Q: How are concrete masonry units made?
-Curious About Manufacturing
At our facility we manufacture both structural grey and architectural units. Most architectural finishes expose the beauty of local aggregates and we have a variety of aggregate colors available to us. Deep blacks, grey speckled granites, stones that range from peachy to brown, and others that range from pink to purplish. We also use pigments to create a variety of color variations. Our manufacturing process starts with the delivery of powdered cement and raw aggregates that have either been crushed or naturally have the appropriate gradation for the mix design. Our computerized batching system provides consistency and weighs the cement, aggregate, admixtures, and pigment if required. All of the raw materials including water are combined in the mixer to make a zero-slump concrete which is poured into the block molds. The block machine then compacts and vibrates the concrete. This is partially how CMUs gain their strength and generally speaking, CMUs use less cement than poured concrete due this process. When the block first comes out of the mold it holds its shape, but if you were to touch it, it would crumble in your hands. They get racked and then head to the kilns where they stay for 24 – 48 hours. The kiln temperature isn’t all that high, ranging from 120°-140° depending on the mix design. The main purpose of the low temperature kiln is to have a consistent humidity and temperature to jump start the hydration process. From there, grey structural units get cubed and split units head to the splitter. Ground face and polished units head to our finishing facility.
Heidi Jandris is a technical expert and trusted voice of the industry. She part of the family business’s 3rd generation, grew up immersed in all things concrete block and worked as a welder at the plant before getting her BArch at Pratt Institute in Brooklyn NY. She is the Sustainability Manager and provides technical and design services for A. Jandris & Sons.