Question 1

Concrete, how is it made?

Accepted Answer

Concrete is made by mixing proper portions of cement sand and aggregate. Concrete is basically cement with stone and sand filler added. Different chemicals and substances can be added to the concrete depending where and how the concrete is used.

Question 2

What is Fly Ash?

Accepted Answer

Fly ash, consisting mostly of silica, alumina, and iron, forms a compound similar to Portland cement when mixed with lime and water. Fly ash is a non-combusted by-product of coal-fired power plants and generally ends up in a landfill. However, when high volumes are used in concrete (displacing more than 25% of the cement), it creates a stronger, more durable product and reduces concrete’s environmental impact considerably. Due to its strength and lower water content, cracking is reduced.

Question 3

Cement, how is it made?

Accepted Answer

Our friends at Lehigh Cement have developed a great animation on how cement is made. They have authorized us to place a link to their site here for informational purposes. Please click here (http://www.lehighhanson.com/Resources/Documents/how_cement_is_made.2008.pdf#)to visit their site.

Question 4

What are Accelerators and what are they used for?

Accepted Answer

Accelerators reduce the set time of fresh concrete and speed up the early strength gain of hardening concrete. Many accelerators include water reducing agents to produce faster setting concrete with reduced water content in cold or freezing weather.
a. Chloride- This has corrosive properties and is not used when rebar or other metals are used.
b. Non-Chloride- This has non-corrosive properties and can be used in the presence of metals in the concrete.

Question 5

What are Admixtures?

Accepted Answer

Admixtures are used to increase the slump without adding water. Using less water increases the strength of the concrete. Admixtures are ingredients other than water, aggregates, hydraulic cement, and fibers that are added to the concrete batch immediately before or during mixing. A proper use of admixtures offers certain beneficial effects to concrete, including improved quality, acceleration or retardation of setting time, enhanced frost and sulfate resistance, control of strength development, improved workability, and enhanced finish ability. It is estimated that 80% of concrete produced in North America these days contains one or more types of admixtures. According to a survey by the National Ready Mix Concrete Association, 39% of all ready-mixed concrete producers use fly ash, and at least 70% of produced concrete contains a water-reducer admixture.

Admixtures vary widely in chemical composition, and many perform more than one function. Two basic types of admixtures are available: chemical and mineral. All admixtures to be used in concrete construction should meet specifications; tests should be made to evaluate how the admixture will affect the properties of the concrete to be made with the specified job materials, under the anticipated ambient conditions, and by the anticipated construction procedures.

Question 6

Why add “Air” to a concrete mix?

Accepted Answer

Air-Entraining agent is used to develop millions of tiny air bubbles in concrete. Entrained Air improves concretes freeze-thaw durability. It is used for concrete that is exposed to water and freezing temperatures.

Question 7

Why use fibers in concrete mix?

Accepted Answer

Fibers are used in many concrete applications. They reduce plastic shrinkage cracking, and improve the impact resistance of the concrete.

Question 8

What causes Plastic Shrinkage Cracking?

Accepted Answer

Plastic Shrinkage cracking is most likely to occur on hot, dry, and windy days when the concrete surface dries out before the concrete has set and hardened.

Question 9

What does PSI stand for?

Accepted Answer

This stands for “Pounds Per Square Inch”. The strength of concrete is measured by the PSI. If you increase the PSI, you increase the strength of the concrete.

Question 10

Why are “Retarders” used in concrete?

Accepted Answer

Retarders are used to delay the concrete setting time and are commonly used in hot weather.

Question 11

What does the term “Slump” stand for?

Accepted Answer

Slump is a measure of the consistency of concrete, or how “wet” or “dry” the mix is. The lower the slump, the dryer the mix.

Question 12

What are “Superplasticizers” used for?

Accepted Answer

Superplasticizers are used to further reduce water demand over water reducing admixtures. It is generally used to produce high strength concrete or to improve the workability of the mix.

Question 13

What are Water Reducing Admixtures?

Accepted Answer

These are used to increase the slump without adding water. Using less water increases the strength of the concrete.