ACI Report Recognizes Shrinkage Compensation Abilities of Magnesium Oxide
Magnesium oxide, calcium oxide, and other expansive additives are now categorized as shrinkage compensating admixtures (SCAs), according to the American Concrete Institute (ACI).
A recent ACI report, which includes reviews of several categories and types of chemical admixtures, introduced a new category for magnesium oxide because it recently gained acceptance in North America due to its ability to expand at a rate closely matching the drying shrinkage of cement. Magnesium oxide has been used in dam construction in China for several decades.
The ACI 212 Report on Chemical Admixtures for Concrete presents each category with common uses, sustainability attributes, and potential benefits of a properly proportioned concrete mixture to various professionals, including the concrete contractor, concrete producer, and design professional.
The report states, “Magnesium oxide behavior will vary depending on the quality and the heat of calcination. In general, high-quality light burnt magnesium oxide is most successful in compensating for the drying and autogenous shrinkage without deleterious effects on the concrete. Success has also been achieved when using a hybrid material that combines shrinkage reducing admixtures to reduce the pore water tension and SCAs, specifically lightly burnt magnesium oxide, to provide a controlled expansion.”
PREVent-C®, the most effective admixture in mitigating shrinkage cracks and curling, is a magnesia-based product that works in multiple ways to not only reduce cracks but prevent them altogether. PREVent-C® blends the expansive components of magnesia with a glycol ether blend that reduces surface water tension to defend against cracks.
Typical PREVent-C addition rates range from 2 percent to 7 percent, based on cement content, or 2 lbs. to 7 lbs. for each 100 lbs. of cement in concrete, mortar or grout. When used at 5 percent addition rate, PREVent-C has been shown to reduce shrinkage cracking as high as 90 percent to 100 percent. These crack-free results also improve the construction sequence and project durability, while significantly reducing repair and maintenance costs over the life of the structure.
PREVent-C® is the most effective solution for any project that wants to avoid shrinkage cracks.
The most common applications are:
– Water/wastewater treatment
– Bridge decks
– Airport runways and pavements
– Architectural concrete
– Elevated decks and slabs
– Packaged materials
– Secondary containment