I have encountered many different approaches among concrete countertop professionals in using CSA cements. Some use portland cement, CSA cement and pozzolan blends to achieve high-quality concrete. I recommend against this approach, as it adds complication and negates the benefits conveyed by CSA cements.
Pozzolans are substituted for portland cement to address a host of problems caused by a by-product of the reaction of portland cement with water: calcium hydroxide. Calcium hydroxide makes concrete weak and causes effloresence. Pozzolans consume calcium hydroxide, thus improving the quality of the concrete.
When CSA cements react with water, they do not produce calcium hydroxide. Therefore, simply substituting CSA cement for 100% of the portland cement eliminates all of the problems listed above and obviates the need for pozzolans.
Let me say that again: Simply using 100% CSA cement (and 0% portland cement) completely eliminates all the problems that portland cement caused and pozzolans were trying to solve. Why in the world would you substitute CSA cement for only part of the portland cement, leaving all the problems that then need to be remedied with pozzolans? In my opinion this merely adds complication and expense without providing much benefit. It causes people to spend endless hours tweaking their mix proportions when they should be focusing on selling countertops. I recommend the simple “100% replacement” approach that saves time and money and maximizes benefits.
