Q: Cement vs. concrete, what's the difference?

A: Sometimes to really appreciate the difference between commonly misused terms it helps to use an example that creates a mental picture for future reminders. Our favorite for the cement vs. concrete difference is, "flour is to bread as cement is to concrete," in other words you wouldn't make a sandwich out of flour and similarly you would not have a cement driveway.

Portland cements are hydraulic cements composed of hydraulic calcium silicates. Hydraulic cements set and harden by reacting chemically with water. During this reaction, called hydration, cement combines with water to form a stonelike mass. When the paste (cement & water) is added to aggregates (sand & gravel or stone) it acts as an adhesive and binds the aggregates together to form concrete.

Q: What is the difference between a performance mix and a straight bag mix?

A: Traditionally concrete was mixed using a ratio of cement:stone:sand. Cement was packaged in bags and for convenience full bags were used for practical purposes. Typically the only difference in concrete mixes was the cement content, that is, how many bags of cement were in a cubic yard. Therefore concrete was ordered by it's cement content or bags per cubic yard. As concrete construction practices improved and the demand for reliable, durable concrete increased, it became necassary to develop a universal standard for concrete acceptance. At the same time the main ingredients of concrete were enhanced with admixtures that decreased the need for "full" bags of cement. These design mixes were developed to meet a performance requirement and eventually replaced the use of straight bag mixes. In summary performance mixes have replaced traditional straight bag mixes with enhanced performance for any particular specification.

Q: What is a slump?

A: Slump is a measure of concrete uniformity from batch to batch. It is not a measure of concrete quality, however it is often used to measure the plasticity and the placeability of the concrete mix. For given proportions of cement and aggregates, the higher the slump, the wetter the mixture.

Q: What is water-cement ratio?

A: The water-cement ratio is simply the weight of water divided by the weight of the cement. During the concrete mix design process selection of the appropriate water-cement ratio for the durability and strength needed of the hardened concrete is determined by the quality of the cement paste. The lower the ratio, the higher the compressive strength.