Q: What is ISO 9001?
A: ISO 9001 is a proven quality management system designed as a guide for any company to use. All concrete producers all preach quality. But how do you measure quality? Common criteria include mix design, production, quality control, training and product performance. In short, it relates to "Customer Satisfaction".
Our ISO 9001 certification is verification that our design, production, quality control, training procedures are among the most efficient and well documented in the world.
Q: Where does Thomas Concrete have Concrete Plants?
A: Thomas Concrete has concrete plants in Metro Atlanta, Raleigh & Charlotte North Carolina, and Greenville/Spartanburg (upstate) South Carolina. As of this writing we have 42 concrete plants and 4 concrete laboratories.
Q: Why are joints required in concrete?
A: Concrete cracks. That is the nature of the beast. Shrinkage that occurs during the drying stage causes stresses and cracking in the concrete. Joints are placed in the concrete to control the location of the cracks and prevent unsightly random cracking. Typically, joints are placed in concrete every 2.5 to 3 times in feet the depth of the concrete in inches. For instance, a four inch slab should have joints every 10 to 12 feet. Joint depth should be at least a quarter the depth of the slab. A 4" slab will require 1" deep joints to be effective.
Q: What is curing concrete?
A: Curing, stated simply, refers to the maintenance of adequate moisture and a moderate temperature in concrete while it hardens. Curing is a vital step in the process of placing concrete. If concrete is allowed to dry out too soon it will adversely affect the durability, strength, permeability and other desired properties in concrete.
Q: How long must concrete be kept moist (cured)?
A: The period of time needed to properly cure concrete depends upon the type of cement, mixture, proportions, required strength, size and shape of the structure, weather conditions and future exposure conditions. It can range from 3 hours to 3 weeks. Typically, a concrete driveway or sidewalk should be cured for a minimum of 3 days and up to 7 days if possible.
Q: How much does concrete weigh?
A: The unit weight of concrete varies, typically depending on the use of the concrete. Conventional concrete is normally used in pavements, buildings, and other structures and has a unit weight of 140 to 150 pounds per cubic foot. Lightweight concrete is often used in high-rise construction and weights between 100 to 120 pounds per cubic foot. Heavy weight concrete is used where very low density is required, such as X-ray and nuclear containment facilities, can weigh up to 210 pounds per cubic foot.
Q: What is entrained air and why is it used?
A: Entrained air is a quantity microscopic air bubbles generated by a chemical admixture that is added to the concrete. Air entrainment helps improve concrete's resistance to freezing and thawing while exposed to moisture. It also helps the concrete to stand up to the use of deicing chemicals and salts.
Q: What is Hydration?
A: Hydration refers to the chemical reaction that takes place between water and cement. This reaction is what gives the concrete its strength and durability. As long as hydration is taking place the concrete will continually gain strength. If the moisture in concrete is depleted, hydration will cease. This may result in lower than desired strength and durability.
Q: What are admixtures and why are they used?
A: Admixtures are materials that are added to the concrete to enhance certain characteristics that might be adversely affected by the addition of more cement or more water. Examples of some of these characteristics are set time, strength gain, slump, shrinkage resistance, and freeze/thaw resistance. There are liquid chemical admixtures such as water reducers, retarders, accelerators, air entrainers, and plasticizers. There are dry admixtures such as flyash and slag, which are by products of coal-fired power plants and steel production plants. There are fibers and colors used for shrinkage resistance and cosmetic enhancement.
Q: How does temperature affect concrete?
A: There are three (3) factors that control the set time, strength gain and overall durability of concrete. These factors are time, temperature, and moisture. These factors are interdependent on each other. If the temperature is too high (Hot Weather) the concrete can dry out prematurely and not reach its desired strength. It can also crack from rapid shrinkage.
If the temperature is to low (Cold Weather) the concrete set time and strength gain can be reduced and the concrete can be subjected to freezing while water is present and have severe freeze/thaw damage.
A rule of thumb is that the ideal temperature for concrete is 50oF/10oC. Temperatures above that are considered hot and below that are considered cold by the concrete.
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