A Chocolate Bloom Analogy for Crumbling Concrete in Home Foundations*

lrzbe_detailHave you ever unwrapped a piece of chocolate only to find it has a whitish powder surrounding it? It almost stops you from eating the chocolate, right? Chocolate that gets the whitish powdery appearance is said to have undergone a bloom – called chocolate bloom. Fast temperature changes or exposure to moisture can hasten the process. To understand it, you have to know that chocolate is a mixture of several ingredients that include sugars and fats, among other things. The temperature changes or moisture can make these ingredients bunch together allowing them to move around in the mixture all the way to the surface. Once separated, things like sugars (think of sugar crystals) have different properties than the original chocolate mixture. That whitish chocolate is often more crumbly than regular chocolate.

A process akin to chocolate bloom is happening with the concrete used in the foundations of houses in eastern Connecticut. The ingredients for concrete are cement, sand, and aggregate. Sand and aggregate are filler materials held together by the cement. When pyrrhotite happens to be a component of aggregate, it can chemically react with air and moisture over time. Sulfur in the pyrrhotite gets converted into sulfuric acid and sulfate salts. Sulfuric acid is bad because it eats away at the structure of the concrete. Sulfate salts are bad because they can join with the cement to make new crystalline materials that are more brittle than regular concrete. As the crystals form, they push up against the concrete mixture, causing even more stress. These events change the structure of the concrete (chocolate) because some of the components like pyrrhotite have been transformed (like sugar or fat in chocolate), making it weaker. Whereas in the chocolate bloom ingredients that are already present merely separate, the pyrrhotite changes, over time, to a different and now deleterious chemical that makes concrete crumble. In either case, however, the strength of the original material is compromised in the process.

“Bloomed” chocolate is completely edible and tastes almost as good as regular chocolate. Crumbling concrete, on the other hand, is very hard to swallow.

* This post was prompted by the release of the “Concrete Expert’s Final Report” regarding crumbling concrete in foundations of homes in eastern CT.

^ photo: bloomed chocolate by Mark Agbuya on Seasoned Advice

Related News Articles 

AG Issues Final Report on Cause of Crumbling Foundations Hartford Courant – November 4, 2016

Financial Relief Eludes Connecticut Homeowners With Crumbling Foundations New York Times – November 14, 2016

With Connecticut Foundations Crumbling ‘Your Home Is Now Worthless’ New York Times – June 7, 2016