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Air Entraining Admixtures:
- These liquid chemical admixtures are added to concrete during mixing to create minuscule air bubbles within the concrete and are used for exterior jobs such as parking lots, patios, sidewalks and driveways which are exposed to patterns of freezing and thawing. The higher level of entrained air enhances the concrete's resistance to such conditions.
- Wet concrete also benefits from air entraining by allowing less bleeding and segregation while improving the concrete's workability.
Water Reducers & Superplasticizers (High Range Water Reducers):
- Water reducers serve two means, one being to lessen the water content and enhance the durability and strength, the second being to increase slump by means other than adding additional water to the mixture.
- Off-setting the use of water during hot weather concreting makes them very useful.
- Superplasticizers can reduce the water content of your concrete by 12-40% while still retaining slump.
- These admixtures yield a significantly higher durability and resilience for jobs with more strict specifications
Retardants and Accelerators:
- Concrete retardants are typically an ingredient of water reducers and are used during high temperatures to slow the setting of the concrete so that more time is allowed to finish before setting.
- Accelerators decrease the setting time while still yielding an enhanced strength early on in the setting of the concrete, usually during colder temperatures.
- They are also used when the job demands faster finishing such as on road work that needs to be opened to traffic quickly or jobs that entail rapid form removal.
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To better understand mineral admixtures it helps to understand what a pozzolan is:
- a pozzolan is a hard, nonreactive, colorless chemical compound which is the principal make-up of sandstone and other rocks.
- natural pozzolans are typically of volcanic origin while artificial pozzolans, for example, can be produced as a byproduct of coal-fired electricity production
- Alone they do not possess the ability to become cement but when introduced to water, calcium hydroxide (slaked lime) and the correct temperature, can attain the ability to form cement.
Fly Ash:
- Fly ash is a by-product of coal production and is an environmentally safe option with a long list of benefits when used as an admixture in concrete finishing
- It is of pozzolan properties and if used correctly can replace up to 50% of the cement being used
- These benefits include but are not limited to:
- higher strength and lowered permeability
- more durability and ease of workability while minimizing water usage and leaving a refined finish
- minimizes bleeding and lessens slump while decreasing segregation
- fly ash is very economical, it is low in cost while still greatly improving the finished product
Other Natural Pozzolans:
- The use of natural pozzolans dates back to 2000 B.C., they were introduced to North America in the beginning stages of the 1900s
- Commonly used today are materials that are processed and heat treated and then processed again to a fine sand-like powder. These include metakaolin (smaller than cement particles but larger than silica fume), calcined shale, and calcined clay, silica fume and fly ash
- one benefit of using natural pozzolans is that they enhance durability and control heat rise in large concrete masses
- They increase opposition to sulfate attack while being among the only material known to diminish the reaction that causes concrete cancer (alkali–silica reaction). Concrete Cancer is a reaction that happens among the alkaline cement and the reactive silica that are found in most aggregates. This reaction causes swelling in the concrete which leads to spalling and loss of strength in the concrete which eventually leads to the concrete failing
- They can replace up to 40% of cement when mixed properly and used correctly which makes them a very economic and environmentally safe option
- All pozzolans are environmentally friendly because they can reduce the amount of cement needed. Producing one ton of cement creates roughly one ton of carbon dioxide compared with no carbon dioxide in the production of fly ash, for example.
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IN CONCLUSION:
By implementing the use of admixtures in your next project you can reap all the benefits that will positively affect the quality of your concrete work, your pocketbook, and the environment.
By using these admixtures correctly not only will it yield a more durable and longer lasting finished product but it will allow the job to be done more efficiently because of the heightened ease of work-ability that admixtures offer.
Your budget will benefit because admixtures are less costly and can not only replace up to 50% of concrete but they can also save a batch that may have been ruined due to any number of factors, such as extreme temperatures.
Lastly, we all want to help the environment and by using admixtures in your next project you can take your part in helping to keep concreting GREEN.
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