The first commercially successful concrete block machine was invented by Harmon S. Palmer in 1900. When the industry first developed, the machines used to make concrete block were hand operated. It was even possible to order machines that could make one block at a time from the Sears catalog.
Over the next 50 years, the development of the Portland Cement industry in the United States, innovations in block manufacturing machinery, and the expanding U.S. economy all helped fuel the use of concrete block as a construction material. The versatile, modular construction system took off because of its many benefits — from strength and durability, to ease of installation, ability to accommodate design changes in the field, and the rugged beauty and variety of textures and colors possible with architectural concrete masonry units.
In the post World War II construction boom, the block industry took off, with new ideas and products coming fast and hard. Lightweight block was and is one of the big ones. Concrete block is made with a mixture of cement and aggregate — sand, crushed stone or lightweight aggregate.
Lightweight concrete masonry units came into wide use in the U.S. in the 1950s. It’s easy to see why the product gained rapidly in popularity. The average normal weight concrete masonry unit tips the scales at 34 pounds or more, medium weight units at between 28 and 34 pounds. Lightweight units weigh less than 28 pounds, and have a concrete density less than 105 pounds per cubic foot.
ESCS is produced by mining the raw material, crushing and screening it for size, and transferring it to rotary kilns, where it is heated to as much as 2200º F. It’s the lightweight aggregate that makes lightweight block weigh less than conventional block. The most common lightweight aggregate used to produce concrete masonry units today is expanded clay, shale, or slate (ESCS).
During the heating process, gas bubbles cause the material to expand to approximately twice its size. Upon cooling, the resulting aggregate is a structural grade, ceramic material with a bulk density less than half that of ordinary stone and gravel. As a result, lightweight block weighs about 20 to 25 percent less than normal weight block, while meeting the same ASTM C 90 standard for concrete masonry unit strength as its bulkier normal weight brother. And it does so while actually having better insulating properties and a higher fire rating than either normal or medium-weight block.
Concrete block is part of a building system. Like any building system, labor plays a huge part in its viability. It’s easy to understand why masons can lay more block in less time with a product that is 25 percent lighter than the alternative. Additionally, because the product is so much lighter, it is possible to specify units that are larger than the standard 8x8x16-inch workhorse of the industry. On one Maryland project, a mason contractor estimated that he gained 50 percent more wall area per hour because 8x8x24 lightweight block were specified for the project rather than 8x8x16-inch units.
Lightweight block can provide labor savings of up to 50 percent over heavyweight block, based on a wide range of industry productivity studies. Beyond that, lighter units mean fewer job-related injuries and easier compliance with applicable labor laws and contracts. Even though it is harder to quantify, anyone with job site experience will tell you that lightweight block can put smiles on the faces of masons. Happier, less fatigued employees are more productive and deliver better quality work. “Anyone who has ever been on a construction job site knows that the more physically difficult it is to install a product, the less the employees like it,” said Jeff Speck of Arcosa Lightweight.
“Specifying lightweight block wherever possible is an investment not only in productivity, thermal efficiency, fire resistance — but also in wall system quality, job site injury reduction, and employee morale. Sometimes it just takes one person involved in the process — whether it is the mason contractor, the block manufacturer, or the specifier — to say: ‘Hey, could we use lightweight block here?’ In most cases the answer is resounding yes,” Speck added.
Over one million lightweight concrete block are being used to construct a new psychiatric hospital campus in Central Missouri. The concrete masonry units were manufactured by Midwest Block and Brick and utilize Arcosa Lightweight’s Riverlite® produced in Erwinville, Louisiana.
It’s one thing to read a pile of technical white papers about the performance, superior fire resistance, aesthetic properties, quality and productivity improvements possible with lightweight concrete masonry units (CMU) or concrete block. It’s another to hear it straight from the folks who are out in the field installing the product.
Crowds attending a game or event at Houston's NRG Stadium probably won't notice the 800-thousand lightweight concrete masonry units (CMU’s) in the walls. Each block making up the massive stadium contains rotary-kiln lightweight aggregates. In fact, lightweight is incorporated throughout the 1.9 million sq. ft. facility.
A new high school in a fast growing Middle Tennessee community has been built using about 450,000 lightweight block produced by Southland Brick and Block of Murfreesboro.
For years Shannon Tayes, owner of Tayes Masonry in Smithville, Tennessee, has used Q-LITE® in his projects and he's still amazed at how the lightweight block achieves its fire rating. “It’s actually amazing how light they are…I don’t know how they do it,” he says.
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