Bulldozers push and graders grade. The one exception to this is the humble cement mixer, beloved by children, hated by in-a-hurry drivers, and misunderstood by most people outside the cab of the 30,pound 13,kilogram behemoths.
While concrete has been around in one form or another since before the Romans built the Appian Way, the transit mixer is a child of the 20th century. But recent invention or not, the mixer is here to stay. The misunderstanding begins with the name. What people refer to as a cement mixer is known in the construction industry as a concrete mixer and comes in a large number of types, sizes and configurations to handle the many tasks set before it each day.
That need to fill so many roles means the machine is dynamic, changing shape and form as the needs of the people using concrete change as well.
In this article we'll examine some of the major types of mixers, from the traditional drum-shaped ready-mix transit mixer to the less-common but growing in popularity volumetric mixer, essentially a concrete plant on wheels. How cement mixers work and why they work the way they do is a fascinating combination of old and new technology.
You'll never see a cement mixer the same way again. But before we begin, let's clarify the difference between cement and concrete. In baking terms, the difference between concrete and cement is the difference between flour and a loaf of bread. Concrete is a generic term for a mix of aggregate -- usually stone or gravel, water and cement.
Modern cement is a complex blend of finely ground minerals, and goes by the generic name of "portland. Stephen Stepanian developed and applied to patent the first motorized transit mixer in , in an effort to replace the horse-drawn concrete mixer used at the time. Wooden paddles churned the mixture as the cart wheels turned, but the design was of limited use -- it was cumbersome and slow. The same, however, could be said of the engines and trucks during that period.
But by the s, engines and truck-frame construction caught up to the need for a rugged vehicle capable of hauling thousands of pounds of wet, or unset, concrete. As the building boom following World War II went into full swing, mixer trucks came into their own. The large drum mixer seen on roads today hasn't changed much from Stepanian's vision of a better concrete hauler. Mobile transit mixers are a mix-and-match selection of engine, truck frame and rotating mixer.
The mixer is similar, though larger in scale, than the smaller ones found on construction sites. A large motor , separate from the engine, rotates the drum on the truck body, and a series of blades or a screw powered by the same motor keeps the aggregate, water and cement in constant motion. This keeps the premixed concrete from setting, though the clock is often ticking to get the load to the construction site, road section or parking lot.
Most cement manufacturers suggest keeping the time between mixing and pouring to 90 minutes at most. It's even better to get it to the site in less than an hour. As technology has changed, so has the basic mixer design. While many transit mixers still have rotating drums, most don't simply pick up a load of wet cement and transport it. The few that still do head mostly to road sites where it's possible to pour the mixture immediately.
Most transit mixers have a separate water tank in the truck. The spinning drum keeps the dry ingredients, aggregate and cement mixing during most of the trip. When the driver is within a few miles of the site, water is added to create concrete fresh for delivery.
This is considered "batch" delivery of ready-mixed concrete, mixing ingredients off site and trucking them where they're needed. Advances in technology have made it possible to mix concrete at the job site, though transit mixers are still the workhorse of the field. Volumetric and metered mixers are becoming more common. Both types are essentially on-site custom concrete plants.
Separate holding tanks of aggregate, cement and water are contained in one truck with a computer hooked to augers and pumps. At the site, the customer can order a specific type of concrete there are more than a dozen that can be mixed by the truck. Volumetric and metered mixers are often used during high-rise construction and can be paired with pumper trucks to deliver concrete more than 15 stories above the ground.
Some form of concrete -- the mix of a binder, aggregate and water -- has existed since the dynasties of the Egyptian pharaohs when water, sand and lime were mixed to use as mortar in building sections of the pyramids.
Romans also used a form of concrete in constructing their aqueducts, the Coliseum and other major constructions. Scientists in the s began experimenting and perfecting hydraulic cement , which is what the construction industry still uses today. The name for portland cement came from the Isle of Portland, off the English coast, where deposits of the mineral components used in modern concrete were first found and chemically isolated.
By , Thomas Edison was experimenting with building pre-cast concrete houses in Union, N. Most of those houses are still standing and being used. Then there are the famed Hoover and Grand Coulee dams, built in , that stand among the wonders of the world. While concrete comes in bewildering array of types, one thing is certain -- it's heavy.
A large batch of concrete can weigh more than 30, pounds 13, kilograms , not counting the weight of the truck itself, anywhere from 10, to 30, pounds 4, to 13, kilograms.
For a truck to haul that weight, it has to be powerful. And to get that load over the rough terrain of a construction site, the truck has to be tough. The trucks come in three separate parts -- engine , frame and mixer.
Most truck companies provide the engine and frame, with amenities ranging from sleeper cab to computer navigation. The mixer, or volumetric plant , is added on at a later time. Each company has specific wants and needs and requires a truck tailored to those. For example, some may need a truck with a heavier engine and a lighter drum, which could be removed at a later time and turned into a trash hauler with a few modifications.
Share via. Your Name required. Your Email required. Your Message. Posted by sean in Construction Equipment Tool Hire on January 29, with no comments Before , when Stephen Stepanian developed the first patented motorised concrete mixer, concrete was mixed using horse-drawn contraptions that relied of wooden paddles to churn the mixture. They are constantly churning the concrete held within to keep it from setting, and can carry up to 20, kilograms of pre-mixed concrete at a time. Shilpa Medicare investors eye Laurus-like returns, but past capex yet to fire.
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