Blended Cements

The American Concrete Institute’s (ACI) Cement and Concrete Terminology, defines blended cement as “hydraulic cement that is produced by intergrinding portland cement clinker with the other materials or by blending portland cement with the other materials or a combination of intergrinding and blending.”  As recently as 2012, there were changes made in blended cements that have been approved by the ASTM for both special applications and general use.   

 

From the ASTM’s C595 abstract on hydraulic blended cements, they describe Type IS as Portland Blast-furnace Slag cement and Type IP as Portland-pozzolan cement.  They state that, “They can also be described according to air-entraining, moderate sulfate resistance, moderate heat of hydration, high sulfate resistance, or low heat of hydration properties.”  Type I (SM) Slag-modified Portland cement has a standard that contains less than 25% slag by mass of the cement.  The ASTM’s C595 permits Type IS Portland Blast-furnace Slag cement to contain between 25 and 70% by mass of the finished cement. 

Blended cements are used to prolong the life span of concrete as it reduces the concrete’s permeability to water.  Whereas concrete mixes made of portland cement are more porous and are susceptible to cracking during freeze/thaw cycles.  It can even be a cause of deterioration in the rebar as moisture can seep in over time.  Another benefit to blended cements is they reduce the water-cement ratio (w/c), which is one way to produce high-strength concrete. 

Blends can be customized by varying the proportions of the mix and be produced to meet the demands of a specific project.   Most importantly the ASTM dictates that, “cement shall undergo different tests to determine the following properties: chemical analysis, fineness by sieving, fineness by air-permeability, autoclave expansion, time of setting, air content of mortar, compressive strength, heat of hydration, normal consistency, specific gravity, water requirement, mortar expansions of blended cement and pozzolan, drying shrinkage, activity index with Portland cement, and sulfate resistance.”

* ACI 116R-00, Cement and Concrete Terminology, American Concrete Institute, Farmington Hills, Michigan, 2000

* http://precast.org/2012/12/new-astm-blended-cement-types/

* http://www.astm.org/Standards/C595.htm

 

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