LIGHTWEIGHT CONCRETE MASONRY
Today, building owners, designers, and specifiers have more choices than ever in structural wall systems. There are lots of new systems out there. But often, a time-tested, proven construction system — with solid economic and aesthetic advantages — is the way to go. Walls constructed with lightweight concrete masonry units — or concrete block — fall into the latter category, delivering benefits that range from structural, to thermal, to aesthetic.
A SOLID TRACK RECORD
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.
BLOCK IS GREAT. HOW CAN WE MAKE IT MORE ECONOMICAL, AND EASIER TO INSTALL?
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.
Expanded clay, shale, or slate (ESCS) is produced by mining raw materials, transferring it to rotary kilns, where it is heated to as much as 2200º F. During the heating process, gas bubbles cause the material to expand to approximately twice its size.
Upon cooling, crushing and screening, 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 cousin. And it does all this while actually having better insulating properties and a higher fire rating than either normal or medium-weight block.
PRODUCTIVITY BOOSTERS: ON-THE-JOB INJURY REDUCERS
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.
A SAFER WORK ENVIRONMENT AND HAPPIER, MORE PRODUCTIVE EMPLOYEES
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.
SELECTED CASE STUDIES
OVER 1-MILLION LIGHTWEIGHT IN MISSOURI HOSPITAL
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.
The product is shipped by barge to three of Midwest’s production facilities near St. Louis, Missouri. ARCOSA’s Jeff Speck says the lightweight aggregate is perfect for the units being produced for this large scale project.
“Lightweight aggregate is manufactured specifically for production of concrete masonry units,” says Speck. “We grade the material to provide a consistent texture to the surface of the block so that when it's painted, it looks uniform across the face of the wall. You have much fewer of what I would call pockmarks or indentations where there was a gap in the grading of the aggregate.”
USE OF LIGHTWEIGHT CONCRETE MASONRY IN SOUTHEAST
When the city of Fort Payne, Alabama embarked on an initiative to bolster its educational facilities, they chose concrete masonry for a new $19-million elementary school.
The 100-thousand square foot building is constructed of lightweight grey concrete masonry units produced by Kirkpatrick Concrete’s Guntersville, Alabama block division. Arcosa Lightweight’s Jeff Speck says masons tasked with building the new school benefited from the fact this long-time producer only makes lightweight units.
“Guntersville Block has been a longtime customer buying material from our Livingston, Alabama plant,” says Speck. “They make only lightweight block because masons in that market want lighter units for better productivity. It makes concrete masonry more competitive in the marketplace.”