The Evolution of Block Making
In 1918, a group of like-minded entrepreneurs came together to form a trade organization that today is recognized as the National Concrete Masonry Association (NCMA). These individuals were manufacturers of concrete block, a new economical building product in great demand. They agreed to set standards, exchange ideas and promote the merits of their product. At the time, these manufacturers were manually producing a nominal standard 8” x 8” x 16” block on a one-at-a-time (1-aat) machine similar to the apparatus first in 1899 patented by Harmon Palmer. Figure 1
This apparatus was comprised of a mold that was open at the top to receive mixed materials (cement and aggregates of low moisture content, 6%) that could then be tamped in place to form the dense shape of a concrete block. Once this consolidation was complete, the mold was rotated 90° and the collapsible sides were pivoted to open the mold. The finished product could then be removed with its bottom pallet to be set aside to naturally cure. A group of three men could manufacture some 20 concrete block per hour by this method. Soon, 2-aat machines were also used for block production. From this early beginning, we will now attempt to recognize some of the amazing innovations that have occurred in the manufacturing of concrete block over the past 100 years.
Mechanical Assists for Production Efficiencies
From early use of manual block making machinery, the industry proceeded to add mixing equipment and mechanical tamping of the mixture inside a mold box. The production pallet could then be stripped vertically from the mold and set aside for curing. Figure 2
Total weight of these units and speed of mechanically-tamped molds provided challenges for plant operators. The first major improvement in pallet handling became affectionately known as a Monkey-on-a-Stick. An operator, with this air-operated lift or hoist with a horizontal blade, could effectively pick up a production pallet from in front of the block machine and articulate the hoist to place the pallet onto a steel rack. Figure 3
This innovation cut down on physical labor, increased the speed of production and afforded the use of motorized forklifts to transport the loaded rack into a kiln for curing.
Conversely, a cured rack could be unloaded in the same fashion. This allowed the production pallet to be positioned for unloading of the block and then to return the pallet to the block machine for the next cycle .
Admixtures Improve Performance
As production became more automated, quantities increased making CMU more readily available to builders. To meet the growing demand, producers began using chemical admixtures to assist the freshly mixed concrete move more efficiently and homogeneously from hoppers and feed drawers into mold cavities; which in turn sped machine time, optimized texture and reduced mold wear. With the introduction of new, highly valued concrete products, higher-performing chemical admixtures were introduced for further reducing water absorption and strongly resisting efflorescence, caused by salt deposits, all to maintain concrete aesthetic properties.
Today, the concrete masonry admixture industry focuses its efforts on additives for better color retention, stronger water penetration resistance, and enhancement of cementitious materials performance, further expanding the appeal of structural and architectural units to designers.
Color Adds Opportunity
Pigments were added to the manufacturing of concrete products and suddenly, earth toned block opened new markets for block makers. As the art of integrally pigmented CMU evolved throughout the 1960s and 1970s, powdered pigments that were weighed and added by hand soon gave way to use of liquid pigment preparations. These liquid pigments, coupled with automated liquid dispensing systems, increased acceptance among manufacturers because liquid colors were cleaner and easier to use. As colors expanded, consistency improved. Acceptance and demand improved. Simultaneously, manufacturers began to develop processes that created multi-colored products. Now, instead of solid red, brown or gray, they began making products that included several distinct shades for a more natural look.
Early in the 1990s, pigment manufacturers introduced granulated pigments and equipment necessary for metering them to block machines. This further increased user friendliness and flexibility through evermore precise and sophisticated automation.
Automatic Pallet Loading and Unloading
The automatic loading and unloading of the block rack became the next innovation in the technology of concrete block production. Figure 4
This automatic equipment replaced the Monkey-on-a-Stick.
The loader equipment would pick up one or more production pallets from an accumulating conveyor supply and index them vertically until the load was positioned in alignment with a shelf on a stationary rack. The loader would then travel horizontally to put down the load on that shelf of the rack. As rack bays are loaded, a rack conveyor indexes the rack to the next bay until the rack is totally loaded. Once loaded, the rack is picked up by an operator with forklift or by way of an automated rack transporter, for transit to a kiln. Figure 5
Simultaneously, with this loading function, the unloader equipment would unload a cured rack, utilizing the same technology. The unloaded pallet would travel by way of a conveyor to a de-palleting station where the product would be removed from the production pallet. The product then moved to a cubing area while the production pallet returned to the block machine for its next cycle.
This rack loading and unloading equipment, along with semi-automatic cubers, greatly increased the rate of production and foretold the advancements yet to come.
In 1939, the Besser Company introduced the first 3-aat block machine which increased production to about 500 standard block per hour in a 10-hour shift. Figure 6
In the years following WW2, both the Stearns Company and Columbia Machine would introduce 3-aat machines.
Today, weigh idlers are being incorporated into weigh batching systems to increase the speed of processing a given mix
Along with innovations in concrete block production, batching and mixing of cement and aggregates underwent a revolution in automation as well. From transistors and relay logic to computers and microwave moisture control of the mix, actual weighing of the ingredients progressed from balance scales, to potentiometers, to load cells, as these technologies were incorporated into the block industry. Today, weigh idlers are being incorporated into some new weigh batching systems to increase the speed of processing a given mix.
The weigh idler is a single conveyor idler incorporating a load cell for sensing weight of the conveyed material. Thus, an aggregate can be weighed accurately, on-the-fly, as it is moving toward the mixer or to a holding hopper above the mixer.
By 1975, the industry was commonly utilizing low pressure steam (170° F), in individual kilns, to accelerate the curing of cementitious materials in the block and therefore gain a higher one-day strength of the unit. This early gain in block strength allowed the producer to handle the product more efficiently and stack cubes vertically atop each other in inventory.
Research was undertaken suggesting that concrete block cured at a lower temperature (100° to 120° F) for the same period of time in a continuous kiln would result in the same gain in block strength. Further, this analysis of the chemistry of different cements resulted in a better understanding of which temperature should be used to cure a given cement.
Curing of concrete block at this lower standard temperature in a continuous kiln was in high demand among manufacturers due to the obvious reduction in curing costs. It is still utilized today, although with much different pallet handling equipment.
Big Board Manufacturing
In the late 1970s and 1980s, the industry demanded higher production. Capacity afforded by big board block machines and equipment was manufactured that would offer 5-aat and 6-aat block machines. Figure 7 These machines required much heavier pallet handling systems. The industry responded with rack transporters and finger-cars which could accommodate these needs. Figure 8. Big board provides not only 5 or 6 aat but also units up to 500 mm high for oversize units.
Block plants would be built accommodating this new technology for manufacturing many products with larger capacity block making machines, more sophisticated pallet handling systems, semi- or fully-automatic cubers and stretch wrappers for film packaging of the finished products. Figure 10
Also, during this current era, foreign manufacturers of large scale machinery technology began to focus on the US as a new market for their landscape products equipment. This machinery influenced development and the surge of concrete pavers and retaining wall products in the US.
Along with this move to higher production capacity, today, pallet handling equipment has been hardened to allow the rack transporters and finger-cars to operate inside a continuous kiln (at a temperature range of 100° to 120° F) . These new high production machines are capable of producing up to 12 standard block per cycle or approximately 2500 units per hour.
Thus, manufacturing of concrete block and other masonry products has continuously matured to ensure that it is always prepared to offer innovative and competitive construction building materials to architects and engineers to meet any design and high performance challenges.
At a gathering of today’s Like-Minded Young Professionals and Entrepreneurs, looking into the future, you might hear someone say, Come On…Let’s Roll!
New high production machines are capable of producing up to 12 block per cycle or 2500 units per hour
Billy Wauhop, president of Billy Wauhop & Associates in NC is an inventor who has designed Tunnel Kilns in the Ceramic Brick Industry as well as Blast Furnaces in the Steel Producing Industry. In 1973, he began designing block plants and was awarded his first US patent for the Low Temperature Curing of Concrete Block in a closed continuous kiln in 1977. In the last 45 years, he has designed and built Block Plants and Material Handling Systems throughout the US, Canada, the Czech Republic and Poland. Wauhop is a 1965 graduate of West Virginia Tech with a Mechanical Engineering degree.