Another Way to Make Concrete Stronger

Mineral admixtures are an economical way to create even stronger concrete and provide an environmentally responsible way to recycle industrial and other waste by-products.  In addition while chemical admixtures only make up about 5% of the concrete mass, mineral admixtures can be used in large amounts to replace portland cement and/or fine aggregates. 

So what are mineral admixtures?   Wikipedia states that mineral admixtures are “inorganic materials that also have pozzolanic or latent hydraulic properties. These very fine-grained materials are added to the concrete mix to improve the properties of concrete, or as a replacement for portland cement (blended cements).”  They are defined by the American Concrete Institute as “a siliceous or siliceous and aluminous material that in itself possesses little or no cementitious value but will, in finely divided form and in the presence of moisture, chemically reacts with calcium hydroxide at ordinary temperatures to form compounds having cementitious properties.” 

The most common mineral admixtures are fly ash, silica fume, blast furnace slag, and metakaolin.  Fly ash is a by-product from coal plants and is used to replace up to 60% of portland cement.  Silica fume is a by-product of silicon and ferrosilicon alloys and has particle size 100 times smaller than fly ash.  Blast furnace slag is a by-product of steel production and can replace portland cement by up to 80% of the mass. 

So what are the advantages of using mineral admixtures?  According to the U.S. Department of Transportation, when mineral admixtures are added to concrete in larger amounts, “it enhances the workability of fresh concrete.”  DOT also states that it improves the resistance of concrete to thermal cracking, alkali-aggregate expansion, and sulfate attack as well as enables a reduction in cement content.

1.en.wikipedia.org/wiki/Concrete

2. concrete.org/TopicsinConcrete/TopicDetail.aspx?id=71&Search=Pozzolans

3. fhwa.dot.gov/infrastructure/materialsgrp/admixture.html

 

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