement mixers.”
How do you cure concrete?
Portland cement needs water to hydrate (harden). Curing is the name given to the procedures and products necessary to maintain and provide moisture for cement to hydrate. Adequate curing offers additional strength and durability. Concrete cured for three days will have only 66 percent of the strength of concrete cured for 28 days. Chemical moisture barriers and mechanical processes are effective curing methods.
How big is a cubic yard?
One cubic yard of concrete measures three feet long, three feet wide, and three feet high—the equivalent of 27 cubic feet. It will weigh about 4,000 pounds and cover an area of 81 square feet when placed four inches thick. Gerken’s ready-mixed concrete trucks can deliver up to ten cubic yards per truckload.
What is PSI?
A pound per square inch (psi) is the unit of measurement used to describe the compressive strength of concrete. The most desirable strength for external concrete slabs varies based on climatic conditions. In broad terms, the colder the climate, the higher the desired psi. Areas that experience many freeze-and-thaw cycles also require a higher psi concrete mix design. The typical concrete strength used for a driveway in Northwest Ohio and Southeast Michigan is 4,000 psi, whereas it may be 3,000 psi in Southwest Florida. The concrete used on a highway bridge may have a compressive strength of 5,000 psi or more.
Why does concrete crack?
Like all construction materials, concrete contracts and expands under various moisture and temperature conditions. Cracks may result from the movement of the subgrade or the application of heavy loads. The lack of proper curing and control joints will contribute to random cracking.
What is air-entrained concrete?
When we want our concrete to be watertight and durable when exposed to freezing and thawing, we add a small amount (5 to 7 percent) of microscopic air bubbles into the mixture. The bubbles provide expansion space for water that may saturate the concrete, freeze, and expand. Specify air-entrained concrete for exposed (outdoor) concrete.
What is slump?
Slump is the term used to describe fresh concrete’s uniformity, stiffness, and workability. A slump test measures the consistency between different truckloads of concrete. Most commercial concrete mixes have a three- to five-inch slump. That measures the distance the concrete settles after removal from a standard slump testing cone. Increasing the amount of water in a mix will increase the slump; however, chemical admixtures are available to achieve the same results. Adding more water to a mix can damage concrete strength and durability.
When can I drive on my new driveway?
Always consult with your builder, but as a rule of thumb, a new concrete driveway installed in the summer may be opened to cars (not trucks) after five to seven days with proper curing. Uncured concrete will require three weeks to achieve the same strength. In cool weather, wait an additional three to five days. Avoid constructing concrete driveways during the winter unless you take extreme protective measures to prevent damage. In Northwest Ohio and Southeast Michigan, the best time of year to construct a driveway is generally between April 15 and October 31.