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According to the Portland Cement Association, although the terms cement and concrete often are used interchangeably, cement is actually an ingredient of concrete. Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement. Concrete gets stronger as it gets older. Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. Cement comprises from 10 to 15 percent of the concrete mix, by volume. Through a process called hydration, the cement and water harden and bind the aggregates into a rock-like mass. This hardening process continues for years, meaning that concrete gets stronger as it gets older.

Curing is one of the most important steps in concrete construction, because proper curing greatly increases concrete strength and durability. Concrete hardens as a result of hydration, the chemical reaction between cement and water. However, hydration occurs only if water is available and if the concrete's temperature stays within a suitable range. During the curing period (5-7 days after placement for conventional concrete) the concrete surface needs to be kept moist to permit the hydration process. New concrete can be kept wet with soaking hoses, sprinklers, or by covering it with wet burlap. Alternately, it can be coated with commercially available curing compounds which seal in moisture.

Concrete, like all other materials, will change in volume slightly when it dries. In typical concrete this change amounts to about 500 millionths. Translated into dimensions, this is about 1/16 of an inch in 10 feet (0.4 cm in 3 meters). The reason contractors put joints in concrete pavements and floors is to allow the concrete to crack in a neat, straight line at the joint when the volume of the concrete changes due to shrinkage.

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Air-Entraining Admixture (AEA) generates an air-void system for increased protection for exterior concrete against damage from freezing, thawing, or severe weather.

Type A Water Reducing Admixtures (WRA)

Type A water reducing admixtures are added to concrete to reduce the water-cement ratio or to improve the workability of concrete without changing the water-cement ratio. Water reducers typically decrease water content by 5 to 10 percent.

Mid-Range Water Reducing Admixtures (MRWRA)

Mid-range water reducing admixtures can be used in a variety of concrete mixtures because of dosage flexibility. Particularly suited for flatwork applications, mid-range water reducers contain ingredients that improve finishability without significantly affecting the time of setting. With up to 20 percent water reduction possible, this multi-purpose product can be a real benefit to your project.

High-Range Water Reducing Admixtures (HRWRA)

Also known as superplasticizer, high-range water reducers provide flowing concrete with slumps of 8 inches and higher. Concrete with very low water-cementitious ratios can be made while maintaining workability, minimizing bleed water, and controlling segregation. Most engineering qualities of concrete are enhanced by reducing water up to 40 percent. Normal doses of high-range water reducer can help save time and money through improved production and reduced labor. Use high-range water reducer anywhere increased plasticity is desired.

Corrosion Inhibitors

Two different products are available to help protect reinforcing steel by reducing the rate at which chloride and moisture enter the concrete: Product A and Product B. These additives can extend the service life of reinforced concrete structures. Parking garages, bridge decks, or other applications requiring corrosion protection can benefit from the use of corrosion inhibitors.

Shrinkage Reducing Admixture (SRA)

Shrinkage reducing admixtures are specifically developed to reduce drying shrinkage and the potential for subsequent cracking. When concrete mixtures with SRA are drying, shrinkage-cracking and micro-cracking are reduced and water tightness and durability are improved, as well as aesthetics.

Mineral Admixtures

Mineral Admixtures in finely divided forms are added to supplement or as a partial replacement of the cement in concrete. These products combine with by-products of Portland cement's hydration process and form additional cementitious compounds. Extensive studies of both long- and short- term properties performed on these materials show that they can improve the desirable qualities of concrete.

Fly Ash CFA/FFA

Due to the spherical nature of fly ash, it acts like tiny ball bearings, lubricating the concrete, and thus allowing lower water content for a given slump. All the benefits of less water content such as increased strength, durability, etc., are realized when using fly ash. Segregation, bleeding, and heat from hydration are reduced. Pumping, finishability, and sometimes alkali-aggregate reactivity and sulphate resistance are improved through the use of fly ash. Normal cement replacement is 15 percent to 25 percent.

FIBERS

Synthetic Fibers

Synthetic fiber reinforcement inhibits the formation of plastic shrinkage cracks by providing an internal support system when concrete is most vulnerable to cracking. Literally millions of small polypropylene fibers are integrally mixed, providing reinforcement throughout the entire concrete section. Synthetic fiber provides an alternative to small gauge wire mesh and provides impressive improvements in permeability, impact resistance, and abrasion resistance.

Steel Fibers

Steel fibers can be used to replace rebar in certain applications and because they come premixed in concrete, valuable time can be saved. Steel fiber enhances concrete's flexural and shear strength, impact resistance and ductility. Steel fibers inhibit cracks in concrete, and are often requested for jobs requiring more durability.

Blends

A blend of steel and synthetic fibers may be used to gain the benefits of both.

Color

Pigments may be added to concrete to produce architectural effects. The pigment is added as a percentage of the cement to produce many different colors. For cleaner, brighter colors, pigment can be used with white cement instead of the normal gray variety. Many factors - such as temperature, finishing operations, added water, and curing - affect the final color, so no guarantee of final product can be made; however, with proper care, a beautiful effect can be obtained.

Others

• High density concrete
• Shotcrete
• Pervious concrete
• Polymer modified concrete
• Lightweight concrete
• Exposed Aggregate
• Backfill Material CLSM
• High early strength
• Mass concrete